While it is true that some saturated blue-green colors will never be reproducible with only 3 primary colors, the CIE 1931 chromaticity diagram used in TFA overemphasizes their importance, because human vision cannot distinguish many colors in that area of the diagram.
In reality, the greatest defect of the sRGB color space, which is still too frequently the default color space, is that it is not able to reproduce many saturated orange/red/purple colors, which are very frequently encountered around us, e.g. in flowers, fruits and clothes.
The missing orange-red-purple corner appears small in the diagram in comparison with the missing blue-green corner, but in reality humans perceive much more different colors in the orange/red/purple corner, so the relation between those areas would be opposite in a uniform color space.
The Display P3 color space is much better than sRGB for reproducing orange/red/purple colors and now it is available even in many cheap monitors. However many monitors that can reproduce Display P3 come configured by default to use just sRGB. Such monitors should always be reconfigured to use Display P3.
Monitors that can reproduce an even greater part of the Rec. 2020 color space are obviously better than those that can do only Display P3, but such monitors with a higher color gamut are usually more expensive.
I took up acrylics painting a few years back and I've been surprised by how much is lost in photos and videos. The two colors with which I've noticed this the most are ultramarine blue and prussian blue. I don't think it's just the color though, part of it comes down to how light is reflected off the painting and where you're standing, as well as the texture and the brush strokes. I have a few paintings hanging in my room and occasionally I'll look at them for a while and it'll reveal a new perspective to me that I had previously missed, despite being the one who made it.
This post is making me feel a bit inspired to go outside and immerse myself in the forest to take in the greens. Thanks for sharing.
Really nice article, I'll look closer to green lights next time I see one.
The most striking experience I had was working with a blue laser (430nm). The best way I found to describe its color is that it was screaming "blue" at me. Since then, I'm always disappointed when looking at a screen displaying #0000FF.
"This is a good time to spare a thought for our red-green colorblind brethren. [...] it is to them that we owe the beautiful color of green traffic lights. The spectral requirements that make the green signals distinguishable from red in their eyes make them beautiful in ours."
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.
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!
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.)
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?
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.
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.
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.
Ultramarine pigment is too blue for your screen to replicate properly, for example. I don't know if there's a pigment that reflects only 520nm light, though.
What an truly incredible article, particularly the way the color space diagrams are used to gradually tell the story (and the prose is great too). I actually want to read it again tomorrow morning in more depth.
While it is true that some saturated blue-green colors will never be reproducible with only 3 primary colors, the CIE 1931 chromaticity diagram used in TFA overemphasizes their importance, because human vision cannot distinguish many colors in that area of the diagram.
In reality, the greatest defect of the sRGB color space, which is still too frequently the default color space, is that it is not able to reproduce many saturated orange/red/purple colors, which are very frequently encountered around us, e.g. in flowers, fruits and clothes.
The missing orange-red-purple corner appears small in the diagram in comparison with the missing blue-green corner, but in reality humans perceive much more different colors in the orange/red/purple corner, so the relation between those areas would be opposite in a uniform color space.
The Display P3 color space is much better than sRGB for reproducing orange/red/purple colors and now it is available even in many cheap monitors. However many monitors that can reproduce Display P3 come configured by default to use just sRGB. Such monitors should always be reconfigured to use Display P3.
Monitors that can reproduce an even greater part of the Rec. 2020 color space are obviously better than those that can do only Display P3, but such monitors with a higher color gamut are usually more expensive.
I took up acrylics painting a few years back and I've been surprised by how much is lost in photos and videos. The two colors with which I've noticed this the most are ultramarine blue and prussian blue. I don't think it's just the color though, part of it comes down to how light is reflected off the painting and where you're standing, as well as the texture and the brush strokes. I have a few paintings hanging in my room and occasionally I'll look at them for a while and it'll reveal a new perspective to me that I had previously missed, despite being the one who made it.
This post is making me feel a bit inspired to go outside and immerse myself in the forest to take in the greens. Thanks for sharing.
Really nice article, I'll look closer to green lights next time I see one.
The most striking experience I had was working with a blue laser (430nm). The best way I found to describe its color is that it was screaming "blue" at me. Since then, I'm always disappointed when looking at a screen displaying #0000FF.
"This is a good time to spare a thought for our red-green colorblind brethren. [...] it is to them that we owe the beautiful color of green traffic lights. The spectral requirements that make the green signals distinguishable from red in their eyes make them beautiful in ours."
Sounds like we need the next VR glasses to shine colorful lasers into our eyes instead of screens.
"Destroy them with lasers!" https://youtu.be/u6-U-apEUZI
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.
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!
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.)
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
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?
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.
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.
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.
Oh right. I feel silly for forgetting about that even though it's mentioned in the article. Thank you!
Off topic, but the other articles are well made too. I enjoyed this one: https://moultano.wordpress.com/2025/02/24/you-should-make-cr...
Can these colours be replicated or captured using ink, paint or traditional film photography?
Ultramarine pigment is too blue for your screen to replicate properly, for example. I don't know if there's a pigment that reflects only 520nm light, though.
What an truly incredible article, particularly the way the color space diagrams are used to gradually tell the story (and the prose is great too). I actually want to read it again tomorrow morning in more depth.
Tl;dr.... It's LSD.