Assuming I already have a working convolution matrix algorithm in place, I'm looking for practical examples of general matrices that are useful for image processing in particular.
The canonical examples you'll find everywhere are non-gaussian box blur:
1 1 1
1 1 1
1 1 1
Image sharpening:
0 -1 0
-1 5 -1
0 -1 0
Edge detection:
0 1 0
1 -4 1
0 1 0
and emboss:
-2 -1 0
-1 1 1
0 1 2
Are there more I'm missing?