Image Dithering: Eleven Algorithms and Source Code

Re:Image Dithering: Eleven Algorithms and Source Code by jacobolus on Friday October 06, 2017 @05:11AM (#15415425)

Unless you are integrating many pixels (how many and with what weights depends on the future processing, intended output, and viewing conditions for the image) I would not expect using a fancy color difference formula for comparing individual pixels to give a particularly useful result. Indeed, the whole point of dithering (especially with high resolution output) is that we can adjust the average light coming from a several-pixel-wide blob by brightening or darkening individual pixels, and thereby make finer distinctions in light level, since the individual pixels are not really noticed. I’m also pretty skeptical about the space-filling curve thing. Those both sound like placebo features to me.

[ Parent | on HN ]

Re:Image Dithering: Eleven Algorithms and Source Code by microcolonel on Friday October 06, 2017 @05:19AM (#15415440)

Well, I did say experimenting, didn't I?

I found the thing which inspired my space filling curve exploration: https://www.compuphase.com/riemer.htm

The Butteraugli score between the standard lena and the Riemersma dither is about 0.5 better than the standard Floyd-Steinberg one.

Approaches like this come closer to back-propagation of errors, the lack of which is where some of the artifacts of unidirectional dither come from. In practice, any decent (full bleed) error diffusion dither works perfectly fine going between 16 and 8 bit planes, but why shouldn't I try some things out which (as you are quick to point out) may have very little value.

Heck, even gamma correction isn't strictly necessary when you're going from 16 to 8 bit sRGB.

[ Parent | on HN ]

Re:Image Dithering: Eleven Algorithms and Source Code by jacobolus on Friday October 06, 2017 @03:50PM (#15419847)

I don’t know enough about Butteraugli (in particular in the range of very very tiny differences in the image) to know whether it’s a reasonable metric for comparing dithering algorithms.

Why do you think this Riemersma method does better at that metric? Maybe it just keeps the diffused errors spatially closer to the original pixel?

[ Parent | on HN ]

Re:Image Dithering: Eleven Algorithms and Source Code by mark-r on Friday October 06, 2017 @09:23AM (#15416568)

Yes, once you start working on a very small segment of the curve it's close enough to linear and gamma correction becomes overkill.

[ Parent | on HN ]

Re:Image Dithering: Eleven Algorithms and Source Code by jacobolus on Friday October 06, 2017 @03:52PM (#15419856)

I could see it making a difference in average color of very noisy regions, especially brightly colored ones. I suspect you could deliberately construct an image where the difference could be seen by human observers.

[ Parent | on HN ]