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Why do we need dithering?

57 points by ibobev

by susam

1 subcomments

This is going to be an odd comment, but I immediately recognised the parrot in the test images. It's the scarlet macaw from 2004 which is often used in many Wikipedia articles about colour graphics.
I think this is the original, photographed and contributed by Adrian Pingstone: https://commons.wikimedia.org/wiki/File:Parrot.red.macaw.1.a...
But this particular derivative is the one that appears most often in the Wikipedia articles: https://commons.wikimedia.org/wiki/File:RGB_24bits_palette_s...
This parrot has occurred in several articles on the web. For example, here's one article from a decade or so ago: https://retroshowcase.gr/index.php?p=palette
Parrots are often used in articles and research papers about computer graphics and I think I know almost all the parrots that have ever appeared in computing literature. This particular one must be the oldest computing literature parrot I know!
By the way, I've always been fascinated by dithering ever since I first noticed it in newspapers as a child. Here was a clever human invention that could produce rich images with so little, something I could see every day and instinctively understand how it creates the optical illusion of smooth gradients, long before I knew what it was called.

by OCTAGRAM

0 subcomment

I have noticed author uses values 0-255 for shades of grey. When 0-255 range is used, this is usually nonlinear scale with average gamma 2.2. And de facto there is a standard function that maps 0-31 to linear function and the rest to power 2.4. Average power 2.2. Checkmate black 0 and white 255 is equavalent to uniform grey shade 185 or 186 as opposed to 127 or 128. Proper calculations should be done in linear space, and 16 bits per channel is desired at least.

by raajg

0 subcomment

This was recently shared on HN: https://visualrambling.space/dithering-part-1/
For anyone interested in seeing how dithering can be pushed to the limits, play 'Return of the Obra Dinn'. Dithering will always remind you of this game after that.
- https://visualrambling.space/dithering-part-1
- https://store.steampowered.com/app/653530/Return_of_the_Obra...

by mrandish

0 subcomment

A related bit of tech trivia is that digital audio also often involves dithering, and not just decimated or compressed audio. Even very high-quality studio mastered audio benefits from an audio specific kind of dithering called noise shaping. Depending on the content, studio mixing engineers may choose different noise shaping algorithms.
https://en.wikipedia.org/wiki/Noise_shaping

by andai

1 subcomments

Also by the author: https://www.makingsoftware.com/
Recent discussions:
Making Software - https://news.ycombinator.com/item?id=43678144
How does a screen work? - https://news.ycombinator.com/item?id=44550572
What is a color space? - https://news.ycombinator.com/item?id=45013154

by kettlecorn

0 subcomment

Dithering is super useful in dark scenes in games and movies.
By adding random noise to the screen it makes bands of color with harsh transitions imperceptible, and the dithering itself also isn't perceptible.
I'm sure there are better approaches nowadays but in some of my game projects I've used the screen space dither approach used in Portal 2 that was detailed in this talk: https://media.steampowered.com/apps/valve/2015/Alex_Vlachos_...
It's only a 3 line function but the jump in visual quality in dark scenes was dramatic. It always makes me sad when I see streamed content or games with bad banding, because the fix is so simple and cheap!
One thing that's important to note is that it's a bit tricky to make dithering on / off comparisons because resizing a screenshot of a scene with dithering makes the dithering no longer work unless one pixel in the image ends up exactly corresponding to one pixel on your screen

by Gigachad

0 subcomment

Even though it looks less accurate, I prefer the look of the Ordered Bayer image. It looks artistically low-fi while the others look more like a highly compressed image to me. Considering we are able to just represent images with full colour today, the only reason I'd dither is for the aesthetic.

by hcs

0 subcomment

You still see dithering from time to time as a cheap transparency, it's been a few years since Mario Odyssey but that's when last I recall it really stood out: https://xcancel.com/chriswade__/status/924071608976924673

by cmovq

0 subcomment

Dithering is still very common in rendering pipelines. 8 bits per channel is not enough to capture subtle gradients, and you’ll get tons of banding. Particularly in mostly monochrome gradients produced by light sources. So you render everything to a floating point buffer and apply dithering.
Unlike the examples in this post, this dithering is basically invisible at high resolutions, but it’s still very much in use.

by olivia-banks

0 subcomment

The figures in this article are really great. How where they made? If I was to try and recreate them I might render things individually and then lay it out in Illustrator to get that 3D isomorphic look, but I assume there's a better way.

by WheatMillington

0 subcomment

What an insanely beautiful website. Reminds me of the golden days of the internet, remastered tastefully.

by tinkelenberg

0 subcomment

This is the best explanation I’ve come across. I enjoy dithering as a playful way to compress file size when it makes sense.

by dcrazy

0 subcomment

Slightly frustrating the author started out with color images and then switched to grayscale.

by Dylan16807

1 subcomments

> Before we all mute the word 'dithering'
Is this a reply to something?

by efilife

0 subcomment

What's with the dithering trend? Why do I keep hearing about it everywhere at least once a week? Where did this originate from?

by firebot

0 subcomment

We really don't anymore.
Back in the late 90s maybe. Gifs and other paletted image formats were popular.
I even experimented with them. I designed various formats for The Palace. The most popular was 20-bit (6,6,6,2:RGBA, also 5,5,5,5; but the lack of color was intense, 15 bits versus 18 is quite a difference). This allowed fairly high color with anti-aliasing -edges that were semi transparent.

by abstractspoon

3 subcomments

They answered the question in the first two sentences: We don't need it, it's just an aesthetic nowadays.

by kragen

0 subcomment

We've had a couple of other recent discussions on dithering: https://news.ycombinator.com/item?id=45750954 and https://news.ycombinator.com/item?id=45698323. I commented specifically about the history of blue-noise dithering at https://news.ycombinator.com/item?id=45728231.
The article points out that, historically, RAM limitations were a major incentive for dithering on computer hardware. (It's the reason Heckbert discussed in his dissertation, too.) Palettizing your framebuffer is clearly one solution to this problem, but I wonder if chroma subsampling hardware might have been a better idea?
The ZX Spectrum did something vaguely like this: the screen was 256×192 pixels, and you could set the pixels independently to foreground and background colors, but the colors were provided by "attribute bytes" which each provided the color pairs for an 8×8 region http://www.breakintoprogram.co.uk/hardware/computers/zx-spec.... This gave you a pretty decent simulation of a 16-color gaming experience while using only 1.125 bits per pixel instead of the 4 you would need on an EGA. So you got a near-EGA-color experience on half the RAM budget of a CGA, and you could move things around the screen much faster than on even the CGA. (The EGA, however, had a customizable palette, so the ZX Spectrum game colors tend to be a lot more garish. The EGA also had 4.6× as many pixels.)
Occasionally in ZX Spectrum game videos like https://www.youtube.com/watch?v=Nx_RJLpWu98 you will see color-bleeding artifacts where two sprites overlap or a sprite crosses a boundary between two background colors. For applications like CAD the problem would have been significantly worse, and for reproducing photos it would have been awful.
The Nintendo did something similar, but I think had four colors per tile instead of two.
So, suppose it was 01987 and your hardware budget permitted 8 bits per pixel. The common approach at the time was to set a palette and dither to it. But suppose that, instead, you statically allocated five of those bits to brightness (a Y channel providing 32 levels of grayscale before dithering) and the other three to a 4:2:0 subsampled chroma (https://www.rtings.com/tv/learn/chroma-subsampling has nice illustrations). Each 2×2 4-pixel block on the display would have one sample of chroma, which could be a 12-bit sample: 6 bits of U and 6 bits of V. Moreover, you can interpolate the U and V values from one 2×2 block to the next. As long as you're careful to avoid drawing text on backgrounds that differ only in chroma (as in the examples in that web page) you'd get full resolution for antialiased text and near-photo-quality images.
That wouldn't liberate you completely from the need for dithering, but I think you could have produced much higher quality images that way than we in fact did with MCGA and VGA GIFs.

by 01HNNWZ0MV43FF

0 subcomment

Playdead Games did a really nice presentation about dithering for games, it gets passed around and I'm sure it's been on HN already: https://loopit.dk/banding_in_games.pdf