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Ditherpunk: The article I wish I had about monochrome image dithering

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Re: Ditherpunk: The article I wish I had about monochrome image dithering

#181

Post by jVinc »

croissants wrote: post #158
jVinc wrote: post #64

I am in the same boat as the author of having only recently played Return of the Obra Dinn between Christmas and new years. I cannot recommend it enough, if you haven't played it and like puzzlers you should pick it up. It's an extremely engaging story, and a narrative tool I have not previously encountered. No spoilers as this is revealed immediately, but essentially you are navigating past events through frozen tim…

May as well ask here, the ESRB rating at the bottom of the Obra Dinn page [1] highlights "intense violence". Is this accurate? I'm a big wimp about visceral violence, so I'd prefer to have some idea before paying up. If 1/4 of the crew got disemboweled or something, I'm probably out. [1] https://obradinn.com/

There definitely is violent scenes and sounds in the game. I would not recommend playing it with young children for instance. However I would myself not put in the same box as other games in the "intense violence" category.

Mostly because and this may sound silly, but it's not "violence in motion". You are viewing a murder scene, and someone died, and you might hear someone take the last breaths of their life. Which has a very high emotional impact which should not be ignored. But that to me is still fundamentally different from gory/bloody games with often fast visceral violence. As mentioned by others, the scenes themselves are calmed a lot by the dithering art-style.

I would say about the emotional content though that this hits differently from other stories where characters die because of the narrative tool. You never have a Game of Thrones moment where a character you are heavily invested in suddenly dies, because even though you learn about the passengers and feel for them in their misery, you also realize up front even before you learn about them that they have died and you are just looking at memories before that event.

Re: Ditherpunk: The article I wish I had about monochrome image dithering

#182

Post by steerablesafe »

BlueTemplar wrote: post #173
steerablesafe wrote: post #157

Earlier quoted context omitted.

sRGB gamma is often approximated to 2.2 [1], but the actual function has a linear section near 0, and a non-linear section with gamma of 2.4, possibly to avoid numerical difficulties near 0. The document you cite claims that CRT gamma is typically between 2.35 and 2.55. Human eye gamma can probably be approximated with cieLAB, that is designed to be a perceptually uniform colorspace, which seemingly has a gamma of 3…

> ciaLAB is not state of the art though in perceptually uniform colorspaces. Which are state of the art ? > 1. It brings in perceptually uniform colorspaces to the discussion, while it's completely unnecessary. Perceptually uniform colorspaces are mostly unsuitable for arithmetic on colors like any other non-linear colorspace. I don't get what you mean, linearity (dL'star') being defined wrt perceptual uniformity, is…

> I don't get what you mean, linearity (dL'star') being defined wrt perceptual uniformity, isn't CIELAB 76 linear by definition (to an approximation) ?? And color arithmetic pretty much by definition implies dealing with distances and angles in a perceptually uniform color space, doesn't it ??

No. Linearity is about physical light intensities relating to perceived color. Imagine having two light sources on the same spot that you can turn on or off separately. If you turn the first one on you perceive a certain color, if you turn the other on you perceive an other color and if you turn both on you perceive a third one. It turns out the perceivable colors (under normal viewing conditions) are representable in a three dimensional vector-space (for most people) so that the first two colors add up to the third color for every possible two light sources. Such a linear colorspace is XYZ for example [1].

This has nothing to do with perceptual uniformity. Perceptual uniformity is about the capability of distinguishing near colors. This defines a distance between colors, and there are three dimensional colorspace representations where the Euclidean distance approximate this perceptual distance well. cieLAB is such a colorspace, but AFAIK there are better state of the art colorspaces for the same purpose. I'm not very well versed in this, I learned from them from this video [2].

[1] https://en.wikipedia.org/wiki/CIE_1931_color_space

[2] https://www.youtube.com/watch?v=xAoljeRJ3lU

edit: gimp 2.10 now defaults to use a linear colorspace (not perceptually uniform!) for most if not all of its functionalities. This affects alpha-blending layers, the paintbrush, resizing, blur, and pretty much everything that involves adding/averaging colors. There is still a "legacy" option on these tools to turn back to the probably wrong sRGB methods, probably for compatibility with old gimp files. There is a dramatic difference when you use a soft green brush on a red background for example, it's worth to try out.

Re: Ditherpunk: The article I wish I had about monochrome image dithering

#183

Post by crazygringo »

enriquto wrote: post #138
crazygringo wrote: post #71

Earlier quoted context omitted.

That's fascinating -- do you have any links to examples? I'm searching online but can't find anything at all. I've never heard of using Retinex in the context of dithering, and wondering what specifically you mean by Retinex-"like"? I'm also really curious what contexts this has been most successful in. E.g. was it used for dithering in images or games back in the 1990's when we were limited to 16-bit or 256-bit colo…

> I'm also really curious what contexts this has been most successful in. E.g. was it used for dithering in images or games back in the 1990's when we were limited to 16-bit or 256-bit color? Or is this something more recently explored in academia or in some niche imaging applications? No need to speak in the past tense! It is not a "niche" application, either. Think about it: gray ink is almost never used. All print…

Huh, to be honest I feel like I've only ever seen halftoning when printing onto paper -- I've never associated dithering with printing at all.

And the "linear dithering" you're describing, when I think of images in certain banknotes and passports or quality seals that I'd call "engraved", I've always assumed were hand-drawn by an artist.

But I like what you're describing and linking to, as a way to achieve that hand-drawn effect algorithmically, to include a directional texture element! Thanks for sharing.

Re: Ditherpunk: The article I wish I had about monochrome image dithering

#184

Post by BlueTemplar »

steerablesafe wrote: post #182
BlueTemplar wrote: post #173

Earlier quoted context omitted.

> ciaLAB is not state of the art though in perceptually uniform colorspaces. Which are state of the art ? > 1. It brings in perceptually uniform colorspaces to the discussion, while it's completely unnecessary. Perceptually uniform colorspaces are mostly unsuitable for arithmetic on colors like any other non-linear colorspace. I don't get what you mean, linearity (dL'star') being defined wrt perceptual uniformity, is…

> I don't get what you mean, linearity (dL'star') being defined wrt perceptual uniformity, isn't CIELAB 76 linear by definition (to an approximation) ?? And color arithmetic pretty much by definition implies dealing with distances and angles in a perceptually uniform color space, doesn't it ?? No. Linearity is about physical light intensities relating to perceived color. Imagine having two light sources on the same s…

Ok, my bad, I should have re-read our lesson more carefully : we're actually supposed to do sRGB => XYZ > CIELAB (and later back).

And it looks like that you can either have an Euclidean vector (linear) space (linear sRGB, XYZ), or a perceptually uniform one (CIELAB), but not both !?

(I guess that I should have figured that out myself, sigh… this is why it isn't CIELAB that is used for monitor calibration, but CIELU'V' ? EDIT : Nope : "[CIELUV is] a simple-to-compute transformation of the 1931 CIE XYZ color space, but which attempted perceptual uniformity. It is extensively used for applications such as computer graphics which deal with colored lights. Although additive mixtures of different colored lights will fall on a line in CIELUV's uniform chromaticity diagram (dubbed the CIE 1976 UCS), such additive mixtures will not, contrary to popular belief, fall along a line in the CIELUV color space unless the mixtures are constant in lightness. ")

So you have to pick the best color space for the job, in the case of doing color averages that would be one of the linear ones (linear sRGB, XYZ), while if you are trying to design a perceptually uniform gradient for data visualization, you would better pick a perceptually uniform space (CIELAB, CIELUV) ?

Re: Ditherpunk: The article I wish I had about monochrome image dithering

#185

Post by BlueTemplar »

labawi wrote: post #164
BlueTemplar wrote: post #142

Earlier quoted context omitted.

Are you sure about sRGB being already good enough for averaging ? (As long as we don't want to go to a wider color space of course.) We have been recently taught how to do it 'properly', and we had to go through CIELAB 76 (which, AFAIK, is still an approximation, as human perception is actually non-euclidean).

If you want physically accurate averaging (resize, blur etc), then RGB is fine, as long as you use linear values (or do long-winded transformed math). AFAIU it is by definition 100% physically accurate. As was said, sRGB uses gamma values, where typical math creates ill effects, as in many if not most typical programs. If you want to do perceptually uniform averaging of colors, color mixing / generating / artistic ef…

My bad, I was wrong – can't have both linearity and perceptual uniformity, and I guess that in use cases like dithering, linearity is more important ?

https://news.ycombinator.com/item?id=25648490

Re: Ditherpunk: The article I wish I had about monochrome image dithering

#186

Post by linuxlizard »

willis936 wrote: post #94
linuxlizard wrote: post #75

Back when I worked at Marvell Semiconductor (circa 2005), we made laser printer ASICs for HP. We did a lot of dithering in hardware. We had a hardware block that did error diffusion, we had a hardware block that did regular diffusion. We also had a hardware block that did Blue Noise. I was responsible for implementing the firmware that drove those printers' scan/copy path: scan an image in monochrome, run through the…

There is no math.Random() in hardware, so I have to ask: what algorithm did the noise block use? :)

We had to generate values in firmware then populate a LUT. IIRC we just used a simple pseudo-random number generator from the C library. Non-crypto so it didn't matter too much.

Re: Ditherpunk: The article I wish I had about monochrome image dithering

#187

Post by linuxlizard »

darusnna wrote: post #156
willis936 wrote: post #119

Earlier quoted context omitted.

The period needs to be sufficiently long such that it won’t show up as visible artifacts. I would think something like PRBS23 would do the trick and be trivial to implement. That’s the cheapest choice. Better whiteness could come with some added complexity.

For less visual artifacts it is recommended to use PRBS with 50% of the taps 0, 50% of the primitive polynomial tap 1. Same period (2^n-1), but less short-term correlations.

The great thing ("great") was we did the lower end laser printer niche for HP. We were able to make ASICs cheaper than HP could make them for themselves. So we had the (cough) less impressive hardware (scan sensors, laser engines, motors) to work with. So image quality was so-so at even the best of times.

We were able to bury a lot of bodies under the sensor noise and engine output. But we made a super reliable, super cheap laser printer -- VW Bug of Laser Printers, if I may brag a bit. Twelve years later, the M1005 is still selling like hotcakes I hear.

Re: Ditherpunk: The article I wish I had about monochrome image dithering

#188

Post by linuxlizard »

dassurma wrote: post #79
linuxlizard wrote: post #75

Back when I worked at Marvell Semiconductor (circa 2005), we made laser printer ASICs for HP. We did a lot of dithering in hardware. We had a hardware block that did error diffusion, we had a hardware block that did regular diffusion. We also had a hardware block that did Blue Noise. I was responsible for implementing the firmware that drove those printers' scan/copy path: scan an image in monochrome, run through the…

This is a lovely compliment. Thank you for taking the time to write it :)

Thank you for such a great blog post that even years later, I could catch up and understand!

(We never did turn on the blue noise block. Even today, it sits idle. Sad.)

Re: Ditherpunk: The article I wish I had about monochrome image dithering

#189

Post by dandep »

Great resource! I played myself with dithering, applying it to images fetched from nasa's apis, from the rovers on mars and open sourced it. I really enjoyed the visual outcome, you can see it here: https://github.com/danieledep/rovers-dithering-playground

Re: Ditherpunk: The article I wish I had about monochrome image dithering

#190

Post by raphlinus »

BlueTemplar wrote: post #184
steerablesafe wrote: post #182

Earlier quoted context omitted.

> I don't get what you mean, linearity (dL'star') being defined wrt perceptual uniformity, isn't CIELAB 76 linear by definition (to an approximation) ?? And color arithmetic pretty much by definition implies dealing with distances and angles in a perceptually uniform color space, doesn't it ?? No. Linearity is about physical light intensities relating to perceived color. Imagine having two light sources on the same s…

Ok, my bad, I should have re-read our lesson more carefully : we're actually supposed to do sRGB => XYZ > CIELAB (and later back). And it looks like that you can either have an Euclidean vector (linear) space (linear sRGB, XYZ), or a perceptually uniform one (CIELAB), but not both !? (I guess that I should have figured that out myself, sigh… this is why it isn't CIELAB that is used for monitor calibration, but CIELU'…

See the recent Oklab post[0] for guidance on choosing a perceptually uniform color space for gradients. It's better than CIELab and CIELuv, both of which I would consider inferior to newer alternatives. In particular CIELab has particularly bad hue shifts in the blue range.

I'm also working on a blog post on this topic (there's an issue open in the repo for my blog, for the curious).

[0]: https://news.ycombinator.com/item?id=25525726

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