Date: Tue, 4 Jan 2005 09:53:01 -0800
From: "William Skaggs" <[EMAIL PROTECTED]>
2) The jpeg plug-in now pretty closely adheres to the instructions
in the exif specifications concerning which fields should be
altered by an image-editing program. There are a couple of
fields remaining that I haven't yet figured out how to set
properly.
There is now a file called "exif-handling.txt" in devel-docs
that summarizes my understanding, based on the exif
specifications, of how an image editor is supposed to handle the
exif data in a file. Of course we need not take the
specifications as gospel (among other things, they specify that
a proper EXIF file must have a file name in 8.3 format, ending
in .JPG!), but they should serve as a good default.
Adobe at least had an excuse with PPD files 10 years ago. There's no
excuse for 8.3 any more.
4) When the exif specifies that an image is rotated, the plug-in
pops up a query asking the user whether to rotate it into
standard alignment. I thought it was better to ask rather than
do it automatically, because there are probably a substantial
number of existing images that have been edited without having
their exif information properly updated (for example, by earlier
versions of GIMP). When an image is saved with exif, the
orientation is set to "top-left", as the exif specifications
require. (See bug #121810)
I'd suggest making this a preference. If someone's careful about
maintaining their images (or hasn't edited them before), they'll get
very annoyed by having to answer this question every time they open an
EXIF file that's rotated. Wouldn't earlier versions of the GIMP have
destroyed the EXIF data?
2) Exif is not relevant only to jpeg: it can appear in TIFF and Raw
files, and there are draft standards for including it in PNG and
other file types. I would like to extract the generic parts of
the exif handling code for jpeg-exif.c and place it into a new
library for generic file-handling code, libgimpfile, which we
have discussed creating some time ago (see bug #139354). The
file jpeg-exif.c will still however need to exist, because the
exif specifications require some different fields for compressed
(jpeg) vs uncompressed (tiff) exif files.
FYI, Canon raw (.crw) files have an embedded JPEG file, but the EXIF
information is stored in both the raw file and in a thumbnail (.thm)
file with the same basename. The .thm file is actually a JPEG file
with embedded EXIF data.
--
Robert Krawitz <[EMAIL PROTECTED]>
Tall Clubs International -- http://www.tall.org/ or 1-888-IM-TALL-2
Member of the League for Programming Freedom -- mail [EMAIL PROTECTED]
Project lead for Gimp Print -- http://gimp-print.sourceforge.net
"Linux doesn't dictate how I work, I dictate how Linux works."
--Eric Crampton
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