I’ve spent a lot of time recently converting nitrofurano‘s sdlBasic retro computing picture converter programs into Python-Fu image filters for The GIMP. I’ve also been adding a few ideas of my own – particularly in the area of half-toning techniques.
After successfully getting Error Diffusion working, I decided to see if I could get Ordered Dithering working. Ordered Dithering is a technique akin to the half-toning you see on images in newspapers. From an image made up of many colours you can create an image made up of only a handful of colours stippled such a way as to give the illusion of many colours.
Ordered Dithering is much simpler than Error Diffusion (which is probably why it took me longer to get it working!). As it’s a much simpler process it’s lightning fast in comparison, even when coded in Python.
As a test, I took John Liven’s picture of a Somerset cottage.
As you can see above, it produces a very pleasing regular patterning on the colours – to allow you to compare, here is the same image with Floyd-Steinberg Error Diffusion:
On a small image such as this, larger grids don’t really add much. Here is an ordered dither using a 4 x 4 threshold matrix:
But, the proof of the pudding is in the eating. If you have The GIMP installed on your computer you might like to try the ordered dither filter for yourself – it’s available from here.