One document matched: draft-ietf-fax-tiffplus-04.txt
Differences from draft-ietf-fax-tiffplus-03.txt
File Format for Internet Fax
<draft-ietf-fax-tiffplus-04.txt>
Status
This document is an Internet Draft. Internet Drafts are working
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ftp.isi.edu (US West Coast).
Abstract
This Internet Draft describes the TIFF (Tag Image File Format)
representation of image data specified by the ITU-T Recommendations for
black-and-white and color facsimile. This file format specification is
commonly known as TIFF-FX. It formally defines minimal, extended and
lossless JBIG modes for black-and-white fax, and base JPEG, lossless
JBIG and Mixed Raster Content modes for color and grayscale fax. These
modes or profiles correspond to the content of the applicable ITU-T
Recommendations. Files formatted according to this specification use the
image/tiff MIME Media Type.
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Table of Contents
1. INTRODUCTION........................................................4
1.1. Scope..........................................................4
1.2. Approach.......................................................5
1.3. Overview of this draft.........................................5
2. TIFF and Fax........................................................6
2.1. TIFF Overview..................................................6
2.1.1. File Structure.............................................6
2.1.2. Image Structure............................................7
2.1.3. TIFF File Structure for Fax Applications...................8
2.2 TIFF Fields for All Fax Applications...........................10
2.2.1. TIFF Fields required for all fax modes....................11
2.2.2. Additional TIFF Fields required for all fax modes.........11
2.2.3. TIFF Fields recommended for all fax modes.................13
2.2.4. New TIFF Fields recommended for fax modes.................13
3. Minimal Black-and-White Fax Mode...................................15
3.1. Overview......................................................15
3.2. Required TIFF Fields..........................................15
3.2.1 Baseline Fields............................................16
3.2.2 Extension Fields...........................................17
3.2.3 New Fields.................................................17
3.3. Recommended TIFF Fields.......................................17
3.4. End of Line (EOL) and Return to Control (RTC).................18
3.4.1 RTC Exclusion..............................................18
3.5. File Structure................................................19
3.6. Minimal Black-and-White Mode Summary..........................19
4. Extended Black-and-White Fax Mode..................................21
4.1. TIFF-F Overview...............................................21
4.2. Required TIFF Fields..........................................22
4.2.1. Baseline Fields...........................................22
4.2.2. Extension Fields..........................................24
4.2.3. New Fields................................................25
4.3. Recommended TIFF Fields.......................................25
4.3.1. Baseline Fields...........................................25
4.3.2. Extension Fields..........................................25
4.3.3. New Fields................................................26
4.4. Technical Implementation Issues...............................27
4.4.1. Strips....................................................27
4.4.2. Bit Order.................................................27
4.4.3. Multi-Page................................................27
4.4.4. Compression...............................................28
4.4.5. Example Use of Page-quality Fields........................28
4.4.6. Practical Guidelines for Writing and Reading Multi-Page
TIFF-F Files..............................................29
4.4.7. Use of TIFF-F for Streaming Applications..................30
4.5. Implementation Warnings.......................................30
4.5.1. Uncompressed Data.........................................30
4.5.2. Encoding and Resolution...................................31
4.5.3. EOL byte-aligned..........................................31
4.5.4. EOL.......................................................32
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4.5.5. RTC Exclusion.............................................32
4.5.6. Use of EOFB for T.6 Compressed Images.....................32
4.6. Example Use of TIFF-F.........................................33
4.7. Extended Black-and-white Fax Mode Summary.....................33
5. Lossless JBIG Black-and-White Fax Mode.............................35
5.1. Overview......................................................35
5.2. Required TIFF Fields..........................................35
5.2.1. Baseline Fields...........................................35
5.2.2. Extension Fields..........................................36
5.2.3. New Fields................................................36
5.3. Recommended TIFF Fields.......................................36
5.4. Lossless JBIG Black-and-White Mode Summary....................36
6. Base Color Fax Mode................................................38
6.1. Overview......................................................38
6.2. Required TIFF Fields..........................................38
6.2.1. Baseline Fields...........................................38
6.2.2. Extension Fields..........................................39
6.2.3. New Fields................................................41
6.3. Recommended TIFF Fields.......................................41
6.4. Base Color Fax Mode Summary...................................41
7. Lossless Color Mode................................................43
7.1. Overview......................................................44
7.1.1. Color Encoding............................................44
7.1.2. JBIG Encoding.............................................44
7.2. Required TIFF Fields..........................................45
7.2.1. Baseline Fields...........................................45
7.2.2. Extension Fields..........................................46
7.2.3. New Fields................................................46
7.3. Recommended TIFF Fields.......................................46
7.4. Lossless Color Fax Mode Summary...............................46
8. Mixed Raster Content Mode..........................................48
8.1 Overview.......................................................48
8.1.1. MRC 3-layer model.........................................49
8.1.2. A TIFF Representation for the MRC 3-layer model...........49
8.2. Required TIFF Fields..........................................51
8.2.1. Baseline Fields...........................................51
8.2.2. Extension Fields..........................................52
8.2.3. New Fields................................................53
8.3. Recommended TIFF Fields.......................................54
8.4. Rules and Requirements for Images.............................54
8.5. MRC Fax Mode Summary..........................................55
9. Security Considerations............................................58
10. Copyright.........................................................58
11. References........................................................59
12. Authors' Addresses................................................60
Annex A: Summary of TIFF Fields for Internet Fax .....................61
Appendix 1: Open Issues...............................................64
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1. Introduction
This document describes the use of TIFF (Tag Image File Format) to
represent the data content and structure generated by the current suite
of ITU-T Recommendations for Group 3 facsimile. These Recommendations
and the TIFF fields described here support six facsimile modes or profiles:
1. minimal black-and-white mode, using binary MH compression [T.4]
2. extended black-and-white mode, using binary MH, MR and MMR
compression [T.4, T.6]
3. lossless JBIG black-and-white mode, with JBIG compression [T.85,
T.82]
4. lossy color and grayscale mode, using JPEG compression [T.42,
T.81]
5. lossless color and grayscale mode, using JBIG compression [T.43,
T.82]
6. mixed raster content mode [T.44], using a combination of
compression methods in 1-5
As noted, each of these six modes corresponds to the content of ITU-T
Recommendations shown. This Internet Draft is known informally as TIFF-
FX, where "FX" stands for "Fax eXtended."
The first mode describes a minimal interchange set of fields, which will
guarantee that, at least, binary black-and-white images will be
supported. Implementations are required to support this minimal
interchange set of fields.
With the intent of specifying a file format for Internet Fax, this
draft:
1. specifies the structure of TIFF files for facsimile data,
2. defines ITU fax-compatible values for existing TIFF fields,
3. defines new TIFF fields and values required for compatibility
with ITU color fax.
1.1 Scope
This document defines a TIFF-based file format specification for
enabling standardized messaging-based fax over the Internet. It
specifies the TIFF fields and field values required for compatibility
with the existing ITU-T Recommendations for Group 3 black-and-white,
grayscale and color facsimile. TIFF has historically been used for
handling fax image files in applications such as store-and-forward
messaging. Implementations that support this file format specification
for import/export may elect to support it as a native format. This
document recommends a TIFF file structure that is compatible with
low-memory and page-level streaming implementations.
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Unless otherwise noted, the current TIFF specification [TIFF] and
selected TIFF Technical Notes [TTN1, TTN2] are the primary references
for defining TIFF fields. This document is the primary reference for
defining TIFF field values for Internet fax applications.
1.2 Approach
The basic approach to using TIFF for facsimile data is to insert the
compressed fax data in a TIFF file and use TIFF fields to encode the
parameters that describe the image data. These fields will have values
that comply with the ITU-T Recommendations. The MIME media type of the
resulting file will be image/tiff, with an optional Application
parameter [TIFF-REG].
This approach takes advantage of TIFF features and structures that
bridge the data formats and performance requirements of both legacy fax
machines and host-based fax applications. TIFF constructs for pages,
images, and strips allow a TIFF file to preserve the fax data stream
structure and the performance advantages that come with it. A TIFF-based
approach also builds on an established base of users and implementors
and ensures backward compatibility with existing TIFF-based IETF
proposals and work in progress for Internet fax.
1.3 Overview of this draft
Section 2 gives an overview of TIFF. Section 2.1 describes the structure
of TIFF files, including practical guidelines for structuring multi-page
TIFF files. Section 2.2 lists the TIFF fields that are required or
recommended for all fax modes. The TIFF fields used by some but not all
fax modes are described in Sections 3-8, which describe the individual
fax modes. These sections also specify the ITU-compatible field values
(image parameters) for each mode.
Section 3 defines the representation of the minimal black-and-white
facsimile mode required of all implementations. Section 4 defines the
optional extended black-and-white fax capabilities and provides a
standard definition of TIFF-F. Section 5 describes the lossless black-
and-white mode using JBIG compression. Section 6 defines the base color
mode for the representation of lossy color and grayscale facsimile data.
Section 7 defines the representation of lossless color and grayscale
facsimile data and Section 8 defines the representation of Mixed Raster
Content facsimile data. Each of these sections concludes with a table
summarizing the required and recommended fields for each mode and the
values they can have.
Sections 9, 10 and 11 give Security Considerations, References and
Authors' Addresses. Annex A gives a summary of the TIFF fields used or
defined in this document and provides a convenient reference for
implementors.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", " NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are
to be interpreted as described in [REQ].
To implement only the minimal interchange black-and-white set of fields
and values, one need read only Sections 1, 2, 3 and 9. To implement
TIFF-F, the only sections needed are 1, 2, 3, 4 and 9.
2. TIFF and Fax
2.1. TIFF Overview
TIFF provides a means for describing, storing and interchanging raster
image data. A primary goal of TIFF is to provide a rich environment
within which applications can exchange image data. The current TIFF
specification [TIFF] defines a commonly used, core set of TIFF fields
known as Baseline TIFF. The current specification and TIFF Technical
Notes 1 and 2 [TTN1, TTN2] define several TIFF extensions. The TIFF-
based specification for fax applications uses Baseline TIFF fields with
selected extensions, as described in this document. In a few cases, this
document defines new fields specifically for fax applications.
2.1.1. File Structure
TIFF is designed for scanned images, which makes it a good match for
facsimile documents, which are multi-page scanned raster images. Each
raster image consists of a number of rows or scanlines, each of which
has the same number of pixels, the unit of sampling. Each pixel has at
least one sample (exactly one for black-and-white images).
A TIFF file begins with an 8-byte image file header. The first two bytes
describe the byte order used within the file. Legal values are "II"
(0x4949) when bytes are ordered from least to most significant (little-
endian), and "MM" (0x4D4D), when bytes are ordered from most to least
significant (big-endian) within a 16- or 32-bit integer. Either byte
order can be used, except in the case of the minimal black-and-white
mode, which SHALL use value "II". The next two bytes contain the value
42 that identifies the file as a TIFF file and is ordered according to
the value in the first two bytes of the header. The last four bytes give
the offset that point to the first image file directory (IFD). This and
all other offsets in a TIFF file are with respect to the beginning of
the TIFF file. An IFD can be at any location in the file after the
header but must begin on a word boundary. Section 2.1.3 gives
requirements and practical guidelines on the location of IFDs within a
TIFF file for the fax modes or profiles described in this document.
An IFD is a sequence of tagged fields, sorted in ascending order by tag
value. An IFD consists of a 2-byte count of the number of fields, a
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sequence of field entries and a 4-byte offset to the next IFD. The
fields contain information about the image and pointers to the image
data. Each separate raster image in the file is represented by an IFD.
Each field entry has 12 bytes and consists of a 2-byte Tag, 2 bytes
identifying the field type (e.g. short, long, rational, ASCII), 4 bytes
giving the count (number of values or offsets), and the 4-byte offset of
the field value. If, based on the type and count, the value takes 4
bytes or less, then it replaces the offset in the field entry. Details
are given in the TIFF specification [TIFF].
A TIFF file can contain more than one IFD, where each IFD is a subfile
whose type is given in the NewSubfileType field. Multiple IFDs can be
organized either as a linked list, with the last entry in each IFD
pointing to the next IFD (the pointer in the last IFD is 0), or as a
tree, using the SubIFDs field in the primary IFD [TTN1]. The SubIFDs
field contains an array of pointers to child IFDs of the primary IFD.
Child IFDs describe related images, such as reduced resolution versions
of the primary IFD image. The same IFD can point both to a next IFD and
to child IFDs, and child IFDs can themselves point to other IFDs.
All fax modes represent a multi-page fax image as a linked list of IFDs,
with a NewSubfileType field containing a bit that identifies the IFD as
one page of a multi-page document. Each IFD has a PageNumber field,
identifying the page number in ascending order, starting at 0 for the
first page. While a Baseline TIFF reader is not required to read any
IFDs beyond the first, an implementation that reads the files that
comply with this specification SHALL read multiple IFDs. Only the Mixed
Raster Content fax mode, described in Section 8, requires the use of
child IFDs.
2.1.2 Image Structure
An IFD stores an image as one or more strips. A strip consists of 1 or
more scanlines (rows) of raster image data in compressed form. An image
may be stored in a single strip or may be divided into several strips,
which would require less memory to buffer. (Baseline TIFF [TIFF]
recommends about 8k bytes per strip, but existing fax usage is typically
one strip per image.)
Each IFD requires three strip-related fields: StripOffsets, RowsPerStrip
and StripByteCounts. The StripOffsets field is an array of pointers to
the strip or strips that contain the actual image data. The
StripByteCounts field gives the number of bytes in each strip after
compression. TIFF requires that each strip, except the last, contain the
same number of scanlines, which is given in the RowsPerStrip field. This
document introduces the new StripRowCounts field that allows a variable
number of scanlines per strip, which is required by the Mixed Raster
Content fax mode (Section 8).
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Image data is stored as uninterpreted, compressed data streams within a
strip. The formats of these streams follow the ITU-T Recommendations.
The Compression field in the IFD indicates the type of compression, and
other TIFF fields in the IFD describe image attributes, such as color
encoding and spatial resolution. Compression parameters are stored in
the compressed data stream, rather than in TIFF fields. This makes the
TIFF representation and compressed data format specification independent
of each another. This approach, modeled on [TTN2], allows TIFF to
gracefully add new compression schemes as they become available.
Some attributes can be specified both in the compressed data stream and
within a TIFF field. It is possible that the two values will differ.
When this happens for values required to interpret the data stream, then
the values in the data stream take precedence. For informational values
that are not required to interpret the data stream, such as author name,
then the TIFF field value takes precedence.
2.1.3 TIFF File Structure for Fax Applications
The TIFF specification has a very flexible file structure, which does
not specify the ordering of IFDs, fields values and image data in a
file. It is up to individual applications to require or recommend an
ordering.
This section describes a file structure for the writing of TIFF files
that is required in the minimal black-and-white mode (Section 3) and
recommended in all other modes (Sections 4-8). This file structure
orders data in a TIFF file in the same way it is ordered in a fax
transmission. Although this file structure simplifies the implementation
of TIFF writers and readers in fax applications, for interchange
robustness, readers SHOULD be prepared to read TIFF files whose
structure is consistent with [TIFF], which supports a more flexible file
structure than is described in this section.
The writing of TIFF files for fax is based on a small number of ordering
principles: (1) there SHOULD be an IFD for each page in a multi-page fax
document; (2) the IFDs SHOULD occur in the same order in the file as the
pages occur in the document; (3) the IFD SHOULD precede the image data
to which it has offsets; (4) the image data SHOULD occur in the same
order in the file as the pages occur in the document; and (5) the IFD,
the value data and the image data it has offsets to SHOULD precede the
next image IFD.
For minimal black-and-white mode (Section 3.5), the SHOULDs become
SHALLs. For the extended black-and-white mode (Section 4.4.6), SHOULD in
the fifth principle becomes MAY. In effect, this document recommends for
all modes what is required for the minimal mode and notes an exception
based on past practice in the extended black-and-white mode (TIFF-F),
which historically has not always placed the IFD, the value data and the
image data it has offsets to before the next image IFD
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An IFD entry in an IFD either contains the value associated with that
entry or, if the value length is longer than four bytes, the IFD entry
contains an offset to the value stored outside the IFD. Long values are
needed for resolution and such (meta) data as dates, names and
descriptions. The long values SHOULD be ordered to follow the IFD that
contains an offset to them and before the image data for that IFD.
The effect of these ordering principles is that the IFD for the first
page should come first, followed by the any data values (dates,
descriptions, ...), followed by the image data for the first page, then
the IFD for second page, etc. This is shown in the following figure. ach
IFD is required to have a PageNumber field, which has value 0 for the
first page, 1 for the second page, and so on.
+-----------------------+
| Header |------------+
+-----------------------+ | First IFD
| IFD (page 0) | <----------+ Offset
+---| |------------+
| | |--+ |
Value | +-----------------------+ | |
Offset +-->| Long Values | | |
+-----------------------| | Strip |
| Image Data (page 0) |<-+ Offset |
+-----------------------+ | Next IFD
| IFD (page 1) | <----------+ Offset
+---| |------------+
| | |--+ |
Value | +-----------------------+ | |
Offset +-->| Long Values | | |
+-----------------------| | Strip |
| Image Data (page 1) |<-+ Offset |
+-----------------------+ | Next IFD
| IFD (page 2) | <----------+ Offset
+-----------------------+
| : |
In addition to the above ordering principles, minimal black-and-white
mode (Section 3) requires that image data for each page SHALL be a
single strip. For the extended black-and-white mode, the image data for
each page SHOULD be contained within a single strip.
If the image data is stored in multiple strips, then the strips SHOULD
occur in the file in the same order that the data they contain occurs in
the facsimile transmission, starting at the top of the page.
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This specification introduces an optional new GlobalParametersIFD field,
defined in Section 2.2.4. This field has type IFD and indicates
parameters describing the fax session. While it is often possible to
obtain these parameters by scanning the file, it is convenient to make
them available together in one place for fast and easy access. If the
GlobalParametersIFD occurs in a TIFF file, it is recommended that it be
located in the first IFD, immediately following the 8-byte image file
header.
2.2 TIFF Fields for All Fax Applications
The TIFF specification [TIFF] is organized as a baseline set and
several extensions, including technical notes [TTN1, TTN2] that will be
incorporated in the next release of TIFF. The baseline and extensions
have required and optional fields.
Facsimile applications require (and recommend) a mixture of baseline and
extensions fields, as well as some new fields that are not part of the
TIFF specification and that are defined in this document. This sub-
section lists the fields that are required or recommended for all modes.
In particular, Section 2.2.1 list the fields that are required by all
modes and that have values which do not depend on the mode. Section
2.2.2 lists the fields that are required by all modes and that have
values which do depend on the mode. Section 2.2.3 lists the fields that
are recommended for all modes. Fields that are required or recommended
by some but not all modes are given in the section (Section 3-8) that
describes that mode. The sections for each fax mode have sub-sections
for required and recommended fields; each sub-section organizes the
fields according to whether they are baseline, extension or new.
The fields required for facsimile have only a few legal values,
specified in the ITU-T Recommendations. Of these legal values, some are
required and some are optional, just as they are required (mandatory) or
optional in fax implementations that conform to the ITU-T
Recommendations. The required and optional values are noted in the
sections on the different fax modes.
This section describes the fields required or recommended by all fax
modes. The pattern for the description of TIFF fields in this draft is:
FieldName(TagValueInDecimal) = values. TYPE
WhetherRequiredByTIFForTIFFforFAX
Count = (omitted if =1) = (if not in current spec but available)
Explanation of the field, how it's used, and the values it can have.
Default value, if any, as specified in [TIFF]
When a field's default value is the desired value, that field may be
omitted from the relevant IFD unless specifically required by the text
of this specification.
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2.2.1. TIFF fields required for all fax modes
The TIFF fields listed in this section SHALL be used by all fax modes,
but have values that are not specified by the ITU standards, i.e. the
fields do not depend on the mode. The next sub-section lists the fields
that SHALL be used by all fax modes SHALL use, but which do have values
specified by the ITU-specified or mode-specific values. Fields that
SHALL be used by some not all modes are given in the sections (3-8)
which describe the modes that uses them.
ImageLength(257) SHORT or LONG
RequiredByTIFFBaseline
Total number of scanlines in image.
No default, must be specified.
NewSubFileType(254) = (Bit 1=1). LONG
RequiredByTIFFforFAX, RequiredByTIFFBaseline
Bit 1 is 1 if the image is a single page of a multi-page document.
Default = 0 (no subfile bits on)
PageNumber(285) SHORT
RequiredByTIFFforFAX, TIFFExtension
Count = 2
The first number represents the page number (0 for the first page);
the second number is the total number of pages in the document. If
the second value is 0, then the total page count is not available.
RowsPerStrip(278) SHORT or LONG
RequiredByTIFFBaseline
The number of scanlines per TIFF strip. For a single strip image,
this is the same as the value of the ImageLength field.
Default = 2**32 - 1 (meaning all scanlines in one strip)
StripByteCounts(279) SHORT or LONG
RequiredByTIFFBaseline
Count = number of strips
For each strip, the number of bytes in that strip after compression.
No default, must be specified.
StripOffsets(273) SHORT or LONG
RequiredByTIFFBaseline
Count = number of strips
For each strip, the byte offset from the beginning of the file to
that strip.
No default, must be specified.
2.2.2 Additional TIFF fields required for all fax modes
The TIFF fields listed in this section SHALL be used by all fax modes,
but the values associated with them depend on the mode being described
and the associated ITU Recommendations. Therefore, only the fields are
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defined here; the values applicable to a particular fax mode are
described in Sections 3-8. Also, fields that SHALL be used by some not
all modes are given in the section (3-8) that describes the mode that
SHALL use them.
BitsPerSample(258) SHORT
RequiredByTIFFBaseline
Number of bits per image sample
Default = 1 (field may be omitted if this is the value)
Compression(259) SHORT
RequiredByTIFFBaseline
Compression method used for strip data
Default = 1 (no compression, so may not be omitted for FAX)
ImageWidth(256) SHORT or LONG
RequiredByTIFFBaseline
The number of samples per scanline (row) of the image
No default, must be specified.
PhotometricInterpretation(262) SHORT
RequiredByTIFFBaseline
The color space of the image data
No default, must be specified
ResolutionUnit(296) SHORT
RequiredByTIFFBaseline
The unit of measure for resolution. 2 = inch, 3 = centimeter;
Default = 2 (field may be omitted if this is the value)
SamplesPerPixel(277) SHORT
RequiredByTIFFBaseline
The number of components per pixel
Default =1 (field may be omitted if this is the value)
XResolution(282) RATIONAL
RequiredByTIFFBaseline
The horizontal resolution of the image is expressed in pixels per
resolution unit. The allowed XResolution values for each mode are
given in the section defining that mode. Per [T.4], it is
permissible for applications to treat the following XResolution
values as being equivalent: <204, 200> and <400,408> in pixels/inch.
These equivalencies were allowed by [T.4] to permit conversions
between inch and metric based facsimile terminals.
No default, must be specified
YResolution(283) RATIONAL
RequiredByTIFFBaseline
The vertical resolution of the image is expressed in pixels per
resolution unit. The allowed XResolution values for each mode are
given in the section defining that mode. Per [T.4], it is
permissible for applications to treat the following YResolution
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values as being equivalent: <98, 100>, <196, 200>, and <391, 400> in
pixels/inch. These equivalencies were allowed by [T.4] to permit
conversions between inch and metric based facsimile terminals.
No default, must be specified
2.2.3 TIFF fields recommended for all fax modes
The TIFF fields listed in this section MAY be used by all fax modes.
Recommended fields that are mode-specific are described in Sections 3-8.
DateTime(306) ASCII
OptionalInTIFFBaseline
Date/time in the format "YYYY:MM:DD HH:MM:SS" in 24-hour format.
No default.
DocumentName(269) ASCII
OptionalInTIFFExtension(DocumentStorageAndRetrieval)
The name of the scanned document. This is a TIFF extension field,
not a Baseline TIFF field.
No default.
ImageDescription(270) ASCII
OptionalInTIFFBaseline
A string describing the contents of the image.
No default.
Orientation(274) = 1-8. SHORT
OptionalinTIFFBaseline
1: 0th row represents the visual top of the image; the 0th column
represents the visual left side of the image. See the current TIFF
spec [TIFF] for further values; Baseline TIFF only requires value=1.
Default = 1.
Note: It is recommended that a writer that is aware of the
orientation will include this field to give a positive indication of
the orientation, even if the value is the default. If the
Orientation field is omitted, the reader SHALL assume a value of 1.
Software(305) ASCII
OptionalInTIFFBaseline
The optional name and release number of the software package that
created the image.
No default.
2.2.4 New TIFF fields recommended for fax modes
The new TIFF fields listed in this section MAY be used by all fax modes,
but their support is not expected for the minimal black-and-white fax
mode described in Section 3. These fields describe "global" parameters
of the fax session that created the image data. They are optional, not
part of the current TIFF specification, and are defined in this
document.
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The first new field, GlobalParametersIFD, is an IFD that contains global
parameters and is located in a Primary IFD.
GlobalParametersIFD. IFD
An IFD containing global parameters. It is recommended that a TIFF
writer place this field in the first IFD, where a TIFF reader would
find it quickly.
Each field in the GlobalParametersIFD is a TIFF field that is legal in
any IFD. Required baseline fields should not be located in the
GlobalParametersIFD, but should be in each image IFD. If a conflict
exists between fields in the GlobalParametersIFD and in the image IFDs,
then the data in the image IFD shall prevail.
Among the GlobalParametersIFD entries is a new ProfileType field which
generally describes information in this IFD and in the TIFF file.
ProfileType(TagToBeAssigned) LONG
The type of image data stored in this IFD:
0 = Unspecified
1 = Group 3 fax
other values for further study
The following new global fields are defined in this document as IFD
entries for use with fax applications.
ITUFaxMode(TagToBeAssigned) = 0 - 5. BYTE
The currently defined values are:
0: does not conform to ITU-T Recommendations for facsimile,
1: minimal black & white lossless (ITU-T Rec. T.4),
2: extended black & white lossless (ITU-T Rec. T.4, T.6),
3: lossless JBIG black & white (ITU-T Rec. T.85)
4: lossy color and grayscale (ITU-T Rec. T.42),
5: lossless color and grayscale (ITU-T Rec. T.43),
6: Mixed Raster Content (ITU-T Rec. T.44).
Notes: A file can use an ITU encoding with non-ITU parameters, such as
using JPEG to compress a CMYK image. In this case, ITUFaxMode is 0.
CodingMethods(TagToBeAssigned) LONG
This field indicates which coding methods are used in the file. A
bit value of 1 indicates:
Bit 0: unspecified compression,
Bit 1: 1-dimensional coding, ITU-T Rec. T.4 (MH - Modified Huffman),
Bit 2: 2-dimensional coding, ITU-T Rec. T.4 (MR - Modified Read),
Bit 3: 2-dimensional coding, ITU-T Rec. T.6 (MMR - Modified Modified
Read),
Bit 4: ITU-T Rec. T.82 coding, applying ITU-T Rec. T.85 (JBIG),
Bit 5: ITU-T Rec. T.81 (Baseline JPEG),
Bits 6-31: reserved for future use
Note: There is a limit of 32 compression types to identify standard
compression methods.
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VersionYear(TagToBeAssigned) BYTE
Count: 4
The year of the standard specified by the ITUFaxMode field, given as
4 characters, e.g. '1997'; used in lossy and lossless color modes.
ModeNumber (TagToBeAssigned) BYTE
The mode of the standard specified by the ITUFaxMode field. A
value of 0 indicates Mode 1.0; used in Mixed Raster Content mode.
3. Minimal Black-and-White Fax Mode
This section defines the minimal black-and-white subset of TIFF for
facsimile. All implementations will support the minimal subset.
Black-and-white mode is the binary fax application most users are
familiar with today. This mode is appropriate for black-and-white text
and line art. Black-and-white mode is divided into two levels of
capability. This section describes the minimal interchange set of TIFF
fields that must be supported by all implementations in order to assure
that some form of image, albeit black-and-white, can be interchanged.
This minimum interchange set is a strict subset of the fields and values
defined for the extended black-and-white mode (TIFF-F) in Section 4,
which describes extensions to the minimal interchange set of fields that
provide a richer set of black-and-white capabilities.
3.1. Overview
The minimal interchange portion of the black-and-white facsimile mode
supports 1-dimensional Modified Huffman (MH) compression, with the
original Group 3 fax resolutions, commonly called "standard" and "fine."
To assure interchange, this mode uses the minimal set of fields, with a
minimal set of values. There are no recommended fields in this mode.
Further, the TIFF file is required to be "little endian," which means
that the byte order value in the TIFF header is "II". This mode is
required to follow the guidelines laid out in Section 2.1.3 for TIFF
file structure, with the added requirement that a single strip contain
the image data for each page; see Section 3.5. The image data may
contain RTC sequences, as specified in Section 3.4.
3.2. Required TIFF Fields
Besides the fields listed in Section 2.2.1, the minimal black-and-white
fax mode requires the following fields. The fields listed in Section
2.2.1 and the fields and fax-specific values specified in this sub-
section must be supported by all implementations.
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3.2.1 Baseline fields
BitsPerSample(258) = 1. SHORT
RequiredByTIFFBaseline
Binary data only.
Default = 1 (field may be omitted if this is the value)
Compression(259) = 3. SHORT
RequiredByTIFFBaseline
3 = 1- or 2- dimensional coding.
The value 3 is a TIFF extension value [TIFF]. The T4Options field
must be specified and its value specifies that the data is encoded
using the Modified Huffman (MH) encoding of [T.4].
FillOrder(266) = 2. SHORT
RequiredByTIFFBaseline
2 = Pixels are arranged within a byte such that pixels with lower
column values are stored in the lower-order bits of the bytes, i.e.,
least significant bit first (LSB).
The FillOrder field is used to describe how 1 bit pixels are stored
within a byte of compressed image data. There are two possible
FillOrders for each byte: 1) the pixels are stored with the lowest
numbered pixel in the byte in the Most Significant Bit (MSB) of the
byte, or 2) the pixels are stored with the lowest numbered pixel in
the byte in the Least Significant Bit (LSB) of the byte.
NOTE: Baseline TIFF readers are only required to support FillOrder = 1,
where the lowest numbered pixel is stored in the MSB of the byte.
However, because many devices, such as modems, transmit the LSB first
when converting the data to serial form, it is common for black-and-
white fax products to use the second FillOrder =2, where the lowest
numbered pixel is stored in the LSB. Therefore, this value is specified
in the minimal black-and-white mode.
ImageWidth(256) = 1728. SHORT or LONG
RequiredByTIFFBaseline
This mode only supports a page width of 1728 pixels. This width
corresponds to North American Letter and Legal and to ISO A4 size
pages.
No default, must be specified.
PhotometricInterpretation(262) = 0. SHORT
RequiredByTIFFBaseline
0 = pixel value 1 means black
No default, must be specified
ResolutionUnit(296) = 2. SHORT
RequiredByTIFFBaseline
The unit of measure for resolution. 2 = inch.
Default = 2 (field may be omitted if this is the value)
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SamplesPerPixel(277) = 1. SHORT
RequiredByTIFFBaseline
The number of components per pixel; 1 for black-and-white
Default =1 (field may be omitted if this is the value)
XResolution(282) = 200, 204. RATIONAL
RequiredByTIFFBaseline
The horizontal resolution of the image is expressed in pixels per
resolution unit. In pixels/inch, the allowed values are 200 and 204,
which may be treated as equivalent. See Section 2.2.2 for inch-
metric equivalency.
No default, must be specified
YResolution(283) = 98, 100, 196, 200. RATIONAL
RequiredByTIFFBaseline
The vertical resolution of the image is expressed in pixels per
resolution unit. In pixels/inch, the allowed values are 98, 100,
196 and 200; 98 and 100 may be treated as equivalent, and 196 and
200 may be treated as equivalent. See Section 2.2.2 for inch-metric
equivalency.
No default, must be specified
3.2.2 Extension fields
T4Options(292) = (Bit 0 = 0, Bit 1 = 0, Bit 2 = 0, 1) LONG
RequiredTIFFExtension (when Compression = 3)
Bit 0 = 0 indicates MH encoding.
Bit 1 must be 0
Bit 2 = 1 indicates that EOLs are byte aligned, = 0 EOLs not byte
aligned
Default is all bits are 0 (applies when EOLs are not byte aligned)
Note: The T4Options field is required when the Compression field has a
value of 3. Bit 0 of this field specifies the encoding used (MH only in
this mode) and Bit 2 indicates whether the EOL codes are byte-aligned or
not. If they are byte aligned, then fill bits have been added as
necessary so that the End of Line (EOL) codes always end on byte
boundaries. See Section 3.4 for details.
3.2.3. New Fields
None.
3.3. Recommended TIFF Fields
None.
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3.4. End of Line (EOL) and Return to Control (RTC)
The handling of End of Line (EOL) codes and Return to Control (RTC)
sequences illustrate the differences between conventional fax, which is
bit and stream oriented, and TIFF, which is byte and file oriented.
Conventional fax, Baseline TIFF and TIFF extensions for fax all handle
EOLs and RTCs differently.
In conventional fax, an MH-compressed fax data stream for a page
consists of the following sequence:
EOL, compressed data (first line), EOL, compressed data, ... ,
EOL, compressed data (last line), RTC (6 consecutive EOL codes)
Baseline TIFF does not use EOL codes or Return to Control (RTC)
sequences for MH-compressed data, and does not use fill bits to byte
align EOL codes. However, the TIFF extension field T4Options used in
this specification for MH compression (Compression = 3) allows EOLs.
Furthermore, Bit 2 in the T4Options field indicates whether or not the
EOL codes are byte aligned. If Bit 2 = 1, indicating the EOL codes are
byte aligned, then fill bits have been added as necessary before EOL
codes so that an EOL code always ends on a byte boundary, and the first
bit of data following an EOL begins on a byte boundary. Without fill
bits, an EOL code may end in the middle of a byte. Byte alignment
relieves application software of the burden of bit-shifting every byte
while parsing scan lines for line-oriented image manipulation (such as
writing a TIFF file). Not all TIFF readers historically used for fax are
able to deal with non-byte aligned data.
While TIFF extension allows EOL codes, TIFF in fax applications has
traditionally excluded RTC sequences. Implementations that want common
processing and interfaces for fax data streams and Internet fax files
would prefer that the TIFF data include RTC sequences.
To reconcile these differences, RTCs are allowed in cases where EOL
codes are not byte aligned and no fill bits have been added to the data.
This corresponds to situations where the fax data is simply inserted in
a strip without being processed or interpreted. RTCs should not occur in
the data when EOLs have been byte aligned. This is formally specified in
the next sub-section.
3.4.1. RTC Exclusion
Implementations which wish to maintain strict conformance with TIFF and
compatibility with the historical use of TIFF for fax SHOULD NOT include
the RTC sequence when writing TIFF files. However, implementations which
need to support “transparency” of T.4-generated image data MAY include RTCs when writing TIFF files if the flag settings of the T4Options field are set for non-byte aligned data, i.e. Bit 2 is 0. Implementors of TIFF
readers should be aware that there are some existing TIFF
implementations for fax that include the RTC sequence in MH image data.
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3.5. File Structure
The TIFF header, described in Section 2.1.1, contains two bytes which
describe the byte order used within the file. For the minimal black-and-
white mode, these bytes SHALL have the value "II" (0x4949), denoting
that the bytes in the TIFF file are in LSByte-first order (little-
endian). The first or 0th IFD immediately follows the header, so that offset to the first IFD is 8. The headers values are shown in the
following table, based on [WIDE]
+--------+-------------------+--------+-----------+
| Offset | Description | Value |
+--------+-------------------+--------+-----------+
| 0 | Byte Order | 0x4949 (II) |
+--------+-------------------+--------+-----------+
| 2 | Identifier | 0x0042 |
+--------+-------------------+--------+-----------+
| 4 | Offset of 0th IFD | 0x 0000 0008 |
+--------+-------------------+--------+-----------+
The minimal black-and-white SHALL order IFDs and image data within a
file according to the file structure described in Section 2.1.3.
Furthermore, the image data for each page SHALL be contained within a
single strip. This means that the StripOffsets field will contain the
pointer to the image data. With two exceptions, the field entries in the
IFD contain the field values instead of offsets to field values located
outside the IFD. The two exceptions are the values for the XResolution
and YResolution fields, both of which are type RATIONAL and require 2 4-
byte numbers. They are placed immediately after the IFD which contains
the offsets to them, as shown in Section 2.1.3, and before the image
data pointed to by that IFD.
Using the file structure in Section 2.1.3 can reduce the memory
requirements in implementations. It is also provides some support for
streaming, in which a file can be processed as it is received and before
the entire file is received.
3.6 Minimal Black-and-white Mode Summary
The table below summarizes the TIFF fields that comprise the minimal
interchange set for black-and-white facsimile. The Baseline and
Extension fields must be supported by all implementations. For
convenience in the table, certain fields which have a value that is a
sequence of flag bits are shown taking integer values that correspond to the flags that are set. An implementation should test the setting of the
relevant flag bits individually, however, to allow extensions to the
sequence of flag bits to be appropriately ignored. (See, for example,
T4Options below.)
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+---------------------------+--------------------------------+
| Baseline Fields | Values |
+---------------------------+--------------------------------+
| BitsPerSample | 1 |
+---------------------------+--------------------------------+
| Compression | 3: 1D Modified Huffman coding |
| | set T4Options = 0 or 4 |
+---------------------------+--------------------------------+
| FillOrder | 2: least significant bit first |
+---------------------------+--------------------------------+
| ImageWidth | 1728 |
+---------------------------+--------------------------------+
| ImageLength | n: total number of scanlines |
| | in image |
+---------------------------+--------------------------------+
| NewSubFileType | 2: Bit 1 identifies single |
| | page of a multi-page document |
+---------------------------+--------------------------------+
| PageNumber | n,m: page number n followed by |
| | total page count m |
+---------------------------+--------------------------------+
| PhotometricInterpretation | 0: pixel value 1 means black |
+---------------------------+--------------------------------+
| ResolutionUnit | 2: inch |
+---------------------------+--------------------------------+
| RowsPerStrip | number of scanlines per strip |
| | = ImageLength, with one strip |
+---------------------------+--------------------------------+
| SamplesPerPixel | 1 |
+---------------------------+--------------------------------+
| StripByteCounts | number or bytes in TIFF strip |
+---------------------------+--------------------------------+
| StripOffsets | offset from beginning of |
| | file to single TIFF strip |
+---------------------------+--------------------------------+
| XResolution | 204, 200 (pixels/inch) |
+---------------------------+--------------------------------+
| YResolution | 98, 196, 100, 200 (pixels/inch)|
+---------------------------+--------------------------------+
| Extension Fields |
+---------------------------+--------------------------------+
| T4Options | 0: MH coding, EOLs not byte |
| | aligned |
| | 4: MH coding, EOLs byte aligned|
+---------------------------+--------------------------------+
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4. Extended Black-and-White fax mode
This section defines the extended black-and-white mode or TIFF-F. It
provides a standard definition of what has historically been known as
TIFF Class F and now TIFF-F. In doing so, it aligns this mode with
current ITU-T Recommendations for black-and-white fax and with existing
industry practice.
The previous section described the minimal interchange set of TIFF
fields that must be supported by all implementations in order to assure
that some form of image, albeit black-and-white, can be interchanged.
This section describes extensions to the minimal interchange set of
fields that provide a richer set of black-and-white capabilities. The
fields and values described in this section are a superset of the fields
and values defined for the minimal interchange set in Section 3. In
addition to the MH encoding, Modified READ (MR) and Modified Modified
READ (MMR) encoding as described in [T.4] and [T.6] are supported.
Section 4.1 gives an overview of TIFF-F. Section 4.2 describes the TIFF
fields that SHALL be used in this mode. Section 4.3 describes the fields
that MAY be used in this mode. In the spirit of the original TIFF-F
specification, Sections 4.4 and 4.5 discuss technical implementation
issues and warnings. Section 4.6 gives an example use of TIFF-F. Section
4.7 gives a summary of the required and recommended fields and their
values.
4.1 TIFF-F Overview
Though it has been in common usage for many years, TIFF-F has previously
never been documented in the form of a standard. An informal TIFF-F
document was originally created by a small group of fax experts led by
Joe Campbell. The existence of TIFF-F is noted in [TIFF] but it is not
defined. This document serves as the formal definition of the F
application of [TIFF] for Internet applications. For ease of reference,
the term TIFF-F will be used throughout this document as a shorthand for
the extended black-and-white mode or profile of TIFF for facsimile.
Up until the TIFF 6.0 specification, TIFF supported various "Classes"
which defined the use of TIFF for various applications. Classes were
used to support specific applications. In this spirit, TIFF-F has been
known historically as "TIFF Class F". Previous informal TIFF-F
documents [TIFF-F0] used the "Class F" terminology. As of TIFF 6.0
[TIFF], the TIFF Class concept has been eliminated in favor of the
concept of Baseline TIFF. Therefore, this document updates the
definition of TIFF-F as the F application of TIFF, by using Baseline
TIFF as defined in [TIFF] as the starting point and then adding the TIFF
extensions to Baseline TIFF which apply for TIFF-F. In almost all
cases, the resulting definition of TIFF-F fields and values remains
consistent with those used historically in earlier definitions of TIFF
Class F. Where some of the values for fields have been updated to
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provide more precise conformance with the ITU-T [T.4] and [T.30] fax
recommendations, these differences are noted.
4.2. Required TIFF Fields
This section lists the required fields and the values they must have to
be ITU-compatible. Besides the fields listed in Section 2.2.1, the
extended black-and-white fax mode SHALL use the following fields.
4.2.1. Baseline fields
BitsPerSample(258) = 1. SHORT
RequiredByTIFFBaseline
Binary data only.
Default = 1 (field may be omitted if this is the value)
Compression(259) = 3, 4. SHORT
RequiredByTIFFBaseline
3 = 1- or 2- dimensional coding, must have T4Options field This is
a TIFF Extension value [TIFF].
4 = 2-dimensional coding, ITU-T Rec. T.6 (MMR - Modified Modified
Read, must have T6Options field)) This is a TIFF Extension value.
Default = 1 (and is not applicable; field must be specified)
NOTE: Baseline TIFF permits use of value 2 for Modified Huffman
encoding, but the data is presented in a form which is not byte aligned
and so this value is not specified for fax applications.
See Sections 4.4.4, 4.5.1 and 4.5.2 for more information on compression
and encoding.
FillOrder(266) = 1 , 2. SHORT
RequiredByTIFFBaseline
1 = Pixels are arranged within a byte such that pixels with lower
column values are stored in the higher-order bits of the bytes,
i.e., most significant bit first (MSB).
2 = Pixels are arranged within a byte such that pixels with lower
column values are stored in the lower-order bits of the bytes, i.e.,
least significant bit first (LSB).
The FillOrder field is used to describe how 1 bit pixels are stored
within a byte of compressed image data. There are two possible
FillOrders for each byte: 1) the pixels are stored with the lowest
numbered pixel in the byte in the Most Significant Bit (MSB) of the
byte, or 2) the pixels are stored with the lowest numbered pixel in
the byte in the Least Significant Bit (LSB) of the byte.
NOTE: Baseline TIFF readers are only required to support the first
FillOrder (value = 1) where the lowest numbered pixel is stored in the
MSB of the byte. However, because many devices, such as modems, transmit
the LSB first when converting the data to serial form, it is common for
black-and-white fax products to use the second FillOrder (value =2),
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where the lowest numbered pixel is stored in the LSB. Therefore, this
value is specified in the minimal black-and-white mode. However, TIFF-F
is required to support both bit orders.
See Section 4.4.2 for more information on bit order.
ImageWidth(256)= : 1728, 2048, 2432, 2592, 3072, SHORT or LONG
3456, 3648, 4096, 4864
RequiredByTIFFBaseline
This mode supports the following fixed page widths: 1728, 2592, 3456
(corresponding to North American Letter and Legal, ISO A4 paper
sizes), 2048, 3072, 4096 (corresponding to ISO B4 paper size), and
2432, 3648, 4864 (corresponding to ISO A3 paper size).
No default; must be specified
NOTE: Historical TIFF-F did not include support for the following widths
related to higher resolutions: 2592, 3072, 3648, 3456, 4096 and 4864.
Historical TIFF-F documents also included the following values related
to A5 and A6 widths: 816 and 1216. Per the most recent version of [T.4],
A5 and A6 documents are no longer supported in Group 3 facsimile, so the
related width values are now obsolete. See section 4.5.2 for more
information on inch/metric equivalencies and other implementation
details.
NewSubFileType(254) = (Bit 1=1). LONG
RequiredByTIFFforFAX, RequiredByTIFFBaseline
Bit 1 is 1 if the image is a single page of a multi-page document.
Default = 0 (no subfile bits on)
NOTE: Bit 1 is always set to 1 for TIFF-F, indicating a single page of a
multi-page image. The same bit settings are used when TIFF-F is used for
a one page fax image.
See Section 4.4.3 for more details on multi-page files.
PhotometricInterpretation(262) = 0, 1. SHORT
RequiredByTIFFBaseline
0 = pixel value 1 means black, 1 = pixel value 1 means white.
This field allows notation of an inverted or negative image.
No default, must be specified
ResolutionUnit(296) = 2, 3. SHORT
RequiredByTIFFBaseline
The unit of measure for resolution. 2 = inch, 3 = centimeter; TIFF-F
has traditionally used inch-based measures.
Default = 2 (field may be omitted if this is the value)
SamplesPerPixel(277) = 1. SHORT
RequiredByTIFFBaseline
1 = monochrome, bilevel in this case (see BitsPerSample)
Default =1 (field may be omitted if this is the value)
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XResolution(282) = 200, 204, 300, 400, 408 RATIONAL
RequiredByTIFFBaseline
The horizontal resolution of the image is expressed in pixels per
resolution unit. In pixels/inch, the allowed values are: 200, 204,
300, 400, and 408. See Section 2.2.2 for inch-metric equivalency.
No default, must be specified
NOTE: The values of 200 and 408 have been added to the historical TIFF-F
values, for consistency with [T.30]. Some existing TIFF-F
implementations may also support values of 77 pixels/cm. See section
4.5.2 for more information on implementation details.
YResolution(283) = 98, 100, 196, 200, 300, 391, and 400 RATIONAL
RequiredByTIFFBaseline
The vertical resolution of the image is expressed in pixels per
resolution unit. In pixels/inch, the allowed values are: 98, 100,
196, 200, 300, 391, and 400 pixels/inch.
See Section 2.2.2 for inch-metric equivalency.
No default, must be specified
Note: The values of 100, 200, and 391 have been added to the historical
TIFF-F values, for consistency with [T.30]. Some existing TIFF-F
implementations may also support values of 77 and 38.5 (cm). See section
4.5.2 for more information on implementation details.
Not all combinations of XResolution, YResolution and ImageWidth are
legal. The following table gives the legal combinations and
corresponding paper size [T.30].
+--------------+-----------------+---------------------------+
| XResolution x YResolution | ImageWidth |
+--------------+-----------------+---------------------------+
| 200x100, 204x98 | | | |
| 200x200, 204x196 | 1728 | 2048 | 2432 |
| 204x391 | | | |
+--------------+-----------------+---------------------------+
| 300 x 300 | 2592 | 3072 | 3648 |
+--------------+-----------------+---------------------------+
| 408 x 391, 400 x 400 | 3456 | 4096 | 4864 |
+--------------+-----------------+---------------------------+
|Letter,A4| B4 | A3 |
| Legal | | |
+---------+--------+--------+
| Paper Size |
+---------------------------+
4.2.2. Extension fields
T4Options(292) = (Bit 0 = 0 or 1, Bit 1 = 0, Bit 2 = 0 or 1) LONG
RequiredTIFFExtension (when Compression = 3)
T4Options was also known as Group3Options in a prior version of
[TIFF].
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Bit 0 = 1 indicates MR encoding, = 0 indicates MH encoding.
Bit 1 must be 0
Bit 2 = 1 indicates that EOLs are byte aligned, = 0 EOLs not byte
aligned
Default is all bits are 0 (applies when MH encoding is used and EOLs
are not byte aligned EOLs) (See Section 3.2.2.)
The T4Options field is required when the Compression field has a
value of 3. This field specifies the encoding used (MH or MR) and
whether the EOL codes are byte-aligned or not. If they are byte
aligned, then fill bits have been added as necessary so that the End
of Line (EOL) codes always end on byte boundaries See Sections 3.4,
4.5.3 and 4.5.4 for details.
NOTE: The data in a TIFF-F image using a T.4 encoding is not terminated
with an RTC; see Section 4.5.5.
T6Options(293) = (Bit 0 = 0, Bit 1 = 0). LONG
RequiredTIFFExtension (when Compression = 4)
Used to indicate parameterization of 2D Modified Modified Read
compression. T6Options was also known as Group4Options in a prior
version of [TIFF].
Bit 0 must be 0.
Bit 1 = 0 indicates uncompressed data mode is not allowed; = 1
indicates uncompressed data is allowed (see [TIFF]).
Default is all bits 0. For FAX, the field must be present and have
the value 0. The use of uncompressed data where compression would
expand the data size is not allowed for FAX.
NOTE: MMR compressed data is two-dimensional and does not use EOLs. Each
MMR encoded image MUST include an "end-of-facsimile-block" (EOFB) code
at the end of each coded strip; see Section 4.5.6.
4.2.3. New fields
None.
4.3. Recommended TIFF fields
4.3.1. Baseline fields
See Section 2.2.3.
4.3.2. Extension fields
See Section 2.2.3.
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4.3.3. New fields
Three new, optional fields, used in the original TIFF-F description to
describe page quality, are defined in this specification. The
information contained in these fields is usually obtained from receiving
facsimile hardware (if applicable). They SHOULD NOT be used in writing
TIFF-F files for facsimile image data that is error corrected or
otherwise guaranteed not to have coding errors. Some applications need
to understand exactly the error content of the data. For example, a CAD
program might wish to verify that a file has a low error level before
importing it into a high-accuracy document. Because Group 3 facsimile
devices do not necessarily perform error correction on the image data,
the quality of a received page must be inferred from the pixel count of
decoded scan lines. A "good" scan line is defined as a line that, when
decoded, contains the correct number of pixels. Conversely, a "bad" scan
line is defined as a line that, when decoded, comprises an incorrect
number of pixels.
BadFaxLines(326) SHORT or LONG
The number of "bad" scan lines encountered by the facsimile device
during reception. A "bad" scanline is defined as a scanline that,
when decoded, comprises an incorrect number of pixels. Note that
PercentBad = (BadFaxLines/ImageLength) * 100
No default.
CleanFaxData(327) = 0, 1, 2. SHORT
Indicates if "bad" lines encountered during reception are stored in
the data, or if "bad" lines have been replaced by the receiver.
0 = No "bad" lines
1 = "bad" lines exist, but were regenerated by the receiver,
2 = "bad" lines exist, but have not been regenerated.
No default.
NOTE: Many facsimile devices do not actually output bad lines. Instead,
the previous good line is repeated in place of a bad line. Although this
substitution, known as line regeneration, results in a visual
improvement to the image, the data is nevertheless corrupted. The
CleanFaxData field describes the error content of the data. That is,
when the BadFaxLines and ImageLength fields indicate that the facsimile
device encountered lines with an incorrect number of pixels during
reception, the CleanFaxData field indicates whether these bad lines are
actually still in the data or if the receiving facsimile device replaced
them with regenerated lines.
ConsecutiveBadFaxLines(328) LONG or SHORT
Maximum number of consecutive "bad" scanlines received. The
BadFaxLines field indicates only the quantity of bad lines. The
consecutiveBadFaxLines field is an indicator of the distribution of
bad lines and may therefore be a better general indicator of
perceived image quality.
No Default.
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NOTE: The BadFaxLines and ImageLength data indicate only the quantity of
such lines. The ConsecutiveBadFaxLines field is an indicator of their
distribution and may therefore be a better general indicator of
perceived image quality. See Section 4.4.5 for examples of the use of
these fields.
While the GlobalParameters IFD is recommended for use by all fax modes,
except the minimal black-and-white mode, it use is optional in the
extended black-and-white fax mode.
4.4. Technical Implementation Issues
4.4.1 Strips
In general, TIFF files divide an image into "strips," also known as
"bands." Each strip contains a few scanlines of the image. By using
strips, a TIFF reader need not load the entire image into memory, thus
enabling it to fetch and decompress small random portions of the image
as necessary.
The number of scanlines in a strip is described by the RowsPerStrip
value and the number of bytes in the strip after compression by the
StripByteCount value. The location in the TIFF file of each strip is
given by the StripOffsets values.
Strip size is application dependent. The recommended approach for multi-
page TIFF-F images is to represent each page as a single strip. Existing
TIFF-F usage is typically one strip per page in multi-page TIFF-F files.
See Sections 2.1.2 and 2.1.3.
4.4.2 Bit Order
The current TIFF specification [TIFF] does not require a Baseline TIFF
reader to support FillOrder=2, i.e. lowest numbered 1-bit pixel in the
least significant bit of a byte. It further recommends that FillOrder=2
be used only in special purpose applications.
Facsimile data appears on the phone line in bit-reversed order relative
to its description in ITU-T Recommendation T.4. Therefore, a wide
majority of facsimile applications choose this natural order for data in
a file. Nevertheless, TIFF F readers must be able to read data in both
bit orders and support FillOrder values of 1 and 2.
4.4.3. Multi-Page
Many existing applications already read TIFF-F-like files, but do not
support the multi-page field. Since a multi-page format greatly
simplifies file management in fax application software, TIFF-F specifies
multi-page documents (NewSubfileType = 2) as the standard case.
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It is recommended that applications export multiple page TIFF-F files
without manipulating fields and values. Historically, some TIFF-F
writers have attempted to produce individual single-page TIFF-F files
with modified NewSubFileType and PageNumber (page one-of-one) values for
export purposes. However, there is no easy way to link such multiple
single page files together into a logical multiple page document, so
that this practice is not recommended.
4.4.4. Compression
In Group 3 facsimile, there are three compression methods which had been
standardized as of 1994 and are in common use. The ITU-T T.4
Recommendation [T.4] defines a one-dimensional compression method known
as Modified Huffman (MH) and a two-dimensional method known as Modified
READ (MR) (READ is short for Relative Element Address Designate). In
1984, a somewhat more efficient compression method known as Modified
Modified READ (MMR) was defined in the ITU-T T.6 Recommendation [T.6].
MMR was originally defined for use with Group 4 facsimile, so that this
compression method has been commonly called Group 4 compression. In
1991, the MMR method was approved for use in Group 3 facsimile and has
since been widely utilized.
TIFF-F supports these three compression methods. The most common
practice is the one-dimensional Modified Huffman (MH) compression
method. This is specified by setting the Compression field value to 3
and then setting bit 0 of the T4Options field to 0. Alternatively, the
two dimensional Modified READ (MR) method, which is much less frequently
used in historical TIFF-F implementations, may be selected by setting
bit 0 of the T4Options field to 1. The value of Bit 2 in this field is
determined by the use of fill bits.
Depending upon the application, the more efficient two-dimensional
Modified Modified Read (MMR)compression method from T.6 may be selected
by setting the Compression field value to 4 and then setting the first
two bits (and all unused bits) of the T6Options field to 0. More
information to aid the implementer in making a compression selection is
contained in Section 4.5.2.
Baseline TIFF also permits use of Compression=2 to specify Modified
Huffman compression, but the data is presented in a form that is not
byte aligned. As a result, TIFF-F uses Compression=3 instead of
Compression=2 to specify Modified Huffman compression.
4.4.5. Example Use of Page-quality Fields
Here are examples for writing the CleanFaxData, BadFaxLines, and
ConsecutiveBadFaxLines fields:
1. Facsimile hardware does not provide page quality
information: MUST NOT write page-quality fields.
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2. Facsimile hardware provides page quality information, but
reports no bad lines. Write only BadFaxLines = 0.
3. Facsimile hardware provides page quality information, and
reports bad lines. Write both BadFaxLines and
ConsecutiveBadFaxLines. Also write CleanFaxData = 1 or 2 if
the hardware's regeneration capability is known.
4. Source image data stream is error-corrected or otherwise
guaranteed to be error-free such as for a computer generated
file: SHOULD NOT write page-quality fields.
TIFF Writers SHOULD only generate these fields when the image has been
generated from a fax image data stream where error correction, e.g.
Group 3 Error Correction Mode, was not used.
4.4.6. Practical Guidelines for Writing and Reading Multi-Page TIFF-F Files
Traditionally, historical TIFF-F has required readers and writers
to be able to handle multi-page TIFF-F files. Based on the
experience of various TIFF-F implementors, it has been seen that
the implementation of TIFF-F can be greatly simplified if certain
practical guidelines are followed when writing multi-page TIFF-F
files. These guidelines or simplifying assumptions are a subset of
the ordering principles in Section 2.1.3.
The structure for a multi-page TIFF-F file will include one IFD per
page of the document; this corresponds to the first principle in
Section 2.1.3. In this case, this IFD will define the attributes for
a single page. A second simplifying assumption is that the writer
of TIFF-F files SHOULD present IFDs in the same order as the actual
sequence of pages. (The pages are numbered within TIFF-F beginning
with page 0 as the first page and then ascending (i.e. 0, 1, 2,
...). However, as noted in 2.1.3, any field values over 4 bytes
will be stored separately from the IFD. TIFF-F readers SHOULD
expect IFDs to be presented in page order, but be able to handle
exceptions.
Per [TIFF], the exact placement of image data is not specified.
However, the strip offsets for each strip of image are defined from
within each IFD. Where possible, another simplifying assumption
for the writing of TIFF-F files is to specify that the image data
for each page of a multi-page document SHOULD be contained within a
single strip (i.e. one image strip per fax page). The use of a
single image strip per page is very useful for applications such as
store and forward messaging, where the file is usually prepared in
advance of the transmission, but other assumptions may apply for
the size of the image strip for applications which require the use
of "streaming" techniques (see section 4.4.7). In the event a
different image strip size assumption has been used (e.g. constant
size for image strips that may be less than the page size), this
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will immediately be evident from the values/offsets of the fields
that are related to strips.
A third simplifying assumption is that each IFD SHOULD be placed in
the TIFF-F file structure at a point which precedes the image which
the IFD describes.
In addition, a fourth simplifying assumption for TIFF-F writers and
readers is to place the actual image data in a physical order
within the TIFF file structure which is consistent with the logical
page order. In practice, TIFF-F readers will need to use the strip
offsets to find the exact physical location of the image data,
whether or not it is presented in logical page order.
TIFF-F writers MAY make a fifth simplifying assumption, in which the
IFD, the value data and the image data to which the IFD has offsets
precede the next image IFD. These elements SHALL precede the next image
IFD in the minimal mode (Section 3) and SHOULD precede it in the other
modes (Sections 5-8). However, this principle has been relaxed in the
case of TIFF-F to reflect past practices.
So, a TIFF-F file which is structured using the guidelines of this
section will essentially be composed of a linked list of IFDs,
presented in ascending page order, which in turn each point to a
single page of image data (one strip per page), where the pages of
image data are also placed in a logical page order within the TIFF-
F file structure. (The pages of image data may themselves be
stored in a contiguous manner, at the option of the implementor).
4.4.7. Use of TIFF-F for Streaming Applications
TIFF-F has historically been used for handling fax image files in
applications such as store and forward messaging where the entire
size of the file is known in advance. While TIFF-F may also
possibly be used as a file format for cases such as streaming
applications, assumptions may be required that differ from those
provided in this section (e.g., the entire size and number of pages
within the image are not known in advance). As a result, a
definition for the streaming application of TIFF-F is beyond the
scope of this document.
4.5. Implementation Warnings
4.5.1 Uncompressed data
TIFF-F requires the ability to read and write at least one-dimensional
T.4 Huffman ("compressed") data. Uncompressed data is not allowed.
This means that the "Uncompressed" bit in T4Options or T6Options must be
set to 0.
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4.5.2. Encoding and Resolution
Since two-dimensional encoding is not required for Group 3
compatibility, some historic TIFF-F readers have not been able to read
such files. The minimum subset of TIFF-F REQUIRES support for one
dimensional (Modified Huffman) files, so this choice maximizes
portability. However, implementers seeking greater efficiency SHOULD
use T.6 MMR compression when writing TIFF-F files. Some TIFF-F readers
will also support two-dimensional Modified READ files. Implementers
that wish to have the maximum flexibility in reading TIFF-F files SHOULD
support all three of these compression methods (MH, MR and MMR).
For the case of resolution, almost all facsimile products support both
standard (98 dpi) vertical resolution and "fine" (196 dpi) resolution.
Therefore, fine-resolution files are quite portable in the real world.
In 1993, the ITU-T added support for higher resolutions in the T.30
recommendation including 200 x 200, 300 x 300, 400 x 400 in dots per
inch based units. At the same time, support was added for metric
dimensions which are equivalent to the following inch based resolutions:
391v x 204h and 391v x 408h. Therefore, the full set of inch-based
equivalents of the new resolutions are supported in the TIFF-F writer,
since they may appear in some image data streams received from Group 3
facsimile devices. However, many facsimile terminals and older versions
of TIFF-F readers are likely to not support the use of these higher
resolutions.
Per [T.4], it is permissible for applications to treat the following
XResolution values as being equivalent: <204,200> and <400,408>. In a
similar respect, the following YResolution values may also be treated as
being equivalent: <98, 100>, <196, 200>, and <391, 400>. These
equivalencies were allowed by [T.4] to permit conversions between inch
and metric based facsimile terminals.
In a similar respect, the optional support of metric based resolutions
in the TIFF-F reader (i.e. 77 x 38.5 cm) is included for completeness,
since they are used in some legacy TIFF-F applications, but this use is
not recommended for the creation of TIFF-F files by a writer.
4.5.3. EOL byte-aligned
The historical convention for TIFF-F has been that all EOLs in Modified
Huffman or Modified READ data must be byte-aligned. However, Baseline
TIFF has permitted use of non-byte-aligned EOLs by default, so that a
large percentage of TIFF-F reader implementations support both
conventions. Therefore, the minimum subset of TIFF-F as defined in
this document includes support for both byte-aligned and non-byte-
aligned EOLs; see Section 3.2.2.
An EOL is said to be byte-aligned when Fill bits have been added as
necessary before EOL codes such that EOL always ends on a byte boundary,
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thus ensuring an EOL-sequence of a one byte preceded by a zero nibble:
xxxx0000 00000001.
Modified Huffman encoding encodes bits, not bytes. This means that the
end-of-line token may end in the middle of a byte. In byte alignment,
extra zero bits (Fill) are added so that the first bit of data following
an EOL begins on a byte boundary. In effect, byte alignment relieves
application software of the burden of bit- shifting every byte while
parsing scan lines for line-oriented image manipulation (such as writing
a TIFF file).
For Modified READ encoding, each line is terminated by an EOL and a one
bit tag bit. Per [T.4], the value of the tag bit is 0 if the next line
contains two dimensional data and 1 if the next line is a reference
line. To maintain byte alignment, fill bits are added before the
EOL/tag bit sequence, so that the first bit of data following an MR tag
bit begins on a byte boundary.
4.5.4. EOL
As illustrated in FIGURE 1/T.4 in [T.4], facsimile documents encoded
with Modified Huffman begin with an EOL, which in TIFF-F is byte-
aligned. The last line of the image is not terminated by an EOL. In a
similar respect, images encoded with Modified READ two-dimensional
encoding begin with an EOL, followed by a tag bit.
4.5.5. RTC Exclusion
Aside from EOLs, TIFF-F files have historically only contained image
data. This means that applications which wish to maintain strict
conformance with the rules in [TIFF] and compatibility with historical
TIFF-F, SHOULD NOT include the Return To Control sequence (RTC)
(consisting of 6 consecutive EOLs) when writing TIFF- F files.
However, applications which need to support "transparency" of [T.4]
image data MAY include RTCs if the flag settings of the T4Options field
are set for non-byte aligned MH or MR image data. Implementors of TIFF
readers should also be aware that there are some existing TIFF-F
implementations which include the RTC sequence in MH/MR image data.
Therefore, TIFF-F readers MUST be able to process files which do not
include RTCs and SHOULD be able to process files which do include RTCs.
4.5.6 Use of EOFB for T.6 Compressed Images
TIFF-F pages which are encoded with the T.6 Modified Modified READ
compression method MUST include an "end-of-facsimile-block" (EOFB) code
at the end of each coded strip. Per [TIFF], the EOFB code is followed by
pad bits as needed to align on a byte boundary. TIFF readers SHOULD
ignore any bits other than pad bits beyond the EOFB.
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4.6. Example Use of TIFF-F
The application F of TIFF (i.e. TIFF-F content) is a secondary component
of the VPIM Message, as defined in [VPIM2]. Voice messaging systems can
often handle fax store-and-forward capabilities in addition to tradi-
tional voice message store-and-forward functions. As a result, TIFF-F
fax messages can optionally be sent between compliant VPIM systems, and
may be rejected if the recipient system cannot deal with fax.
Refer to the VPIM Specification for proper usage of this content.
4.7. Extended Black-and-white Fax Mode Summary
Recommended fields are shown with an asterisk *.
Required fields or values are shown with a double asterisk **. If the
double asterisk is on the field name, then all the listed values are
required of implementations; if the double asterisks are in the Values
column, then only the values suffixed with a double asterisk are
required of implementations.
+---------------------------+--------------------------------+
| Baseline Fields | Values |
+---------------------------+--------------------------------+
| BitsPerSample | 1** |
+---------------------------+--------------------------------+
| Compression | 3**: 1D Modified Huffman and |
| | 2D Modified Read coding |
| | 4: 2D Modified Modified Read |
| | coding |
+---------------------------+--------------------------------+
| DateTime* | {ASCII}: date/time in 24-hour |
| | format "YYYY:MM:DD HH:MM:SS" |
+---------------------------+--------------------------------+
| FillOrder** | 1: most significant bit first |
| | 2: least significant bit first |
+---------------------------+--------------------------------+
| ImageDescription* | {ASCII}: A string describing |
| | the contents of the image. |
+---------------------------+--------------------------------+
| ImageWidth | 1728**, 2048, 2432, 2592, |
| | 3072, 3456, 3648, 4096, 4864 |
+---------------------------+--------------------------------+
| ImageLength** | n: total number of scanlines |
| | in image |
+---------------------------+--------------------------------+
| NewSubFileType** | 2: Bit 1 identifies single |
| | page of a multi-page document |
+---------------------------+--------------------------------+
| Orientation | 1**-8, Default 1 |
+---------------------------+--------------------------------+
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+---------------------------+--------------------------------+
| PhotometricInterpretation | 0: pixel value 1 means black |
| ** | 1: pixel value 1 means white |
+---------------------------+--------------------------------+
| ResolutionUnit** | 2: inch |
| | 3: centimeter |
+---------------------------+--------------------------------+
| RowsPerStrip** | n: number of scanlines per |
| | TIFF strip |
+---------------------------+--------------------------------+
| SamplesPerPixel** | 1 |
+---------------------------+--------------------------------+
| Software* | {ASCII}: name & release |
| | number of creator software |
+---------------------------+--------------------------------+
| StripByteCounts** | <n>: number or bytes in TIFF |
| | strip |
+---------------------------+--------------------------------+
| StripOffsets** | <n>: offset from beginning of |
| | file to each TIFF strip |
+---------------------------+--------------------------------+
| XResolution | 200, 204**, 300, 400, 408 |
| | (written in pixels/inch) |
+---------------------------+--------------------------------+
| YResolution | 98**, 196**, 100, |
| | 200, 300, 391, 400 |
| | (written in pixels/inch) |
+---------------------------+--------------------------------+
| Extension Fields |
+---------------------------+--------------------------------+
| T4Options | 0**: required if Compression |
| | is Modified Huffman, EOLs are |
| | not byte aligned |
| | 1: required if Compression is |
| | 2D Modified Read, EOLs are |
| | byte aligned |
| | 4**: required if Compression |
| | is Modified Huffman, EOLs are |
| | not byte aligned |
| | 5: required if Compression |
| | is 2D Modified Read, EOLs are |
| | byte aligned |
+---------------------------+--------------------------------+
| T6Options | 0: required if Compression is |
| | 2D Modified Modified Read |
+---------------------------+--------------------------------+
| DocumentName* | {ASCII}: name of scanned |
| | document |
+---------------------------+--------------------------------+
| PageNumber** | n,m: page number followed by |
| | total page count |
+---------------------------+--------------------------------+
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+---------------------------+--------------------------------+
| New Fields |
+---------------------------+--------------------------------+
| BadFaxLines* | number of "bad" scanlines |
| | encountered during reception |
+---------------------------+--------------------------------+
| CleanFaxData* | 0: no "bad" lines |
| | 1: "bad" lines exist, but were |
| | regenerated by receiver |
| | 2: "bad" lines exist, but have |
| | not been regenerated |
+---------------------------+--------------------------------+
| ConsecutiveBadFaxLines* | Max number of consecutive |
| | "bad" lines received |
+---------------------------+--------------------------------+
5. Lossless JBIG Black-and-White Fax Mode
This section defines the lossless JBIG mode for black-and-white
facsimile.
The previous section described the extended interchange set of TIFF
fields for black-and-white fax, which provided support for the MH, MR
and MMR compression of black-and-white images. This section adds a mode
with JBIG compression capability.
5.1. Overview
This section describes a black-and-white mode that uses JBIG
compression. The ITU-T has approved the single-progression sequential
mode of JBIG [T.82] for Group 3 facsimile. JBIG coding offers improved
compression for halftoned originals. JBIG compression is used in
accordance with the application rules given in ITU-T Rec. T.85 [T.85].
This mode is essentially the extended black-and-white mode with JBIG
compression used instead of MH, MR or MMR.
5.2. Required TIFF Fields
This section lists the required fields and the values they must have to
be ITU-compatible. Besides the fields listed in Section 2.2.1, the
extended black-and-white fax mode requires the following fields.
5.2.1. Baseline fields
The TIFF fields that SHALL be used in this mode are the same as those
described in Section 4.2.1 for the extended black-and-white mode, with
one exception: the following text is used for the Compression field in
place of the Compression field text given in Section 4.2.1.
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Compression(259) = 9. SHORT
RequiredByTIFFBaseline
9 = ITU-T Rec. T.82 coding, applying ITU-T Rec. T.85 (JBIG). This is
a TIFF extension value.
Default = 1 (and is not applicable; field must be specified).
5.2.2. Extension fields
None beyond those listed in Section 2.2.1.
5.2.3. New fields
None.
5.3. Recommended TIFF Fields
See Section 2.2.3 and 2.2.4.
5.4. Lossless JBIG Black-and-white Fax Mode Summary
Recommended fields are shown with an asterisk *.
Required fields or values are shown with a double asterisk **. If the
double asterisk is on the field name, then all the listed values are
required of implementations; if the double asterisks are in the Values
column, then only the values suffixed with a double asterisk are
required of implementations.
+---------------------------+--------------------------------+
| Baseline Fields | Values |
+---------------------------+--------------------------------+
| BitsPerSample | 1** |
+---------------------------+--------------------------------+
| Compression | 9**: JBIG coding |
+---------------------------+--------------------------------+
| DateTime* | {ASCII}: date/time in 24-hour |
| | format "YYYY:MM:DD HH:MM:SS" |
+---------------------------+--------------------------------+
| FillOrder** | 1: most significant bit first |
| | 2: least significant bit first |
+---------------------------+--------------------------------+
| ImageDescription* | {ASCII}: A string describing |
| | the contents of the image. |
+---------------------------+--------------------------------+
| ImageWidth** | 1728, 2048, 2432, 2592, |
| | 3072, 3456, 3648, 4096, 4864 |
+---------------------------+--------------------------------+
| ImageLength** | n: total number of scanlines |
| | in image |
+---------------------------+--------------------------------+
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+---------------------------+--------------------------------+
| NewSubFileType** | 2: Bit 1 identifies single |
| | page of a multi-page document |
+---------------------------+--------------------------------+
| Orientation | 1**-8, Default 1 |
+---------------------------+--------------------------------+
| PhotometricInterpretation | 0: pixel value 1 means black |
| ** | 1: pixel value 1 means white |
+---------------------------+--------------------------------+
| ResolutionUnit** | 2: inch |
| | 3: centimeter |
+---------------------------+--------------------------------+
| RowsPerStrip** | n: number of scanlines per |
| | TIFF strip |
+---------------------------+--------------------------------+
| SamplesPerPixel** | 1 |
+---------------------------+--------------------------------+
| Software* | {ASCII}: name & release |
| | number of creator software |
+---------------------------+--------------------------------+
| StripByteCounts** | <n>: number of bytes in TIFF |
| | strip |
+---------------------------+--------------------------------+
| StripOffsets** | <n>: offset from beginning of |
| | file to each TIFF strip |
+---------------------------+--------------------------------+
| XResolution | 200, 204**, 300, 400, 408 |
| | (written in pixels/inch) |
+---------------------------+--------------------------------+
| YResolution | 98**, 196**, 100, |
| | 200, 300, 391, 400 |
| | (written in pixels/inch) |
+---------------------------+--------------------------------+
| Extension Fields |
+---------------------------+--------------------------------+
| DocumentName* | {ASCII}: name of documnent |
| | scanned |
+---------------------------+--------------------------------+
| PageNumber** | n,m: page number followed by |
| | total page count |
+---------------------------+--------------------------------+
| New Fields |
+---------------------------+--------------------------------+
| GlobalParametersIFD* | <IFD>: global parameters IFD |
+---------------------------+--------------------------------+
| ProfileType* | n: type of data stored in file |
+---------------------------+--------------------------------+
| ITUFaxMode* | n: ITU-compatible fax mode |
+---------------------------+--------------------------------+
| CodingMethods* | n: compression algorithms used |
| | in file |
+---------------------------+--------------------------------+
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6. Base Color Fax Mode
6.1. Overview
This section defines the lossy color mode of TIFF for facsimile.
This is the base mode for color and grayscale facsimile, which means
that all applications that support color fax must support this mode. The
basic approach is the lossy JPEG compression [T.81] of L*a*b* color data
[T.42]. Grayscale applications use the L* lightness component; color
applications use the L*, a* and b* components.
This mode uses a new PhotometricInterpretation field value to describe
the L*a*b* encoding specified in [T.42]. This encoding differs in two
ways from the other L*a*b* encodings used in TIFF [TIFF, TTN1]: it
specifies a different default range for the a* and b* components, based
on a comprehensive evaluation of existing hardcopy output, and it
optionally allows selectable range for the L*, a* and b* components.
6.2. Required TIFF Fields
This section lists the required fields, in addition to those given in
Section 2.2.1, and the values they must support to be compatible with
ITU-T Rec. T.42 and Annex E in ITU-T Rec. T.4.
6.2.1. Baseline Fields
ImageWidth(256). SHORT or LONG
This mode supports the following fixed page widths: 864, 1024, 1216,
1728, 2048, 2432, 2592, 3072, 3456, 3648, 4096, 4864.
BitsPerSample(258) = 8, 12. SHORT
Count = SamplesPerPixel
The base color fax mode requires 8 bits per sample, with 12 as an
option. 12 bits per sample is not baseline TIFF.
Compression(259) = 7. SHORT
Base color fax mode uses Baseline JPEG compression. Value 7
represents JPEG compression as specified in [TTN2].
PhotometricInterpretation(262) = 10. SHORT
Base color fax mode requires pixel values to be stored using the CIE
L*a*b* encoding defined in ITU-T Rec. T.42. This encoding is
indicated by the PhotometricInterpretation value 10, referred to as
ITULAB. With this encoding, the minimum sample value is
mapped to 0 and the maximum sample value is mapped to (2^n - 1),
i.e. the maximum value, where n is the BitsPerSample value.
The conversion from unsigned ITULAB-encoded samples values to signed
CIE L*a*b* values is determined by the Decode field; see Sec. 6.2.2
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NOTE: PhotometricInterpretation values 8 and 9 specify encodings for CIE
L*a*b* [TIFF] and ICC L*a*b* [TTN1], but they are fixed encodings, which
use different minimum and maximum samples than the T.42 default
encoding. As currently defined, they are not able to represent fax-
encoded L*a*b* data.
ResolutionUnit(296) = 2, 3. SHORT
The unit of measure for resolution. 2 = inch, 3 = centimeter;
Default = 2 (field may be omitted if this is the value)
SamplesPerPixel(277) = 1, 3. SHORT
1: L* component only
3: L*, a*, b* components
Encoded according to PhotometricInterpretation field
XResolution(282) = 100, 200, 300, 400. RATIONAL
YResolution(283) = 100, 200, 300, 400. RATIONAL
The resolution of the image is expressed in pixels per resolution
unit. In pixels per inch, allowed XResolution values are: 100, 200,
300, and 400. The base color fax mode requires the pixels to be
square, hence YResolution must equal XResolution. Base resolution is
200 pixels per inch and SHALL be supported by all implementations of
this mode. See Section 2.2.2 for inch-metric equivalency.
NOTE: Not all combinations of XResolution, YResolution and ImageWidth
are legal. The following table gives the legal combinations for inch-
based resolutions and the corresponding paper sizes [T.30].
+--------------------------------+---------------------------+
| XResolution x YResolution | ImageWidth |
+--------------------------------+---------------------------+
| 100 x 100 | 864 | 1024 | 1216 |
+--------------------------------+---------------------------+
| 200 x 200 | 1728 | 2048 | 2432 |
+--------------------------------+---------------------------+
| 300 x 300 | 2592 | 3072 | 3648 |
+--------------------------------+---------------------------+
| 400 x 400 | 3456 | 4096 | 4864 |
+--------------------------------+---------------------------+
|Letter,A4| B4 | A3 |
| Legal | | |
+---------------------------+
| Paper Size |
+---------------------------+
6.2.2 Extension Fields
The JPEG compression standard allows for the a*b* chroma components of
an image to be subsampled relative to the L* lightness component. The
extension fields ChromaSubSampling and ChromaPositioning define the
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subsampling. They are the same as YCbCrSubSampling and YCbCrPositioning
in [TIFF], but have been renamed to reflect their applicability to other
color spaces.
ChromaSubSampling(530). SHORT
Count = 2
Specifies the subsampling factors for the chroma components of a
L*a*b* image. The two subfields of this field, ChromaSubsampleHoriz
and ChromaSubsampleVert, specify the horizontal and vertical
subsampling factors respectively.
SHORT 0: ChromaSubsampleHoriz = 1, 2, 4.
1: equal numbers of lightness and chroma samples horizontally,
2: twice as many lightness samples as chroma samples horizontally,
4: four times as many lightness samples as chroma samples
horizontally.
SHORT 1: ChromaSubsampleVert = 1, 2, 4.
1: equal numbers of lightness and chroma samples vertically,
2: twice as many lightness samples as chroma samples vertically,
4: four times as many lightness samples as chroma samples
vertically.
The default value for ChromaSubSampling is (2,2), which is the
default for chroma subsampling in color fax [T.42]. No chroma
subsampling, i.e. ChromaSubSampling = (1,1), is a T.42 option.
ChromaPositioning(531) = 1, 2. SHORT
Specifies the spatial positioning of chroma components relative to
the lightness component. See the current TIFF specification under
YCbCrPositioning for further information.
1: centered,
2: cosited.
Default = 1, which is what ITU-T T.4, Annex E specifies.
Decode(TagToBeAssigned). SHORT
Count = 2 * SamplesPerPixel
Describes how to map image sample values into the range of values
appropriate for the current color space. In general, the values are
taken in pairs and specify the minimum and maximum output value for
each color component. For the base color fax mode, Decode maps the
ITULAB encoding to L*a*b* and has a count of 6 values. In this case,
the input is an unsigned ITULAB-encoded value (Lsample, asample,
(bsample) and the output is a signed L*a*b* value.
L* = Decode[0] + Lsample x (Decode[1]-Decode[0])/(2^n -1)
a* = Decode[2] + asample x (Decode[3]-Decode[2])/(2^n -1)
b* = Decode[4] + bsample x (Decode[5]-Decode[4])/(2^n -1)
where Decode[0] is the minimum value for L*, Decode[1] is the
maximum value, etc. and n is the BitsPerSample field value, either 8
or 12. ITU-T Rec. T.42 specifies the ITULAB encoding in terms of a
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range and offset for each component, which are related to the Decode
field values as follows:
Decode[0] = - (Lrange x Loffset) / 2^n
Decode[1] = Decode[0] + Lrange
NOTE: The following table gives the default range and offsets, as
specified in ITU-T Rec. T.42, and the corresponding minimum and maximum
L*a*b* component and ITULAB encoded values.
+-----------------------------------------------------------+
| Component | Rec. T.42 | L*a*b* | ITULAB |
| | defaults | values | encoding |
+-----------+------------------+------------+---------------+
| | Range | Offset | Min | Max | Min | Max |
+-----------+--------+---------+------+-----+-----+---------+
| L* | 100 | 0 | 0 | 100 | 0 | 2^n - 1 |
+-----------+--------+---------+------+-----+-----+---------+
| a* | 170 | 128 | -85 | 85 | 0 | 2^n - 1 |
+-----------+--------+---------+------+-----+-----+---------+
| b* | 200 | 96 | -75 | 125 | 0 | 2^n - 1 |
+-----------+--------+---------+------+-----+-----+---------+
The default value for Decode is (0, 100, -85, 85, -75, 125), which is
based on the ITULAB encoding, with PhotometricInterpretation 10,
SamplesPerPixel 3, and BitsPerSample 8.
6.2.3. New Fields
None.
6.3. Recommended TIFF Fields
See Sections 2.2.3. and 2.2.4.
6.4 Base Color Fax Mode Summary
Recommended fields are shown with an asterisk *
Required fields or values are shown with a double asterisk **. If the
double asterisk is on the field name, then all the listed values are
required of implementations; if the double asterisks are in the Values
column, then only the values suffixed with a double asterisk are
required of implementations.
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+---------------------------+--------------------------------+
| Baseline Fields | Values |
+---------------------------+--------------------------------+
| BitsPerSample | 8**: 8 bits per color sample |
| | 12: optional 12 bits/sample |
+---------------------------+--------------------------------+
| Compression** | 7: JPEG |
+---------------------------+--------------------------------+
| DateTime* | {ASCII}: date/time in 24-hour |
| | format "YYYY:MM:DD HH:MM:SS" |
+---------------------------+--------------------------------+
| ImageDescription* | {ASCII}: A string describing |
| | the contents of the image. |
+---------------------------+--------------------------------+
| ImageWidth | 864, 1024, 1216, 1728**, 2048**|
| | 2432**, 2592, 3072, 3456, 3648 |
| | 4096, 4864 |
+---------------------------+--------------------------------+
| ImageLength** | n: total number of scanlines |
| | in image |
+---------------------------+--------------------------------+
| NewSubFileType** | 2: Bit 1 identifies single page|
| | of a multi-page document |
+---------------------------+--------------------------------+
| Orientation | 1**-8, Default 1 |
+---------------------------+--------------------------------+
| PhotometricInterpretation | 10**: ITULAB |
+---------------------------+--------------------------------+
| ResolutionUnit** | 2: inch |
| | 3: centimeter |
+---------------------------+--------------------------------+
| RowsPerStrip** | n: number of scanlines per |
| | TIFF strip |
+---------------------------+--------------------------------+
| SamplesPerPixel** | 1: L* (lightness) |
| | 3: LAB |
+---------------------------+--------------------------------+
| Software* | {ASCII}: name & release number |
| | of creator software |
+---------------------------+--------------------------------+
| StripByteCounts** | <n>: number or bytes in |
| | TIFF strip |
+---------------------------+--------------------------------+
| StripOffsets** | <n>: offset from beginning |
| | of file to each TIFF strip |
+---------------------------+--------------------------------+
| XResolution | 100, 200**, 300, 400 (written |
| | in pixels/inch) |
+---------------------------+--------------------------------+
| YResolution | 100, 200**, 300, 400 |
| | (must equal XResolution) |
+---------------------------+--------------------------------+
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+---------------------------+--------------------------------+
| Extension Fields |
+---------------------------+--------------------------------+
| DocumentName* | {ASCII}: name of scanned |
| | document |
+---------------------------+--------------------------------+
| PageNumber** | n,m: page number followed by |
| | total page count |
+---------------------------+--------------------------------+
| Decode** | minL, maxL, mina, maxa, minb, |
| | maxb: minimum and maximum |
| | values for L*a*b* |
+---------------------------+--------------------------------+
| ChromaSubSampling | ChromaSubsampleHoriz: |
| | 1: equal numbers of lightness |
| | and chroma samples |
| | 2**: twice as many lightness |
| | samples as chroma samples |
| | 4: four times as many |
| | lightness samples as chroma |
| | samples |
| | ChromaSubsampleVert: |
| | 1: equal numbers of lightness |
| | and chroma samples |
| | 2**: twice as many lightness |
| | samples as chroma samples |
| | 4: four times as many lightness|
| | samples as chroma samples |
+---------------------------+--------------------------------+
| ChromaPositioning | 1**: centered |
| | 2: cosited |
+---------------------------+--------------------------------+
| New Fields |
+---------------------------+--------------------------------+
| GlobalParametersIFD* | <IFD>: IFD containing |
| | global parameters |
+---------------------------+--------------------------------+
| ProfileType* | n: type of data stored in |
| | TIFF file |
+---------------------------+--------------------------------+
| ITUFaxMode* | n: ITU-compatible fax mode |
+---------------------------+--------------------------------+
| CodingMethods* | n: compression algorithms |
| | used in file |
+---------------------------+--------------------------------+
| VersionYear* | byte sequence: year of ITU std |
+---------------------------+--------------------------------+
7. Lossless Color Mode
This section defines the lossless color mode of TIFF for facsimile.
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7.1. Overview
This mode, defined in [T.43], uses JBIG to losslessly code three types
of color and grayscale images: one bit per color CMY, CMYK and RGB
images; a palettized (i.e. mapped) color image; and continuous tone
color and grayscale images. The last two are multi-level and use the
L*a*b* encoding specified in [T.42].
7.1.1. Color Encoding
While under development, this mode was called T.Palette, as one of its
major additions was palette or mapped color images. Baseline TIFF only
allows RGB color maps, but ITU-T Rec. T.43 requires L*a*b* color maps,
using the encoding specified in ITU-T Rec. T.42. Palette color images
are expressed with indices (bits per sample) of 12 bits or less, or
optionally 13 to 16 bits, per [T.43].
Enabling T.43 color maps in TIFF requires the extension field Indexed,
defined in [TTN1], and the PhotometricInterpretation field value 10,
defined in Section 6.2.1. The following table shows the corresponding
PhotometricInterpretation, SamplesPerPixel, BitsPerSample and Indexed
field values for the different T.43 image types.
+----------------------------------------------------------+
| Image Type |PhotometricIn| Samples | Bits Per | Indexed |
| |-terpretation| PerPixel | Sample | |
|------------+-------------+----------+----------+---------|
| RGB | 2=RGB | 3 | 1 | 0 |
+----------------------------------------------------------+
| CMY | 5=CMYK | 3 | 1 | 0 |
+------------+-------------+----------+----------+---------+
| CMYK | 5=CMYK | 4 | 1 | 0 |
+------------+-------------+----------+----------+---------+
| Palette | 10=ITULAB | 1 | n | 1 |
+------------+-------------+----------+----------+---------+
| Grayscale | 10=ITULAB | 1 | 8, 12 | 0 |
+------------+-------------+----------+----------+---------+
| Color | 10=ITULAB | 3 | 8, 12 | 0 |
+------------+-------------+----------+----------+---------+
7.1.2. JBIG Encoding
T.43 uses the single-progression sequential mode of JBIG, defined in
ITU-T Rec. T.82, in accordance with the application rules described in
ITU-T Rec. T.85. To code multi-level images using JBIG, which is a
bi-level compression method, an image is resolved into a set of
bit-planes using Gray code conversion, and each bit-plane is then JBIG
compressed. The Gray code conversion is part of the data stream
encoding, and is therefore invisible to TIFF.
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7.2. Required TIFF Fields
This section lists the required fields, in addition to those in Section
2.2.1, and the values they must have to be compatible with ITU-T Rec.
T.43.
7.2.1. Baseline Fields
ImageWidth(256). SHORT or LONG
Same page widths as the base color mode; see Section 6.2.1.
BitsPerSample(258) = 1, 8, 9-16. SHORT
Count = SamplesPerPixel
RGB, CMY, CMYK: 1 bit per sample
Continuous tone (L*a*b*): 8 bits per sample, 12 bits optional
Palette color: 12 or fewer bits per sample, 13-16 bits optional
Note: More than 8 bits per sample is not baseline TIFF.
ColorMap(320). SHORT
Count = 3 * (2**BitsPerSample)
Lossless color fax mode supports palette-color (indexed) images
where the single component value is used as an index into a full
color lookup table stored in the ColorMap field. With lossless color
fax mode, only the ITULAB encoding with 8 bits per sample is
supported for palette-color images. To utilize a color map, the TIFF
Indexed field must be present. TIFF orders the color map values so
that all the L* values come first, followed by all the a* values and
then all the b* values. Because ITU-T Rec. T.43 specifies a "chunky"
ordering with the L*a*b*components of the first value, followed by
those of the second value, and so on, transferring color map values
between a TIFF file and fax data stream requires reordering values.
Compression(259) = 9. SHORT
9: ITU-T Rec. T.82 coding, applying ITU-T Rec. T.85 (JBIG)
FillOrder(266) = 1, 2. SHORT
This field is only relevant for 1 bit per sample color (RGB, CMY,
CMYK); see Section 4.2.1 for further information.
PhotometricInterpretation(262) = 2, 5, 10. SHORT
2: RGB
5: CMYK, including CMY
10: ITULAB
Image data may also be stored as palette color images, where pixel
values are represented by a single component that is an index into a
color map using the ITULAB encoding. This color map is specified by
the ColorMap field. To use palette color images, set the
PhotometricInterpretation to 10,SamplesPerPixel to 1, and Indexed to
1. The color map is stored in the ColorMap field. See Section 7.1.1
for further discussion on the color encoding.
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ResolutionUnit(296) = 2, 3. SHORT
The unit of measure for resolution. 2 = inch, 3 = centimeter;
Default = 2 (field may be omitted if this is the value)
SamplesPerPixel(277) = 1, 3, 4. SHORT
1: Palette color image, or L*-only if Indexed = 0 and
PhotometricInterpretation is 10 (ITULAB).
3: RGB, or L*a*b*, or CMY if PhotometricInterpretation is 5 (CMYK).
4: CMYK.
XResolution(282) = 100, 200, 300, 400. RATIONAL
YResolution(283) = 100, 200, 300, 400. RATIONAL
The resolution of the image is expressed in pixels per resolution
unit. In pixels per inch, allowed XResolution values are: 100, 200,
300, and 400. The lossless color fax mode requires the pixels to be
square, hence YResolution must equal XResolution. Base resolution is
200 pixels per inch. See Section 2.2.2 for inch-metric equivalency.
7.2.2. Extension Fields
Indexed(364) = 0, 1. SHORT
0: not a palette-color image
1: palette-color image
This field is used to indicate that the sample values are an index
into an array of color values specified in the ColorMap field.
Lossless color fax mode supports palette-color images with the
ITULAB encoding. The SamplesPerPixel value must be 1.
Decode(TagToBeAssigned) SHORT
Decode is used in connection with the ITULAB encoding of image data;
see Section 6.2.2.
7.2.3. New Fields
None.
7.3. Recommended TIFF Fields
See Sections 2.2.3. and 2.2.4.
7.4. Lossless Color Fax Mode Summary
Recommended fields are shown with an asterisk *
+--------------------|--------------------------------------+
| Baseline Fields | Values |
+--------------------+--------------------------------------+
| BitsPerSample | 1: Binary RGB, CMY(K) |
| | 8: 8 bits per color sample |
| | 9-16: optional |
+--------------------+--------------------------------------+
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+--------------------+--------------------------------------+
| ColorMap | n: LAB color map |
+--------------------+--------------------------------------+
| Compression | 9: JBIG |
+--------------------+--------------------------------------+
| DateTime* | {ASCII}: date/time in the 24-hour |
| | format "YYYY:MM:DD HH:MM:SS" |
+--------------------+--------------------------------------+
| FillOrder | Applies only to 1 bit/sample encoding|
| | 1: Most significant bit first |
| | 2: Least significant bit first |
+--------------------+--------------------------------------+
| ImageDescription* | {ASCII}: A string describing the |
| | contents of the image. |
+--------------------+--------------------------------------+
| ImageWidth | 864, 1024, 1216, 1728, 2048, 2432, |
| | 2592, 3072, 3456, 3648, 4096, 4864 |
+--------------------+--------------------------------------+
| ImageLength | n: total number of scanlines in image|
+--------------------+--------------------------------------+
| NewSubFileType | 2: Bit 1 identifies single page of a |
| | multi-page document |
+--------------------+--------------------------------------+
| Orientation | 1**-8, Default 1 |
+--------------------+--------------------------------------+
| PhotometricInter- | 2: RGB |
| pretation | 5: CMYK |
| | 10: ITULAB |
+--------------------+--------------------------------------+
| ResolutionUnit | 2: inch |
| | 3: centimeter |
+--------------------+--------------------------------------+
| RowsPerStrip | n: number of scanlines per TIFF strip|
+--------------------+--------------------------------------+
| SamplesPerPixel | 1: L* (lightness) |
| | 3: LAB, RGB, CMY |
| | 4: CMYK |
+--------------------+--------------------------------------+
| Software* | {ASCII}: name & release number of |
| | creator software |
+--------------------+--------------------------------------+
| StripByteCounts | <n>: number or bytes in TIFF strip |
+--------------------+--------------------------------------+
| StripOffsets | <n>: offset from beginning of file to|
| | each TIFF strip |
+--------------------+--------------------------------------+
| XResolution | 100, 200, 300, 400 (written in |
| | pixels/inch) |
+--------------------+--------------------------------------+
| YResolution | equal to XResolution (pixels must be |
| | square) |
+--------------------+--------------------------------------+
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+--------------------+--------------------------------------+
| Extension Fields |
+--------------------+--------------------------------------+
| Decode | minL, maxL, mina, maxa, minb, maxb: |
| |minimum and maximum values for L*a*b* |
+--------------------+--------------------------------------+
| DocumentName* | {ASCII}: name of scanned document |
+--------------------+--------------------------------------+
| PageNumber | n,m: page number followed by total |
| | page count |
+--------------------+--------------------------------------+
| Indexed | 0: not a palette-color image |
| | 1: palette-color image |
+--------------------+--------------------------------------+
| New Fields |
+--------------------+--------------------------------------|
| GlobalParameters | <IFD>: global parameters IFD |
| IFD* | |
+--------------------+--------------------------------------+
| ProfileType* | n: type of data stored in TIFF file |
+--------------------+--------------------------------------+
| ITUFaxMode* | n: ITU-compatible fax mode |
+--------------------+--------------------------------------+
| CodingMethods* | n:compression algorithms used in |
| | file |
+--------------------+--------------------------------------+
| VersionYear* | byte sequence: year of ITU fax std |
+--------------------+--------------------------------------+
8. Mixed Raster Content Mode
This section defines the Mixed Raster Content mode of TIFF for
facsimile.
8.1. Overview
Unlike previous fax modes, which use a single coding method and spatial
resolution for an entire fax page, the Mixed Raster Content mode [T.44]
enables different coding methods and resolutions within a single page.
For example, consider a page that contains black-and-white text, which
is best coded with MMR or JBIG, a color bar chart, best coded with JBIG,
and a scanned color image, best coded with JPEG. Similarly, while
spatial resolution of 400 pixels per inch may be best for the black-and-
white text, 200 pixel per inch is usually sufficient for a color image.
Rather than applying one coding method and resolution to all elements,
MRC allows multiple coders and resolutions within a page. By itself, MRC
does not define any new coding methods or resolutions. Instead it
defines a 3-layer model for structuring and combining the scanned image
data.
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8.1.1. MRC 3-layer model
The 3 layers of the MRC model are Foreground and Background, which are
both multi-level, and Mask, which is bi-level. Each layer may appear
only once on a page and is coded independently of the other two. In our
earlier example, the black-and-white text could be in the Mask layer,
the color chart in the Foreground layer, and the color image in the
Background layer. The distribution of content among layers is determined
by the writer, as is the choice of compression method, color encoding
and spatial resolution for a layer.
The final image is obtained by using the Mask layer to select pixels
from the other two layers. When the Mask layer pixel value is 1, the
corresponding pixel from the Foreground layer is selected; when it is 0,
the corresponding pixel from the Background layer is selected. Details
are given in the Introduction of [T.44].
Not all pages, and not all parts of a page, require 3 layers. If there
is only one layer present, then that layer is the primary image and must
be page size. If there is more than one layer, then the Mask must be one
of the layers, in which case it is the primary image and must be page
size.
MRC allows a page to be split into strips, with a variable number of
scanlines in a strip. A strip can have 1, 2 or 3 layers. A single,
stripped layer may be stored as a single, stripped image in an IFD,
e.g., all strips associated with the Background layer may be treated as
a single image. Alternatively, each strip associated with a layer may be
stored as a separate image or IFD, e.g., the Background layer can be
composed of several images that are offset vertically with respect to
the page. In this case, there can be no overlap between images
associated with a single layer.
Furthermore, color fax also requires the spatial resolutions of
Background and Foreground images to be legal fax values that are also
integer factors of the Mask image resolution. For example, if the Mask Layer resolution is 400 pixels per inch, then allowed resolutions for the Foreground and Background layers are 100, 200 or 400 pixels per inch; if the Mask is at 300 pixels per inch, then allowed values are 100 and 300. The Foregound and Background layer resolutions can be independently set.
8.1.2. A TIFF Representation for the MRC 3-layer model
In the TIFF representation of the 3-layer MRC model, each page is
represented by a single IFD, called the Primary IFD, that represents the
Mask layer (unless the Foreground or Background is the single layer
present), and a set of child IFDs that are referenced through the
SubIFDs extension field [TTN1]. To distinguish MRC-specific SubIFDs from
other SubIFDs, the NewSubFileType field will have Bit 4 ON, indicating
an MRC-related IFD. A new ImageLayer field is also introduced that
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consists of two values which identify the layer (Foreground, Background,
or Mask) and the order within the layer (first, second, ... image of the
layer); see Section 8.2.3.
Because MRC allows strips with variable numbers of scanlines, the
StripRowCounts field may be used in place of the RowsPerStrip field in
this mode. The StripRowCounts field allows each layer, with a variable
number of scanlines in each strip, to be represented by a single IFD, when the coding parameters are the same for all strips in the layer.
The MRC standard [T.44] allows the Foreground and Background layers to
have strips with different coding parameters. In this case, a separate
IFD is required to represent the strips which use different coding
parameters; see text in next paragraph. In all cases, the Mask layer is
required to be represented by a single IFD and a single set of coding
parameters.
The use of SubIFDs to store child IFDs is described in [TTN1]. An
example is shown graphically below. The Primary IFD associated with page
1 (PrimaryIFD 0) points to page 2 (PrimaryIFD 1) with the nextIFD
offset. The Primary IFD, corresponding to the Mask layer
(ImageLayer=[2,1]), contains a SubIFDs field that points to a list of
child IFDs. The first child IFD represents one image of the Background
layer, i.e., ImageLayer=[1,1]. This child IFD points to the second child
IFD via the nextIFD offset. This child represents the second Background
layer image, ImageLayer=[1,2]. Finally, the second child points to the
third child, which corresponds to the single Foreground layer image,
ImageLayer=[3,1]. The next IFD offset associated with this Foreground
image is 0, indicating no more child IFDs exist. Each primary IFD has
the NewSubFileType set to 18, indicating the IFD is MRC-specific (bit 4)
and that it is a single page of a multi-page document (bit 1). Each
child IFD has the NewSubFileType set to 16, indicating the IFD is
MRC-specific. The 'V' character should be read as a down-pointing arrow.
(nextIFD)
PRIMARY IFD 0 ------------> PRIMARY IFD 1--> ...
ImageLayer = [2,1]
NewSubFileType = 18
SubIFDs
|
V
Child IFD
ImageLayer = [1,1]
NewSubFileType = 16
|
|(nextIFD)
|
V
Child IFD
ImageLayer = [1,2]
NewSubFileType = 16
|
|(nextIFD)
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|
V
Child IFD
ImageLayer = [3,1]
NewSubFileType = 16
|
|(nextIFD)
V
0
In the example above, the SubIFDs field of the Primary IFD points to the
first IFD in a list of child IFDs. TIFF allows the SubIFDs field to
point to an array of IFDs, each of which can be the first of a list of
IFDs. An MRC-enabled TIFF reader must scan all available child IFDs to
locate and identify IFDs associated with MRC layers.
In the case where the Background or Foreground layers are described with
multiple IFDs, the XPosition and YPosition TIFF fields specify the
offset to the upper-left corner of the IFD with respect to the Mask
layer; see Section 8.2.2. When there is only a single layer (Mask,
Foreground, or Background), it is stored as the Primary IFD.
8.2. Required TIFF Fields
This section describes the TIFF fields required, in addition to those in
Section 2.2.1, to represent MRC mode fax images. Since MRC mode stores
fax data as a collection of images corresponding to layers or parts of
layers, the compression mechanisms, color encodings and spatial
resolutions used by previous modes apply to MRC. Therefore, the
descriptions here will typically reference the appropriate earlier
section. Fields and values specific to MRC mode are pointed out.
8.2.1. Baseline Fields
ImageWidth(256). SHORT or LONG
Same page widths as the base color mode; see Section 6.2.1.
BitsPerSample(258) = 1, 8, 9-16 SHORT
Compression(259) = 3, 4, 7, 9. SHORT
SamplesPerPixel(277) = 1, 3, 4. SHORT
FillOrder(266) = 1, 2. SHORT
ResolutionUnit(296) = 2, 3. SHORT
PhotometricInterpretation(262) = 0, 1, 2, 5, 10. SHORT
For Mask layer, see Section 4.2.1.
For Foreground and Background layers, see Sections 6.2.1 and 7.2.1.
ColorMap(320). SHORT
Count = 3 * (2**BitsPerSample)
Used when Foreground or Background layer is a palette-color image;
see Section 7.2.1.
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NewSubFileType(254) = 16, 18. LONG
For MRC fax mode, the NewSubFileType field has two bits that are
required.
Bit 1 indicates a single page of a multi-page document and must be
set for the Primary IFDs;
Bit 4 indicates MRC imaging model as described in ITU-T
Recommendation T.44 [T.44], and must be set for Primary IFDs
and all MRC-specific child IFDs.
StripRowCounts(559). LONG
Count = number of strips
The number of scanlines stored in a strip. MRC allows each fax strip
to store a different number of scanlines, up to a specified maximum
strip size, which is either 256 scanlines or the page length in
scanlines, depending on the implementation. This field replaces
RowsPerStrip for IFDs with variable-sized strips. Only one of the
two fields, StripRowCounts and RowsPerStrip, may be used in an IFD.
XResolution(282) = 100, 200, 300, 400. RATIONAL
YResolution(283) = 100, 200, 300, 400. RATIONAL
The resolution of the image is expressed in pixels per resolution
unit. In pixels per inch, allowed XResolution values for all layers
are: 100, 200, 300, and 400. MRC color fax mode requires the pixels
to be square, hence YResolution must equal XResolution for all
layers. The resolution of Background and Foreground layers must each
be an integer factor of the Primary image, which is the Mask layer,
when it is present; see Section 8.4.
See Section 2.2.2 for inch-metric equivalency.
8.2.2. Extension Fields
ChromaSubSampling(530). SHORT
ChromaPositioning(531). SHORT
Decode(TagToBeAssigned). SHORT
For Foreground and Background layers, see Section 6.2.2.
Indexed(346) = 0, 1. SHORT
For Foreground and Background layers: 1 indicates a palette-color
image, see Section 7.2.2.
T4Options(292) = 0, 1, 4, 5. SHORT
T6Options(293) = 0. SHORT
For Mask layer, see Section 4.2.2.
DefaultImageColor(TagToBeAssigned). SHORT or LONG
Count = SamplesPerPixel
In areas where no image data is available, a default color is needed
to specify the color value. If the StripByteCounts value for a strip
is 0, then the color for that strip must be defined by a default
image color.
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The DefaultImageColor field uses the same encoding as the image
data, and its value is therefore interpreted using the
PhotometricInterpretation, SamplesPerPixel, BitsPerSample, and
Indexed fields. If the fax data stream requires a different
encoding, then transferring the default color value between a TIFF
file and fax data stream requires a color conversion.
The default value for the DefaultImageColor field is white.
SubIFDs(330). IFD
Count = number of child IFDs
Each value is an offset from the beginning of the TIFF file to a
child IFD [TTN1].
XPosition(286). RATIONAL
YPosition(287). RATIONAL
Specifies the horizontal and vertical offsets of the top-left of the
IFD from the top-left of the Primary IFD in page resolution units.
For example, if the Primary IFD is at 400 pixels per inch, and a
foreground layer IFD is at 200 pixels per inch and located at pixel
coordinate (345, 678) with respect to the Primary IFD, the XPosition
value is 345/400 and the YPosition value is 678/400.
Color fax does not currently allow overlap of any component images
within a single layer.
Default values for XPosition and YPosition are 0.
8.2.3. New Fields
The Mixed Raster Content mode requires one new field: ImageLayer.
ImageLayer (34732). SHORT or LONG.
Count = 2
Image layers are defined such that layer 1 is the Background layer,
layer 3 is the Foreground layer, and layer 2 is the Mask layer that
selects pixels from the Background and Foreground layers. The
ImageLayer tag contains two values, describing the layer to which
the image belongs and the order in which it is imaged.
ImageLayer[0] = 1, 2, 3.
1: Image is a Background image, i.e., the image that will appear
whenever the Mask contains a value of 0. Background images
typically contain low-resolution, continuous-tone imagery.
2: Image is the Mask layer. In MRC, if the Mask layer is present, it
must be the Primary IFD and be full page in extent (no gaps.)
3: Image is a Foreground image, i.e., the image that will appear
whenever the Mask contains a value of 1. The Foreground image
generally defines the color of text or lines, but may also
contain high-resolution imagery.
ImageLayer[1]:
1: first image to be imaged in this layer (e.g., first fax strip),
2: second image to be imaged in this layer (e.g., second fax strip),
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3: ...
Value describing the image order. In MRC, this may be considered
the strip number. Since MRC mode currently does not allow overlap
between images within a layer, the order value does not have any
visual effect.
In MRC fax mode, it is possible that only a single layer is transmitted.
For example, if a page contains only a single continuous-tone
photograph, then only the Background layer may be transmitted. In this
case, the Background layer will be full page and stored as the Primary
IFD. ImageLayer[0] will be 1 indicating Background; ImageLayer[1] will
be 1 since the layer must be full page and there can be no other IFDs
associated with that layer. No Mask layer will exist.
8.3. Recommended TIFF Fields
See Sections 2.2.3. and 2.2.4.
8.4. Rules and Requirements for Images
The MRC mode defines a fundamental set of rules for images in the
3-layer representation.
1. If more than one layer exists, then the binary Mask layer must be
present and it is the primary image. If only one layer exists, then
the image corresponding to that layer is the primary image.
2. The Primary image defines and extends to the entire page boundary;
all attached model images cannot extend beyond the Primary image.
Resolution differences may cause some pixels to "hang over" the page
boundary, but no new pixels should exist completely beyond the page
extent
3. The Background and Foreground images may use any color encoding
defined in Sections 5 and 6, and may optionally cover only a portion
of the region defined by the Primary image, unless one of them is the
primary image.
4. Each Primary IFD and each MRC-specific SubIFD must have an ImageLayer
field to specify which layer the IFD belongs to, and the imaging
order of that IFD within the layer.
5. Each Primary IFD must have a NewSubFileType field value set to 18,
indicating a single page of a multi-page document (bit 1) and MRC
mode (bit 4).
6. Each MRC-specific child IFD must have a NewSubFileType field value
set to 16, indicating MRC mode (bit 4).
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7. In MRC mode, each layer is transmitted as a sequence of strips. It is
possible that each strip of each layer can be stored as a separate
IFD. In this case, the SubIFDs structure pointed to by the Primary
IFD will contain several IFDs that have an ImageLayer field with the
layer identified as either Background (layer 1) or Foreground (layer
3). There may be no overlap in the vertical direction between IFDs
associated with a single layer, although there may be a gap from one
of these images to the next. The TIFF XPosition and YPosition fields
are used to indicate the placement of these images with respect to
the primary image.
8. The resolution of Background and Foreground images must each be an
integer factor of the Primary image. For example, if the Primary
image is 400 pixels/inch, then the model images may be at 400
pixels/inch (400 / 1), 200 pixels/inch (400 / 2), 100 pixels/inch
(400 / 4), etc.
8.5. MRC Fax Mode Summary
Recommended fields are shown with an asterisk *
+------------------+-----------------------------------------+
| Baseline Fields | Values |
|------------------|-----------------------------------------|
| BitsPerSample | 1: binary mask |
| | 8: 8 bits per color sample |
| | 9-16: optional 12 bits/sample |
+------------------+-----------------------------------------+
| ColorMap | n: LAB color map |
+------------------+-----------------------------------------+
| Compression | 3: Modified Huffman and Modified Read |
| | 4: Modified Modified Read |
| | 7: JPEG |
| | 9: JBIG |
+------------------+-----------------------------------------+
| DateTime* | {ASCII): date/time in the 24-hour format|
| | "YYYY:MM:DD HH:MM:SS" |
+------------------+-----------------------------------------|
| FillOrder | Applies only to 1 bit/sample encodings |
| | 1: Most significant bit first |
| | 2: Least significant bit first |
+------------------+-----------------------------------------|
| ImageDescription*| {ASCII}: A string describing the |
| | contents of the image. |
+------------------+-----------------------------------------+
| ImageWidth | 864, 1024, 1216, 1728, 2048, 2432, 2592,|
| | 3072, 3456, 3648, 4096, 4864 |
+------------------+-----------------------------------------+
| ImageLength | n: total number of scanlines in image |
+------------------+-----------------------------------------|
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+------------------+-----------------------------------------+
| NewSubFileType | 16, 18: |
| | Bit 1 indicates single page of a multi- |
| | page document on Primary IFD |
| | Bit 4 indicates MRC model |
+------------------+-----------------------------------------+
| Orientation | 1**-8, Default 1 |
+------------------+-----------------------------------------+
| PhotometricInter | 0: WhiteIsZero |
| pretation | 1: BlackIsZero |
| | 2: RGB |
| | 5: CMYK |
| | 10: ITULAB |
+------------------+-----------------------------------------+
| ResolutionUnit | 2: inch |
| | 3: centimeter |
+------------------+-----------------------------------------+
| RowsPerStrip | n: number or scanlines per strip |
+------------------+-----------------------------------------+
| SamplesPerPixel | 1: L* (lightness) |
| | 3: RGB, LAB, CMY |
| | 4: CMYK |
+------------------+-----------------------------------------+
| Software* | {ASCII}: name & release number of |
| | creator software |
+------------------+-----------------------------------------+
| StripByteCounts | <n>: number or bytes in each strip |
+------------------+-----------------------------------------+
| StripRowCounts | <n>: number of scanlines in each strip |
+------------------+-----------------------------------------+
| StripOffsets | <n>: offset from beginning of file to |
| | each TIFF strip |
+------------------+-----------------------------------------|
| XResolution | 100, 200, 300, 400 (written in |
| | pixels/inch) |
+------------------+-----------------------------------------|
| YResolution | equal to XResolution (pixels must be |
| | square) |
+------------------+-----------------------------------------+
| Extension Fields |
+------------------+-----------------------------------------+
| T4Options | 0: required if Compression is Modified |
| | Huffman, EOLs not byte aligned |
| | 1: required if Compression 2D Modified |
| | Read, EOLs are byte aligned |
| | 4: required if Compression Modified |
| | Huffman, EOLs not byte aligned |
| | 5: required if Compression 2D Modified |
| | Read, EOLs are byte aligned |
+------------------+-----------------------------------------+
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+------------------+-----------------------------------------+
| T6Options | 0: required if Compression is 2D |
| | Modified Modified Read |
+------------------+-----------------------------------------+
| DocumentName* | {ASCII}: name of scanned document |
+------------------+-----------------------------------------+
| PageNumber | n,m: page number followed by total page |
| | count |
+------------------+-----------------------------------------+
| Decode | minL, maxL, mina, maxa, minb, maxb: |
| | minimum and maximum values for L*a*b* |
+------------------+-----------------------------------------+
| ChromaSubSampling| ChromaSubsampleHoriz: |
| | 0: equal numbers of lightness and chroma|
| | samples |
| | 1: twice as many lightness samples as |
| | chroma samples |
| | 2: four times as many lightness samples |
| | as chroma samples |
| | ChromaSubsampleVert: |
| | 0: equal numbers of lightness and chroma|
| | samples |
| | 1: twice as many lightness samples as |
| | chroma samples |
| | 2: four times as many lightness samples |
| | as chroma samples |
+------------------+-----------------------------------------+
| ChromaPositioning| 1: centered |
| | 2: cosited |
+------------------+-----------------------------------------+
| DefaultImageColor| <n>: background color |
+------------------+-----------------------------------------+
| Indexed | 0: not a palette-color image |
| | 1: palette-color image |
+------------------+-----------------------------------------+
| SubIFDs | <IFD>: byte offset to fg/bg IFDs |
+------------------+-----------------------------------------+
| XPosition | horizontal offset in primary IFD |
| | coordinates |
+------------------+-----------------------------------------+
| YPosition | vertical offset in primary IFD |
| | coordinates |
+------------------+-----------------------------------------+
| New Fields |
+------------------+-----------------------------------------+
| ImageLayer | n, m: layer number, imaging sequence |
| | (e.g., strip number) |
+------------------+-----------------------------------------+
| GlobalParameters | <IFD>: global parameters IFD |
| IFD* | |
+------------------+-----------------------------------------+
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+------------------+-----------------------------------------+
| ProfileType* | n: type of data stored in TIFF file |
+------------------+-----------------------------------------+
| ITUFaxMode* | n: ITU-compatible fax mode |
+------------------+-----------------------------------------+
| CodingMethods* | n: compression algorithms used in file |
+------------------+-----------------------------------------+
| ModeNumber* | n: version of ITU fax standard |
+------------------+-----------------------------------------+
| VersionYear* | byte sequence with year of ITU fax |
| | standard |
+------------------+-----------------------------------------+
9. Security Considerations
This document describes a file format for Internet fax, which is an
application of the TIFF encoding. As such, it does not create any
security issues not already existing in TIFF (though, none have been
identified).
Further, the encoding specified in this document does not in any way
preclude the use of any Internet security protocol to encrypt,
authenticate, or non-repudiate TIFF-encoded facsimile messages.
10. Copyright
(c) The Internet Society (1997). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it or
assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are included
on all such copies and derivative works. However, this document itself
may not be modified in any way, such as by removing the copyright notice
or references to the Internet Society or other Internet organizations,
except as needed for the purpose of developing Internet standards in
which case the procedures for copyrights defined in the Internet
Standards process must be followed, or as required to translate it into
languages other than English.
The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an "AS
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT
INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR PURPOSE."
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11. References
[REQ] S. Bradner, Key words for use in RFCs to Indicate Requirement
Levels, RFC 2119, March 1997.
[T.4] ITU-T Recommendation T.4, Standardization of group 3 facsimile
apparatus for document transmission, July 1996
[T.6] ITU-T Recommendation T.6, Facsimile coding schemes and coding
control functions for group 4 facsimile apparatus, November 1988
[T.30] ITU-T Recommendation T.30 - Procedures for Document Facsimile
Transmission in the General Switched Telephone Network, June 1996
[T.42] ITU-T Recommendation T.42, Continuous-tone colour representation
method for facsimile, February 1996
[T.43] ITU-T Recommendation T.43, Colour and gray-scale image
representations using lossless coding scheme for facsimile, February
1997
[T.44] ITU-T Recommendation T.44, Mixed Raster Content (MRC), October 1997.
[T.81] ITU-T Recommendation T.81, Information technology - Digital
compression and coding of continuous-tone still images - Requirements
and guidelines, September 1992
[T.82] ITU-T Recommendation T.82, Information technology - Coded
representation of picture and audio information - Progressive bi-level
image compression, March 1995
[T.85] ITU-T Recommendation T.85, Application profile for Recommendation
T.82 - Progressive bi-level image compression (JBIG coding scheme) for
facsimile apparatus, August 1995
[TIFF] Tag Image File Format, Revision 6.0, Adobe Developers
Association, June 3, 1992, ftp://ftp.adobe.com/pub/adobe/devrelations/
devtechnotes/pdffiles/tiff6.pdf
The TIFF 6.0 specification dated June 3, 1992 specification (c)
1986-1988, 1992 Adobe Systems Incorporated. All Rights Reserved.
[TIFF-F] G. Parsons and J. Rafferty, Tag Image File Format (TIFF) -
Application F, Sept. 22, 1997, work in progress,
ftp://ftp.ietf.org/internet-drafts/draft-ietf-fax-tiff-04.txt
[TIFF-F0] TIFF Class F specification, Apr 28, 1990,
ftp://ftp.faximum.com/pub/documents/tiff_f.txt
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[TIFF-REG] G. Parsons, J. Rafferty and S. Zilles, Tag Image File Format
(TIFF) - image/tiff MIME Sub-type Registration, Sept. 22, 1997, work in
progress, ftp://ftp.ietf.org/internet-drafts/draft-ietf-fax-reg-02.txt
[TTN1] Adobe PageMaker 6.0 TIFF Technical Notes, Sept. 14, 1995,
http://www.adobe.com/supportservice/devrelations/PDFS/TN/TIFFPM6.pdf
[TTN2] Draft TIFF Technical Note 2, Replacement TIFF/JPEG specification,
March 17, 1995, ftp://ftp.sgi.com/graphics/tiff/TTN2.draft.txt
[VPIM2] G. Vaudreuil and G. Parsons, Voice Profile for Internet Mail -
version 2, July 1997, work in progress, <draft-ema-vpim-06.txt>
[WIDE] K. Toyoda, H. Ohno and J. Murai, WDIE Message-based Fax over the
Internet, July 29, 1997, work in progress, ftp://ftp.ietf.org/internet-
drafts/draft-ietf-fax-wide-00.txt
The ITU-T Recommendations are available at http://www.itu.ch.
12. Authors' Addresses
Lloyd McIntyre Stephen Zilles
Xerox Corporation Adobe Systems Inc.
Mailstop PAHV-305 Mailstop W14
3400 Hillview Ave. 345 Park Avenue
Palo Alto, CA 94304 USA San Jose, CA 95110-2704, USA
Voice: +1-415-813-6762 Voice: +1-408-536-4766
Fax: +1-415-845-2340 Fax: +1-408-536-4042
Email: lmcintyre@adoc.xerox.com Email: szilles@adobe.com
Robert Buckley Dennis Venable
Xerox Corporation Xerox Corporation
Mailstop 0128-27E Mailstop 0128-27E
800 Phillips Road 800 Phillips Road
Webster, NY 14580, USA Webster, NY 14580, USA
Voice: +1-716-422-1282 Voice: +1-716-422-8009
Fax: +1-716-422-6117 Fax: +1-716-422-6117
Email: Rob_Buckley@wb.xerox.com Email: venable@wrc.xerox.com
Glenn S. Parsons James Rafferty
Northern Telecom Human Communications
P.O. Box 3511, Station C 12 Kevin Drive
Ottawa, ON K1Y 4H7, Canada Danbury, CT 06811-2901, USA
Phone: +1-613-763-7582 Phone: +1-203-746-4367
Fax: +1-613-763-2697 Fax: +1-203-746-4367
Email: Glenn.Parsons@Nortel.ca Email: Jrafferty@worldnet.att.net
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Annex A: Summary of TIFF Fields for Internet Fax
This annex includes tables which list by mode the TIFF fields used in
the proposed fax file format. The fields are organized into 3
categories:
1) TIFF Baseline Fields
2) TIFF Extension Fields
3) New Fields.
The tables include the allowed values for each fax mode.
Entries other than explicit numbers are described by:
n - single number
n, m - 2 numbers
a, b, c - 3 numbers
r - rational number
<n> - array of numbers
<b> - byte sequence
{ASCII} - string
<IFD> - array of IFD byte offsets
A blank entry in the table indicates that the field is not used by that
particular fax mode.
Table A.1 TIFF Baseline Fields
+---------------------------------------------------------+
| Fax Mode |
+---------------------------------------------------------|
| Minimal | Extended | JBIG | Lossy |Lossless| Mixed |
+----------| B&W | B&W | B&W | Color | Color | Raster |
| Field | | | | | | Content|
+----------+---------+----------+--------+---------+--------+--------+
| BitsPer | 1 | 1 | 1 | 8, 12 | 1, 8 | 1, 8 |
| Sample | | | | | 9-16 | 9-16 |
+----------+---------+----------+--------+---------+--------+--------+
| ColorMap | | | | | <n> | <n> |
+----------+---------+----------+--------+---------+--------+--------+
| Compres- | 3 | 3, 4 | 9 | 7 | 9 | 3, 4, |
| sion | | | | | | 7, 9 |
+----------+---------+----------+--------+---------+--------+--------+
| DateTime | | {ASCII} | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
+----------+---------+----------+--------+---------+--------+--------+
| FillOrder| 2 | 1, 2 | 1, 2 | | 1, 2 | 1,2 |
+----------+---------+----------+--------+---------+--------+--------+
| ImageDes-| | {ASCII} | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
| cription | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
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+----------+---------+----------+--------+---------+--------+--------+
| Image- | 1728 | 1728, 2048, 2432 | 864, 1024, 1216, 1728, |
| Width | | 2592, 3072, 3456 | 2048, 2432, 2592, 3072, |
| | | 3648, 4096, 4864 | 3456, 3648, 4096, 4864 |
+----------+---------+----------+--------+---------+--------+--------+
| Image- | n | n | n | n | n | n |
| Length | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| BitsPer | 1 | 1 | 1 | 8, 12 | 1 | 1 |
| Sample | | | | | 8, 9-16| 8, 9-16|
+----------+---------+----------+--------+---------+--------+--------+
| ColorMap | | | | | <n> | <n> |
+----------+---------+----------+--------+---------+--------+--------+
| NewSub- | 2 | 2 | 2 | 2 | 2 | 16, 18 |
| FileType | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Orien- | 1 | 1 | 1 | 1 | 1 | 1 |
| tation | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Photo- | 0 | 0, 1 | 0, 1 | 10 | 2, 5, | 0, 1, |
| metric- | | | | | | 2, 5, |
| Interp- | | | | | | 10 |
| retation | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Resolu- | 2 | 2, 3 | 2, 3 | 2, 3 | 2, 3 | 2, 3 |
| tionUnit | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| RowsPer- | n | n | n | n | n | n |
| Strip | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Samples- | 1 | 1 | 1 | 1, 3 | 1, 3, 4| 1, 3, 4|
| PerPixel | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Software | | {ASCII} | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
+----------+---------+----------+--------+---------+--------+--------+
| Strip- | n | <n> | <n> | <n> | <n> | <n> |
| Byte- | | | | | | |
| Counts | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Strip- | n | <n> | <n> | <n> | <n> | <n> |
| Offsets | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| XResolu- | 204 | 200, 204, 300 | 100, 200, 300, 400 |
| tion | 200 | 400, 408 | |
+----------+---------+----------+--------+---------+--------+--------+
| YResolu- | 98, 196 | 98, 196, 100, 200 | 100, 200, 300, 400 |
| tion | 100,200 | 300, 391, 400 | |
+----------+---------+----------+--------+---------+--------+--------+
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Table A.2 TIFF Extension Fields
+---------------------------------------------------------+
| Fax Mode |
+---------------------------------------------------------|
| Minimal | Extended | JBIG | Lossy |Lossless| Mixed |
+----------| B&W | B&W | B&W | Color | Color | Raster |
| Field | | | | | | Content|
+----------+---------+----------+--------+---------+--------+--------+
| T4Options| 0, 4 | 0, 1, | | | | 0, 1, |
| | | 4, 5 | | | | 4, 5 |
+----------+---------+----------+--------+---------+--------+--------+
| T6Options| | 0 | | | | 0 |
+----------+---------+----------+--------+---------+--------+--------+
| Document-| | {ASCII} | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
| Name | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Page- | n, m | n, m | n, m | n, m | n, m | n, m |
| Number | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| XPosition| | | | | | r |
+----------+---------+----------+--------+---------+--------+--------+
| YPosition| | | | | | r |
+----------+---------+----------+--------+---------+--------+--------+
| SubIFDs | | | | | | <IFD> |
+----------+---------+----------+--------+---------+--------+--------+
| Indexed | | | | | 0,1 | 0,1 |
+----------+---------+----------+--------+---------+--------+--------+
| Chroma- | | | | n, m | | n, m |
| SubSampl-| | | | | | |
| ing | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Chroma- | | | | 1, 2 | | 1,2 |
| Position-| | | | | | |
| ing | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Decode | | | | <n> | <n> | <n> |
+----------+---------+----------+--------+---------+--------+--------+
| Default- | | | | | | <n> |
|ImageColor| | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Strip- | | | | | | <n> |
| RowCounts| | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
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Internet Draft File Format for Internet Fax December 12, 1997
Table A.3 New Fields
+---------------------------------------------------------+
| Fax Mode |
+---------------------------------------------------------|
| Minimal | Extended | JBIG | Lossy |Lossless| Mixed |
+----------| B&W | B&W | B&W | Color | Color | Raster |
| Field | | | | | | Content|
+----------+---------+----------+--------+---------+--------+--------+
| BadFax- | | n | | | | |
| Lines | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| CleanFax-| | 0, 1, 2 | | | | |
| Data | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Consecu- | | n | | | | |
| tiveBad- | | | | | | |
| FaxLines | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Image- | | | | | | n, m |
| Layer | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Global- | | | <IFD> | <IFD> | <IFD> | <IFD> |
| Parame- | | | | | | |
| tersIFD | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Profile- | | | n | n | n | n |
| Type | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| ITUFax- | | | n | n | n | n |
| Mode | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Coding- | | | n | n | n | n |
| Method | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Mode- | | | | | | n |
| Number | | | | | | |
+----------+---------+----------+--------+---------+--------+--------|
| Version- | | | | <b> |<b> | |
| Year | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
Appendix 1: Open Issues
This section is temporary until the draft turns into an RFC; it includes
an identification of the issues that have been identified with respect
to this document. The issues are numbered and contain a short
identification of the issue plus an optional discussion of the issues.
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Internet Draft File Format for Internet Fax December 12, 1997
1. Synchronization with the TIFF-F.
Until the TIFF-F Informational RFC is published, there is always the
possibility of technical changes being made to TIFF-F. The intent of the
authors is that the description of TIFF-F in this document will be
technically the same as the informational RFC; therefore, this item will
remain open until the RFC is published.
2. Having a separate label for the minimum subset of TIFF-F
The authors have taken the position that having a separate application
label for the minimum subset of TIFF-F is appropriate. This topic was,
unfortunately, not explicitly discussed at the Munich meeting. The
reasoning for a separate label is:
In revising the TIFF-FX draft to incorporate the Munich agreements, it
became clear that there was a difference between the labeling of TIFF
applications in TIFF-FX and in TIFF-F. The TIFF-F document defines only
one TIFF application, namely Application F of TIFF. This labeling seems
to be used both for the minimum subset of TIFF-F and for the complete
set of TIFF-F. On the other hand, TIFF-FX gives the minimum subset its
own label, Application S of TIFF (S for simple mode) and uses pplication
F of TIFF to refer only to the full TIFF-F specification.
This may seem to be unimportant, but not having a clear meaning to the
label, Application F of TIFF, can create interoperability problems. For
example, a writer that can generate either the minimum set of TIFF-F
functionality or the full set sends a document with Media Type
image/tiff; application F to a reader that only supports the minimum
set. How does the reader know whether it should try to read the document
or should reject it as not supported. For interchange to work, all
writers would have to limit themselves to the minimum set or all readers
would have to be able to read the full set. In either case, the
distinction between the two sets becomes academic as only one of the
meanings, full or minimum, will have a practical use.
NOTE: This appendix, including this section, was inserted in the
previous version of this Internet Draft, dated Nov. 17, 1997, in which
the different modes or profiles of TIFF for facsimile were identified by
different values of the Application parameter of the image/tiff MIME
Media Type. As a result of the December 12, 1997 meeting of the IETF
Internet Fax Working Group, this version of the Internet Draft still
defines separate modes or profiles of TIFF for facsimile, including one
for minimum subset of TIFF-F, but no longer uses the Application
parameter to reference or label them.
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