# Counting number of same neighbourhood pixels between two matrices.

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Stewart Tan on 10 Sep 2019
Commented: Shunichi Kusano on 10 Sep 2019
So i have two made up matrices, which represents an image block.
p1 = [4 7 1 2;
4 5 3 1;
8 9 1 10;
8 19 2 1];
p2 = [4 7 1 2;
4 5 3 2;
5 1 0 11;
8 19 2 0]
and what i want to do is to count how many neighbourhood pixels are similar between both matrices above. To do so, i first locate the centre pixel in each matrices:
centre_pix = floor(([4 4]+1)/2)
p1_centre = p1(2,2) %2,2 is the output of centre pix
p2_centre = p2(2,2)
Hence the number 5 in row 2, column 2 in each matrix is the centre pixel.
What I'm trying to do now is to count the number of neighbourhood pixel of the centre pixel that are similar between the two matrices.
Which would be 4,7,1,4,3 therefore the count is 5.

Shunichi Kusano on 10 Sep 2019
Edited: Shunichi Kusano on 10 Sep 2019
Hi Tan,
If "similar" means "exactly the same" or "the difference is zero", it is not difficult to implement. What the following codes do is to take the difference between the two matrices, then to count the number of neighbourhood pixels whose value is zero.
dif_p = double(p1) - double(p2);
indSame = dif_p == 0; %
fun = @(x) nnz(x) - uint8(x(2,2));
result = nlfilter(indSame, [3 3], fun)
hope this helps.

Bruno Luong on 10 Sep 2019
Edited: Bruno Luong on 10 Sep 2019
This command counts the number of 3x3 neigbouring pixels that exactly match
conv2(p1==p2,ones(3),'same')

#### 1 Comment

Shunichi Kusano on 10 Sep 2019
very simple! I like this better!