Matlab: How can I find the number of black pixels in a color image?

Question

I wish to find the number of black pixels in a color image using MATLAB, how can I do it?

Thanks.

Answer 1

Use nnz like this -

nnz(all(im==0,3))

where im is your image data.

Alternatives - sum(reshape(all(im==0,3),[],1)) and sum(sum(all(im==0,3))) .

The assumption here is that black pixels are triplets (0,0,0) .

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Instead if you define black pixels as pixels that have values in the interval [0 th] for the same pixel location across all channels, use this -

nnz(all(im<=th,3))