Train yourself to see impossiblecolors

Alasdair WilkinsFiled to: MAD SCIENCE 12/09/10 1:25pm

Hiding in the shadows between the colors we see everyday are weird, impossible

shades, colors that you shouldn't be able to see and generally don't...unless you

know how. Here's a simple guide to seeing impossible and imaginary colors.

Image by Cody James.

Understanding a little about how humans perceive color is crucial to seeing

impossible colors. Our eyes use something called opponent process to work more

efficiently. This plays upon the fact that the eye's primary light receptors, the

cones, have certain overlaps in what light wavelengths they can perceive. To save

energy, our eyes measure the differences between the responses of various cones

rather than figuring out each cone's individual response.

We long ago found out that there are three opponent channels: red vs. green, blue

vs. yellow, and black vs. white. (Technically, black and white aren't colors, and

their opponent process has more to do with brightness than anything else.) Now,

let's say you stare right at the bluest object you've ever seen. Your cones that

primary perceive the blue wavelengths are going to be excited, while the cones

responsible for yellow will be inhibited. If you then switched to looking at the

yellowest thing you've ever seen, the exact opposite would happen.

It probably isn't all that shocking to point out the cones can't be excited and

inhibited at the same time. That means that it's impossible to see an object that's

simultaneously blue and yellow or red and green. I'm not talking about what

happens when you mix those colors and then look at them ­ obviously, you'd get

green and a sort of murky brown if you did that. No, what I'm talking about here

are colors that are equal parts blue and yellow at the exact same time. Can you

imagine that? Well, you shouldn't be able to, because that's an impossible color.

This might all seem a bit abstract, but there's some evidence backing up the

existence of such colors. A 1983 experiment featured a special machine which

separated the fields of vision of the test subject's eyes. One eye would see a red

screen, while the other would see a green screen. Given time, the colors would mix

together, but the mixing only occurred in the brain. Without the eye there to

mediate the mixing, red and green didn't become brown ­ they became a new

color, a reddish­green color that none of the test subjects had ever seen before,

and that includes an artist with an extensive knowledge of different hues and

shades.

Admittedly, the methodology of that experiment has since been criticized, and

many vision researchers say impossible colors are called that for a reason – they

really are impossible. There are, to be sure, a lot of alternative explanations for the

colors the people saw: they were just intermediate colors between the two, the

experimenters hadn't properly controlled for luminance and that threw off the

results, or the test subjects were really just see red, then green, then red, and so on,

and never actually viewing them simultaneously.

These are all fair points. However, if I may make a counterpoint, you're ruining

all the fun, vision experts. Sure, impossible colors might actually be impossible, but

that doesn't change the fact that test subjects saw colors they had never seen

469 6

before. Impossible colors might not exist, but if it's possible to fool our brains into

thinking they do, then I'd say that's still pretty awesome.

This is one of the least scientific viewpoints I've ever put forward, and I'm not

exactly proud of it, but hey...impossible colors are cool. Now relax each eye on

these two plus signs and see if you can't make some impossible colors appear. Let

your eyes cross so that the two pluses are right on top of each other. I'll say right

now that not everyone is going to be able to see these weird colors ­ I'm almost

certain that I can't ­ but I'd still say it's worth a try.

I'd be remiss if I didn't also mention imaginary colors. These are colors that cannot

be produced in the physical light spectrum, and yet it's possible to derive them

mathematically. The easiest way to understand what an imaginary color is would

be to think about the three wavelengths of cones ­ short, medium, and long. Like I

said when talking about the imaginary colors, there's an overlap in the responses

of these different wavelengths.

But what if you had a color that only created a response in the medium

wavelengths? In real life, this can't happen, as anything that excites the medium

wavelengths is going to excite one or both of the other wavelengths. But if you did

have a color that only excited the medium, green wavelengths while leave the

other two types alone, then you'd be able to see a color greener than any real

green.

So that's the theory ­ here's how you do it. Again, you've to be smart about your

opponent processes. If you want to see an imaginary green, you need to find an

example of heavily saturated red and one of a heavily saturated green. Stare at the

red color for as long as you can, then switch to looking at the green. The red

receptors have become too fatigued to do their job and be inhibited by the green

color. That means your green receptors are getting excited with nothing to

counterbalance them. The result is the greenest color you've ever seen, one that

can't exist in the physical world.

Again, this might all seem a bit out there, but America's most lovable evil geniuses

have known about this for years. Walt Disney World took advantage of this effect

in their design of the EPCOT park, making the pavements a particular shade of

pink that tires out the red receptors and forces the park's grass to look greener

than it really is. On second thought, I'm not sure that makes this seem any less out

there.

For more, check out "Impossible" Colors: See Hues That Can't Exist (Scientific

American).

orionx3000 Alasdair Wilkins12/09/10 5:09pm

a

hen i was studying yoga in an ashram some one told me that tribes in africa

define the boundrys to colors differently so their color spectrum is different

much like how different cultures have different musical scales.its all a matter

of perspective.:)

Ivriniel orionx300012/09/10 5:10pm

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@orionx3000: That is true for a lot of cultures, actually.

izikavazo orionx300012/09/10 5:35pm

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@orionx3000: That's awesome.

I'm sure kids are like that too. My nephew loves to come up with "matching"

outfits and they're amazingly clashing. For example, he's sure that purple

and brown look great next to each other. To me that's horrific, but I can't

express to him why it's so ugly.

I figure kids don't have the bias of the color wheel or accepted stylistic

conventions rammed into their minds so they're more open to form their

own opinions. Of course we try to squash that kind of thinking as soon as we

can.

bakana orionx300012/09/10 5:46pm

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@orionx3000: In Russia, "blue" (синий) and "sky blue" (голубой) are

considered totally different colors, with their own 'stripe' in the rainbow.

Conversely, in Mandarin, "青" is a single color, but it includes both what we

would call blue and green, which are just considered different shades of

"青." (I think this is similar in Japan, too.)

I remember reading about some Middle Eastern culture (Persians?) that

had no word/concept for 'blue', all blues falling under either 'purple' or

'green'. I'm fuzzy on this one, anyone that can clarify would be much

appreciated.

kagekiri bakana12/09/10 6:23pm

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@bakana: I don't know that much Mandarin (can't read it for crap), but

isn't blue "lanse" 藍色 and green "luse" 綠色?

So even if they have an ambiguous words like "zhen" (I think that's the

pinyin for the character you wrote), they do have concrete ways to

differentiate between green and blue than on shades of 青 alone.

RemusShepherd Alasdair Wilkins12/09/10 5:19pm

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I'm colorblind. Can someone train me to see actual colors, please?

zero_gravitas RemusShepherd12/09/10 5:30pm

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@RemusShepherd: I've always wondered exactly what a colorblind person

sees...I mean, is basically everything in black & white for you?

Sorry, just really wondering...

ksf RemusShepherd12/09/10 6:03pma

@RemusShepherd: I feel your pain.

bookwench zero_gravitas12/09/10 6:24pm

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@thethirdchimpanzee: There's colorblind, and then there's colorblind. Most

colorblind folks can see color, but they can't tell some colors appart, like red

and green ­ both look like a messy brown to them.

Then there's folks who see in black and white because they're born with a

mutation that messes up their receptors. These folks are *really* rare and

most have loads of problems with bright lights, excessive darkness, etc. They

have trouble differentiating edges and fast­moving things can mess them

up. It's not cool, like seeing the world as a black and white photograph.

more here:

[en.wikipedia.org]

zero_gravitas bookwench12/09/10 7:52pm

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@bookwench: Thanks. That's what I was always wondering about. For the

longest time I thought "colorblind" meant you don't see colors *at all* ­ but

statements by people who are colorblind made me question that...

I think it's something similar with "tone deafness"...

jitpleecheep Alasdair Wilkins12/09/10 9:50pm

a

Oh here's io9 explaining science, again.

Theres so many things just wrong in this post. You haven't understood

colour vision at all...

And. Here. We. Go.

"Our eyes use something called opponent process to work more efficiently."

No.

Our eyes don't. Our brain does.

You're totally mixing up the response of the eyes' cones and the processing

that occurs in the 'corpus geniculatum laterale', which is, like, a totally

different thing...

"Your cones that primary perceive the blue wavelengths are going to be

excited, while the cones responsible for yellow will be inhibited. [...] It

probably isn't all that shocking to point out the cones can't be excited and

inhibited at the same time."

It's quite shocking to me that you again fail to differ between the cones and

the brain, and that you imply by this that the cones excited by 'blue'

wavelenghts are the same that are excited by 'yellow' wavelengths...

Of course the 'blue' cones can be excited at the same time the 'yellow' ones

are. Because there's no such thing as 'blue' and 'yellow' cones!

(Which would be rather obvious, if you would have shown not only the

(estimated) output of the corpus geniculatum laterale, but the actual output

of the cones as well:

[upload.wikimedia.org] )

Furthermore, how do you explain the line of purples in colour vision which

cannot be replicated by pure spectral colours, prey tell?

(Hint: It's because different cones _can_ be excited at the same time)

"That means that it's impossible to see an object that's simultaneously blue

and yellow [...]."

Oh really, is it? It may come as a surprise to you, but that's just exactly how

your basic white LED works...

"I'm not talking about what happens when you mix those colors and then

look at them [...]"

I' not talking about the fact that you haven't understood the difference

between the additive and subtractive colour model...

"[T]he cones have certain overlaps in what light wavelengths they can

perceive. To save energy, our eyes measure the differences between the

responses of various cones rather than figuring out each cone's individual

response."

Oh, now you're talking about overlap. Weren't you just saying that 'cones

can't be excited and inhibited at the same time'...?

One sort of cones is just excited by one wavelength to a certain degree, in a

gaussian distribution sort­of way. This means, that at a certain wavelength

its response reaches a maximum (let's say '1' at 555nm for the cone type 'M').

But the cone 'M' cannot discern by itself whether a response lower than '1' is

excited by a wavelength lower or higher than 555nm. So, what the colour

vision system is actually doing, it's triangulating between the S, M, and L

cones. It knows, that when 'M' reads lower than 1, and 'S' reads higher than

'L', the colour must be somewhat off to the blue side.

Fact is: you shouldn't be talking about colour vision. At least not on io9.

Unspellable jitpleecheep12/09/10 10:28pm

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@jitpleecheep: Wow.

Just: "Wow".

(No, really ­ thanks for the info.)

gd01skorpius jitpleecheep12/09/10 10:39pm

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@jitpleecheep: I really hate to promote your comment, but you moved me to

a response.

Good for you for having a deeper understanding of the process, but jeez

lighten up!

We all get that io9 isn't a hardcore science info site. We don't come here to

get educated we come here to get interested.

The above article is just the author's interpretation of something interesting,

and then he even sited the source.

When you get really excited about something you don't fully understand, do

your friends get mad, break down in detail everything you got wrong, and

tell you to never bring it up again?

hungryemo jitpleecheep12/09/10 10:49pm

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@jitpleecheep: Oh hai Grinch!

BoxOfScraps jitpleecheep12/09/10 11:47pm

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@jitpleecheep: I bet you tear up children's drawings because they paint the

sky green and the sky isn't fucking green you stupid fucking kids.

SinDonor2 Alasdair Wilkins12/09/10 5:58pm

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We shall name this new color "fnord".

Vexxarr SinDonor212/09/10 6:08pm

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@SinDonor2: What? Name it what? You started a sentance there and just

never finshed it.

Chip Overclock® Vexxarr12/09/10 6:27pm

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@Vexxarr: Image upload fail, too.

sometingwong SinDonor212/09/10 6:39pm

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@SinDonor2: I see the FNORDS!

Vexxarr sometingwong12/09/10 7:43pm

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@sometingwong: You see the WHAT? What do you see?

You start a sentence and then leave off the last word!

Annalee Newitz Alasdair Wilkins12/10/10 1:14am

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I just saw a colour out of space. What does that mean?

jmicha Annalee Newitz12/10/10 2:58am

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@Annalee Newitz: wasn't it a double rainbow?

dgoat Annalee Newitz12/10/10 11:22am

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@Annalee Newitz: It means you probably shouldn't eat any of the vegetables

in your garden, now.

Jason Callina Annalee Newitz12/10/10 11:26am

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@Annalee Newitz: That you should move out of Massachusetts. ;)

crosis101 Alasdair Wilkins12/09/10 4:43pm

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But what if you had a color that only created a response in themedium wavelengths? In real life, this can't happen, as anythingthat excites the medium wavelengths is going to excite one orboth of the other wavelengths. But if you did have a color thatonly excited the medium, green wavelengths while leave theother two types alone, then you'd be able to see a color greenerthan any real green.

isn't this the definition of a Laser?

icelight crosis10112/09/10 5:00pm

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@crosis101: No. Even a pure green laser will still activated the red and blue

cones, just to a very low degree.

John Forsberg crosis10112/09/10 5:22pm

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@crosis101: No, because the green laser will still excite the short and long

wavelength receptors to some degree (as their absorption ranges stretch into

green).

Alternatively (as he mentioned), by tiring out the long or short wavelength

receptors (or are they down­regulated?), the middle wavelength receptor

signaling appears that much stronger, you can produce a perception of

ultra­vivid green.

Prismatist crosis10112/15/10 5:33pm

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@crosis101: To elaborate on icelight's note:

Even though a Laser does produce a pure wavelength, it's the eye's response

to that wavelength that we're talking about here. Every wavelength excites

the three receptor types differently, and our brain interprets the ratios and

absolute amplitude of the three signals as the colours and brightnesses that

we see. What your quoted text describes is that you take the neural signal

from the eye and selectively eliminate one or two of the three signal

components. The resulting signal would be interpreted by the brain in a way

that would produce a perceived colour that cannot exist in physical reality.

Prismatist icelight12/15/10 5:34pm

a

@icelight: To elaborate:

Even though a Laser does produce a pure wavelength, it's the eye's response

to that wavelength that we're talking about here. Every wavelength excites

the three receptor types differently, and our brain interprets the ratios and

absolute amplitude of the three signals as the colours and brightnesses that

we see. What the quoted text describes is that you take the neural signal

from the eye and selectively eliminate one or two of the three signal

components. The resulting signal would be interpreted by the brain in a way

that would produce a perceived colour that cannot exist in physical reality.

Reply

8x10 Alasdair Wilkins12/09/10 4:44pm

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Besides a head ache, this is all I got.

Bismod 8x1012/09/10 4:55pm

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@8x10: Same with me, with a hint of neon green that i wouldn't call an

impossible color so much as the effect of opposites next to one another

(unless that's the point). Also, nice visual.

Layn 8x1012/09/10 4:57pm

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@8x10: yep, me too, minus the headache

8x10 Bismod12/09/10 5:14pm

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@Bismod: Photoshop.

Necoras 8x1012/09/10 5:22pm

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@8x10: I get that, but the colors move and shift. Kinda like a weird

screensaver.

GetRevenge32 Alasdair Wilkins12/10/10 12:31am

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Why does everyone say black and white are not colors?! How are they not

colors?... should we only consider pink or gray half colors since they are

being mixed with non colors? It sounds so stupid saying black and white are

not colors.

and if they are not colors then what are they?

GamerKT GetRevenge3212/10/10 1:25am

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@GetRevenge32: Black is a shade. white is a...tint, I believe.

Middle school art class.

Aaron Crabtree GetRevenge3212/10/10 1:45am

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@GetRevenge32: Black means there's so little light reaching your eye that

the optical nerves are not adequately stimulated for your brain to infer a

color. White means there are equal parts of red, green, and blue hitting your

eye ­ or, alternatively, the amplitude (brightness) of the light wave hitting

your eye is high enough that nerves become overstimulated and the brain

stops paying attention to what color it is, as it's more interested in getting

you to stop looking at the bright object.

So, no, they are not colors. A "color" refers to light of a certain wavelength.

There is no "white" wavelength. There is no "black" wavelength.

InnerRayg GetRevenge3212/10/10 1:47am

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@GetRevenge32: Shades.

riser411 GetRevenge3212/10/10 2:22am

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@GetRevenge32: they're tones.

In order for something to be a 'color', it needs to contain basic pigmentation

elements. But obviously, there are things that lack pigmentation yet our eyes

can still 'see' them based on variances in the amount of light something's

surface absorbs. Those variances are called tonality.

See that's what you get for falling asleep in jr. high science and art classes.

hawkingdo Alasdair Wilkins12/09/10 10:21pm

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On the blue yellow test: Really cool effect.

I'm sure everyone process the information differently, but for me it was like

seeing a water pattern that oscillated from the blue and the yellow. No stops

in between, but it just looked like a lake rippling in straight lines changing

the pattern from blue to yellow. Really cool.

hawkingdo hawkingdo12/09/10 10:30pm

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@hahn: As for the red green test: I did that with 2 fullscreen paint images

with 255 Red and 255 Green with 120 Luminosity.

It wasn't as intense. The red looked more pink and the green looked more ...

I don't know "forest­ish" I guess.

hdgotham Alasdair Wilkins12/09/10 4:48pm

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Load More

I see very muddy green, that was too blue, but also too yellow. It also kept

shifting as each eye tried to make one image go 'on top' of the other.

Make sense?

More than impossible colors, I'm fascinated by the question ­ when other

people see the color blue, do they see the same color I do?

BioLady is bored with her name hdgotham12/09/10 4:55pm

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@hdgotham (Hannah Wilson): haha. you must be smoking pot in your

college dorm right now. Far out, man.

hdgotham BioLady is bored with her name12/09/10 4:57pm

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@BioLady: This is me without pot. With pot.... well... that's a whole other

thing.

DasStan hdgotham12/09/10 5:10pm

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@hdgotham (Hannah Wilson): I love playing that thought experiment.

"What if my [color/concept/thought proccess here] is different than that

persons?"

Mr.CardHolder and Mr.Doe hdgotham12/09/10 5:40pm

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@hdgotham (Hannah Wilson): i have always wondered about that. i mean

you could perceive reality differently from everyone else, but you would

never know it. cant really hop to a new body to try it out.

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