Matrix convolution only on some elements

Hi, I'm a junior with matlab experience. I tried to search whatever like my problem on internet without find any answer. I have to do a convolution on a matrix A using conv2 but only if the central element (overlaped on the mask) is 1

For example

A=[ 1 0 1 0 ; 0 1 0 0 ; 1 0 0 0 ; 0 1 0 0]

F=[1 1 1; 1 0 1; 1 1 1]

The convolution conv2(A,F,'same') have to been made only if the central element is 1 (like 1', 3', 5',... elements) skipping the convolution if is 0. Obvious i can accept any other functions like conv2 to do the convolution. Thanks if everybody can help me

Answer 1

[Image Analyst]

Try this:

A=[ 1 0 1 0 ; 0 1 0 0 ; 1 0 0 0 ; 0 1 0 0]

A = 4×4

1 0 1 0 0 1 0 0 1 0 0 0 0 1 0 0

F=[1 1 1; 1 0 1; 1 1 1]

F = 3×3

1 1 1 1 0 1 1 1 1

% Do the complete convolution.
AF = conv2(A, F, 'same')

AF = 4×4

1 3 1 1 3 3 2 1 2 3 2 0 2 1 1 0

% Since we want the convolution ONLY where A == 1, 
% we can replace ONLY those places with AF
Aout = A; % Initialize
mask = A == 1

mask = 4×4 logical array
   1   0   1   0
   0   1   0   0
   1   0   0   0
   0   1   0   0

Aout(mask) = AF(mask) % Replace with AF but only where A is 1.

Aout = 4×4

1 0 1 0 0 3 0 0 2 0 0 0 0 1 0 0

[KRISTIAN MARCON]

Thank you! It's exactly what I need