| .TH RDJPGCOM 1 "02 April 2009" |
| .SH NAME |
| rdjpgcom \- display text comments from a JPEG file |
| .SH SYNOPSIS |
| .B rdjpgcom |
| [ |
| .B \-raw |
| ] |
| [ |
| .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 \-raw |
| Normally |
| .B rdjpgcom |
| escapes non-printable characters in comments, for security reasons. |
| This option avoids that. |
| .PP |
| .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 |
