Practice with linear filters

original
filter
0 0 0
0 1 0
0 0 0
shifted left by 1 pexel
0 0 0
0 0 1
0 0 0
blur
1 1 1
1 1 1
1 1 1
sharpening filter
0 0 0 1 1 1
0 2 0- 1 1 1
0 0 0 1 1 1
unsharp mask