RDJPGCOM(1) UNIX System V (11 October 1997) 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 markers 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
Page 1 (printed 12/16/98)
