rfc1314.txt

RFC 的详细文档！

      above representations.

4.  A Sample TIFF Image File

   Below is a sample of what might be in a TIFF file for an MMR (G4)
   encoded single image which is about 100K bytes compressed at 400 dpi.
   A generic outline is given first, followed by a more detailed hex
   listing.

4.A. Sample File

   Comments are to the right and are preceded by a semicolon.  Note that
   tags must be sorted in order of the tag codes.

   0:, IFDADDR:, and STRIP0: are addresses within the file and denote
   the number of bytes from the beginning of the file.

   Header:

    0:  Byte Order=     hex 4D4D        ;first bytes of the file, from
                                        ;most significant bit to least
                                        ;significant (big endian)
        Version=        42 (hex 002A)   ;Must be 42
        First IFD=      IFDADDR         ;Address of first (and only) IFD

   Image File Directory (the only one in this example):

   IFDADDR:

        IFD Entry Count=      24        ;(NOT A TAG) Count of
                                        ; Number of IFD Entries


        NewSubFileType=        0
        ImageWidth=         3400        ;8.5 inches at 400 dpi
        ImageLength=        4400        ;11 inches at 400 dpi
        BitsPerSample=         1        ;Bi-Level



Katz & Cohen                                                   [Page 18]

RFC 1314                 Image Exchange Format                April 1992


        Compression=           4        ;MMR
        Photometric-
           Interpretation=     0
        DocumentName=       "LAMap1"
        ImageDescription=   "A map of Los Angeles"
        Make=               "Fujitsu"
        Model=              "M3093E"
        StripOffsets=       <STRIP0>    ;There is only one strip in
                                        ;this example.  However, note
                                        ;that strips can be in any
                                        ;order.  (Offsets are from the
                                        ;beginning of the TIFF file.)

        SamplesPerPixel=       1        ;Bi-Level
        RowsPerStrip=       4400        ;Entire image in 1 strip
        StripByteCounts=    <COUNT0>    ;Byte count of entire
                                        ;compressed image

        XResolution=        400/1
        YResolution=        400/1
        XPosition=            0/1       ;position of left side of image
        YPosition=            0/1       ;position of top of image
        Group4Options=    hex 00000002  ;bit 1 on means uncompressed
                                        ;mode MAY be used

        ResolutionUnit=        2        ;Inches
        Software=           "Xionics"
        DateTime=           "1990:10:05 15:00:00"
        Artist=             "Joe Pro"
        HostComputer=       "Tardis.Isi.Edu"

        Next IFD Pointer=  hex 00000000 ;(NOT A TAG) Indicates no
                                        ; more IFDs in this file

    Image Data:

    <STRIP0>:       <actual compressed image data>

    [end of TIFF file]

   In this example there is only one strip.  Note that if there were
   more than one, the TIFF specification does not require them to be in
   any particular order.  Strips may be given in any order and TIFF
   readers must use the StripOffsets to locate them.

   Also, the TIFF document recommends not relying on the default values
   of the tags.




Katz & Cohen                                                   [Page 19]

RFC 1314                 Image Exchange Format                April 1992


4.B. Detailed Hex Listing

   All offsets and values are represented by hex except for ASCII
   strings which are double quoted.  Remember that Value Offsets must
   always be an even number since the value it points to must always be
   on a 16-bit word boundary.

   Entries in the Name column are for reference and are not actually a
   part of the TIFF file.

   Offset      Name                  Value
   ----        -------------------   -------------------------------------
  Header (first byte is Offset 0):
   0000        Byte Order             4D4D
   0002        Version                002A
   0004        1st. IFD pointer       00000010

  IFD (IFDADDR from above is 0010 here):
   0010        Entry Count            0018
   0012        NewSubFileType         00FE   0004   00000001  00000000
   001E        ImageWidth             0100   0004   00000001  00000D48
   002A        ImageLength            0101   0004   00000001  00001130
   0036        BitsPerSample          0102   0003   00000001  00010000
   0042        Compression            0103   0003   00000001  00040000
   004E        Photometric Interp.    0106   0003   00000001  00000000
   005A        DocumentName           010D   0002   00000007  00000136
   0066        ImageDescription       010E   0002   00000015  0000013E
   0072        Make                   010F   0002   00000008  00000154
   007E        Model                  0110   0002   00000007  0000015C
   008A        StripOffsets           0111   0004   00000001  000001A8
   0096        SamplesPerPixel        0115   0003   00000001  00010000
   00A2        RowsPerStrip           0116   0004   00000001  00001130
   00AE        StripByteCounts        0117   0004   00000001  <COUNT0>
   00BA        XResolution            011A   0005   00000001  00000164
   00C6        YResolution            011B   0005   00000001  00000164
   00D2        XPosition              011E   0005   00000001  0000016C
   00DE        YPosition              011F   0005   00000001  0000016C
   00EA        Group4Options          0125   0004   00000001  00000002
   00F6        ResolutionUnit         0128   0003   00000001  00020000
   0102        Software               0131   0002   00000008  00000174
   010E        DateTime               0132   0002   00000014  0000017C
   011A        Artist                 013B   0002   00000008  00000190
   0126        HostComputer           013C   0002   0000000F  00000198
   0132        Next IFD Pointer       00000000

  Fields Offsets Point to:
   0136        DocumentName          "LAMap1"
   013E        ImageDescription      "A map of Los Angeles"



Katz & Cohen                                                   [Page 20]

RFC 1314                 Image Exchange Format                April 1992


   0154        Make                  "Fujitsu"
   015C        Model                 "M3093E"
   0164        X,Y Resolution        00000190 00000001
   016C        X,Y Position          00000000 00000001
   0174        Software              "Xionics"
   017C        DateTime              "1990:10:05 15:00:00"
   0190        Artist                "Joe Pro"
   0198        HostComputer          "Tardis.Isi.Edu"

  Image Data (<STRIP0> from above is here 01A8)
   01A8        Compressed Data for single strip, of length <COUNT0> bytes

    [end of TIFF file]

NOTE:  Since in this example there is only a single strip, there is only
       one count for StripByteCounts and one offset for StripOffsets.
       Thus, each of these only takes 4 bytes and will fit in the
       Value Offset instead of being pointed to.

5.  Conclusions

   Bitmapped images transferred within the Internet should be in the
   following format:

        1. The file format should be TIFF-B with multi-page files
           supported.  Images should be encoded as one TIFF strip
           per page.

        2. Images should be compressed using MMR when possible.  Images
           may also be MH or MR compressed or uncompressed.  If MH or MR
           compression is used, scan lines should be "byte-aligned".

        3. For maximum interoperability, image resolutions should
           either be 600, 400, or 300 dpi; or else be one of the
           standard Group 3 fax resolutions (98 or 196 dpi
           vertically and 204 dpi horizontally).

   Note that this specification is self contained and an implementation
   should be possible without recourse to the TIFF references, and that
   only the specific TIFF documents cited are relevant to this
   specification.  Updates to the TIFF documents do not change this
   specification.

   Existing commercial off-the-shelf products are available which can
   handle images in the above format.  ISI would be delighted to help
   those interested in assembling a system.





Katz & Cohen                                                   [Page 21]

RFC 1314                 Image Exchange Format                April 1992


6.  Acknowledgments

   Many contributions to this work were made by members of the IETF
   Network Fax Working Group especially by its chairman, Mark Needleman
   and by Clifford Lynch of the University of California Office of the
   President, Library Automation.  Also, Kiyo Inaba of Ricoh Co. Ltd.
   made a number of helpful suggestions.

7.  References

   [1] Borenstein, N., and N. Freed, "Mechanisms for Specifying and
       Describing the Format of Internet Message Bodies", RFC in
       preparation.

   [2] International Telegraph and Telephone Consultative Committee
       (CCITT), Red Book, October, 1984.

   [3] Aldus Corp., Microsoft Corp., "Tag Image File Format
       Specification", Revision 5.0, Final, 1988.

   [4] Cygnet Corporation, "The Spirit of TIFF Class F, 1990", available
       from Cygnet Technologies, 2560 9th., Suite 220, Berkeley, CA
       94710, FAX: [phone].

   [5] Welch, T., "A Technique for High Performance Data Compression",
       IEEE Computer, Vol. 17, No. 6, Page 8, June 1984.

8.  Security Considerations

   While security issues are not directly addressed by this document, it
   is important to note that the file format described in this document
   is intended for the communications of files between systems and
   across networks. Thus the same precautions and cares should be
   applied to these files as would be to any files received from remote
   and possibly unknown systems.
















Katz & Cohen                                                   [Page 22]

RFC 1314                 Image Exchange Format                April 1992


9.  Authors' Addresses

   Alan Katz
   USC Information Sciences Institute
   4676 Admiralty Way #1100
   Marina Del Rey, CA  90292-6695

   Phone: [phone]
   Fax:  [phone]
   EMail: [e-mail]

   Danny Cohen
   USC Information Sciences Institute
   4676 Admiralty Way #1100
   Marina Del Rey, CA  90292-6695

   Phone: [phone]
   Fax:  [phone]
   EMail: [e-mail]
































Katz & Cohen                                                   [Page 23]