10 ms·

Impossible color

245 points by sumnulu 8y ago

king_nothing 8y ago
That explains the invisible pink unicorn and colorless green dreams sleeping furiously. Flying spaghetti monster is still a mystery.
ohiovr 8y ago
When adjusting paint colors if what you have is too red “or on the red side” you can correct it by adding green. If what you have is on the blue side add yellow then kind of straighten out the undesirable green by adding a smidge of red. This is the sort of thing a skilled shader technician would do to match automotive or sign paint. I did this for a while for PPG You might find playing with the LAB color scale in photoshop an interesting toy to see why a reddish green color has no sense. by adding red to green you end up on the gray side. basically the colors just neutralize each other.
- empath75 8y ago
  Isn’t brown just a reddish green. Or a greenish red.
  - jacobroyquebec 8y ago
    In substractive color theory, yes, you’ll end up with a brown when mixing red and green in near equal parts. Keep in mind that the red and green you’ll be mixing is not 100% color pigments, so it cannot merge into a dark grey.
    - tgb 8y ago
      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.
      - OscarCunningham 8y ago
        The best explanation I've found is in the online book "The Dimensions of Colour" by David Briggs. In particular the section on "Colour Mixing in Paints" (http://www.huevaluechroma.com/061.php http://www.huevaluechroma.com/061.php). You might have to read some of the preceding sections to get a complete understanding. The website https://www.handprint.com/ https://www.handprint.com/ is also very good. In practice it is possible to mix a grey from coloured paints, but you need disproportionately much blue. Brown is just dark orange, and blue is the complementary colour to orange, so you need to move in the blue direction if you want to get to grey. Also, if you're using red, yellow and blue, you generally need less yellow than red. Try a ratio of 1:2:4 = R:Y:B.
      - BenFrantzDale 8y ago
        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 absorbs, so white light goes into the paint layer and starts bouncing around. The resulting reflectance spectrum you see is a function of the ratio of absorption and scattering across the spectrum. Mixing paint mixes the absorption and scattering spectra. One weird result is that adding white can increase a paint’s saturation. (Think of adding apparently-black blue food coloring to white frosting.) Weirder still is you can have two identical-looking paints that, mixed with a third paint make different shades depending on which you use. As a related weird example, yellow plus black can give you a blueish-gray, since the black paint may absorb yellow more than blue (so long as it doesn’t scatter much that’ll still look black) and the yellow will scatter some blue and not absorb all blue (it’s not perfect). So when you mix those you can get something that scatters blue more than it absorbs it and absorbs yellow more than it scatters it. But pick a different black and you’ll get a different result! Color theory is tricky stuff; paint mixing is perhaps the least intuitive part of it.
        tgb 8y ago
        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-paint.pdf http://blog.everydayscientist.com/wp-content/uploads/feynman...
  - coldseattle 8y ago
    Read the article.
  - BenFrantzDale 8y ago
    Yes and no. Brown is just dark orange, which you can sort of get by mixing red and green paints. Paint mixing is weird, though. (I’ve written paint-matching software professionally.)
    - ajross 8y ago
      Sorta, except when dark orange is dark orange and not brown. Your brain will decide between them based on context. The shaded half of a (fruit) orange may well have the same spectrum as the lighted tree trunk it's hanging on, but you will see two different colors.
- princekolt 8y ago
  The thing though (if I got the article right) is that these "reddish green" and "bluish yellow" colours are "virtual". It is almost like they're the result of a glitch in the brain. So I guess standard colour mixing rules don't apply.
deckar01 8y ago
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 https://en.m.wikipedia.org/wiki/Fechner_color
- King-Aaron 8y ago
  Anecdotally, in my first year of university a tutor of mine did a demonstration on Fechner Colour. We walked into the lab and he had a spinning disc on a motor, that was apparently pink in colour. He asked the class (*first year students) what colours we thought each half of the disc were to create the pink shade. Most people guessed pink and white, while a couple of people had correct guesses.. When he stopped the motor, the disc spun down and it was yellow on one side, and blue on the other.
- skrebbel 8y ago
  Seems like you're well positioned to add that to the article‽
  - camillomiller 8y ago
    The interrobang is spreading all over hackernews!
    - superflyguy 8y ago
      From the people who brought you uptalking? and the Indian Head Wobble, comes another thing which means absolutely nothing.
      - deleted 8y ago
        [deleted]
      - gugagore 8y ago
matte_black 8y ago
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?
- zokier 8y ago
  Traditional displays (such as what would be used in vr goggles) do not produce yellow light. You only get reddish-green with rgb colors
  - AstralStorm 8y ago
    Technically you could make such an extended gamut OLED screen, 4-stimulus. Probably RBGY variant. Some such screens are on the market already but they do not really produce superior results. Some phone screens use RBGW pattern too.
  - matte_black 8y ago
    Crap, guess we’re stuck with reddish green :(
  - BenFrantzDale 8y ago
    Not really, if you look at the CIE chromaticity diagram, you’ll find that the experience of spectral yellows are very closely approximated by an RGB monitor. It’s spectral cyan that is really out of gamut for a standard display. Take a photo of a green traffic light (which is a little cyan so colorblind people can see it’s not red). I’m pretty sure that green-light color is out of gamut for most displays. https://en.wikipedia.org/wiki/SRGB https://en.wikipedia.org/wiki/SRGB
  - jpindar 8y ago
    Your comment inspired me to look at my phone under a microscope (I opened a paint program's color picker). As with many things I have examined under a microscope, I didn't actually learn anything new, but it was still interesting to see for myself.
- speps 8y ago
  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/chi2012_beyondstereo1.pdf http://www.shengdongzhao.com/wp-content/uploads/2012/06/chi2...
divs1210 8y ago
Reminds me of The Color Out of Space. https://en.m.wikipedia.org/wiki/The_Colour_Out_of_Space https://en.m.wikipedia.org/wiki/The_Colour_Out_of_Space
- ardillaroja 8y ago
  Reminds me of Pratchett's Octarine. And seems reasonable to assume that impossible colours are only visible to wizards and cats.
  - mrob 8y ago
    Or "ulfire" and "jale" from "A Voyage to Arcturus" by David Lindsay.
foobar1962 8y ago
Is this something to do the THAT DRESS?
- dsr_ 8y ago
  No, it's a different bug in the human optical system. Impossible colors are derived from the frequency-response curve of the three standard pigments in the retina. (There are people with 2 pigments and thus have a reduced color space, and people with 4 pigments who have an increased color space.) Since the pigments are not evenly distributed, the brain synthesizes some colors from incomplete information. The dress problem stems from luminance-color correction in the brain itself. The eye has quite an amazing dynamic contrast ratio, but a much narrower static contrast ratio. If you have picked up on clues that the photograph was over-exposed in one way, your brain interprets that as a signal that the colors are washed out. If you have picked up on clues that the photograph is undersaturated, your brain says that the colors should be brighter than the pixels are. The photograph in question gave ambiguous clues. https://en.wikipedia.org/wiki/The_dress https://en.wikipedia.org/wiki/The_dress
- zipwitch 8y ago
  Nah. Not Han Solo coat on Hoth, either.
daddyhole2 8y ago
Now I want to visit Manchester to see if Reddish Green is also impossible
azernik 8y ago
Playing off the "chimerical color" examples - it's possible to approximate the effect of "imaginary colors" (activation of only one cone cell type) by fatiguing the other two and then looking at the target color. e.g. staring for a while at #FF00FF and then switching immediately to a #00FF00 makes the green "pop" in a strange way.
- eganist 8y ago
  For anyone looking to save skimming through the page: https://upload.wikimedia.org/wikipedia/commons/5/56/Chimerical-color-demo.svg https://upload.wikimedia.org/wikipedia/commons/5/56/Chimeric...
ecpottinger 8y ago
What happens when someone with tetrachromacy looks at these same test colour tests? See: https://en.wikipedia.org/wiki/Tetrachromacy https://en.wikipedia.org/wiki/Tetrachromacy
Waterluvian 8y ago
Still looking for neon brown.
- BenFrantzDale 8y ago
  You joke, but that’s a great example: brown is really dark orange; neon is fluorescent, and so brighter than your eye thinks should be possible for reflection, so sadly, no neon poo emoji.
  - deleted 8y ago
    [deleted]
Severian 8y ago
I get intensely vivid 'stygian blue' hypnagogic hallucinations right before I fall asleep. It's an intensely dark/bright blue. Very hard to describe. It usually manifests as a blob of color that pulses from the outer-edges inwards. Humorously, Negativland, the amazing decades old plunderphonics group, had a whole prank site[1] and a Over the Edge[2] radio show[3] regarding the 'fourth primary color', Squant. This was also the only color with it's own smell as well. Negativland also had a plugin for web-browser that allowed you to 'see' this magical fourth primary color. [1]https://www.negativland.com/archives/015squant/story.html https://www.negativland.com/archives/015squant/story.html [2]https://en.wikipedia.org/wiki/Over_the_Edge_(radio) https://en.wikipedia.org/wiki/Over_the_Edge_(radio) [3]https://www.youtube.com/watch?v=lt8biSTQ7wk https://www.youtube.com/watch?v=lt8biSTQ7wk
pjungwir 8y ago
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?
- rini17 8y ago
  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 https://midimagic.sgc-hosting.com/huvision.htm
- deleted 8y ago
  [deleted]
- pogimabus 8y ago
  My completely made up intuitive understanding of it is that it's the same as musical pitches; there are many versions of each named pitch e.g A through G that are each an "octave" away from each other. The difference between "Middle C" and the one above it is that the frequency of the higher version is exactly double that of the lower. As a listener the two notes sound extremely similar, the higher one just feels more "energetic" or something. I imagine colors would be the same if our eyes could see more than one "octave" but we are only sensitive to approximately one "octave" of light, ~ 480Thz-750Thz. Given that, violet appears to be between red and blue in the same way the pitch of G appears to be between the pitches F and A.
  - OscarCunningham 8y ago
    Good guess, but completely wrong I'm afraid.
    - pogimabus 8y ago
      Interesting! Although I don't think this means I'm completely wrong, just that there are "true/full violet" values that we can't see that would make the semi-circle that is visible light into a full circle if we could see a full "octave"; instead we are limited to seeing just violets that are mixes of other colors.
tedunangst 8y ago
> 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.
- vernie 8y ago
  So do it then.
  - tedunangst 8y ago
    It would probably be better if somebody who understands the article does it.

245 points by sumnulu 8y ago

That explains the invisible pink unicorn and colorless green dreams sleeping furiously. Flying spaghetti monster is still a mystery.

ohiovr 8y ago

When adjusting paint colors if what you have is too red “or on the red side” you can correct it by adding green. If what you have is on the blue side add yellow then kind of straighten out the undesirable green by adding a smidge of red. This is the sort of thing a skilled shader technician would do to match automotive or sign paint. I did this for a while for PPG You might find playing with the LAB color scale in photoshop an interesting toy to see why a reddish green color has no sense. by adding red to green you end up on the gray side. basically the colors just neutralize each other.

empath75 8y ago
Isn’t brown just a reddish green. Or a greenish red.
- jacobroyquebec 8y ago
  In substractive color theory, yes, you’ll end up with a brown when mixing red and green in near equal parts. Keep in mind that the red and green you’ll be mixing is not 100% color pigments, so it cannot merge into a dark grey.
  - tgb 8y ago
    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.
    - OscarCunningham 8y ago
      The best explanation I've found is in the online book "The Dimensions of Colour" by David Briggs. In particular the section on "Colour Mixing in Paints" (http://www.huevaluechroma.com/061.php http://www.huevaluechroma.com/061.php). You might have to read some of the preceding sections to get a complete understanding. The website https://www.handprint.com/ https://www.handprint.com/ is also very good. In practice it is possible to mix a grey from coloured paints, but you need disproportionately much blue. Brown is just dark orange, and blue is the complementary colour to orange, so you need to move in the blue direction if you want to get to grey. Also, if you're using red, yellow and blue, you generally need less yellow than red. Try a ratio of 1:2:4 = R:Y:B.
    - BenFrantzDale 8y ago
      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 absorbs, so white light goes into the paint layer and starts bouncing around. The resulting reflectance spectrum you see is a function of the ratio of absorption and scattering across the spectrum. Mixing paint mixes the absorption and scattering spectra. One weird result is that adding white can increase a paint’s saturation. (Think of adding apparently-black blue food coloring to white frosting.) Weirder still is you can have two identical-looking paints that, mixed with a third paint make different shades depending on which you use. As a related weird example, yellow plus black can give you a blueish-gray, since the black paint may absorb yellow more than blue (so long as it doesn’t scatter much that’ll still look black) and the yellow will scatter some blue and not absorb all blue (it’s not perfect). So when you mix those you can get something that scatters blue more than it absorbs it and absorbs yellow more than it scatters it. But pick a different black and you’ll get a different result! Color theory is tricky stuff; paint mixing is perhaps the least intuitive part of it.
      - tgb 8y ago
        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-paint.pdf http://blog.everydayscientist.com/wp-content/uploads/feynman...
- coldseattle 8y ago
  Read the article.
- BenFrantzDale 8y ago
  Yes and no. Brown is just dark orange, which you can sort of get by mixing red and green paints. Paint mixing is weird, though. (I’ve written paint-matching software professionally.)
  - ajross 8y ago
    Sorta, except when dark orange is dark orange and not brown. Your brain will decide between them based on context. The shaded half of a (fruit) orange may well have the same spectrum as the lighted tree trunk it's hanging on, but you will see two different colors.
princekolt 8y ago
The thing though (if I got the article right) is that these "reddish green" and "bluish yellow" colours are "virtual". It is almost like they're the result of a glitch in the brain. So I guess standard colour mixing rules don't apply.

deckar01 8y ago

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 https://en.m.wikipedia.org/wiki/Fechner_color

King-Aaron 8y ago
Anecdotally, in my first year of university a tutor of mine did a demonstration on Fechner Colour. We walked into the lab and he had a spinning disc on a motor, that was apparently pink in colour. He asked the class (*first year students) what colours we thought each half of the disc were to create the pink shade. Most people guessed pink and white, while a couple of people had correct guesses.. When he stopped the motor, the disc spun down and it was yellow on one side, and blue on the other.
skrebbel 8y ago
Seems like you're well positioned to add that to the article‽
- camillomiller 8y ago
  The interrobang is spreading all over hackernews!
  - superflyguy 8y ago
    From the people who brought you uptalking? and the Indian Head Wobble, comes another thing which means absolutely nothing.
    - deleted 8y ago
      [deleted]
    - gugagore 8y ago

matte_black 8y ago

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?

zokier 8y ago
Traditional displays (such as what would be used in vr goggles) do not produce yellow light. You only get reddish-green with rgb colors
- AstralStorm 8y ago
  Technically you could make such an extended gamut OLED screen, 4-stimulus. Probably RBGY variant. Some such screens are on the market already but they do not really produce superior results. Some phone screens use RBGW pattern too.
- matte_black 8y ago
  Crap, guess we’re stuck with reddish green :(
- BenFrantzDale 8y ago
  Not really, if you look at the CIE chromaticity diagram, you’ll find that the experience of spectral yellows are very closely approximated by an RGB monitor. It’s spectral cyan that is really out of gamut for a standard display. Take a photo of a green traffic light (which is a little cyan so colorblind people can see it’s not red). I’m pretty sure that green-light color is out of gamut for most displays. https://en.wikipedia.org/wiki/SRGB https://en.wikipedia.org/wiki/SRGB
- jpindar 8y ago
  Your comment inspired me to look at my phone under a microscope (I opened a paint program's color picker). As with many things I have examined under a microscope, I didn't actually learn anything new, but it was still interesting to see for myself.
speps 8y ago
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/chi2012_beyondstereo1.pdf http://www.shengdongzhao.com/wp-content/uploads/2012/06/chi2...

divs1210 8y ago

Reminds me of The Color Out of Space. https://en.m.wikipedia.org/wiki/The_Colour_Out_of_Space https://en.m.wikipedia.org/wiki/The_Colour_Out_of_Space

ardillaroja 8y ago
Reminds me of Pratchett's Octarine. And seems reasonable to assume that impossible colours are only visible to wizards and cats.
- mrob 8y ago
  Or "ulfire" and "jale" from "A Voyage to Arcturus" by David Lindsay.

foobar1962 8y ago

Is this something to do the THAT DRESS?

dsr_ 8y ago
No, it's a different bug in the human optical system. Impossible colors are derived from the frequency-response curve of the three standard pigments in the retina. (There are people with 2 pigments and thus have a reduced color space, and people with 4 pigments who have an increased color space.) Since the pigments are not evenly distributed, the brain synthesizes some colors from incomplete information. The dress problem stems from luminance-color correction in the brain itself. The eye has quite an amazing dynamic contrast ratio, but a much narrower static contrast ratio. If you have picked up on clues that the photograph was over-exposed in one way, your brain interprets that as a signal that the colors are washed out. If you have picked up on clues that the photograph is undersaturated, your brain says that the colors should be brighter than the pixels are. The photograph in question gave ambiguous clues. https://en.wikipedia.org/wiki/The_dress https://en.wikipedia.org/wiki/The_dress
zipwitch 8y ago
Nah. Not Han Solo coat on Hoth, either.

daddyhole2 8y ago

Now I want to visit Manchester to see if Reddish Green is also impossible

azernik 8y ago

Playing off the "chimerical color" examples - it's possible to approximate the effect of "imaginary colors" (activation of only one cone cell type) by fatiguing the other two and then looking at the target color. e.g. staring for a while at #FF00FF and then switching immediately to a #00FF00 makes the green "pop" in a strange way.

eganist 8y ago
For anyone looking to save skimming through the page: https://upload.wikimedia.org/wikipedia/commons/5/56/Chimerical-color-demo.svg https://upload.wikimedia.org/wikipedia/commons/5/56/Chimeric...

ecpottinger 8y ago

What happens when someone with tetrachromacy looks at these same test colour tests? See: https://en.wikipedia.org/wiki/Tetrachromacy https://en.wikipedia.org/wiki/Tetrachromacy

Waterluvian 8y ago

Still looking for neon brown.

BenFrantzDale 8y ago
You joke, but that’s a great example: brown is really dark orange; neon is fluorescent, and so brighter than your eye thinks should be possible for reflection, so sadly, no neon poo emoji.
- deleted 8y ago
  [deleted]

Severian 8y ago

I get intensely vivid 'stygian blue' hypnagogic hallucinations right before I fall asleep. It's an intensely dark/bright blue. Very hard to describe. It usually manifests as a blob of color that pulses from the outer-edges inwards. Humorously, Negativland, the amazing decades old plunderphonics group, had a whole prank site[1] and a Over the Edge[2] radio show[3] regarding the 'fourth primary color', Squant. This was also the only color with it's own smell as well. Negativland also had a plugin for web-browser that allowed you to 'see' this magical fourth primary color. [1]https://www.negativland.com/archives/015squant/story.html https://www.negativland.com/archives/015squant/story.html [2]https://en.wikipedia.org/wiki/Over_the_Edge_(radio) https://en.wikipedia.org/wiki/Over_the_Edge_(radio) [3]https://www.youtube.com/watch?v=lt8biSTQ7wk https://www.youtube.com/watch?v=lt8biSTQ7wk

pjungwir 8y ago

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?

rini17 8y ago
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 https://midimagic.sgc-hosting.com/huvision.htm
deleted 8y ago
[deleted]
pogimabus 8y ago
My completely made up intuitive understanding of it is that it's the same as musical pitches; there are many versions of each named pitch e.g A through G that are each an "octave" away from each other. The difference between "Middle C" and the one above it is that the frequency of the higher version is exactly double that of the lower. As a listener the two notes sound extremely similar, the higher one just feels more "energetic" or something. I imagine colors would be the same if our eyes could see more than one "octave" but we are only sensitive to approximately one "octave" of light, ~ 480Thz-750Thz. Given that, violet appears to be between red and blue in the same way the pitch of G appears to be between the pitches F and A.
- OscarCunningham 8y ago
  Good guess, but completely wrong I'm afraid.
  - pogimabus 8y ago
    Interesting! Although I don't think this means I'm completely wrong, just that there are "true/full violet" values that we can't see that would make the semi-circle that is visible light into a full circle if we could see a full "octave"; instead we are limited to seeing just violets that are mixes of other colors.

tedunangst 8y ago

> 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.

vernie 8y ago
So do it then.
- tedunangst 8y ago
  It would probably be better if somebody who understands the article does it.