Gimp, python, and numpy

[Ofnuts]

This just a good way to write scripts that must compute things on pixels. When you write scripts, either you rely on Gimp operations (your unit of work is the layer, or a selection on a layer) or you work pixel-by-pixel. But since the image can contain several million pixels, this can be slow if you write code loops in Python. With something like numpy you can do math operations on a whole layer at a time or even on several layers. The median filter is a typical example of something that cannot be done with layer blend modes so doing it in a script without numpy it would be very slow.

Of course one can also use GMIC...