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
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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