[lug] Looking for image manipulation software

[Tkil]

First off, it's considered good practice to wrap at 72 characters per
line, not at 90...

>>>>> "Paul" == Paul E Condon <Paul> writes:

Paul> By subtract, I mean pixel-by-pixel difference of pixel values so
Paul> that if the two input images are identical, the result is an
Paul> blank image. 

Note that this is one issue (and a relatively simple one, at that)...

>From the command line, consider using 'convert' or the netpbm
toolkits.  With ImageMagick:

   composite -compose difference image1.png image2.png diff.png

Paul> I can get two images I can move one relative to another, and if
Paul> I spent another few hours looking I might find a way to input
Paul> x,y shifts as number of pixels rather than using the mouse to
Paul> drag and drop. 

Translation (the math geek term for shifting by X and/or Y), together
with scaling, is much harder.

You start getting into correlation functions (pure translation), and I
really have no idea what to do in the face of scaled images.

I suspect that what you're really looking for is basically a "burglar
detection" algorithm: with a fixed camera, take a picture of a scene.
Using the same camera with the same settings against the same scene at
some future time, find the differences.  The above command line ought
to be sufficient.  (Although, note that it is not intelligent, and
night v. day will be enough to totally throw it off.)

Paul> But even when I do get them overlaid with the mouse, that only
Paul> increases the contrast of the image. Choosing modes subtract or
Paul> difference doesn't help.

Don't know how to tell gimp to do this, sorry.

Paul> Is there some other software that is more oriented towards
Paul> images as data rather than images as graphic art?

As someone else already pointed out, there are quite a few free and
commercial packages available for data analysis.

Good luck,
t.