Why not add subsection of the convolution?

[Longhao-Chen]

Just like the MATLAB conv function.

'full' — Return the full 2-D convolution.

'same' — Return the central part of the convolution, which is the same size as A.

'valid' — Return only parts of the convolution that are computed without zero-padded edges.

I think this can be achieved by splitting the existing output.