How can I count all pixel values that are not black(0)?

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Serena Tenhumberg
Serena Tenhumberg 2018-7-27
编辑： Ben Frankel 2018-7-27
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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回答（2 个）

Ben Frankel
Ben Frankel 2018-7-27
编辑：Ben Frankel 2018-7-27
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.
Stephen23
Stephen23 2018-7-27
编辑：Stephen23 2018-7-27
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
Ben Frankel 2018-7-27
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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