Is there a way to count the number of different cells

Say I have two jitter matrices (or two planes within the same matrix), and I want to identify which cells are different between the two.

Does it make sense to do an absdiff operation between the two, and then look for the non-zero cells?

Is there a good way to get a total count of the number of different cells?

Basically I'm updating an external device that is rather slow. There is a bulk update mode that is faster than writing each cell individually, but slower than the time it takes to write 2/3 of the cells individually.

So I want to count the number of cells that have changed: if they are over a certain threshould, then I do a bulk update. If the changes are below a certain threshold, then I individually write the changed cells.