https://docs.opencv.org/4.x/d2/de8/group__core__array.html#gaa4b89393263bb4d604e0fe5986723914 Counts non-zero array elements.
single-channel array.
https://docs.opencv.org/4.x/d2/de8/group__core__array.html#gaa4b89393263bb4d604e0fe5986723914 Counts non-zero array elements.