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Impossible Colors (wikipedia.org)
80 points by arseny-n on Sept 3, 2020 | hide | past | favorite | 51 comments

I've used this as an example of (non)-vector spaces in a linear algebra class before. Light perception is based off the stimulation of three color cones, so three (positive) values. The light available to us stimulates those cones in certain ways and three light colors are enough to form a "basis" of the space of perceived colors. But the fact that the values are always non-negative means that there are possible cone-stimulation values that are never achievable by our light.

However, super-saturating your eyes with a color and then removing the stimulus effectively allows you to also "subtract" out some light and therefore reach parts of the perceivable-color-spectrum otherwise unobtainable.

I thought it was a clever application but my students didn't seem too impressed!

It's interesting to think you've almost certainly then impressed more people with this knowledge just posting it online here.

Thanks for sharing, what a neat thing!

That is pretty dope. In my experience, in all the time I’ve been in school, most people seem unimpressed with most of what is presented. I personally try to be effusive and give the teacher or presenter feedback so they have some inkling that they’re lighting up at least a couple of neurons in my brain.

I feel like my appreciation for linear algebra really came after a year or two after I finished lin alg in college :P

If you have a VR headset, I recommend playing around with showing different colors to either eye. You can get some really nice iridescent effects, very hard to achieve in real life and impossible on flat screen (well, you can cheat a bit by doing a cross-eye 3D image). Be sure to try both complementary and analogous colours and put iridescent objects into ordinarily looking environment, if you simply change colour balance on one eye camera the effect will be too unpleasant.

Oh man, I've wanted to do something like this for a while, but I didn't know the software to do it had already been written, and also I don't have a VR headset.

So you can have it render an object which shows different colors to different eyes, while rendering the rest of the scene normally?

What software supports this?

I used old version of Unity (5.4? maybe even older) and tested it on both Google Cardboard and Oculus CV1. It used to have separate cameras for left and right eye. Unity has a system of layers and every camera has a bitmask that defines which layers are rendered by it. So I simply left environment on default layer rendered by both cameras, put one copy of an object on 'Left' layer and another copy with different material on 'Right' layer. Worked really nice for "vampire" eyes (specifically irises) rendering.

Few years ago they switched to single pass stereo rendering to avoid rendering whole scene twice. In theory this legacy option to use two cameras is still there, but quick googling says that it has some issues on modern Oculus SDK's and new Unity render pipelines but workarounds are possible.




That's exactly my problem as well. I have GearVR headset which fits seversal Samsung smartphones and it's really nice to play around (and it's cheap), but the only piece of software written for WebVR is Three.js module, which doesn't allow different scene presentation to each eye.

But maybe I'll get back to work on my hack. Some suggestions are here: https://stackoverflow.com/questions/53775620/webvr-update-sc...

I used Unity's layers system (more on that in sibling comment: https://news.ycombinator.com/item?id=24367460).

I have zero experience with WebVR, but solution you linked seems sensible.

> If you have a VR headset, I recommend playing around with showing different colors to either eye.

Do you have any idea how to do this? I was trying to hack Three.js to enable binocular presentation (I have only Gear VR headset for my Samsung smartphone), but I wasn't able to do it. And as far as I'm concerned it's the only library providing WebWR functionality.

what VR setup would you recommend for someone without any? I've got a ps4. I don't want to overspend on deprecated / imminently-obsolete gear, but would love to experience it at home. is there a sweet spot beyond "toy" level but short of $$$$?

If you are fine with Facebook then Oculus Quest is the sweet spot at the moment. It does not have photorealistic rendering like PC-based VR but it is self-contained, does not need a PC but can be connected to a PC to play PCVR titles, has solid library on its own and being wireless is huge advantage. There are strong rumours that they will announce new Quest model on September 16th at base price of 299$ - but do not quote me on that.

I'd avoid PSVR, it is obsolete in 2020.

For Occulus, you have to be fine being forced to log-in with your Facebook account to use it and giving FB a direct access to cameras + mics (+ a total access to anything on your PC with the Rift)

Given their total lack of ethics, I don't think Facebook deserves our $$$. But it's true that the Oculus price is attractive (as with everything where we pay with our privacy)

what about the valve index? Oculus' facebook connection makes it flat out not in consideration for me

The index is great, honestly. The knuckle controllers are fantastic (though there's some issues with the surface mounted joysticks not having great longevity), the HMD is fantastic, and the support seems pretty top notch (bad controllers being RMI'd).

The biggest thing seems to be the long lead times between ordering and arrival.

It is top of the line, but definitely in "$$$$" category. Personally, I've grown to dislike wired VR and cannot go back to it even though it has many advantages.

I've been eyeing ;) the HP Reverb 2 (G2 generation 2) which has one of the highest resolutions per eye of any headset.

I have Oculus CV1 and might upgrade to the Reverb this holiday season for the resolution.

I'd recommend finding something used cheap on ebay. If you decide that you like VR and actually use it you can always upgrade to something better. Mine only ever saw minimal use and I never bothered to set up the sensors in my current place the last time I moved.

You might just grab a used PSVR; it is somewhat obsolete technically, but you can’t beat the price.

Something this reminds me of is the mccollugh effect.

WARNING: the following link contains a literal infohazard basalisk image that if stared at for a few minutes will alter your color perception for a significant period of time - potentially months. It is not behind a spoiler, which would be against the rules on English Wikipedia


I induced this effect in me on 17th April (just checked my browser history for exact date) using instruction given in this wiki article and I can still clearly see test bars as red and green, over 4.5 months later, it is incredible.

How long did you look at it?

Hard to remember exactly but it was a few minutes per image. I repeated it a couple times over the day because I was fascinated by it. I'd say 30 minutes per image over 12 hours.

>It is not behind a spoiler, which would be against the rules on English Wikipedia

On the desktop site it has a spoiler box saying, "Show at your own risk."

That's funny. It didn't for years up to at least a month ago or so and also doesn't seem to on mobile now for me, but I didn't check it on desktop before posting the comment!

Edit: it was hidden Aug 16th[1] but previously hiding it has been reverted[2][3][4] for at least 2 years per WP:DISC[5]

[1]: https://en.wikipedia.org/w/index.php?title=McCollough_effect... [2]: https://en.wikipedia.org/w/index.php?title=McCollough_effect... [3]: https://en.wikipedia.org/w/index.php?title=McCollough_effect... [4]: https://en.wikipedia.org/w/index.php?title=McCollough_effect... [5]: https://en.wikipedia.org/wiki/Wikipedia:Content_disclaimer

Desktop link: https://en.wikipedia.org/wiki/McCollough_effect

the OP is the mobile site

Note: just glancing at the images will not do anything - you have to prime your perception by looking at them alternatively for some minutes.

This held true for me. I tried staring at the red and green ones alternating every few seconds for a minute or so before I got bored. After a few times I started seeing what I can best describe as shadows of green horizontal bars when looking at the red image.

I was rather disappointed.

> a literal infohazard basalisk image that if stared at for a few minutes will alter your color perception for a significant period of time - potentially months

That's really scary! It's like looking at the sun.

This might be going off-tangent but I really find things like this fascinating! Reminds me of the Motif of Harmful Sensation[1], one of those tropes that sound fantastical and absurd even in fiction but is actually in real life.

[1] http://www.artandpopularculture.com/Motif_of_harmful_sensati... (Not TVTropes, because I also consider TVTropes as "harmful sensation".)

I am reminded of the "Pokémon Shock"[0] incident in 1997 that triggered epileptic seizures in a number of viewers, resulting in 685 people requiring medical attention.

[0] https://en.wikipedia.org/wiki/Denn%C5%8D_Senshi_Porygon

Thank you for the link, I've tried to look up the trope of "sound/video that kills/makes one go insane" on TVtrope but I haven't been able to find it. It's also strange that there isn't a wikipedia article about it. It's relatively common in movies and literature.

Real life SCP

Fyi on a semi-related topic I learned from a fascinating Youtube video... the color "brown" is a psychological construct[0]. But from an RGB perspective ... there's no such color as "brown"; it's actually just "orange" in a particular context: https://www.youtube.com/watch?v=wh4aWZRtTwU

[0] pedantic alert: yes "every color" is ultimately a mental construct of the brain but hopefully you know what I mean

This is based on the simplistic view that hue equals color. Modern perceptual color models like CIECAM02 define "color" through a much larger number of influences.

Ah yes. Hacker News' daily reference to Alec from Technology Connections. I enjoy his orange with context.

As neuroscience advances, what is the likelihood of truly novel color experiences?

I don't mean discerning ever finer gradations in existing colors, but entirely new color qualia.

What would it be like? Would our brains be able to integrate this new phenomenal experience?

And most importantly, if color is a property of brains rather than something in the external world, does that imply the number of "possible colors" is infinite? I.e. seeing as biological brains "choose" how to internally represent a particular wavelength of EM radiation, is the seemingly Platonic realm from which these colors are plucked from inexhaustible?

We currently have aesthetic preferences over existing colors. I would want to know whether these possible colors can be enumerated, searched through, and have a utility function placed over them so that each human can find what is to them "the best possible color."

> As neuroscience advances, what is the likelihood of truly novel color experiences?

No need for neurosciences, just some fancy spectral filters like those on IMAX 3D glasses. With some practice using these glasses you can experience a six-dimensional color space. When you remove your glasses, this six-dimensional space collapses into the common three-dimensional color space. But with the glasses, you can distinguish many different colors that look exactly the same to regular humans. That white wall? It looks a perfectly uniform white to most people, but you can see clearly that two very different kinds of white have been used here and there.

A similar effect can be obtained indoors by lighting objects with monochromatic lights, but it is not as dramatic as with glasses.

I used to work in highway paving, and I learned how to tell the temp of asphalt with polarized sunglasses. It's not the same as a truly novel color experience but its a neat party trick

You probably can create some novel color experiences, by gazing at color sequences animations.

Warning epileptic risk, experiment at your own risk.

You have some led or screen smoothly changing periodically.

Train your brain to discriminate between the two following sequences.

Going from red to green to blue to red. (Species A) Going from red to blue to green to red. (Species B)

You have to pick the right frequency (i.e. ~10-20hz) fast enough so that your brain sees it as a single unit without thinking about it, but slow enough that is still able to pick some differences.

You can gamify it for example on a screen you can watch color-changing moving balls. And you have to pick one subspecies only.

You can then extend this little game to train your brain to "see" various color rotations (aka rotating a color sphere). It's kind of like learning music. Construct some structure programmatically, then gaze at it until your brain intuitively grasp the underlying structure.

You can also play with the difference of temporal phase if you have some vr-headset you can have a 6D color space input, which you can use to train your brain to visualize 4d rotations, and rotations in higher dimensions spaces which will probably be useful for visualizing QCD intuitively.

If you have the time to train your brain for it you can construct a rotating color based language like you would with music. If you sync-it up to music it can help the learning process by doing some kind of joint training between audio and visual space.

See also: "Martian Colors: What Does A Colorblind Synesthete See?"


>We also observed one case in which we believe cross activation enables a colorblind synesthete to see numbers tinged with hues he otherwise cannot perceive; charmingly, he refers to these as "Martian colors."

There is nothing truly infinite about human brains - while we don't know how to express it, unless you believe in non-physical minds, there will be physical limits to what the mind can do.

In fact, if the mind color space were actually infinite, it would be essentially impossible that any two organisms would share color perceptions, while in reality we share even the impossible colors.

the comment you're responding to is referring to qualia, and there is no evidence (Occam's razor doesn't count) that these are shared at all.

I highly recommend this Captain Disillusion video about color if you want to learn more about color theory: https://youtu.be/FTKP0Y9MVus

You may have to watch the video multiple times though, because the information comes out of a firehouse.

My favorite ever "Impossible Color" illusion:

Eclipse of Titan


Don't miss the link down the bottom - https://en.wikipedia.org/wiki/Tetrachromacy - human perception of colour varies wildly between different people. Basically the opposite of colour blindness.

Can anyone see "yellow-blue" as mentioned in the article? When I try, it just cycles (although not discretely) between yellow and blue.

Try it when you are really tired, and or after having some good sativa, if that is safe and appropriate for you.

I find my mind extremely receptive to these sorts of things when I'm very tired on the edge of sleep.

A good sativa actually opens up quite a bit of pattern recognition and other subtle visual perceptions. One example I can think of is a cardboard box that actually has the manufacturer's logo lightly embossed. You can't really see it at least I never did. But one evening after a good meal and the sativa, I looked at that box and could totally see the subtle difference in the circle for the carport. Interesting lie, I have remained able to see it. Like a little doorway opened.

Past edit time error correction:

>looked at that box and could totally see the subtle difference in the surface of the cardboard. Interestingly, I have remained able to see it.

I saw it as a gradient from left to right, or centre out (radial). I also saw it cycling like you, as if the colours were two planes and one kept shifting behind the other whenever I blinked.

I didn't really perceive it as a "new" colour though.

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