rdjpgcom - display text comments from a JPEG file
rdjpgcom [
-raw ] [
-verbose ] [
filename ]
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.
- -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.
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.
cjpeg(1),
djpeg(1),
jpegtran(1),
wrjpgcom(1)
Independent JPEG Group