rfc2306.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

       F purposes are 3 and 4 as shown.   The default value per Baseline
       TIFF is 1 (Uncompressed), but this value is invalid for facsimile
       images.    Baseline TIFF also permits use of value 2 (Modified
       Huffman encoding), but the data is presented in a form which does
       not contain EOLs. Instead, TIFF-F specifies the value 3 for
       encoding one-dimensional T.4 Modified Huffman or 2-dimensional
       Modified READ data.   The detailed settings which apply for T.4
       encoded data are specified using the T4Options field.  TIFF-F
       also permits use of the value 4 for the compression field, which
       indicates that the data is coded using a [T.6] compression method
       (i.e the Modified Modified READ two-dimensional method). The
       detailed settings which apply for T.6 encoded data are specified
       using the T6Options field.

       Please refer to the definitions of the T4Options and T6Options
       fields in section 3.3, and section 3.8 for more information on
       the encoding of images and conventions used within TIFF-F.

   PhotometricInterpretation (260) = 0,1.  SHORT.
       This field allows notation of an inverted ("negative") image:
               0 = normal
               1 = inverted

   StripOffsets (273).  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.

   RowsPerStrip (278).  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 field.

   StripByteCounts (279).  LONG or SHORT.  LONG 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.  Note that the choice of LONG or
       SHORT depends upon the size of the strip.





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   ResolutionUnit (296) = 2,3.  SHORT.
       The units of measure for resolution:
               2 = Inch
               3 = Centimeter

       TIFF-F has traditionally used inch based measures.

   XResolution (282) = 204, 200, 300, 400, 408 (inches). RATIONAL.
       The horizontal resolution of the TIFF-F image expressed in pixels
       per resolution unit. 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
       (cm).  See section 3.8.2 for more information on inch/metric
       equivalencies and other implementation details.

   YResolution (283) = 98, 196, 100, 200, 300, 391, 400  (inches).
                       RATIONAL.
       The vertical resolution of the TIFF-F image expressed in pixels
       per resolution unit. 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, 38.5 (cm). See section 3.8.2 for more information
       on inch/metric equivalencies and other implementation details.

3.3  TIFF-F Required Fields

   In addition to the Baseline TIFF fields, there are additional
   required fields for TIFF-F. A review of the additional required
   fields for TIFF-F follows:

   BitsPerSample (258) = 1.  SHORT.
       Since TIFF-F  is only used for black-and-white facsimile images,
       the value is  1 (the default) for all files.

   FillOrder (266) = 1, 2.  SHORT.
       TIFF  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.

   NewSubFileType (254)= (Bit 1 = 1).  LONG.
       This field is made up of 32 flag bits.  Unused bits are
       expected to be 0 and bit 0 is the low order bit.   Bit 0 is set
       to 0 for TIFF-F.   Bit 1 is always set to 1 for TIFF-F,
       indicating a single page of a multi-page image. The same bit





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       settings are used when TIFF-F is used for a one page fax image.
       See sections 3.1.1 and 3.1.2 for more details on the structure
       of multi-page TIFF-F image files.

   PageNumber (297).  SHORT/SHORT.
       This field specifies the page numbers in the fax document.  The
       field comprises two SHORT values: the first value is the page
       number, the second is the total number of pages. Single-page
       documents therefore use 0000/0001 hex.  If the second value is
       0, the total number of pages in the document is not available.

   SamplesPerPixel (277) = 1.  SHORT.
       The value of 1 denotes a bi-level, grayscale, or palette color
       image.

   There is also a requirement to include either the T4Options or the
   T6Options field in a TIFF-F IFD, depending upon the setting of the
   Compression field.  These fields are defined in the next section on
   TIFF extensions.

3.4  TIFF-F Extensions

   These are fields which are extensions beyond the required TIFF-F
   fields.  The following fields have been defined as extensions in
   [TIFF].

   T4Options (292) (Bit 0 = 0 or 1, Bit 1 = 0, Bit 2 = 0 or 1).  LONG.
       This field is required if the value for the compression field
       has been set to 3.   The values are set as shown below for TIFF-
       F.   For TIFF-F, uncompressed data is not allowed and EOLs MAY
       be byte aligned (see section 3.8.3).
               bit 0 = 0 for 1-Dimensional, 1 for 2-Dimensional (MR)
               bit 1 = must be 0 (uncompressed data not allowed)
               bit 2 = 0 for non-byte-aligned EOLs or 1 for byte-
                       aligned EOLs

       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.  Please note
       that T4Options was known as G3Options in earlier versions of
       TIFF and TIFF-F.  The data in a TIFF-F image encoded using
       one of the T.4 methods is not terminated with an RTC (see
       section 3.8.5).

   T6Options (293) = (Bit 0 = 0, Bit 1 = 0)  LONG.
       This field is required for TIFF-F if value of the compression
       field has been set to 4. The value for this field is made up of
       a set of 32 flag bits.   Setting bit 0 to 0 indicates that the
       data is compressed using the Modified Modified READ (MMR) two-



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       dimensional compression method.  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 3.8.6). Uncompressed data is not
       applicable for bi-level facsimile images, so that bit 1 must be
       set to 0.  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)

       In earlier versions of TIFF, this field was named Group4Options.
       The significance has not changed and the present definition is
       compatible.

       In addition, three new fields, defined as TIFF-F extensions,
       describe page quality.  The information contained in these fields
       is usually obtained from receiving facsimile hardware (if
       applicable).   These fields are optional.  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 implementations 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
       This field 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 (327). SHORT
       N =
           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





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           2 = Lines with an incorrect pixel count are in the data  and
              were not regenerated by receiving device (i.e. data
              contains bad scan lines)

       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.
       This field 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 field is an
       indicator of their distribution and may therefore be a better
       general indicator of perceived image quality.

3.5  Recommended Fields

   hese are fields that MAY be used in encoding TIFF-F files, but are
   ptional in nature and may be ignored by many TIFF readers.  These
   ields are called recommended consistent with historical TIFF-F
   ractice.

   BadFaxLines (326) [defined in section 3.4]

   CleanFaxData (327) [defined in section 3.4]

   ConsecutiveBadFaxLines (328) [defined in section 3.4]

   DateTime (306).  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 (269).  ASCII.
       This is the name of the document from which the document was
       scanned.



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   ImageDescription (270).  ASCII.
       This is an ASCII string describing the contents of the image.

   Orientation (274).  SHORT.
       This field is designated as "Recommended" for consistency with
       historical TIFF-F, but is also a Baseline TIFF field with a
       default value of 1 per [TIFF]. The default value of 1 applies
       if the field is omitted, but for clarity, TIFF-F writers SHOULD
       include this field.  This field 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.

   Software (305).  ASCII.
       The optional name and release number of the software package
       that created the image.

3.6   Requirements for TIFF-F Minimum Subset

   This section defines the requirements for a minimum subset of TIFF-F
   fields and values that all TIFF-F readers SHOULD support to maximize
   interoperability with current and historical TIFF-F implementations.
   The TIFF-F structure for writing minimum subset files is also
   defined.

3.6.1   Summary of Minimum Subset Fields and Values

   A summary of the minimum subset TIFF-F fields and values is provided
   in the following table.  The required fields for the minimum subset
   are shown under the column labeled "Field".  The values for these
   fields in the minimum subset are shown under the column labeled
   "Minimum".

  Field             | Minimum      | Comment
  ------------------|--------------|-------------------------------
  BitsPerSample     | 1            |one bit per sample
  Compression       | 3            |3 for T.4 (MH)
  FillOrder         | 2            |LSB first
  ImageWidth        | 1728         |
  ImageLength       |              |required
  NewSubFileType    | Bit 1 = 1    |single page of multipage file
  PageNumber        | X/X          |pg/tot, 0 base, tot in 1st IFD
  PhotometricInterp | 0            |0 is white
  ResolutionUnit    | 2            |inches (default)
  RowsPerStrip      |=ImageLength  |
  SamplesPerPixel   | 1            |one sample per pixel



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  StripByteCounts   |              |required
  StripOffsets      |              |required
  T4Options         | Bit 0 = 0    |MH
                    | Bit 1 = 0    |
                    | Bit 2 = 0,1  |Non-Byte-aligned,
                    |              | Byte-Aligned EOLs
  XResolution       | 204          |Units is per inch
  YResolution       | 196,98       |Units is per inch
  ------------------|--------------|------------------------------

3.6.2     TIFF-F Minimum Subset File Structure

   For implementations which need to write minimum subset TIFF-F files,
   the file structure shown in Figure 3.1 MUST be used:

                   +-----------------------+
                   |         Header        |------------+
                   +-----------------------+            | First IFD
                   |      IFD (page 0)     | <----------+ Offset
               +---|                       |------------+
               |   |                       |--+         |
         Value |   +-----------------------+  |         |
        Offset +-->|      Long Values      |  |         |
                   +-----------------------|  | Strip   |