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

I have a binary image with cropped regions that are black, and I need a count of all the pixels that are not cropped?

Answer 1

[Ben Frankel]

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]

You probably want this:

sum(M(:))

Answer 2

[Stephen23]

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.

[Ben Frankel]

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.