Ancestors

Written by demofox on 2025-01-20 at 20:27

Quantizing an image to 2 bits per color channel (64 colors). Dithering with 8x8 bayer (top) and FAST spatiotemporal blue noise (bottom).

Randomly offsetting bayer each frame, it doesn't converge.

That is weird.

The bayer matrix averages to 0.5 so is unbiased in that regard.

I think it must be due to Bayer having 1/64th values, while the blue noise has 1/256th values.

hmm...

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Toot

Written by demofox on 2025-01-20 at 20:29

Bayer totally bites it at 1 bit per pixel (8 colors), with a 2x4 matrix. FAST STBN works just fine.

(I'm working on a dithering & stippling blog post)

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Descendants

Written by demofox on 2025-01-20 at 20:35

At 3 bits per color it doesn't converge either though. Still ugly banding in the sky. That's 512 values, so is 1/512. Something else must be going on.

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Written by demofox on 2025-01-20 at 21:41

oops, 3 bits per color channel is 512 colors, but not 512 values in the bayer matrix. Each channel is treated independently, so this is just a 4x2 bayer matrix = 8 values (shades).

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Written by demofox on 2025-01-20 at 21:46

Yeah mystery solved... it's the quantized values used in Bayer that are causing the banding.

Here the image is dithered and quantized to 2 bits per color channel. Top is white noise limited to 4 discrete values. Bottom is white noise with full range of floating point values.

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Written by DougMerritt (log😅 = 💧log😄) on 2025-01-20 at 20:36

@demofox

Something* needs to explicitly destroy the boundaries on Mach banding.

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Written by demofox on 2025-01-20 at 20:38

@dougmerritt I thought Mach banding was just a perceptual effect, not a real thing.

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Written by DougMerritt (log😅 = 💧log😄) on 2025-01-20 at 20:42

@demofox

I'm not sure it should be categorized that way. Like, is infrared a perceptual effect or real? Both.

The human eye+brain can spot the boundaries on e.g. the classic undithered 16 bit color gradual variation. They are really there, and it's a perceptual artifact, both.

With 24 bit undithered color, the boundaries may still be there, but the human eye+brain isn't sensitive enough to be there.

Are there any cases where they are perceived but not really there? Not that comes to mind, but we do have a human perception expert here if that matters to you. Not sure you should care.

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Written by demofox on 2025-01-20 at 20:45

@dougmerritt Check this out, mach bands are purely illusion. There's an animated gif on the page showing the effect that is pretty wild.

https://en.wikipedia.org/wiki/Mach_bands

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Written by DougMerritt (log😅 = 💧log😄) on 2025-01-20 at 20:47

@demofox

"What's in a name? A rose by any other name would smell as sweet"

You're focusing on what to name it. You need to be focused on what will remove it from human perception.

It is Mach banding.

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Written by demofox on 2025-01-20 at 20:49

@dougmerritt i don't think so. I'm uniform randomly offsetting the bayer matrix each frame and integrating. It's going to converge, or it won't. It's not converging.

The blue noise converges.

Trying to figure out where the bias is coming from.

Right side is the integrated version, left side is a single representative sample in the integration.

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