[subb]

They are very useful to encode stimuli, but stimuli is "not yet" color. When you have an image that is not just a patch of RGB value, a lot of things will influence what color you will compute based on the exact same RGB.

Akiyoshi's color constancy demonstrations are good examples of this. The RGB model (and any three-values "perceptual" model) fails to predict the perceived color here. You are seeing different colors but the RGB values are the same.

https://www.psy.ritsumei.ac.jp/akitaoka/marie-eyecolorconsta...

[dahart]

Here you’re talking about only perception, and not physical color. You could use 100 dimensional spectral colors, or even 1D grayscale values, and still have the same result. So this example doesn’t have any bearing on whether a 3D color space works well for humans or not. Do you have any other examples that suggest a 3D color space isn’t good enough? I still don’t understand what you meant.

[subb]

Yes exactly. I'm intentionally using "color" as a perceptual thing, not as a physical thing. If we are talking about a color model, then it needs to model perception. As such, RGB, as a predictor of perception, can often fail because it doesn't account for much more than what hits the retina, not what happens after. For one, it lacks spatial context - placing the same RGB value with a different surround will feel different, like in the example above. But if you had a real color (as-in, perceptual) picker in Photoshop, you would get a different value.

It's excellent at compressing the visible part of the EM spectrum, however. This is what I meant by stimuli encoding.

[dahart]

Still not seeing why you claimed color is definitely not something you can plug into a 3D model. We can, and do, use 3D color models, of course. And some of them are designed to try to be closer to perceptual in nature, such as the LAB space like @zeroq mentioned at the top of this sub-thread. No well known perceptual color space I know of, and no color space in Photoshop, accounts for context/surround/background, so I don’t understand your claim about Photoshop immediately after talking about the surround problem, but FWIW everyone here knows that RGB is not a perceptual color space and doesn’t have a specification or standard, and everyone here knows that color spaces don’t solve all perceptual problems.

I find it confusing to claim that cone response isn’t color yet, that’s going to get you in trouble in serious color discussions. Maybe better to just be careful and qualify that you’re talking about perception than say something that is highly contestable?

The claim that a color model must model perception is also inaccurate. Whether to incorporate human perception is a choice that is a goal in some models. Having perceptual goals is absolutely not a requirement to designing a practical color model, that depends entirely on the design goals. It’s perfectly valid to have physical color models with no perceptual elements.

[subb]

The problem is that we mix up physical and perception, including in our language. If you look at the physical stuff, there's nothing in this specific range of EM radiation that is different from UV or IR light (or further). The physical stuff is not unique, our reading is. Therefore, color is not a physical thing.

And so when I say "color" I only mean it to be the construction that we make out of the physical thing.

We project back these construction outside of us (e.g. the apple is red), but we must no fool ourselves that the projection is the thing, especially when we try to be more precise about what is happening.

This is why I'm saying a 3D model of color (brain thing) is very far from modelling color (brain thing) at all. But! It's not purely physical either, otherwise it would just be a spectral band or something. So this is pseudo-perceptual. It's the physical stuff, tailored for the very first bits of anatomy that we have to read this physical stuff. It's stimuli encoding.

If you build a color model, it's therefore always perceptual, and needs to be evaluated against what you are trying to model - perception. You create a model to predict things. RGB and all the other models based on three values in a vaccum will always fail at predicting color (brain!) when the stimuli's surround is more complex.

[dahart]

There’s a valid point in there somewhere, but you’re also saying some stuff that seems hyperbolic and getting harder to agree with. You’re right that perception is complicated, and I agree with you when you say 3D models don’t capture all of perception. That is true. That does not imply that people can’t use 3D models for lots of color tasks. Again, it always depends on your goals. You’re making abstract and general claims without stating your goals.

It’s fine for you to think of perception when you say color, but that’s not what everyone means, and therefore, you’re headed for miscommunication when you make assumptions and/or insist on non-standard definitions of these words.

Physical color is of course a thing. (BTW, it seems funny to say it’s not a thing after you introduced the term physical-color to this thread.) Physical color can mean, among other things, the wavelength distribution of light power. A physical color model is also a thing, it can include the quantized numerical representation of a spectral power distribution. Red can mean 700nm light. Some people, especially researchers and scientists, use physical color models all the time. You’re talking about meanings that are more specific than the general terms you’re using, so maybe re-familiarizing yourself with the accepted definitions of color and color model would help? https://en.wikipedia.org/wiki/Color_model

Again, it’s fine to talk about perception and human vision, but FWIW the way you’re talking about this makes it seem like you’re not understanding the specific goals behind 3D color spaces like LAB. Nobody is claiming or fooling themselves to think they solve all perception problems or meet all possible goals, so it seems like a straw man to keep insisting on something that was never an issue in this thread. If you want to talk about 3D models not being good enough for perception, then please be more precise about your goals. That’s why I asked what use cases you’re thinking of, and we haven’t discussed a goal that justifies needing something other than a 3D color model - color constancy illusions do not make that point.

[subb]

Unfortunately, it seems like we will not reach any agreement here.