libjpeg-turbo/rdjpgcom.1

.TH RDJPGCOM 1 "11 October 1997"
.SH NAME
rdjpgcom \- display text comments from a JPEG file
.SH SYNOPSIS
.B rdjpgcom
[
.B \-verbose
]
[
.I filename
]
.LP
.SH DESCRIPTION
.LP
.B 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.
.PP
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.
.SH OPTIONS
.TP
.B \-verbose
Causes
.B rdjpgcom
to also display the JPEG image dimensions.
.PP
Switch names may be abbreviated, and are not case sensitive.
.SH HINTS
.B 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.
.PP
In
.B \-verbose
mode,
.B 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.
.SH SEE ALSO
.BR cjpeg (1),
.BR djpeg (1),
.BR jpegtran (1),
.BR wrjpgcom (1)
.SH AUTHOR
Independent JPEG Group