RDJPGCOM(1) User Commands 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
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

02 April 2009 RDJPGCOM(1)