4 ms·

Blue Noise in Futhark

34 points by Munksgaard 5y ago

127 5y ago
Cool to see how to use Futhark for image processing and blue noise. Here's a couple more dithering algorithms: https://bisqwit.iki.fi/story/howto/dither/jy/ https://bisqwit.iki.fi/story/howto/dither/jy/
PaulAJ 5y ago
Why is dithering still a thing? Is it just academic interest, or does it still have a practical application?
- hatsunearu 5y ago
  it's a way of trading off (effectively) frequency response to gain signal to noise ratio at a lower bandwidth. It is widely used everywhere, from audio ADC/DACs (sigma-delta modulators), and images naturally have dithering due to noise which makes them look pretty nice despite the limited bit depth of 8 bits.
  - MayeulC 5y ago
    That. Dithering is useful if you can trade samples for accuracy. It is useful if your quantization scale is too coarse. As a result, one can inject noise to sense signal that is normally below a sensor threshold, for instance. In graphics, it is still very useful to add some dithering in some cases; one obvious example being to reduce banding on gradients: https://en.wikipedia.org/wiki/Colour_banding https://en.wikipedia.org/wiki/Colour_banding Regardless of the chosen quantization scale, there are corner cases where values measured will fall close one to another; dithering is useful in these cases, and is not limited to images, but any data: https://en.wikipedia.org/wiki/Audio_bit_depth#Dither https://en.wikipedia.org/wiki/Audio_bit_depth#Dither
- thih9 5y ago
  As long as there are people who think it's pretty there will be products that use it. Return of the Obra Dinn got a lot of praise for its visuals.
- WJW 5y ago
  Dithering is super useful in all sorts of applications where you need to record an analog signal into a digital format. If you don't dither you can get weird sampling distortions.
  - cpach 5y ago
    But aren’t those algorithms distinct from graphical dithering techniques?
- deleted 5y ago
  [deleted]
- kryptiskt 5y ago
  If you have a undithered shallow gradient from black, it will look terrible as you can clearly see bands where the pixels go from #000000 to #010101 (or whatever color the gradient goes towards) and further steps. We had one of those gradients in an app where an image faded out to black, it looked great. And then on the next phone model, the black background was really black instead of a dither pattern and it looked absolutely terrible.
- KaiserPro 5y ago
  Mainly for epaper, as it has a reduced bitdepth. However it can be used in other contexts, like in video.
  - MayeulC 5y ago
    It's hard to accurately drive e-paper, so some prefer to consider them black-and-white screens. However, taken at a macroscopic level, it has quite an important bit-depth, as while each individual particle might have only ~two possible states, you are controlling a distribution of more than a hundred of these per pixel. In a sense, the variability (particle size, etc) will already introduce some noise, which, for instance, makes it so that you need less antialiasing. Another use of that variability is that those screens can effectively be driven as if they had a very deep dynamic range. Your statement would be true if all particles were strictly the same, reacted at the same voltage, had exactly two equilibrium points, and didn't interact with each other. Luckily, reality isn't so dull, and you don't really need dither if you put a bit more effort into controlling the voltage being applied: https://news.ycombinator.com/item?id=16140284 https://news.ycombinator.com/item?id=16140284
- rozab 5y ago
  Low Tech Magazine's solar powered site uses dithering to help achieve very low power consumption. I think the results look awesome, just as good as the artfully filtered images used by a lot of sites but with a fraction of the weight. https://solar.lowtechmagazine.com/2018/09/how-to-build-a-lowtech-website.html https://solar.lowtechmagazine.com/2018/09/how-to-build-a-low...
- cma 5y ago
  Many monitors still use it underneath, spatial or temporal dithering, to expand bit depth.
deleted 5y ago
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deleted 5y ago
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hrnnnnnn 5y ago
Off-topic, but I've noticed that certain dithering patterns cause my monitor to fluctuate in brightness. Does anyone know what this could be?
- maeln 5y ago
  A lot of monitor these days have local/micro dimming in order to provide decent contrast and brightness. It's especially true with HDR displays. So there is a high chance that the dithering pattern trigger one or more dimming zone of your monitor.
cpach 5y ago
In case anyone else wonders what Futhark means in this context – it’s a programming language: https://futhark-lang.org/ https://futhark-lang.org/ As someone who grew up in Sweden, Futhark to me is a runic alphabet :) https://en.wikipedia.org/wiki/Elder_Futhark https://en.wikipedia.org/wiki/Elder_Futhark

34 points by Munksgaard 5y ago

127 5y ago

Cool to see how to use Futhark for image processing and blue noise. Here's a couple more dithering algorithms: https://bisqwit.iki.fi/story/howto/dither/jy/ https://bisqwit.iki.fi/story/howto/dither/jy/

PaulAJ 5y ago

Why is dithering still a thing? Is it just academic interest, or does it still have a practical application?

hatsunearu 5y ago
it's a way of trading off (effectively) frequency response to gain signal to noise ratio at a lower bandwidth. It is widely used everywhere, from audio ADC/DACs (sigma-delta modulators), and images naturally have dithering due to noise which makes them look pretty nice despite the limited bit depth of 8 bits.
- MayeulC 5y ago
  That. Dithering is useful if you can trade samples for accuracy. It is useful if your quantization scale is too coarse. As a result, one can inject noise to sense signal that is normally below a sensor threshold, for instance. In graphics, it is still very useful to add some dithering in some cases; one obvious example being to reduce banding on gradients: https://en.wikipedia.org/wiki/Colour_banding https://en.wikipedia.org/wiki/Colour_banding Regardless of the chosen quantization scale, there are corner cases where values measured will fall close one to another; dithering is useful in these cases, and is not limited to images, but any data: https://en.wikipedia.org/wiki/Audio_bit_depth#Dither https://en.wikipedia.org/wiki/Audio_bit_depth#Dither
thih9 5y ago
As long as there are people who think it's pretty there will be products that use it. Return of the Obra Dinn got a lot of praise for its visuals.
WJW 5y ago
Dithering is super useful in all sorts of applications where you need to record an analog signal into a digital format. If you don't dither you can get weird sampling distortions.
- cpach 5y ago
  But aren’t those algorithms distinct from graphical dithering techniques?
deleted 5y ago
[deleted]
kryptiskt 5y ago
If you have a undithered shallow gradient from black, it will look terrible as you can clearly see bands where the pixels go from #000000 to #010101 (or whatever color the gradient goes towards) and further steps. We had one of those gradients in an app where an image faded out to black, it looked great. And then on the next phone model, the black background was really black instead of a dither pattern and it looked absolutely terrible.
KaiserPro 5y ago
Mainly for epaper, as it has a reduced bitdepth. However it can be used in other contexts, like in video.
- MayeulC 5y ago
  It's hard to accurately drive e-paper, so some prefer to consider them black-and-white screens. However, taken at a macroscopic level, it has quite an important bit-depth, as while each individual particle might have only ~two possible states, you are controlling a distribution of more than a hundred of these per pixel. In a sense, the variability (particle size, etc) will already introduce some noise, which, for instance, makes it so that you need less antialiasing. Another use of that variability is that those screens can effectively be driven as if they had a very deep dynamic range. Your statement would be true if all particles were strictly the same, reacted at the same voltage, had exactly two equilibrium points, and didn't interact with each other. Luckily, reality isn't so dull, and you don't really need dither if you put a bit more effort into controlling the voltage being applied: https://news.ycombinator.com/item?id=16140284 https://news.ycombinator.com/item?id=16140284
rozab 5y ago
Low Tech Magazine's solar powered site uses dithering to help achieve very low power consumption. I think the results look awesome, just as good as the artfully filtered images used by a lot of sites but with a fraction of the weight. https://solar.lowtechmagazine.com/2018/09/how-to-build-a-lowtech-website.html https://solar.lowtechmagazine.com/2018/09/how-to-build-a-low...
cma 5y ago
Many monitors still use it underneath, spatial or temporal dithering, to expand bit depth.

deleted 5y ago

[deleted]

deleted 5y ago

[deleted]

hrnnnnnn 5y ago

Off-topic, but I've noticed that certain dithering patterns cause my monitor to fluctuate in brightness. Does anyone know what this could be?

maeln 5y ago
A lot of monitor these days have local/micro dimming in order to provide decent contrast and brightness. It's especially true with HDR displays. So there is a high chance that the dithering pattern trigger one or more dimming zone of your monitor.

cpach 5y ago

In case anyone else wonders what Futhark means in this context – it’s a programming language: https://futhark-lang.org/ https://futhark-lang.org/ As someone who grew up in Sweden, Futhark to me is a runic alphabet :) https://en.wikipedia.org/wiki/Elder_Futhark https://en.wikipedia.org/wiki/Elder_Futhark