Agreed about ``min``. However, I don't think the first pixel is necessarily the best to use, because it basically amounts to the brightest pixel in ``_indices``, but what if two values in the data have the same value and belong to the same structure? Then the order in which they are added is non-deterministic.

However, rather than have to call ``min`` at the end of the computation for all structures, we could keep track of the minimum index every time we add a pixel, much in the same way as we do for ``fmin`` and ``fmax``. I'll run some tests to see what the performance impact is.