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.

   facsimile SHOULD order pages in a TIFF file in the same way that they
   are ordered in a fax data stream. In a TIFF file, a page consists of
   several elements: one or more IFDs (including subIFDs), long field
   values that are stored outside the IFDs, and image data (in one or
   more strips).

   The minimal black-and-white mode (Profile S) specifies a required
   ordering of pages and elements within a page (Section 3.5). The
   extended black-and-white mode (Profile F) provides guidelines for
   ordering pages and page elements (Section 4.4.6). Other profiles



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RFC 2301              File Format for Internet Fax            March 1998


   SHOULD follow these guidelines. This recommendation is intended to
   simplify the implementation of TIFF writers and readers in fax
   applications and the conversion between TIFF file and fax data stream
   representations. However, 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
   recommended here.

   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
   SHOULD 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 lists the fields that are
   required by all modes and that have values that 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.






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RFC 2301              File Format for Internet Fax            March 1998


   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) = allowable 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.

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 field 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, but
   which do have values specified by the ITU-specified or mode-specific
   values. Fields that SHALL be used by some but 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.

PageNumber(297)                                                    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.
    No default, must be specified

RowsPerStrip(278)                                          SHORT or LONG
    RequiredByTIFFBaseline
    The number of scanlines per TIFF strip, except for the last 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.



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    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
    the start of 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 defined here; the values applicable to a particular fax
   mode are described in Sections 3-8. Fields that SHALL be used by some
   but not all modes are given in the section (3-8) describing the mode
   that uses 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 image data
    Default = 1 (no compression, so may not be omitted for FAX)

FillOrder(266)                                                     SHORT
    RequiredByTIFFforFax
    The default bit order in Baseline TIFF per [TIFF] is indicated by
    FillOrder=1, where bits are not reversed before being stored.
    However, TIFF for Fax typically utilizes the setting of FillOrder=2,
    where the bit order within bytes is reversed before storage (i.e.,
    bits are stored with the Least Significant Bit first).
    Default = 1 (field may be omitted if this is the value)
    Facsimile data appears on the phone line in bit-reversed order
    relative to its description in the relevant ITU compression
    Recommendation. Therefore, a wide majority of facsimile
    implementations choose this natural order for storage. Nevertheless,
    all readers conforming to this specification must be able to read
    data in both bit orders.

ImageWidth(256)                                            SHORT or LONG
    RequiredByTIFFBaseline
    The number of pixels (columns) per scanline (row) of the image
    No default, must be specified.



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NewSubFileType(254)                                                 LONG
    RequiredByTIFFforFAX
    A general indication of the kind of data contained in this IFD
    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)                                     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 color components per pixel; SamplesPerPixel is 1 for a
    black-and-white, grayscale or indexed (palette) image.
    Default =1 (field may be omitted if this is the value)

XResolution(282)                                                RATIONAL
    RequiredByTIFFBaseline
    The horizontal resolution of the image in pixels per resolution
    unit. The ITU-T Recommendations for facsimile specify a small number
    of horizontal resolutions: 100, 200, 300, 400 pixels per inch, and
    80, 160 pixels per centimeter (or 204, 408 pixels per inch). 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.
    TIFF for Facsimile Writers SHOULD express XResolution in inch based
    units, for consistency with historical practice and to maximize
    interoperability. See the table below for information on how to
    convert from an ITU-T metric value to its inch based equivalent
    resolution.
    No default, must be specified

YResolution(283)                                                RATIONAL
    RequiredByTIFFBaseline
    The vertical resolution of the image in pixels per resolution unit.
    The ITU-T Recommendations for facsimile specify a small number of
    vertical resolutions: 100, 200, 300, 400 pixels per inch, and 38.5,
    77, 154 pixels per centimeter (or 98, 196, 391 pixels per inch). The
    allowed YResolution values for each mode are given in the section



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RFC 2301              File Format for Internet Fax            March 1998


    defining that mode. Per [T.4], it is permissible for applications to
    treat the following YResolution 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. TIFF for Facsimile Writers SHOULD express
    YResolution in inch based units, for consistency with historical
    practice and to maximize interoperability. See the table below for
    information on how to convert from an ITU-T metric value to its inch
    based equivalent resolution. No default, must be specified

      +-----------------------------+-----------------------------+
      |         XResolution         |         YResolution         |
      +--------------+--------------+--------------+--------------+
      |ResolutionUnit|ResolutionUnit|ResolutionUnit|ResolutionUnit|
      |  =2 (inch)   |   =3 (cm)    |  =2 (inch)   |   =3 (cm)    |
      +--------------+--------------+--------------+--------------+
      |     100      |              |     100      |              |
      +--------------+--------------+--------------+--------------+
      |     204      |      80      |      98      |     38.5     |
      |     200      |              |     100      |              |
      +--------------+--------------+--------------+--------------+
      |     204      |      80      |     196      |      77      |
      |     200      |              |     200      |              |
      +--------------+--------------+--------------+--------------+
      |     204      |      80      |     391      |     154      |
      +--------------+--------------+--------------+--------------+
      |     300      |              |     300      |              |
      +--------------+--------------+--------------+--------------+
      |     408      |     160      |     391      |     154      |
      |     400      |              |     400      |              |
      +--------------+--------------+--------------+--------------+