What's the algorithmic difference between these images?

[kleptophobiac]

I wrote a program that should take the grayscale difference between two images. Photoshop has the "difference" combination method of two images. What's the algorithmic difference from a simple subtraction (my program) and photoshop/gimp?

My program:

Photoshop in "difference" blend mode:

Here are the two source images:

 

[Vol]

I don't know what Photoshop is exactly doing but if you use a mean or median filter, I think you could achieve something similar. Using one of these filters on the resulting image would reduce the noise level.

This page briefly describes how the filters work: http://www.markschulze.net/java/meanmed.html

There are more advance filters out there but my knowledge stops here...

 

[kleptophobiac]

Well, I'm wondering why photoshop has such a nice strong white channel where I don't... I don't think that's a noise thing (but the background speckles certainly are, so that's still useful advice).

Thanks!