MATLAB: Summing specific pixel values

pixel values sum

Hi. I am wanting to find the sum of all the positons xi, yi of an image IM. I thought the following would do it – but it doesn't.

sum(im (xi,yi));

Also, If I want to take this a step further and find the sum of all pixels at locations xi, yi but this time include the surrounding 8 pixels (so its a 3×3 centred on xi,yi), how do I do that?

thanks

Best Answer

You can use a for loop:

m=magic(5) % Whatever...
xi=[2,3,4]
yi = [2,3,4]
theSum = 0;
the8Sum = 0;
for k = 1 : length(xi)
  row = yi(k);
  col = xi(k);
  theSum = theSum + m(row, col);
  the8Sum =the8Sum + ...
    m(row-1, col-1) + ...
    m(row-1, col) + ...
    m(row-1, col+1) + ...
    m(row, col-1) + ...
    m(row, col) + ...
    m(row, col+1) + ...
    m(row+1, col-1) + ...
    m(row+1, col) + ...
    m(row+1, col+1);
end
theSum
the8Sum

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Best Answer

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