Do the functions FILTER2 and CONV2 perform correlation or convolution?
Do the functions FILTER2 and CONV2 perform correlation or convolution?
John Michell answered .
2025-11-20
a = magic(5)
a =
17 24 1 8 15
23 5 7 14 16
4 6 13 20 22
10 12 19 21 3
11 18 25 2 9
f = [1 0; 0 0];
filter2(f,a,'full')
ans =
0 0 0 0 0 0
0 17 24 1 8 15
0 23 5 7 14 16
0 4 6 13 20 22
0 10 12 19 21 3
0 11 18 25 2 9
filter2(f,a,'valid')
ans =
17 24 1 8
23 5 7 14
4 6 13 20
10 12 19 21
g = [0 0; 0 1];
filter2(g,a,'full')
ans =
17 24 1 8 15 0
23 5 7 14 16 0
4 6 13 20 22 0
10 12 19 21 3 0
11 18 25 2 9 0
0 0 0 0 0 0
filter2(g,a,'valid')
ans =
5 7 14 16
6 13 20 22
12 19 21 3
18 25 2 9
Here also the 'valid' result is the (2:5,2:5) submatrix of the 'full' result.