Re: [MacPerl] comparing image files

[Rich Morin <rdm@cfcl.com>]

The first thing I'd like to do is thank my respondents for their
time and thought on this matter; we really have put together an
interesting brain trust here, even when the topic has nothing at
all (really) to do with MacPerl!

I don't think I can get away with comparing JPEG images, because
they are compressed.  OTOH, I feel sure that I can convince some
package (once I find it :-) to expand JPEGs into pixmaps.

Greg's comments about signatures miss my intent a little.  While
an MD5 signature would work well for making exact comparisons, a
trivial difference in the images would throw it off.  Since I am
looking for pairs of images which may have been reduced in size
or resolution, an MD5 signature would clearly be different.

Greg's notion of comparing height/width ratios, OTOH, may well be
an interesting first cut.  If I decide to process subsets of the
file set, I might be well advised to group pictures by h/w ratio.

Both Brian and Jeff have given me some interesting ideas about
generating signatures.  One of the approaches I like is that of
picking a signature that does not depend on image resolution or
size.  This might obviate the need to normalize these factors.
OTOH, if I can get a utility to do the work, it may be easiest
to normalize all of the images to a standard resolution and size,
calculate the signature(s) and discard the temporary images.

If I have to, I can move the files to my FreeBSD box for the task,
but I'd be happier to find a totally Mac-based solution.  This
means that ImageMagick and some other Unixish tools are not as
interesting as they might appear.

In any event, I'll let youall know if I come up with anything!

-r
--
Rich Morin:          rdm@cfcl.com, +1 650-873-7841, http://www.ptf.com/~rdm
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