rfc2301.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

2.2.3 TIFF fields recommended for all fax modes

   The TIFF fields listed in this section MAY be used by all fax modes.
   However, Profile S writers (the minimal fax mode described in Section
   3) SHOULD NOT use these fields. Recommended fields that are mode-
   specific are described in Sections 3-8.

DateTime(306)                                                      ASCII
    OptionalInTIFFBaseline
    Date/time of image creation in 24-hour format "YYYY:MM:DD HH:MM:SS".
    No default.

DocumentName(269)                                                  ASCII
    OptionalInTIFFExtension(DocumentStorageAndRetrieval)
    The name of the scanned document. This is a TIFF extension field,
    not a Baseline TIFF field.



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RFC 2301              File Format for Internet Fax            March 1998


    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 fax mode
   described in Section 3. In addition, support for these new TIFF
   fields has not been included in historical TIFF-F readers described
   in Section 4 and [TIFF- F]. 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.

   The first new field, GlobalParametersIFD, is an IFD that contains
   global parameters and is located in a Primary IFD.

GlobalParametersIFD (400)                                            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.



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RFC 2301              File Format for Internet Fax            March 1998


   Among the GlobalParametersIFD entries is a new ProfileType field
   which generally describes information in this IFD and in the TIFF
   file.

ProfileType(401)                                                    LONG
    The type of image data stored in this IFD.
    0 = Unspecified
    1 = Group 3 fax
    No default

   The following new global fields are defined in this document as IFD
   entries for use with fax applications.

FaxProfile(402) = 0 - 6.                                            BYTE
    The profile that applies to this file; a profile is subset of the
    full set of permitted fields and field values of TIFF for facsimile.
    The currently defined values are:
    0: does not conform to a profile defined for TIFF for facsimile
    1: minimal black & white lossless, Profile S
    2: extended black & white lossless, Profile F
    3: lossless JBIG black & white, Profile J
    4: lossy color and grayscale, Profile C
    5: lossless color and grayscale, Profile L
    6: Mixed Raster Content, Profile M

CodingMethods(403)                                                  LONG
    This field indicates which coding methods are used in the file. A
    bit value of 1 indicates which of the following coding methods is
    used:
    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 MR),
    Bit 4: ITU-T Rec. T.82 coding, using ITU-T Rec. T.85 (JBIG),
    Bit 5: ITU-T Rec. T.81 (Baseline JPEG),
    Bit 6: ITU-T Rec. T.82 coding, using ITU-T Rec. T.43 (JBIG color),
    Bits 7-31: reserved for future use
    Note: There is a limit of 32 compression types to identify standard
    compression methods.

VersionYear(404)                                                    BYTE
    Count: 4
    The year of the standard specified by the FaxProfile field, given as
    4 characters, e.g. '1997'; used in lossy and lossless color modes.

ModeNumber (405)                                                    BYTE
    The mode of the standard specified by the FaxProfile field. A
    value of 0 indicates Mode 1.0; used in Mixed Raster Content mode.



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RFC 2301              File Format for Internet Fax            March 1998


3. Minimal Black-and-White Fax Mode

   This section defines the minimal black-and-white subset of TIFF for
   facsimile. This subset is designated Profile S. All implementations
   of TIFF for facsimile SHALL 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 or Profile 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
   defines a required ordering for the pages in a fax document and for
   the IFDs and image data of a page. It also requires 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.

3.2.1 Baseline fields

BitsPerSample(258) = 1.                                            SHORT
    RequiredByTIFFBaseline
    Binary data only.
    Default = 1 (field may be omitted if this is the value)




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RFC 2301              File Format for Internet Fax            March 1998


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 = Least Significant Bit first

   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.

NewSubFileType(254) = (Bit 1=1).                                    LONG
    RequiredByTIFFforFAX
    Bit 1 is 1 if the image is a single page of a multi-page document.
    Default = 0 (no subfile bits on, so may not be omitted for fax)

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)

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



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RFC 2301              File Format for Internet Fax            March 1998


    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