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Posted by moultano 15 hours ago

Where to Find the Colors Your Screen Can't Show You(moultano.wordpress.com)
357 points | 90 commentspage 2
ricardobeat 2 hours ago|
Many modern triple-laser projectors can reproduce or exceed the Rec. 2020 color space. It's still not full coverage but much larger than P3.
zahlman 2 hours ago|
Couldn't we capture more of it by just using a slightly bluer green phosphor?
orthoxerox 11 hours ago||
ACES AP0 is the only color space I know that is designed to represent all possible visible colors. It's a purely theoretical color space, though. The widest color space designed for actual implementation, Rec. 2020, still can't faithfully show most of the natural greens and cyans, like your green laser pointer.
frotaur 10 hours ago||
Its unclear to me why the color space is 2-dimensional. Why wouldn't it be a 3-dimensional space, indexed by how much each of the 3-cones is activated ? Not clear to me from the article!
SideQuark 9 hours ago||
It is 3 dimensional. That commonly repeated CIE diagram is a 2d slice of the color volume. Since 1931 that diagram is obsolete, misleading, and fails at a lot of modern color science, and has been replaced many times, but is what many people go to. The most recent replacement (well, by CIE), is CIE 2015. Comment on it [1]

Modern color modeling is much richer then 3 parameters, because human vision is much more complex than simply color frequencies. CIE 1931 was low brightness, 2 degree field of vision, center of vision derived. As brightness increases, color perception shifts. Colors are NOT linear; sRGB and CIE 1931 chose such a small section of human vision that they approximate that section with a linear assumption. Modern CIECAM models are not linear, are not 3 parameter, because color is not linear (CIECAM02 is 6 parameter [2], there are several after that one). A century of experiments, wide color gamuts, HDR, have thrown out CIE 1931 as a good model. It’s only momentum now, and slowly higher end things are replacing it.

A good introduction is Color Appearance Models, by Mark Fairchild, also any of his technical papers give a starting point into the science.

[1] https://community.acescentral.com/t/cie-2015-cmfs-what-would...

[2] https://en.wikipedia.org/wiki/CIECAM02

ralfd 3 hours ago||
> CIE 2015

Does that look like 3d?

psd1 10 hours ago|||
It is, inasmuch as we have 3 types of cone, which is an inherent orthogonality. It is also not, inasmuch as each cone is a wavelength in the same spectrum.

Either way, you can project a volume onto a plane, which is great for communicating visual data on paper or screen.

The interesting question is "why that arc in particular"; my ignorance will shine through if I speculate.

I assume that the projection encodes something about our relative perception of each cone's band, hence the big green corner.

carlosjobim 6 hours ago||
It is 3 dimensional, because in our perception we see the third dimension of magentas and purples, which do not exist in physical reality on the spectrum.
isoprophlex 10 hours ago|||
There are three cones, but there is an additional constraint that we plot the colors at maximum summed luminosity. So for one cone you would just have a point; two would show a line from 0% cone A+100% cone B -> 100% cone A; three is a plane
audeyisaacs 10 hours ago|||
>indexed by how much each of the 3-cones is activated

This will actually differ from person to person. If you look at a pure yellow wavelength light next to a red/green light mixed such that they create the exact same perceived yellow to you, it will look different to another person.

Aside from that, not really sure what a 3d view with the dimensions being r,g,b would actually offer

HappyPanacea 10 hours ago||
I guess it is the 2-dimensional section such that it have constant total brightness. You can then multiply later by your desired brightness.
whiw 3 hours ago||
If we had a display with n (n>3) pixel colours, say (red, green, cyan, blue) for example, we could display more of the colour space. Shopping list: 4 colour channel display, 4 channel GPU, 4 channel software. Why isn't this a thing already?
mceachen 2 hours ago|
More than 3 channel displays have been attempted by several companies, but I suspect they fail due to:

1) trying to convince content makers to use new custom high-gamut hardware to capture the new spot colors

2) you'd need a full video content production pipeline that can render to that color space

3) finding enough people to care enough to pay the (substantial) premium for niche production numbers.

4) Most content just doesn't warrant high gamut unless it's narrated by David Attenborough.

So, you have both a chicken and egg problem, and not that big of a TAM to warrant the struggle.

zahlman 2 hours ago||
5) You'd need image formats that record those channels, and that in turn would cause problems for raw bitmaps with alpha (they either get twice as big or the pixels are no longer aligned).
oersted 9 hours ago||
Such a cool article chock-full of cool facts!

> Nearly every species of scorpion intensely fluoresces under UV light. […] Scorpions have photoreceptors in their tails, separate from their eyes. […] It is hypothesized that a scorpion uses this fluorescence to tell whether any bit of its body is left exposed from its hiding place. Its tail “looks” down at its body, and if it sees its own fluorescence, it knows it is exposed to light, and in danger.

And a special call-out to the “Andean Cock-on-a-Rock” :), see a photo in the article.

card_zero 7 hours ago||
My debatable factoid is that all vision is movement-dependent, including human vision, and so the bigness and wonderfulness of the tyrannosaur's eyes is beside the point of whether it needed its prey to move around in order to perceive it.

https://en.wikipedia.org/wiki/Stabilized_images , https://en.wikipedia.org/wiki/Fixation_(visual) , https://en.wikipedia.org/wiki/Microsaccade

We fake the movement of anything we're staring at, by means of tiny automatic eye movements, in order to remain able to see the thing at all.

pcrh 5 hours ago||
Very well-written!

I wonder if the inaccurate representation of colors by screens, etc, in any way underlies the distinctive color palette of many AI image generators?

Sophira 11 hours ago||
That was incredibly well-explained. Kudos.

I do have a question that the article doesn't seem to attempt to answer, though. The article says (paraphrased in my new understanding) that any spectra which makes the cones in your eyes react the same way will result in seeing the same colour. Do we know of any examples of this?

(Colour-blindness seems like an obvious example; I'm curious though if there are any examples of two common scenarios where it can be demonstrated that there are different spectra in each, and yet most people will see them as the same colour.)

grumbelbart2 11 hours ago||
This is called metamerism. It can be a practical issue if two pigments have the same color under one light source, but a different one under another. You want your artificial teeth to have the same color as your real teeth in sunlight, led light, and a classic lightbulb for example.
clort 9 hours ago||
Well, now that you mention it, I'd just like to remind you that people are a lot weirder than you might think! Having incisors to be a different colour (say, a brilliant red) under artificial lights could definitely be a thing people desired..
317070 11 hours ago|||
A flower, a picture of the flower in print and the picture shown on a screen will all have different spectra, but look the same.

See the first minutes of this video, where he has a spectrum analyser: https://youtu.be/-DyrBDsKA5s?si=mRJPT2ecy6NqpB4N

Sophira 10 hours ago||
That video was super interesting, thank you!
frotaur 11 hours ago|||
Well, the most common example si precisely screens, no? A screen displaying the color yellow is actually a spectrum of red and green peaks, stimulating your red and green cones just like a spectrum containing a single frequency of the color yellow.
Sophira 10 hours ago||
Oh right. I feel silly for forgetting about that even though it's mentioned in the article. Thank you!
somat 11 hours ago||
Would not the definitive answer to this be a computer screen.

On one side you have an apple, illuminated by natural sunlight. it fills your eye with a rich texture of subtly mixed frequency's covering the whole gamut of visible and invisible light. On the other a picture of an apple composed of brutal pure frequencies only emitting at 430, 540, 570 Nm. Can you tell the difference?

Sophira 10 hours ago||
That makes sense. I feel a little silly that that's not something I considered despite the article saying exactly that. I think I got caught up in the details.
subscribed 4 hours ago||
No, no, the question was great. I read all the answers carefully and I feel a bit smarter now. Thanks for asking it!
divvsaxena 4 hours ago||
Reading this made me realize how much of my day is spent looking at screens. It's weird to think there are colors in the world that I've technically seen before, but have never actually been able to capture or reproduce digitally.
arbourtrary 9 hours ago|
Very well written, super interesting topic. I never understood all these natural reasons why real life colors feel so much more vivid. I guess when I look outside of the rgb triangle in the graphic, the cyans/blues/greens shown (since I'm seeing this on a screen) are sort of shadow colors? Approximations without the full vibrancy?
Macha 3 minutes ago|
> I guess when I look outside of the rgb triangle in the graphic, the cyans/blues/greens shown (since I'm seeing this on a screen) are sort of shadow colors? Approximations without the full vibrancy?

So there's 3 options you have for rendering the colours outside the sRGB space in this kind of image.

1. Don't. This is usually the most honest, and what all but the first diagram in this article opts for.

2. Clamping. You just set the green component to 255 for every colour beyond green=255, which effectively looks like you extend the edges of the triangle to the edge of the visual range. This is the most common, and the approach used in the article's first image, but it's basically a lie. Some articles will dumb the out of range colors to make it clear they're not the real colour, but this article's first image doesn't.

3. HDR: If the author uses an image format capable of decoding HDR data, and your browser, OS and monitor, and the author's authoring pipeline are all correctly configured to pass through that HDR data, you can get a bit more colour, depending on your monitor. Not the full visible gamut, but up to whatever colorspace your monitor is using.

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