[PMunch]

Just did a bit of a deep dive into dithering myself, for my project of creating an epaper laptop. https://peterme.net/building-an-epaper-laptop-dithering.html it compares both error diffusion algorithms as well as Bayer, blue noise, and some more novel approaches. Just in case anyone wants to read a lot more about dithering!

[quag]

After implementing a number of dithering approaches, including blue noise and the three line approach used in modern games, I’ve found that quasi random sequences give the best results. Have you tried them out?

https://extremelearning.com.au/unreasonable-effectiveness-of...

[leguminous]

What is the advantage over blue noise? I've had very good results with a 64x64 blue noise texture and it's pretty fast on a modern GPU. Are quasirandom sequences faster or better quality?

(There's no TAA in my use case, so there's no advantage for interleaved gradient noise there.)

EDIT: Actually, I remember trying R2 sequences for dither. I didn't think it looked much better than interleaved gradient noise, but my bigger problem was figuring out how to add a temporal component. I tried generalizing it to 3 dimensions, but the result wasn't great. I also tried shifting it around, but I thought animated interleaved gradient noise still looked better. This was my shadertoy: https://www.shadertoy.com/view/33cXzM

[PMunch]

Ooh, I haven't actually! I'll need to implement and test this for sure. Looking at the results though it does remind me of a dither (https://pippin.gimp.org/a_dither/), which I guess makes sense since they are created in a broadly similar way.

[PMunch]

Just had a look at this and here is the result for the test image: https://uploads.peterme.net/test-image_qr.png.

Looks pretty good! It looks a bit like a dither, but with fewer artifacts. Definitely a "sharper" look than blue noise, but in places like the transitions between the text boxes you can definitely see a bit more artifacts (almost looks like the boxes have a staggered edge).

Thanks for bringing this to my attention!

[storystarling]

Nice writeup. I've been looking at this for a print-on-demand project and found that physical ink bleed changes the constraints quite a bit compared to e-paper. In my experience error diffusion often gets muddy due to dot gain, whereas ordered dithering seems to handle the physical expansion of the ink better.

[robinsonb5]

> In my experience error diffusion often gets muddy due to dot gain

Absolutely - there's a reason why traditional litho printing uses a clustered dot screen (dots at a constant pitch with varying size).

I've spent some time tinkering with FPGAs and been interested by the parallels between two-dimensional halftoning of graphics and the various approaches to doing audio output with a 1-bit IO pin: pulse width modulation (largely analogous to the traditional printer's dot screen) seems to cope better with imperfections in filters and asymmetries in output drivers than pulse density modulation (analogous to error diffusion dithers).

[zozbot234]

Traditional litho actually uses either lines in curved crosshatch patterns or irregular stippling. Might be doable using an altered error-diffusion approach that rewards tracing a clearly defined line as opposed to placing individual dots or blots.

[PMunch]

Thanks! I would imagine printing on paper would be a completely different ball game. I actually considered scanning the actual epaper display to show each of the dithering techniques in their intended environment as it does change the look quite a bit. From the little I know about typography and things like ink-wells I can definitely see how certain algorithms can change quite significantly. The original post here has a pattern which looks similar to old newspapers, maybe that's worth looking into?

[shultays]

I had a project with those 7 colour e-paper displays and used dithering and it looked amazing. Crazy how much you could fake with just 7 colours and dithering

[PMunch]

Definitely, I've been trying out a lot of dithering algorithms, and while they have big differences with only black and white as soon as you start adding more shades of grey they all look pretty much exactly the same as the input image. I'd imagine good dithering with colours would look amazing