Summing specific pixel values
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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 3x3 centred on xi,yi), how do I do that?
thanks
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Image Analyst
2014-10-22
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
2 个评论
Jason
2014-10-22
Bjorn Gustavsson
2014-10-22
I suggest you do something like this instead:
ind1D = sub2ind(size(im),xi,yi);
sumPixxiyi = sum(im(ind1D));
Then for the nearest Neighbour you'd have to make arrays for them too. In my opinion such a solution is so much easier to maintain since it will be so many fewer lines of code that potential speed losses might be preferable.
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