s it possible to access or set individual pixels of an image?

[Marty Billingsley]

Is it possible to read and set the color of individual pixels in an  
image?  ImageData is a little incomprehensible.

Basically, I'd like to be able to do something like:
for each pixel in image "x",  set the color of that pixel to some  
calculated value (or a value pulled from a pixel of another image)

Thanks for any pointers you can give me!

  - marty

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Marty Billingsley
Department of Computer Science
The University of Chicago Laboratory Schools