Comment by vanderZwan
5 years ago
If you don't mind, I'll plug a little innovation of my own: mixing ordered and error diffusion dithering. The idea behind it is actually pretty simple: technically all forms of dithering use a threshold map, we just don't tend to think of it when it's one flat threshold for the entire image. So there is nothing stopping us from decoupling the threshold map from the rest of the dithering algorithm, meaning it's trivial to combine error diffusion with more complex threshold maps:
https://observablehq.com/@jobleonard/ordered-error-diffusion...
(For the record, I picked a default example that highlighted a "hybrid" dither with a very dramatic difference from its "parents" instead of the prettiest result)
Interestingly, and perhaps not surprisingly, a variable threshold map interacts with the error diffusion itself, making it amplify local contrast and recover some fine detail in shadows and highlights (although also possibly overdoing it and crushing the image again).
What's also somewhat interesting (to me at least) that this is really simple to implement: take any error diffusion dithering kernel and make it use the threshold map from ordered dithering. In principle it should have been possible to use them on any old hardware that can handle error diffusion dithering.
I'll also plug an invention of my own: error diffusion with a random parameter in the diffusion matrix, keeping the sum of weights constant (and equal to 4/5, so boosting contrast slightly).
I came up with this for a Code Golf challenge a few years ago, personally I think it looks really good. I haven't seen it elsewhere.
Disclaimer: yes I like to write ugly Fortran code for fun (and profit).
https://codegolf.stackexchange.com/a/26569
That is a very elegant trick, I love it! I wonder what comes out of that when applied to a flat grayscale image - perhaps it leads to a decent blue noise pattern, or an approximation of it? EDIT: The reason I'm half-expecting that is because semi-randomizing the diffusion matrix reminds me a bit of Bridson's Algorithm, in that it mixes constraints with randomization[0].
And kudos for sticking to the programming language you love and feel comfortable in :)
EDIT: Something I never noticed before: a black and white dithered image causes flickering when scrolling on an LCD screen, as least on mine, and it amplifies regions with patterns, like the checkerboards in ordered dithering, or the regular artifacts like in the example image of the challenge.
However, your "randomized Sierra Lite" version seems to mask that flickering: it's still there, but feels much more like white noise that is relatively easy to ignore.
[0] https://observablehq.com/@techsparx/an-improvement-on-bridso...