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Impossible color

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Re: Impossible color

#41

Post by ajross »

BenFrantzDale wrote: post #29
tgb wrote: post #22

Earlier quoted context omitted.

Can you elaborate on why your don't get grey? That was always what I expected and I was surprised that you just get a muddy brown if you mix random paints.

One practical reason you don’t get gray is that pigments have to be real chemicals and so you can’t have a green that perfectly balances a given red’s spectrum. For transparent inks on a white background, if their spectra did match perfectly, you would get a perfect gray. But those perfect dyes don’t exist (or are expensive), hence the K in the CMYK color model. For opaque paint, it’s weirder: paint scatters and abso…

Nitpick: what you are calling "saturation" corresponds better to the biconic color space coordinate most people call "chroma". Very dark blues may not be perceptively far from black, but they can have very lopsided spectra and be highly "saturated" in the sense of distance from the gray point in the LUV chromaticity plane.

Basically the counterintuitivity you're citing goes away when you talk about color distinct from luminance, which is how most people here understand it anyway.

Re: Impossible color

#42

Post by BenFrantzDale »

tgb wrote: post #37
BenFrantzDale wrote: post #29

Earlier quoted context omitted.

One practical reason you don’t get gray is that pigments have to be real chemicals and so you can’t have a green that perfectly balances a given red’s spectrum. For transparent inks on a white background, if their spectra did match perfectly, you would get a perfect gray. But those perfect dyes don’t exist (or are expensive), hence the K in the CMYK color model. For opaque paint, it’s weirder: paint scatters and abso…

Thanks. This reminds me of the part of "Surely You're Joking, Mr. Feynman" where a painter says you can mix white and red to get yellow and Feynman says it's impossible and it turns out the painter would use a little bit of yellow to "sharpen it up" [1]. Any way that is possible without yellow paint? [1] http://blog.everydayscientist.com/wp-content/uploads/feynman...

Interesting. Without very odd paints, I can’t see how you’d get “yellow”, but if your red is desaturated (scattering and not totally absorbing some blue through yellow), and if your white is a bit gray, but your white absorbs and scatters red more than it absorbs and scatters the rest of the spectrum, the mixing path through Lab* color space would (I think) go from red toward light orange, toward warm light gray, finally coming into the light-gray color from the orange direction. I’m a little rusty, but I think that’s right.

Re: Impossible color

#44

Post by kaybe »

matte_black wrote: post #6

Isn’t it trivial to show impossible colors in VR by texturing an object in different colors like blue and yellow for each eye’s perspective?

My vision seems to oscillate between both eyes in the example picture shown (the yellow-blue one) - in the overlay, the colour changes from yellow to blue and back, with an overlay inbetween. If I concentrate I can see yellow over a blue background consistently though.

Does anyone have the same or a very different experience?

I imagine something similar would happen with your proposal, and possibly make people sick.

(Mixing vision between eyes is really interesting. My eyes are really different (one is good for close-up, one better for distance) so I have some experience with this.)

Re: Impossible color

#45

Post by starshadowx2 »

deckar01 wrote: post #5

I’m surprised the section towards them end about alternating high contrast colors producing impossible colors doesn’t link to “fechner colors” [0]. I am red-green colorblind, but when I was young I would stare at my dark ceiling fan spinning over the white ceiling and see very vivid greens and purples swimming across the blades. [0]: https://en.m.wikipedia.org/wiki/Fechner_color

My local science centre has had a Benham's top that you spin yourself in one of its permanent exhibits for probably over 15 years now and it's always really cool to see. It fascinates me that you can see yellow, purple, and green on a disk of only black and white.

Re: Impossible color

#46

Post by pjungwir »

I have always wondered why there is a transition between violet and red, if they are on opposite ends of the frequency spectrum. Despite that, they don't act like two extremes, just two positions on a "wheel". Why is color so wheel-like when the physics is just linear? What are we "seeing" when we see a violet-red? Why do we feel like violet is between blue & red?

Re: Impossible color

#47

Post by kaybe »

speps wrote: post #15
matte_black wrote: post #6

Isn’t it trivial to show impossible colors in VR by texturing an object in different colors like blue and yellow for each eye’s perspective?

Some interesting work around this research paper: Zhang, Haimo, Xiang Cao, and Shengdong Zhao. "Beyond stereo: an exploration of unconventional binocular presentation for novel visual experience." Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM, 2012. http://www.shengdongzhao.com/wp-content/uploads/2012/06/chi2...

Oh wow, these options are really cool. Some of them are hard to see, but even the experience trying is interesting.

Re: Impossible color

#48

Post by rini17 »

pjungwir wrote: post #46

I have always wondered why there is a transition between violet and red, if they are on opposite ends of the frequency spectrum. Despite that, they don't act like two extremes, just two positions on a "wheel". Why is color so wheel-like when the physics is just linear? What are we "seeing" when we see a violet-red? Why do we feel like violet is between blue & red?

Red receptors are somewhat sensitive in violet part of spectrum too. In standardized response curves it is omitted (I am not sure why), more details: https://midimagic.sgc-hosting.com/huvision.htm

Re: Impossible color

#49

Post by tedunangst »

> Impossible colors or forbidden colors are supposed colors that cannot be perceived in normal seeing of light that is a combination of various intensities of the various frequencies of visible light, but are reported to be seen in special circumstances.

This article could use some serious copy editing.

Re: Impossible color

#50

Post by vernie »

tedunangst wrote: post #49

> Impossible colors or forbidden colors are supposed colors that cannot be perceived in normal seeing of light that is a combination of various intensities of the various frequencies of visible light, but are reported to be seen in special circumstances. This article could use some serious copy editing.

So do it then.
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