I think the left matrix extracts vertical edges and right matrix extracts horizontal edges. If the color doesn't change, the filter will output the same value as the original. If the horizontal or vertical filter is run at the horizontal or vertical edges, then the output is non-zero.
I think the left matrix extracts vertical edges and right matrix extracts horizontal edges. If the color doesn't change, the filter will output the same value as the original. If the horizontal or vertical filter is run at the horizontal or vertical edges, then the output is non-zero.