Hi there, I'm new to this forum and was hoping someone would be able to answer 
a question about the unsharp mask filter.

I'm doing some image processing for work, and was going through various filters 
and found that the unsharp mask has some qualities that I like.  So I read up 
on unsharp masking and implemented it in my own program.  However, my results 
aren't quite the same.

Put simply: gimp's output has more contrast, and appears somewhat smoother.

After playing with my unsharp mask a bit, I downloaded the source to 2.6.11 
(possibly a mistake, since I am using the 2.6.10 binary) and found the code 
that does the unsharp masking (unsharp-mask.c).  Now, looking through the code 
I don't see gimp doing anything really different from me outside of the 
convolution matrix code.  Frankly, I don't understand the convolution matrix 

Why does it take 50 samples and then average them?  Is this significant?

I tried running some numbers through the equation e^-(x^2/2s^2) in the 
comments, and ran that through a calculator.  The numbers largely came out 
negative, but when I used those numbers they gave obviously incorrect output 
(hugely overexposed appearance).

Are there any other non-standard tweaks to this algorithm that I haven't 
spotted yet?

I'm currently using a simple convolution of: .1, .2, .4, .2, .1
For a similar sized convolution matrix, what would gimp be using?  My 
development environment isn't set up to compile gimp.

Thanks for any assistance!

bioster (via gimpusers.com)
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