@ahojnnes : Do you suggest to make a new file `_sum_blocks`? I feel that would not be of much use for this one particular function. Also I can't think of a reasonable place in `skimage.measure` for this function.

Also, the meaning of the parameter `scale` in `skimage.transform._warps.rescale()` is inverse to that of `factors` in current implementation and `scale` can also take float values, which might complicate things. Your thoughts?