some questions about the Rand error computation

[thouis]

I'm having trouble squaring the comments in the code and the code itself.

In this line, it says that background (zero) pixels are excluded from the computation:
https://github.com/cremi/cremi_python/blob/master/cremi/evaluation/rand.py#L13

In this line, the total number of pixels (zero and nonzero) are computed as "n":
https://github.com/cremi/cremi_python/blob/master/cremi/evaluation/rand.py#L42

And "n" is used here in the computation:
https://github.com/cremi/cremi_python/blob/master/cremi/evaluation/rand.py#L60-L61

I would expect n to be something like "np.count_nonzero(segA)"

[funkey]

You are right, n should only reflect the number of valid locations. However, none of the reference implementations of the Adapted Rand Error (see also here) is doing so.

[thouis]

I think this can just be closed. If the bug in #3 is fixed, then it doesn't matter how n is computed, as it falls out of the equation.