1 .TH RDJPGCOM 1 "02 April 2009"

     2 .SH NAME

     3 rdjpgcom \- display text comments from a JPEG file

     4 .SH SYNOPSIS

     5 .B rdjpgcom

     6 [

     7 .B \-raw

     8 ]

     9 [

    10 .B \-verbose

    11 ]

    12 [

    13 .I filename

    14 ]

    15 .LP

    16 .SH DESCRIPTION

    17 .LP

    18 .B rdjpgcom

    19 reads the named JPEG/JFIF file, or the standard input if no file is named,

    20 and prints any text comments found in the file on the standard output.

    21 .PP

    22 The JPEG standard allows "comment" (COM) blocks to occur within a JPEG file.

    23 Although the standard doesn't actually define what COM blocks are for, they

    24 are widely used to hold user-supplied text strings.  This lets you add

    25 annotations, titles, index terms, etc to your JPEG files, and later retrieve

    26 them as text.  COM blocks do not interfere with the image stored in the JPEG

    27 file.  The maximum size of a COM block is 64K, but you can have as many of

    28 them as you like in one JPEG file.

    29 .SH OPTIONS

    30 .TP

    31 .B \-raw

    32 Normally

    33 .B rdjpgcom

    34 escapes non-printable characters in comments, for security reasons.

    35 This option avoids that.

    36 .PP

    37 .B \-verbose

    38 Causes

    39 .B rdjpgcom

    40 to also display the JPEG image dimensions.

    41 .PP

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

    43 .SH HINTS

    44 .B rdjpgcom

    45 does not depend on the IJG JPEG library.  Its source code is intended as an

    46 illustration of the minimum amount of code required to parse a JPEG file

    47 header correctly.

    48 .PP

    49 In

    50 .B \-verbose

    51 mode,

    52 .B rdjpgcom

    53 will also attempt to print the contents of any "APP12" markers as text.

    54 Some digital cameras produce APP12 markers containing useful textual

    55 information.  If you like, you can modify the source code to print

    56 other APPn marker types as well.

    57 .SH SEE ALSO

    58 .BR cjpeg (1),

    59 .BR djpeg (1),

    60 .BR jpegtran (1),

    61 .BR wrjpgcom (1)

    62 .SH AUTHOR

    63 Independent JPEG Group