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What is Color Banding? And what is it not?

simonschreibt.de

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Re: What is Color Banding? And what is it not?

#21

Post by silentplummet »

Bit depth is not a measure of quantity, but of dynamic range. In other words, what matters is not only how many quantization steps you have, but how large of a space you are trying to map them over.

The examples in the article point to this obvious conclusion, but don't quite state it explicitly. The relationship between space and quantization effects is demonstrated for a physical dimension interpretation of space by the horizontal greyscale bar that stretches and contracts.

But what if you stretch and contract the dynamic range of your monitor itself? Each bit in the encoding space (naively) offers a doubling of dynamic range in the natural space, so even your 30 bit encoding can be stretched if you display it on a monitor that intends to output a contrast ratio many times greater than what we are used to.

For instance, imagine a monitor that could output light perceptually as bright as the afternoon sun, next to effectively infinite blackness. Will 30 bits be enough when 'stretched' across these new posts of dynamic range, or will banding (quantization) still be visually evident when examining a narrow slice of the space?

Re: What is Color Banding? And what is it not?

#22

Post by corysama »

silentplummet wrote: post #21

Bit depth is not a measure of quantity, but of dynamic range. In other words, what matters is not only how many quantization steps you have, but how large of a space you are trying to map them over. The examples in the article point to this obvious conclusion, but don't quite state it explicitly. The relationship between space and quantization effects is demonstrated for a physical dimension interpretation of space b…

HDR monitor do exist. BrightSide Technologies was showing them at SIGGRAPH over ten years ago. Looks like consumer OLEDs are starting to get on board [1]. And, they did really want 10 bits per channel. But, even that seems lightweight.

10 bits per channel will carry us for a while. Apparently Dolby bought BrightSide and now they are pushing for 12 bits. 16 bit ints will probably be enough for home use in practice. Internally, most games that do HDR rendering use 16 bit floats for their intermediate frame buffers. That format is popular in film production as well. I would be surprised if consumer display tech ever bothered to go float16-over-DVI. But, maybe it will get cheap enough eventually that we might as well have the best :)

[1] http://www.avsforum.com/forum/40-oled-technology-flat-panels...

Re: What is Color Banding? And what is it not?

#23

Post by hfsktr »

simonschreibt wrote: post #16
hfsktr wrote: post #3

Every image on the page is broken for me (Chrome if it matters). I was hoping they would help understand what I was reading. Console is full of errors for where each image tried to load.

It seems that my site has problems when it's visited for example from behind a firewall which doesn't like my SSL-Proxy. I've heard that sometimes from people visiting the blog from work but at gome everything was fine... Are you behind a firewall?

When I tried it in IE I got loads of popups about SSL/certificate stuff that I just don't get. So it probably is work messing it up. I will hopefully get a chance when I get home to revisit the page.

To the others, I did disable ublock and ghostery but that didn't do anything for me.

Re: What is Color Banding? And what is it not?

#25

Post by mark-r »

I was really surprised the first time I saw banding in a 24-bit gradient image, I spent many years thinking it was impossible. But I'm still not sure if that's an inherent limitation of 24 bits, or whether my display is not capable of displaying all 24 bits with full fidelity. The LCD manufacturers are using tricks to squeeze the last couple of bits out of panels that aren't up to the task.

Re: What is Color Banding? And what is it not?

#26

Post by kevin_thibedeau »

Dumping color table entries from the last frame of the "256" color GIF:

> gifbuild -d colorBanding_255colorsOn1920pixels.gif | tail -n 200 | grep rgb | sort | uniq | wc -l

> 100

What happened here is some sequence of color space conversions with gamma correction added/removed that ended up compressing the darks.

A true 256 color gray gradient will not display so much visible banding. Just throwing together a naive 256 color gradient in Gimp reveals some RGB triplets with mismatched values suggesting the encoder is doing some odd color space conversion. Even then, it has much less perceptible banding when scaled with nearest neighbor to 1920.

I suspect most of the examples stem from improper gamma handling than any true demonstration of the limitations of 8-bit channels.

Re: What is Color Banding? And what is it not?

#27

Post by DanBC »

oflordal wrote: post #15

The greyscale gradient animations that are meant to show banding are full of gif artifacts so they are not actually smooth gradients.

Are you viewing on mobile? Some mobile providers run images through an "optimizing cache", and they use weird bad settings.
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