I think restricting the image size so arbitrarily is a bad idea; 48x48 is
really tiny! All of my other icons are 64x64, and they just don't look all
that large. The same people who want color today will want bigger tomorrow.
> I'm assuming existing standards (JPEG comes to mind) are
> unsuitable for this purpose. Please let me know if not and
> save me lots of work.
I think a good approach might be to use the XPM3 format as the baseline, and
find some way of compressing it efficiently. It's a very nice format, in
that it allows you to efficiently tune your image for color, grayscale, and
monochrome devices without duplicating data. Also there is a good library
for managing color allocation, etc.
> Backward compatibility is impossible without choosing a new
> header title, say `X-Image'.
You could put a magic number in the new format that is unlikely to occur at
the beginning of the old format. For example, some character which the old
format doesn't use. (I don't know how practical this is.) Or just put a
checksum in the new format; if the checksum doesn't match, assume it's the
old format. That should be foolproof for non-corrupted images.
-- Jamie