rdjpgcom



RDJPGCOM(1)                                                        RDJPGCOM(1)




NAME

       rdjpgcom - display text comments from a JPEG file


SYNOPSIS

       rdjpgcom [ -verbose ] [ filename ]



DESCRIPTION

       rdjpgcom  reads  the  named JPEG/JFIF file, or the standard input if no
       file is named, and prints any text comments found in the  file  on  the
       standard output.

       The  JPEG standard allows "comment" (COM) blocks to occur within a JPEG
       file.  Although the standard doesn’t actually define  what  COM  blocks
       are for, they are widely used to hold user-supplied text strings.  This
       lets you add annotations, titles, index terms, etc to your JPEG  files,
       and  later retrieve them as text.  COM blocks do not interfere with the
       image stored in the JPEG file.  The maximum size of a COM block is 64K,
       but you can have as many of them as you like in one JPEG file.


OPTIONS

       -verbose
              Causes rdjpgcom to also display the JPEG image dimensions.

       Switch names may be abbreviated, and are not case sensitive.


HINTS

       rdjpgcom  does  not depend on the IJG JPEG library.  Its source code is
       intended as an illustration of the minimum amount of code  required  to
       parse a JPEG file header correctly.

       In  -verbose  mode, rdjpgcom will also attempt to print the contents of
       any "APP12" markers as text.  Some digital cameras produce APP12  mark-
       ers containing useful textual information.  If you like, you can modify
       the source code to print other APPn marker types as well.


SEE ALSO

       cjpeg(1), djpeg(1), jpegtran(1), wrjpgcom(1)


AUTHOR

       Independent JPEG Group



                                11 October 1997                    RDJPGCOM(1)

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