wrjpgcom - insert text comments into a JPEG file
wrjpgcom [ -replace ] [ -comment text ] [ -cfile name ] [ filename ]
wrjpgcom reads the named JPEG/JFIF file, or the standard input if no file is named, and
generates a new JPEG/JFIF file on standard output. A comment block is added to the file.
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.
wrjpgcom adds a COM block, containing text you provide, to a JPEG file. Ordinarily, the
COM block is added after any existing COM blocks; but you can delete the old COM blocks if
Switch names may be abbreviated, and are not case sensitive.
Delete any existing COM blocks from the file.
Supply text for new COM block on command line.
Read text for new COM block from named file.
If you have only one line of comment text to add, you can provide it on the command line
with -comment. The comment text must be surrounded with quotes so that it is treated as a
single argument. Longer comments can be read from a text file.
If you give neither -comment nor -cfile, then wrjpgcom will read the comment text from
standard input. (In this case an input image file name MUST be supplied, so that the
source JPEG file comes from somewhere else.) You can enter multiple lines, up to 64KB
worth. Type an end-of-file indicator (usually control-D) to terminate the comment text
wrjpgcom will not add a COM block if the provided comment string is empty. Therefore
-replace -comment "" can be used to delete all COM blocks from a file.
Add a short comment to in.jpg, producing out.jpg:
wrjpgcom -c "View of my back yard" in.jpg > out.jpg
Attach a long comment previously stored in comment.txt:
wrjpgcom in.jpg < comment.txt > out.jpg
wrjpgcom -cfile comment.txt < in.jpg > out.jpg
cjpeg(1), djpeg(1), jpegtran(1), rdjpgcom(1)
Independent JPEG Group
15 June 1995 WRJPGCOM(1)