24 ms·

What is a color space?

265 points by vinhnx 1y ago

evaXhill 1y ago
Really great introductory article on color space in general, I really appreciate that they touched on perceptual uniformity and how we all perceive colors differently. It’s great to find out that applications like Oklab came out recently to fix this by manipulating the distances between colors to try compensate for human perception while also being more straightforward to calculate so that it can be used in real-time applications. Also the UI of this blog post was so aesthetically pleasing, that it was worth burning my retinas with the light mode
JKCalhoun 1y ago
What an excellent article. I can't think of anything (except the very esoteric) that it did not cover. If I had to criticize, I wish it had talked a bit more about printer color profiles (although in this paperless, web-world we live in, perhaps printing is in fact esoteric). Unlike displays, a printer can't be simply defined with three primaries and a white point. Printer profiles can be quite large as they rely on someone having printed out a copious number of swatches on a given paper type and then measured (with some kind of colorimeter) device independent color values for each swatch. Those are used to build a large table for mapping from device independent color spaces to the printer's gamut. Those large tables make the profile so large. And then of course interpolation is still required when mapping from a device independent color space to the printer profile. (Now imagine too that you need a different profile for each type of paper you might want to print to since each can represent color differently — plain paper unable to get the levels of saturation that a coated paper can.) What was shocking to me was just how small the gamut of a printer typically is when seen alongside that of a decent display. Consider that, in print, you'll never see an image as vivid as you can display on a nice, modern display. (And then consider that there are colors in nature so vivid that even a modern display cannot represent them. Just look at how much color is outside the triangle on the CIE "shark fin" color representation.) Also not touched on (did I miss it?), all the math presented to map from one color space to another, also allows for "soft proofing" — where in fact you might match to a printer ICC profile but then take the result and match again to the user's display to give you a "preview" of what will be lost when going to said printer.
- pessimizer 1y ago
  > What was shocking to me was just how small the gamut of a printer typically is when seen alongside that of a decent display. What was a nightmare for me when I worked in prepress was how hard it is to get a convincing purple out of a $20K printer. I used tricks which basically produced nothing like purple in a way that gave customers a good purple impression because the things with a closer actual resemblance to purple always looked awful.
  - monster_truck 1y ago
    One of the tricks we used in situations that allowed it was to get paper that matched the most important color, this has other downsides but they are more manageable. They were always the last run before everything was taken apart and cleaned for maitenance.
  - fidotron 1y ago
    Purple and orange were/are common spot colours for that reason. My father used to work on all sorts of R&D involving things like how much K to use in substitution of CMY without getting desaturated etc. It's a real rabbit hole, especially if you want to reduce the amount of ink used to prevent soaking the paper.
- jimnotgym 1y ago
  That reminded me of a time when a printer manufacturer approached my old team with this problem. They needed a custom driver for a certain region of the world. In this region in a certain industry they liked the highly saturated 'bad' colours from a competitor, and wanted theirs to match. Much paper and ink was spent on this.
- bsoles 1y ago
  Not all people see colors the same. The section on "What is color?" could probably mention color blindness.
  - ChrisMarshallNY 1y ago
ChrisMarshallNY 1y ago
That's a terrific article! I spent the majority of my career at an optical equipment manufacturer, and we wrote a color management system to handle 48-bit color, before any OS manufacturers had it. Non-trivial stuff, but powerful. I know of at least one technology that works by converting to an esoteric color space, messing with image data there, then converting back.
- jimnotgym 1y ago
  Indeed... and it was always a huge amount of fun to find that converting from one space to another was not always reversible without distortion!
rylan-talerico 1y ago
Such a great read
tuzemec 1y ago
Such an amazing article. Hope the author continues with the rest of the content in the same manner.
jimnotgym 1y ago
This is a great primer. I used to work in this field, but not as a colour scientist. > So why do we have so many different color spaces? I think there was a missing piece here. Different representations of colour are useful for different things. I'm not going to give any secrets away but...if your trade involves finding out how close one colour is to another, then something that represents colours as points in space could make the maths easier. Then if you wanted to know if one colour was brighter than another, then something that represents a colour with a separate 'brightness factor' would make that trivial.
- gopher_space 1y ago
  We were big fans of Marti’s LCMS.
  - jimnotgym 1y ago
    I can't remember the technical reason we didn't use it...we mostly rolled our own. We were very lucky to have someone who knew how!
    - gopher_space 1y ago
      IIRC the licensing was restrictive for commercial use but it's been a long time. I think we ended up throwing him a few grand for a different license, an option I'd never considered before and one that's stuck with me.
- deadvoid 1y ago
  as post production guy living outside US/EU, a decade or so ago i was surprised that colorimeter was supposed to be regularly calibrated by another, more expensive, device.
  - jimnotgym 1y ago
    I think that depends on what you mean by 'supposed to'. I don't recall this being suggested for normal applications, and if you have a very tight specification then a colorimeter may not be the correct instrument in the first place. As I said above, I'm not a colour scientist, but I do know something about what was done in practice in certain industries.
furyofantares 1y ago
I love that this opens with a matter-of-fact statement that colors aren't real, just a phenomenon of perception. This has come up randomly in my life a few times and people always look at me like I'm stoned outta my mind.
- meindnoch 1y ago
  And what is not just a phenomenon of perception?
  - matsemann 1y ago
    Mathematical proofs based upon axioms?
  - magicalhippo 1y ago
    The light hitting our eyes is not a phenomenon of perception. Each photon hitting our eyes has a certain wavelength, but the resulting color we see is a perception. A related concept is sound vs psychoacoustics[1]. Sound is just pressure waves, but what we hear is a perception and has all sorts of aspects like masking[2]. The pressure waves contains two different signals but thanks to masking we might only perceive one. Personally I think color constancy[3] really drives home that color is a perception and not something fundamental like the wavelength of photons. [1]: https://en.wikipedia.org/wiki/Psychoacoustics https://en.wikipedia.org/wiki/Psychoacoustics [2]: https://en.wikipedia.org/wiki/Auditory_masking https://en.wikipedia.org/wiki/Auditory_masking [3]: https://en.wikipedia.org/wiki/Color_constancy https://en.wikipedia.org/wiki/Color_constancy
  - Daub 1y ago
    The association of specific wavelengths to hue exists only in our perception, nowhere else. On the other hand, we perceive temperature yet its impact on the physical world is universal.
- AlienRobot 1y ago
  Fun fact: just like people have different heights, they have different perceptions of color!
AlienRobot 1y ago
This is a great article about the topic! It covers everything. But can someone explain this to me? >Light is technically something called electromagnetic radiation and it has a frequency and wavelength. That wavelength can vary, depending on the energy of the wave. High energy waves have a higher frequency and shorter wavelength, and low energy waves have a lower frequency and longer wavelength. >This means that the same amount of energy at different wavelengths will not be perceived as the same brightness. For example, a light with a wavelength of 555 nm (green) will appear brighter than a light with a wavelength of 450 nm (blue) even if they have the same energy. The article asserts that the wavelength (thus color) changes with the amount of energy, but then it says that you can have light of different wavelengths (color) with "the same energy."
- moefh 1y ago
  The amount of energy in a wave depends on both its wavelength and amplitude. So a "blue wave" has more energy than a "red wave" if both have the same amplitude (blue has a shorter wavelength, and energy is inversely proportional to wavelength). But you can have a "blue wave" with the same energy as a "red wave" if you increase the amplitude of the "red wave" to compensate for its longer wavelength.
  - AlienRobot 1y ago
    Oh, that makes sense! Thanks. So that means blue has more energy because it pulsates faster, and in spite of this we're less sensitive to it than we are to red, which pulsates slower. It's like our light sensitivity forms some sort of bell curve.
- SideQuark 1y ago
  He confuses two different places there is energy. Light is made (this is a little bit of a cheat) of photons. Each photon has a wavelength λ, and a per photon energy E where E = hc/λ, h is Plank's constant and c is the speed of light constant. So energy and wavelength per photon completely determines each other (and the color of the light of that single photon). These energies are very small. You can add a lot of photons per second, increasing the brightness of that color, and this now has the energy per second of all those photons. So you can have a lot of red photons which sum to some energy, or a different number of blue photons that sums to (very, very close) the total red energy. These are the two energies he confuses in those two places.
anfractuosity 1y ago
Nice article, I came across very cool Python library recently too re. colour science - https://www.colour-science.org/ https://www.colour-science.org/ Just started playing with it with my spectrometer based on one of the examples they have, to convert spectral data to a single RGB value.
- kelsolaar 1y ago
  Awesome! Maintainer here :) We have a companion repo that might be of interest to you: https://github.com/colour-science/colour-specio https://github.com/colour-science/colour-specio
  - anfractuosity 1y ago
    Cool, thanks for the heads up!
Daub 1y ago
A very clear article, written in very accessible language. One potentially relevant thing not covered is the existence of super blacks and super whites, values which (as a budding vfx artist) I often need to consider. These are values which exist in the abstract sence, but not in the perceptual sence. Specifically, values darker than black and lighter than white. They are as good a demonstration as any of the notional nature of color spaces.
- bookofjoe 1y ago
  Vantablack https://en.wikipedia.org/wiki/Vantablack https://en.wikipedia.org/wiki/Vantablack
lettergram 1y ago
One crazy thing you can do with color spaces is dramatically improve detection algorithms and store massive data. https://austingwalters.com/chromatags/ https://austingwalters.com/chromatags/ Think of it this way, a QR code is binary. If you modify color spaces correctly you can get 6 bits (or more) per pixel. In addition, you can improve the detection at distance, localization for robots, and speed (120 fps). Done this to great effect previously and you can do a lot of awesome things with it. Pretty much the easiest hack in computer vision.
chadcmulligan 1y ago
There's a nice YouTube video that covers a bit of the history of colour spaces to I was watching yesterday https://youtu.be/7KYwi2F5Ce4?si=DUxIWDe_SEjwhdeI https://youtu.be/7KYwi2F5Ce4?si=DUxIWDe_SEjwhdeI
yogrish 1y ago
Recently saw this useful video on colors https://aeon.co/videos/after-centuries-of-trying-weve-yet-to-arrive-at-a-perfect-way-to-map-colour https://aeon.co/videos/after-centuries-of-trying-weve-yet-to...
quix0te 1y ago
Great read and excellent website. Is there a specific name for this web design style? I would have liked to see more websites like this or similar ones for inspiration.
adornKey 1y ago
The article skipped a bit on explaining the CIE-XYZ space. Although it is quite simple. There is one axis Grayscale - that gives you the Brightess value. You can use that for black/white TV. Now for colour you have 2 dimensions left. For these you pick one axis, where the eye is most sensitive - and perpendicular to that you have one axis, where the eye is least sensitive. This colour space is the oldest and all axis there make sense. You can easily compare brightness, and you e.g. can assign more bandwidth to the sensitive colour axis if you want.

265 points by vinhnx 1y ago

Really great introductory article on color space in general, I really appreciate that they touched on perceptual uniformity and how we all perceive colors differently. It’s great to find out that applications like Oklab came out recently to fix this by manipulating the distances between colors to try compensate for human perception while also being more straightforward to calculate so that it can be used in real-time applications. Also the UI of this blog post was so aesthetically pleasing, that it was worth burning my retinas with the light mode

JKCalhoun 1y ago

What an excellent article. I can't think of anything (except the very esoteric) that it did not cover. If I had to criticize, I wish it had talked a bit more about printer color profiles (although in this paperless, web-world we live in, perhaps printing is in fact esoteric). Unlike displays, a printer can't be simply defined with three primaries and a white point. Printer profiles can be quite large as they rely on someone having printed out a copious number of swatches on a given paper type and then measured (with some kind of colorimeter) device independent color values for each swatch. Those are used to build a large table for mapping from device independent color spaces to the printer's gamut. Those large tables make the profile so large. And then of course interpolation is still required when mapping from a device independent color space to the printer profile. (Now imagine too that you need a different profile for each type of paper you might want to print to since each can represent color differently — plain paper unable to get the levels of saturation that a coated paper can.) What was shocking to me was just how small the gamut of a printer typically is when seen alongside that of a decent display. Consider that, in print, you'll never see an image as vivid as you can display on a nice, modern display. (And then consider that there are colors in nature so vivid that even a modern display cannot represent them. Just look at how much color is outside the triangle on the CIE "shark fin" color representation.) Also not touched on (did I miss it?), all the math presented to map from one color space to another, also allows for "soft proofing" — where in fact you might match to a printer ICC profile but then take the result and match again to the user's display to give you a "preview" of what will be lost when going to said printer.

pessimizer 1y ago
> What was shocking to me was just how small the gamut of a printer typically is when seen alongside that of a decent display. What was a nightmare for me when I worked in prepress was how hard it is to get a convincing purple out of a $20K printer. I used tricks which basically produced nothing like purple in a way that gave customers a good purple impression because the things with a closer actual resemblance to purple always looked awful.
- monster_truck 1y ago
  One of the tricks we used in situations that allowed it was to get paper that matched the most important color, this has other downsides but they are more manageable. They were always the last run before everything was taken apart and cleaned for maitenance.
- fidotron 1y ago
  Purple and orange were/are common spot colours for that reason. My father used to work on all sorts of R&D involving things like how much K to use in substitution of CMY without getting desaturated etc. It's a real rabbit hole, especially if you want to reduce the amount of ink used to prevent soaking the paper.
jimnotgym 1y ago
That reminded me of a time when a printer manufacturer approached my old team with this problem. They needed a custom driver for a certain region of the world. In this region in a certain industry they liked the highly saturated 'bad' colours from a competitor, and wanted theirs to match. Much paper and ink was spent on this.
bsoles 1y ago
Not all people see colors the same. The section on "What is color?" could probably mention color blindness.
- ChrisMarshallNY 1y ago

ChrisMarshallNY 1y ago

That's a terrific article! I spent the majority of my career at an optical equipment manufacturer, and we wrote a color management system to handle 48-bit color, before any OS manufacturers had it. Non-trivial stuff, but powerful. I know of at least one technology that works by converting to an esoteric color space, messing with image data there, then converting back.

jimnotgym 1y ago
Indeed... and it was always a huge amount of fun to find that converting from one space to another was not always reversible without distortion!

rylan-talerico 1y ago

Such a great read

tuzemec 1y ago

Such an amazing article. Hope the author continues with the rest of the content in the same manner.

jimnotgym 1y ago

This is a great primer. I used to work in this field, but not as a colour scientist. > So why do we have so many different color spaces? I think there was a missing piece here. Different representations of colour are useful for different things. I'm not going to give any secrets away but...if your trade involves finding out how close one colour is to another, then something that represents colours as points in space could make the maths easier. Then if you wanted to know if one colour was brighter than another, then something that represents a colour with a separate 'brightness factor' would make that trivial.

gopher_space 1y ago
We were big fans of Marti’s LCMS.
- jimnotgym 1y ago
  I can't remember the technical reason we didn't use it...we mostly rolled our own. We were very lucky to have someone who knew how!
  - gopher_space 1y ago
    IIRC the licensing was restrictive for commercial use but it's been a long time. I think we ended up throwing him a few grand for a different license, an option I'd never considered before and one that's stuck with me.
deadvoid 1y ago
as post production guy living outside US/EU, a decade or so ago i was surprised that colorimeter was supposed to be regularly calibrated by another, more expensive, device.
- jimnotgym 1y ago
  I think that depends on what you mean by 'supposed to'. I don't recall this being suggested for normal applications, and if you have a very tight specification then a colorimeter may not be the correct instrument in the first place. As I said above, I'm not a colour scientist, but I do know something about what was done in practice in certain industries.

furyofantares 1y ago

I love that this opens with a matter-of-fact statement that colors aren't real, just a phenomenon of perception. This has come up randomly in my life a few times and people always look at me like I'm stoned outta my mind.

meindnoch 1y ago
And what is not just a phenomenon of perception?
- matsemann 1y ago
  Mathematical proofs based upon axioms?
- magicalhippo 1y ago
  The light hitting our eyes is not a phenomenon of perception. Each photon hitting our eyes has a certain wavelength, but the resulting color we see is a perception. A related concept is sound vs psychoacoustics[1]. Sound is just pressure waves, but what we hear is a perception and has all sorts of aspects like masking[2]. The pressure waves contains two different signals but thanks to masking we might only perceive one. Personally I think color constancy[3] really drives home that color is a perception and not something fundamental like the wavelength of photons. [1]: https://en.wikipedia.org/wiki/Psychoacoustics https://en.wikipedia.org/wiki/Psychoacoustics [2]: https://en.wikipedia.org/wiki/Auditory_masking https://en.wikipedia.org/wiki/Auditory_masking [3]: https://en.wikipedia.org/wiki/Color_constancy https://en.wikipedia.org/wiki/Color_constancy
- Daub 1y ago
  The association of specific wavelengths to hue exists only in our perception, nowhere else. On the other hand, we perceive temperature yet its impact on the physical world is universal.
AlienRobot 1y ago
Fun fact: just like people have different heights, they have different perceptions of color!

AlienRobot 1y ago

This is a great article about the topic! It covers everything. But can someone explain this to me? >Light is technically something called electromagnetic radiation and it has a frequency and wavelength. That wavelength can vary, depending on the energy of the wave. High energy waves have a higher frequency and shorter wavelength, and low energy waves have a lower frequency and longer wavelength. >This means that the same amount of energy at different wavelengths will not be perceived as the same brightness. For example, a light with a wavelength of 555 nm (green) will appear brighter than a light with a wavelength of 450 nm (blue) even if they have the same energy. The article asserts that the wavelength (thus color) changes with the amount of energy, but then it says that you can have light of different wavelengths (color) with "the same energy."

moefh 1y ago
The amount of energy in a wave depends on both its wavelength and amplitude. So a "blue wave" has more energy than a "red wave" if both have the same amplitude (blue has a shorter wavelength, and energy is inversely proportional to wavelength). But you can have a "blue wave" with the same energy as a "red wave" if you increase the amplitude of the "red wave" to compensate for its longer wavelength.
- AlienRobot 1y ago
  Oh, that makes sense! Thanks. So that means blue has more energy because it pulsates faster, and in spite of this we're less sensitive to it than we are to red, which pulsates slower. It's like our light sensitivity forms some sort of bell curve.
SideQuark 1y ago
He confuses two different places there is energy. Light is made (this is a little bit of a cheat) of photons. Each photon has a wavelength λ, and a per photon energy E where E = hc/λ, h is Plank's constant and c is the speed of light constant. So energy and wavelength per photon completely determines each other (and the color of the light of that single photon). These energies are very small. You can add a lot of photons per second, increasing the brightness of that color, and this now has the energy per second of all those photons. So you can have a lot of red photons which sum to some energy, or a different number of blue photons that sums to (very, very close) the total red energy. These are the two energies he confuses in those two places.

anfractuosity 1y ago

Nice article, I came across very cool Python library recently too re. colour science - https://www.colour-science.org/ https://www.colour-science.org/ Just started playing with it with my spectrometer based on one of the examples they have, to convert spectral data to a single RGB value.

kelsolaar 1y ago
Awesome! Maintainer here :) We have a companion repo that might be of interest to you: https://github.com/colour-science/colour-specio https://github.com/colour-science/colour-specio
- anfractuosity 1y ago
  Cool, thanks for the heads up!

Daub 1y ago

A very clear article, written in very accessible language. One potentially relevant thing not covered is the existence of super blacks and super whites, values which (as a budding vfx artist) I often need to consider. These are values which exist in the abstract sence, but not in the perceptual sence. Specifically, values darker than black and lighter than white. They are as good a demonstration as any of the notional nature of color spaces.

bookofjoe 1y ago
Vantablack https://en.wikipedia.org/wiki/Vantablack https://en.wikipedia.org/wiki/Vantablack

lettergram 1y ago

One crazy thing you can do with color spaces is dramatically improve detection algorithms and store massive data. https://austingwalters.com/chromatags/ https://austingwalters.com/chromatags/ Think of it this way, a QR code is binary. If you modify color spaces correctly you can get 6 bits (or more) per pixel. In addition, you can improve the detection at distance, localization for robots, and speed (120 fps). Done this to great effect previously and you can do a lot of awesome things with it. Pretty much the easiest hack in computer vision.

chadcmulligan 1y ago

There's a nice YouTube video that covers a bit of the history of colour spaces to I was watching yesterday https://youtu.be/7KYwi2F5Ce4?si=DUxIWDe_SEjwhdeI https://youtu.be/7KYwi2F5Ce4?si=DUxIWDe_SEjwhdeI

yogrish 1y ago

Recently saw this useful video on colors https://aeon.co/videos/after-centuries-of-trying-weve-yet-to-arrive-at-a-perfect-way-to-map-colour https://aeon.co/videos/after-centuries-of-trying-weve-yet-to...

quix0te 1y ago

Great read and excellent website. Is there a specific name for this web design style? I would have liked to see more websites like this or similar ones for inspiration.

adornKey 1y ago

The article skipped a bit on explaining the CIE-XYZ space. Although it is quite simple. There is one axis Grayscale - that gives you the Brightess value. You can use that for black/white TV. Now for colour you have 2 dimensions left. For these you pick one axis, where the eye is most sensitive - and perpendicular to that you have one axis, where the eye is least sensitive. This colour space is the oldest and all axis there make sense. You can easily compare brightness, and you e.g. can assign more bandwidth to the sensitive colour axis if you want.