Network Working Group Glenn Parsons
Internet Draft James Rafferty
Expires in six months January 31, 1997
Tag Image File Format (TIFF) - Class F
<draft-ietf-fax-tiff-00.txt>
Status of this Memo
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Overview
This document describes in detail the definition of TIFF Class F
that is used to store facsimile images and also describes the
registration refinement of the MIME sub-type image/tiff. The Class
F tag encoding has been folklore with no specific reference
definition before this document.
Internet Fax Working Group
This document is a product of the IETF Internet Fax Working Group.
All comments on this document should be forwarded to the email
distribution list at <ietf-fax@imc.org>.
Internet Draft TIFF-F January 31, 1997
1. Abstract
This document formalizes the reference for the Tag Image File
Format (TIFF) and formally defines TIFF Class F that is used to
store facsimile images. As well, the original registration for
image/TIFF from RFC 1528 is refined by this document.
2. TIFF Definition
TIFF (Tag Image File Format) Revision 6.0 is defined in detail by
Adobe in [TIFF]. The documentation can be obtained from Adobe at:
Adobe Developers Association
Adobe Systems Incorporated
1585 Charleston Road
P.O. Box 7900 Mountain View, CA 94039-7900
A copy of this specification can also be found in:
ftp://ftp.adobe.com/pub/adobe/DeveloperSupport/TechNotes/PDFfiles
Only an introduction to the baseline TIFF is included in this
document. The reader is directed to the original TIFF
specification [TIFF] to obtain specific technical details.
2.1 TIFF Scope
TIFF describes image data that typically comes from scanners, frame
grabbers, and paint- and photo-retouching programs. TIFF is not a
printer language or page description language. The purpose of TIFF
is to describe and store raster image data. A primary goal of TIFF
is to provide a rich environment within which applications can
exchange image data. This richness is required to take advantage of
the varying capabilities of scanners and other imaging devices.
Though TIFF is a rich format, it can easily be used for simple
scanners and applications as well because the number of required
fields is small.
2.2 TIFF Features
- TIFF is capable of describing bilevel, grayscale, palette-color,
and full-color image data in several color spaces.
- TIFF includes a number of compression schemes that allow
developers to choose the best space or time tradeoff for their
applications.
- TIFF is not tied to specific scanners, printers, or computer
display hardware.
- TIFF is portable. It does not favor particular operating
systems, file systems, compilers, or processors.
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- TIFF is designed to be extensible-to evolve gracefully as new
needs arise.
- TIFF allows the inclusion of an unlimited amount of private or
special-purpose information.
3. TIFF Class F Definition
Though it has been in common usage for many years, TIFF Class F (or
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 for TIFF Class F for Internet
applications.
3.1 The Spirit of TIFF Class F
TIFF Classes reduce the information burden on TIFF readers and
writers that wish to support narrow applications. For example,
Appendix G-1 of TIFF 5.0 stated that classes enable TIFF readers
"to know when they can stop adding TIFF features." In other words,
defining a Class enables applications interested only in reading
that Class to give up if the characteristic tags and values are not
present. Therefore, TIFF Class F insists on a rather narrow
definition of tags. In a general TIFF file, for example, the writer
would be free to create single-page documents without the
NewSubFileType and PageNumber tags. Not so for a Class F file,
where the multi-page tag is required even for a single page.
TIFF Class F is a sub-class of Class B (Bilevel) [TIFFB]. That is,
all tags that are required in Class B are also required in Class F.
For some common tags, however, Class F limits the range of
acceptable values. The YResolution tag, for example, is a Class B
tag, but within Class F only a limited set of values is permitted.
Such tags are listed in section 3.2
Section 3.3 discusses other Class B tags that have a specific
meaning when applied to facsimile images. Several new Class F tags
are discussed in section 3.4. There are also tags that may be
helpful but are not required. These recommended tags are listed in
the section 3.5.
Several technical topics, including implementation issues, warnings
and conformance are discussed in subsequent sections. Finally,
section 3.9 introduces the TIFF-F Reader and Writer. A table of
the required TIFF-F tags for each of these implementations is
summarized.
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3.2 Class F Required Tags
FillOrder = 1, 2. SHORT.
TIFF Class F readers must be able to read data in both bit
orders, but the vast majority of facsimile products store data
LSB first, exactly as it appears on the telephone line.
1 = Most Significant Bit first.
2 = Least Significant Bit first.
ImageWidth = 1728, 2048, 2482, 2592, 3072, 3723, 3456, 4096, 4964.
SHORT or LONG. These are the fixed page widths in pixels
defined in CCITT Group 3.
NewSubFileType = 2. LONG.
The value 2 identifies a single page of a multi-page image.
PageNumber. SHORT/SHORT.
This tag specifies the page numbers in the fax document. The
tag comprises two SHORT values: the first value is the page
number, the second is the total number of pages. Single-page
documents therefore use 00000001 hex.
ResolutionUnit = 2,3. SHORT.
The units of measure for resolution:
2 = Inch
3 = Centimeter
XResolution = 204, 200, 300, 400, 406 (inches). RATIONAL.
The horizontal resolution of the image expressed in pixels per
resolution unit. Some existing TIFF-F implementations may also
support values of 77 (cm).
YResolution = 98, 196, 100, 200, 300, 392, 400 (inches). RATIONAL.
The vertical resolution of the image expressed in pixels per
resolution unit. Some existing TIFF-F implementations may also
support values of 77, 38.5 (cm).
3.2.1 Class F Tags for Compression Selection
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 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 Addressing). In
1984, a somewhat more efficient compression method known as
Modified Modified READ (MMR) was defined in the T.6 recommendation.
It 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.
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TIFF Class F permits two different compression methods. By
default, the one-dimensional compression method is used.
Optionally, depending upon the application, the more efficient two-
dimensional compression method from T.6 (i.e. MMR or "Group 4
compression") may be selected. More information to aid the
implementor in making this selection is contained in section 3.8 on
Implementation Warnings.
The tags used to specify the compression are shown below:
Compression = 3,4. SHORT.
This is a required Class F tag. Modified Huffman, one-
dimensional encoding with "byte-aligned" EOLs is selected by
setting 3. 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, thus ensuring an EOL-sequence
of a 1 byte preceded by a zero nibble: xxxx0000 00000001. The
data in a Class F image is not terminated with an RTC (see
sections 3.8.4 and 3.8.5). For two-dimensional encoding, set
the value of the compression tag to 4 (see section 3.8.2).
T4Options = 4,5. LONG.
This tag is required for TIFF Class-F if the one-dimensional
compression method has been specified (i.e. by setting the
value of the Compression tag to 3). Data is one-dimensional
and EOLs must be byte-aligned. Uncompressed data is not
allowed.
bit 0 = 0 for 1-Dimensional
bit 1 = must be 0 (uncompressed data not allowed)
bit 2 = 1 for byte-aligned EOLs
T6Options = 0 LONG.
This tag is required for TIFF Class F if the two-dimensional
compression method is specified (i.e. by setting the value of
the Compression tag to 4). Data is two-dimensional and there
is no use of EOLs. Uncompressed data is not allowed. In earlier
versions of TIFF, this tag was named Group4Options. The
significance has not changed and the present definition is
compatible. This field is made up of a set of 32 flag bits.
Unused bits must be set to 0. Bit 0 is the low-order bit. The
default value is 0 (all bits 0).
bit 0 = 0 for 2-Dimensional
bit 1 = must be 0 (uncompressed data not allowed)
3.3 Class B (Bilevel) Required Tags
Although these tags are already required in Class B (Bi-Level)
files, an explanation of their usage for facsimile images may be
helpful.
BitsPerSample = 1. SHORT.
Since facsimile is a black-and-white medium, this must be 1
(the default) for all files.
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ImageLength. SHORT or LONG. LONG recommended.
The total number of scan lines in the image.
PhotometricInterp = 0,1. SHORT.
This tag allows notation of an inverted ("negative") image:
0 = normal
1 = inverted
Software. ASCII.
The optional name and release number of the software package
that created the image.
RowsPerStrip. SHORT or LONG. LONG recommended.
The number of scan lines per strip. When a page is expressed
as one large strip, this is the same as the ImageLength tag.
SamplesPerPixel = 1. SHORT.
The value of 1 denotes a bi-level, grayscale, or palette color
image.
StripByteCounts. SHORT or LONG. SHORT recommended.
For each strip, the number of bytes in that strip. If a page is
expressed as one large strip, this is the total number of bytes
in the page after compression.
StripOffsets. SHORT or LONG.
For each strip, the offset of that strip. The offset is
measured from the beginning of the file. If a page is expressed
as one large strip, there is one such entry per page.
3.4 New Class F Tags
There are only three new tags for Class F. All three tags describe
page quality. The information contained in these tags is usually
obtained from the receiving facsimile hardware, but since not all
devices are capable of reporting this information, the tags are
optional.
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
Tag = 326 (146 hex)
Type = SHORT or LONG
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This tag reports the number of scan lines with an incorrect
number of pixels encountered by the facsimile during reception
(but not necessarily in the file).
Note: PercentBad = (BadFaxLines/ImageLength) * 100
CleanFaxData
Tag = 327 (147 hex)
Type = SHORT
N = 0
0 = Data contains no lines with incorrect pixel counts or
regenerated lines (i.e., computer generated)
1 = Lines with an incorrect pixel count were regenerated by
receiving device
2 = Lines with an incorrect pixel count existed, but were
not regenerated by receiving device
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 tag describes the
error content of the data. That is, when the BadFaxLines and
ImageLength tags indicate that the facsimile device encountered
lines with an incorrect number of pixels during reception, the
CleanFaxData tag indicates whether these lines are actually in
the data or if the receiving facsimile device replaced them
with regenerated lines.
ConsecutiveBadFaxLines
Tag = 328 (148 hex)
Type = LONG or SHORT
This tag reports the maximum number of consecutive lines
containing an incorrect number of pixels encountered by the
facsimile device during reception (but not necessarily in the
file).
The BadFaxLines and ImageLength data indicate only the quantity
of such lines. The ConsecutiveBadFaxLines tag is an indicator
of their distribution and may therefore be a better general
indicator of perceived image quality.
3.5 Recommended Tags
BadFaxLines. LONG.
The number of "bad" scan lines encountered by the facsimile
during reception.
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CleanFaxData = 0, 1, 2. BYTE.
This tag indicates whether lines with incorrect pixel count are
actually in the data or if the receiving facsimile device
replaced them with regenerated lines.
0 = Data contains no lines with incorrect pixel counts or
regenerated lines (i.e., computer generated)
1 = Lines with an incorrect pixel count were regenerated
by receiving device
2 = Lines with an incorrect pixel count existed, but were
not regenerated by receiving device
ConsecutiveBadFaxLines. LONG or SHORT.
The maximum number of consecutive scan lines with incorrect
pixel count encountered by the facsimile device reception.
DateTime. ASCII.
Date and time in the format YYYY:MM:DD HH:MM:SS, in 24-hour
format. String length including NUL byte is 20 bytes. Space
between DD and HH.
DocumentName. ASCII.
This is the name of the document from which the document was
scanned.
ImageDescription. ASCII.
This is an ASCII string describing the contents of the image.
Orientation. SHORT.
This tag might be useful for displayers that always want to
show the same orientation, regardless of the image. The
default value of 1 is "0th row is visual top of image, and 0th
column is the visual left." An 180-degree rotation is 3. See
[TIFF] for an explanation of other values.
3.6 Technical Implementation Issues
3.6.1 Strips
Those new to TIFF may not be familiar with the concept of "strips"
embodied in the three tags RowsPerStrip, StripByteCount,
StripOffsets.
In general, third-party applications that read and write TIFF files
expect the image to be divided into "strips," also known as
"bands." Each strip contains a few lines 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 dimensions of a strip are described by the RowsPerStrip and
StripByteCount tags. The location in the TIFF file of each strip
is contained in the StripOffsets tag.
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The TIFF documentation suggests using strips of an arbitrary size
of about 8K. Although various application programs assert that
they "prefer" banded images, research failed to uncover a single
existing application that could not read a single-strip page where
they could read the same file in a multi-strip format. Indeed,
applications seem to be more sensitive to the total size of the
decoded image and are not particularly fussy about banding. This
result is not surprising, considering that most desktop publishing
programs are prepared to deal with massively larger images than
those one finds in facsimile. In short, each page may be
represented as a single strip of any length.
In fact, there may be a compelling reason to employ a strip size
equal to the length of one A4 page (297 mm). When a document is
imaged, it may be of any length. Not all fax machines, however,
can accept unlimited length documents. Worse, the remote machine's
page-length capability is not known until the fax connection has
been established. The solution is for the transmitting fax device
to image long documents into A4-size strips, then seam them
together at transmission, after the capabilities of the remote fax
machine is known.
3.6.2 Bit Order
Although the TIFF 6.0 documentation lists the FillOrder tag in the
category "No Longer Recommended," Class F resurrects it.
Facsimile data appears on the phone line in bit-reversed order
relative to its description in CCITT Recommendation T.4.
Therefore, a wide majority of facsimile applications choose this
natural order for storage. Nevertheless, TIFF Class F readers must
be able to read data in both bit orders.
3.6.3. Multi-Page
Many existing applications already read Class F-like files, but do
not support the multi- page tag. Since a multi-page format greatly
simplifies file management in fax application software, Class F
specifies multi-page documents (NewSubfileType = 2).
3.6.4. Two-dimensional Encoding
PC Fax applications that wish to support two-dimensional encoding
may do so by setting Bit 0 in the Group3Options tag. Please see
section 3.8.2.
3.6.5. Example Use of Page-quality Tags
Here are examples for writing the CleanFaxData, BadFaxLines, and
ConsecutiveBadFaxLines tags:
1. Facsimile hardware does not provide page quality
information: write no tags.
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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. Computer generated file: write CleanFaxData = 0.
3.7 TIFF Class F Conformance
Fax applications that do not wish to embrace TIFF Class F as a
native format may elect to support it as import/export medium.
Export
The simplest form of support is a Class F writer that produces
individual single-page Class F files with the proper NewSubFile
tag and the PageNumber (page one-of-one) tag.
Import
A Class F reader must be able to handle a Class F file
containing multiple pages.
3.8 Implementation Warnings
3.8.1 Uncompressed data
Class 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.
3.8.2 Encoding and Resolution
Since two-dimensional encoding is not required for Group 3
compatibility, Class F readers may decline to read such files.
therefore, for maximum portability, applications may choose to
write only one- dimensional files. Although the same argument
technically holds for "fine" (196 dpi) vertical resolution, only a
tiny fraction of facsimile products support only 98 dpi.
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: 392v x 203h and 392v x 406h. Therefore, the inch-based
equivalents of the new resolutions are supported in the TIFF 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. In a similar respect, the optional support of
metric based resolutions in the TIFF-F reader (i.e. 77 x 38.5 cm) is
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included for completeness, since they are used in some legacy TIFF-F
applications, but this use is not supported in the TIFF-F writer.
3.8.3 EOL byte-aligned
In the spirit of TIFF, all EOLs in data must be byte- aligned. 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, thus ensuring an EOL-sequence of a one byte preceded by
a zero nibble: xxxx0000 00000001.
Recall that 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).
3.8.4 EOL
As illustrated in FIGURE 1/T.4 in [T.4], facsimile documents begin
with an EOL (which in Class F is byte-aligned). The last line of
the image is not terminated by an EOL.
3.8.5 RTC Exclusion
Aside from EOLs, TIFF Class F files contain only image data. This
means that the Return To Control sequence (RTC) is specifically
prohibited. Exclusion of RTCs not only makes possible the simple
concatenation of images, it eliminates the mischief--failed
communications and unreadable images--that their mistreatment
inevitably produces.
3.9 TIFF-F Tags Summary
Implementations may choose to implement a TIFF-F Reader, TIFF-F
Writer or both, depending upon application requirements. The TIFF-
F Reader is typically used to read an existing TIFF-F file which
resides on a computer or peripheral device. The TIFF-F Writer is
typically used to convert a bi-level image bit stream into a TIFF-F
compliant file. Despite the semantic difference between the Reader
and the Writer, it is often sufficient to implement only the Reader
for most Internet applications. The specific tag support required
for each of these variations is summarized below.
3.9.1 TIFF Reader
The tags in following table are specified for a TIFF Reader. Legal
values are as shown. If required tags are omitted, the default
value will apply. Image data must not have any coding errors.
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As noted within [TIFF], a TIFF file begins with an 8-byte image
file header, of which the first two bytes (0-1) contain the byte
order within the file. The permissible values are:
II- Byte order from least significant byte to the most
significant byte (little-endian)
MM - byte order is always from most significant to least
significant (big-endian)
For a TIFF-F Reader, the legal values are:
ByteOrder: MM,II (Either byte order is allowed)
3.9.1.1 Tags for TIFF-F Reader
Tag | Legal | Default | Comment
------------------|-------------|-------------|----------------------
BitsPerSample | 1 | 1 |one bit per sample
CleanFaxData | 0 | 0 |data has no errors
Compression | 3,4 | 3 |T.4 bi-level encoding,
| | | MH or T.6, MMR
FillOrder | 2,1 | 2 |LSB first or MSB first
ImageWidth | 1728, 2048, | 1728 |depends on XResolution
| 2482, 2592, | |
| 3072, 3723, | |
| 3456, 4096, | |
| 4964 | |
ImageLength | >0 | |required
NewSubFileType | 2 | 2 |single page of
| | |multipage file
Orientation | 1 | 1 |1st row=top left,
| | | 1st col=top
PageNumber | X/X | 0/1 |pg/tot, 0 base,
| | | tot in 1st IFD
PhotometricInterp | 0 | 0 |0 is white
ResolutionUnit | 2,3 | 2 |inches (default)
RowsPerStrip |=ImageLength |=ImageLength |
SamplesPerPixel | 1 | 1 |one sample per pixel
StripByteCounts | >0 | |required
StripOffsets | >0 | |required
T4Options | 4 | 4 |MH (incl if not MMR)
T6Options | 0 | 0 |MMR (incl only if MMR)
Xresolution | 204,200,77, | 204 |
| 300,400,406 | |
Yresolution | 196,98,100, | 196 |
| 200,77,38.5,| |
| 300,392,400 | |
------------------|-------------|-------------|---------------------
Other tags may be present, but must be of the sort that can be
ignored safely by implementations (i.e. purely informational).
Recommended informational tags are:
Software, Datetime, BadFaxLines, ConsecutiveBadFaxLines
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3.9.2 TIFF-F Writer
For the case of writing (creating) a TIFF-F file format from an
image data stream or other raster data, implementations should use
the TIFF-F tags in the following table as a default. The use of
default tags and values for the TIFF-F writer is intended to
encourage consistent use of TIFF-F in Internet applications. Image
data must not have any coding errors.
As noted within [TIFF], a TIFF file begins with an 8-byte image
file header, of which the first two bytes (0-1) contain the byte
order within the file.
For a TIFF-F Writer, the legal value is:
ByteOrder: II (least significant byte to the most significant
byte)
3.9.2.1 TIFF-F Writer Tags
Tag | Legal Value | Comment
------------------|-------------|--------------------------------
BitsPerSample | 1 | one bit per sample
Compression | 3 | T.4 bi-level encoding, MH
FillOrder | 2 | LSB first
ImageWidth | 1728, 2048, | depends on XResolution
| 2482, 2592, |
| 3072, 3723, |
| 3456, 4096, |
| 4964 |
ImageLength | > 0 |
NewSubFileType | 2 | single page of multi-page file
PageNumber | X/X | pg/tot, 0 base, tot in 1st IFD
PhotometricInterp | 0 | 0 is white
ResolutionUnit | 2 | inches
RowsPerStrip | >0 | must be same as ImageLength
SamplesPerPixel | 1 | one sample per pixel
StripByteCounts | >0 | as appropriate
StripOffsets | >0 | as appropriate
T4Options | 4 | MH, byte aligned EOL
Xresolution | 204,200, |
| 300,400,406 |
Yresolution | 196,98,100, |
| 200,300, |
| 392,400 |
------------------|-------------|--------------------------------
For some applications, it may be preferable to use T.6 compression
in place of one-dimensional T.4 compression. For this case, the
defaults are revised as specified in section 3.9.2.3.
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3.9.2.2 Optional TIFF-F Writer Tags
The following tags are optional. If they are present, they must
contain the values as shown:
Tag | Legal Value | Comment
------------------|-------------|-----------------------------------
CleanFaxData | 0 |data doesn't contain bad scan lines
Orientation | 1 |1st row = top left, 1st col = top
------------------|-------------|-----------------------------------
Recommended informational tags are:
Software, Datetime, BadFaxLines, ConsecutiveBadFaxLines
3.9.2.3 TIFF-F Writer Tags for T.6 Compression Option
For some applications, a TIFF-F writer may choose to use the T.6
compression option in place of the one-dimensional Modified Huffman
standardized in [T.4]. In this case, the rules for the TIFF-F
Writer tags and values apply, but the except as specified below:
Tag | Legal Value | Comment
------------------|-------------|-----------------------------------
Compression | 4 | ITU-T T.6 encoding, MMR
T6Options | 0 | Replaces T4Options Tag
------------------|-------------|-----------------------------------
Other tags may be present, but must be of the sort that can be
ignored safely by applications (i.e. purely for information).
4. MIME sub-type image/TIFF
The image/TIFF sub-type was originally defined in RFC 1528 as
containing TIFF 5.0 encoded image data.
This document, in section 6, re-defines the original image/TIFF
definition to refer to TIFF 6.0 encoded image data. The TIFF 6.0
specification is a cleaner document and is compatible with previous
TIFF 5.0 encoded image data. Further, an optional "class"
parameter is defined for image/TIFF to identify the TIFF Class of
the encoded image data, if it is known.
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5. Implementation Usage
5.1 Internet Fax Usage
The usage of TIFF-F is envisaged to be a primary component of
Internet Fax. It is anticipated that Internet Fax will make use of
both a TIFF-F Reader and TIFF-F Writer. The details of these
applications will be specified in other documents.
5.2 VPIM Usage
The image/TIFF sub-type with the Class F parameter (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 traditional voice message store-
and-forward functions. As a result, this sub-type is used to hold
fax messages within the multipart/voice-message content that is
sent between compliant VPIM systems. In this context, the fax
content is optional and may be rejected if the recipient system
cannot deal with fax. VPIM implementations must at least implement
and support the TIFF-F Reader.
Refer to the VPIM Specification for proper usage of this content.
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6. IANA Registration
To: ietf-types@iana.org
Subject: Registration of Standard MIME media type image/TIFF
MIME media type name: image
MIME subtype name: TIFF
Required parameters: none
Optional parameters: class
The Classes of TIFF are denoted by letters. There are
currently five valid values of class:
B - Bilevel
G - Grayscale
P - Palette
R - RGB, and
F - Bi-Level Facsimile
There is no default value for class, as the absence of the
class parameter indicates that the class of the encoded TIFF
image is unknown or unnecessary to be known. The onus is on
the displaying software to determine the class (if
necessary) and present the image to the user.
Encoding considerations: Binary or Base-64 generally preferred
Security considerations: none
Interoperability considerations:
The ability of implementations to handle all the defined
classes of TIFF may not be ubiquitous. As a result, the
absence of the class parameter would force implementations
to decode and attempt to display the encoded TIFF image data
in order to determine if it could actually be viewed.
Published specification:
TIFF (Tag Image File Format) and most of the classes are
defined in:
TIFF (TM) Revision 6.0 - Final - June 3, 1992
Adobe Developers Association
Adobe Systems Incorporated
1585 Charleston Road
P.O. Box 7900 Mountain View, CA 94039-7900
A copy of this specification can be found in:
ftp://ftp.adobe.com/pub/adobe/DeveloperSupport/TechNotes/PDF
files
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TIFF Class F is defined in this document in section 3
Applications which use this media type:
primarily fax and voice messaging
Additional information:
Magic number(s):
II (little-endian): 49 49 42 00 hex
MM (big-endian): 4D 4D 00 42 hex
File extension(s): .TIF
Macintosh File Type Code(s): TIFF
Person & email address to contact for further information:
Glenn W. Parsons
Glenn.Parsons@Nortel.ca
James Rafferty
Jrafferty@worldnet.att.net
Intended usage: COMMON
Author/Change controller:
James Rafferty
7. Authors' Addresses
Glenn W. Parsons
Nortel Technology
P.O. Box 3511, Station C
Ottawa, ON K1Y 4H7
Canada
Phone: +1-613-763-7582
Fax: +1-613-763-8385
Email: Glenn.Parsons@Nortel.ca
James Rafferty
Human Communications
12 Kevin Drive
Danbury, CT 06811-2901
USA
Phone: +1-203-746-4367
Fax: +1-203-746-4367
Email: Jrafferty@worldnet.att.net
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8. References
[MIME4] N. Freed and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Four: Registration Procedures", RFC
2048, Innosoft, First Virtual, Nov 1996.
[T.30] ITU-T Recommendation T.30 - "Procedures for Document
Facsimile Transmission in the General Switched Telephone
Network", June, 1996
[T.4] ITU-T Recommendation T.4 - "Standardization of Group 3
Facsimile Apparatus for Document Transmission", June, 1996
[T.6] ITU-T Recommendation T.6 - "Facsimile Coding Schemes and
Coding Control Functions for Group 4 Facsimile Apparatus",
March, 1993
[TIFFB] D. Cohen, A. Katz, "A File Format for the Exchange of
Images in the Internet", RFC 1314, 04/10/1992.
[TIFF] Adobe Developers Association, TIFF (TM) Revision 6.0 -
Final, June 3, 1992.
[TPC.INT] C. Malamud, M. Rose, "Principles of Operation for the
TPC.INT Subdomain: Remote Printing -- Technical Procedures",
RFC 1528, 10/06/1993
[VPIM2] Greg Vaudreuil and Glenn Parsons, "Voice Profile for
Internet Mail - version 2", Work in Progress, Jan 1997.
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