What is the relation between colour spaces and what is actually displayed on our screens?

Question

I am not entirely sure that this is the right stack exchange, but I couldn't find any other suitable one - please redirect me if necessary.

There exists mathematically defined colour spaces which help us represent colors with accuracy/efficiency in computers, and different color spaces will capture different ranges of the human visible colour gamut, and because our screens cannot represent colors as raw wavelengths we must use these spaces instead.(correct me if anything said there is wrong)

How do these relate to how our computer screens actually show colour? From what I understand, our screens only take in N-bit RGB signals for their LCDs, so why do we worry about having all these complex, computationally expensive colourimetric spaces, when we want to do colour processing or storage etc. For example, the sRGB space has a gamma encoding, to represent a different data range with the same amount of bits... but that gamma encoding (for a greater range of dark tones?) cannot actually be displayed on screen. And CIE xyY might be excellent for spectrum based rendering and accurately producing and grading colours - but I understand that we cannot actually see their results, only RGB approximations. Again correct me if any of the above is wrong! I say none of this with much authority, which is mainly why I have to ask this question :)

We are storing different, nuanced, "perception correct", data in this 8-bit channel format - but is that extra nuance is lost as soon as we send it off to our raw RGB 8-bit channel screens, and if so, doesn't that loss invalidate (to some extent) all our extra measures to produce ever more accurate and wider gamuts?

This question focusses on R8G8B8A8 displays, as I imagine HDR would have a different story.

Answer 1

Several reasons. Im listing them in random order

• There are entire industries that do other things than display things on computer screens. If you were to print a booklet, make a package, movie projection or paint a car you would probably be wise to be able to mathematically model it for design, quality control and documentation purposes.

• Not all screen suck and not all are good. Quite many screens out there can show wider color ranges than sRGB, or wider but still not entire sRGB. See sRGB is well suited for the designs it was designed for namely crt screens. LCD screens have had hard time coming to sRGB gamut, but we are getting there. So many screens can not even do sRGB and many now exceed it.

  The RGB color on each screen is different! Unless you have a screen that has been calibrated to sRGB odds are low that it shows sRGB (even if it does bet goes off in few weeks). Now for most people this is ok they arent aware how much off their screen is (i remember calibrating for first time o was quite shocked).

  Anyway point is that you might be interested is describing the color so that you can do same color, not just same numeric value, on a different screen or display technology.

• You might be doing color science and communicating measurements to others, or calculate how fast humans can separate the colors.

• You might be developing a light simulator, i dunno like for movie special effects and or technical design and your interested in the light spectrums.

• You might need to do distributions of colors visually

And so on...

As for gamna encoding your screen is not linear. If your screen were tuned linear it would be crappy indeed. And in anycase good screens have 10 to 12 bits of color to work with so gamma correcting is no problem.

As for spectral colors CIE is not dealing with spectrums... Not at all. All 3 component color is dealing with human perception. Spectrums are way different things, the thing you call orange on screen and what your physics book called wavelength are different things.

Answer 2

The real story here is actually very interesting and can be enlightening. So I offer this alternate answer to help better answer this question. Also, my answer below is a very specific to this question. The full story is too big to put here, but worth the trouble of learning.

In the 1930-50's researchers started looking into the human visual system. These studies looked into the range and brightness of colors that humans can see. The results were surprising. Our color range is somewhat limited and that color range is effected by how bright the room is. While we can see 6 magnitudes of order with respect to brightness, the number of colors we can see at each of these 1 million brightness levels varies. In a moderately lit room we can see a heck of a lot more colors then we can in a very bright room.

When the television was first being created it had to account for these differences. But a television outputs color at a fairly narrow range of brightness (especially the early television) which is about 1 to 100 nits. (with humans being able to see between 1 and 1 million nits) This is a fairly low lighting level and we see more colors (including black and white) in a dimly lit room. So the television needed to output more dim colors then bright colors at the same brightness and the logarithmic color curve was born.

The sRGB color space is a direct result. It is our eye with its tricky ability to see lots of colors in dim lighting that forces this curve on the hardware.

But, the technology behind monitors continues marching forward and today we have monitors that can produce upwards of 1,000 nits of brightness, not to mention that brightness can be varied much more broadly. Also, modern monitors can produces a wider range of colors then early monitors. Further, movie makers and game developers can not easily "think" in logarithmic space we mere humans tend to think much better in linear space. So there really needs to be a way to translate from logarithmic space to linear space so media creators can more easily reason and about and work with the colors they produce. Also, now that we have monitors that can produce colors at different levels it sure would be nice to be able to convert movies and games into the "native" space that any given monitor actually displays.

In fact, it would be much better to "ship" all our media with the best possible colors and then convert it to whatever the display that media is being shown on is capable of.

And that is exactly what a lot of modern media creators do. So the relationship between the color space and what is shown on your monitor is actually a fairly complex dance between what is shipped in the media, the capabilities of your video hardware and the capabilities of the monitor it is being shown on. An 8 bit color encoding may end up going through multiple translations before it makes it to your 8 bit monitor. While the same media being shown on a 10 bit monitor could go through a very different set of translations.

With monitors showing colors in 8, 10, or 12 bits per color. Many can now easily represent most of the standard media color spaces and choosing one to work or visualize in is more a matter of personal taste or need then physical necessity.