
Impossible color - sumnulu
https://en.wikipedia.org/wiki/Impossible_color
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deckar01
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)

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skrebbel
Seems like you're well positioned to add that to the article‽

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camillomiller
The interrobang is spreading all over hackernews!

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superflyguy
From the people who brought you uptalking? and the Indian Head Wobble, comes
another thing which means absolutely nothing.

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gugagore
Just because you don't, like, literally know what it means, doesn't mean it
means nothing! In any case, I could care less.

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superflyguy
You probably meant "I couldn't care less" \- that is, there is nothing I care
less about.

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ohiovr
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.

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empath75
Isn’t brown just a reddish green. Or a greenish red.

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BenFrantzDale
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.)

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ajross
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.

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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?

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pogimabus
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.

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OscarCunningham
Good guess, but completely wrong I'm afraid.

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pogimabus
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.

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azernik
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.

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eganist
For anyone looking to save skimming through the page:

[https://upload.wikimedia.org/wikipedia/commons/5/56/Chimeric...](https://upload.wikimedia.org/wikipedia/commons/5/56/Chimerical-
color-demo.svg)

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Severian
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)

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matte_black
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?

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zokier
Traditional displays (such as what would be used in vr goggles) do not produce
yellow light. You only get reddish-green with rgb colors

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AstralStorm
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.

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divs1210
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)

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ardillaroja
Reminds me of Pratchett's Octarine. And seems reasonable to assume that
impossible colours are only visible to wizards and cats.

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mrob
Or "ulfire" and "jale" from "A Voyage to Arcturus" by David Lindsay.

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ecpottinger
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)

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Waterluvian
Still looking for neon brown.

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BenFrantzDale
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.

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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.

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vernie
So do it then.

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tedunangst
It would probably be better if somebody who understands the article does it.

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daddyhole2
Now I want to visit Manchester to see if Reddish Green is also impossible

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

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foobar1962
Is this something to do the THAT DRESS?

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dsr_
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)

