How can I count all pixel values that are not black(0)?
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I have a binary image with cropped regions that are black, and I need a count of all the pixels that are not cropped?
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Answers (2)
Ben Frankel
on 27 Jul 2018
Edited: Ben Frankel
on 27 Jul 2018
If the image is stored as a binary matrix M, you can use this:
count = sum(M(:) ~= 0);
For very large images, this runs much faster than sum(M(:)) and nnz(M), and it works for grayscale images as well.
EDIT: Thanks to Stephen for pointing out my mistake.
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Stephen23
on 27 Jul 2018
Edited: Stephen23
on 27 Jul 2018
Where I is your image:
nnz(I)
Note that this is robust to using different values for encoding the non-zero value in the binary image, e.g. sometimes binary images are encoded using 0 and 255 with uint8.
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Ben Frankel
on 27 Jul 2018
If the image is large enough or the count is calculated often enough, sum will be faster because it doesn't require a comparison to 0.
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