rdjpgcom(1)

RDJPGCOM(1)              USER COMMANDS                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  dimen-
          sions.

     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 cam-
     eras produce APP12 markers containing useful textual  infor-
     mation.   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

                  Last change: 11 October 1997                  1