MATLAB: Create 3*3 matrix around a given pixel

create matrix

I have a centroid plotted on a blank image using the command img(a(2),a(1))=1;
I would like to create a 3*3 matrix of ones around this pixel as centroid.
Can someone tell me how i can achieve this.
Thankyou

Best Answer

One solution:
img = zeros(6,7)
a = [4 3]
img(a(2),a(1)) = 1
B = [1 1 1 ; 1 0 1 ; 1 1 1];
img2 = conv2(img, B ,'same')
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