RDJPGCOM(1) General Commands Manual RDJPGCOM(1)
NAME
rdjpgcom - display text comments from a JPEG file
SYNOPSIS
rdjpgcom [ -raw ] [ -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
-raw Normally rdjpgcom escapes non-printable characters in comments,
for security reasons. This option avoids that.
-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
02 April 2009 RDJPGCOM(1)
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