Out of curiosity, what is stopping screen makers from making the entirety of the colour space as defined by the CIE chromaticity diagram its gamut?
Is there some fundamental limitation of liquid crystals? I understand for example, CRTs require red phosphor made of yttrium and europium, which somewhat limits the emitted freq. What about LEDs and LCDs? What are the limitations for making a wider gamut?
Do note my knowledge in this side of things is close to nil (the specific examples of yttrium and europium as red phosphor was a story told to me by a physicist friend, and it stuck)
the gamut is defined by the triangle connecting the RGB primaries. If you could add a primary at a more pure green, you'd get a bigger triangle and a wider gamut, but still not the entirety of the chromaticity space. If you start adding other components that lie outside that triangle, you start expanding the polygon, but there will always be parts of the diagram it doesn't cover.
In order to encompass the entire chromaticity space, you'd have to have a large (technically infinite) number of components. You can never have a component outside the diagram, because the curved hull is the pure chromaticity of light at each wavelength; light outside the curve doesn't exist, and light below the straight "line of purples" is invisible (UV/IR).
Theoretically you could get much more coverage by adding more components as new types of emitters are developed. This is happening in high-end theatrical lighting, where you can cram a ton of different LEDs into a fixture, but it's not (yet) practical to cram them all into an on-screen pixel.
Things get even more mind-bending when you start illuminating objects with light instead of looking at the light directly, because then there's a benefit to adding components even if they don't expand the gamut. Once you have four or more components, you can make many colors an infinite number of ways (metamers), and they might look absolutely indistinguishable when lighting a white wall, but they'll make skin tones look completely different if you made them by combining just RGB versus, say, amber and blue. That's not really related to your question, but I've just started delving into this area in my day job, and it's exciting and trippy. :)
> it's not (yet) practical to cram them all into an on-screen pixel
At the pixel density (>500,000 subpixels per square inch) of current flagship smartphones, I think it would actually work just fine to have 6 or 9 (or whatever) different primaries, make a grid of little pixels in some scattered but regular arrangement, and then use clever digital signal processing to figure out how to convert an RGB image into a RR'GG'BB' (or whatever) image. I would expect it to look visually identical at typical viewing distances for existing images, while potentially allowing someone with low-level hardware access to make a wider gamut / choose their preferred metamer / etc.
I would expect it to be entirely achievable using current technology and not inordinately much more expensive than current displays.
But the engineering effort and additional complexity might not provide enough benefit for display vendors to invest in that, vs. just continuing to optimize their current display concepts. Or they might not even be considering radical changes in strategy.
My understanding is that lot of the limitations of current LCD color gamuts stem from the quality of backlight used. That is why for example quantum dot technology is used to reproduce the wider rec2020 colorspace, because the spectrum of quantum dots is better suited for rgb filtering.
Although now that rec2020 is nearly an achieved goal, I do suspect that going beyond it requires more primaries as others have mentioned. Sharp experimented with a yellow primary, but that effort was fairly limited.
For oled I imagine the situation is much worse as more constraints in making the leds there.
You can make a much wider gamut display (while still avoiding severe observer metamerism) if you have more primaries. You could even do proper multispectral imaging.
It would be awesome if display manufacturers would try to make a display with e.g. 7 primaries in hexagonal pixels.
Pretty well every image that currently shows up on smartphone screens already has to be resampled, so there shouldn’t be any inherent reason why you couldn’t have more sophisticated displays requiring slightly more signal processing to target. It would take a bunch of engineering effort, but nothing extraordinary or out of reach of current technology.
The big problem is that every other stage of the image processing pipeline from cameras and GPUs to software is built on an existing square-grid-of-RGB-pixels model.
> Out of curiosity, what is stopping screen makers from making the entirety of the colour space as defined by the CIE chromaticity diagram its gamut?
A display can't support the entire space because of the way colours combine. Any light source acts as a point in the colour space, so a 3-colour display can only cover a triangle.
That said, wide gamut monitors do exist. They're of limited utility for simply consuming media; because of the chicken-and-egg effect everything produced for mass consumption already targets the reduced sRGB space or an equivalent. However, a wide-gamut display is useful for content generation, especially when targeting print processes that can use spot colours.
The full diagram would require that you are able to produce monochromatic colors along the entire visual spectrum.
So at a minimum you would need a tunable monochromatic light source.
Several actually to blend to any point on the graph. Luckily, due to limits of the human visual system, you don't require a fully tunable spectrum for each pixel.
I'm not aware of any technology that would let us cram this into pixels.
At best you could build a projector from tunable lasers.
Is there some fundamental limitation of liquid crystals? I understand for example, CRTs require red phosphor made of yttrium and europium, which somewhat limits the emitted freq. What about LEDs and LCDs? What are the limitations for making a wider gamut?
Do note my knowledge in this side of things is close to nil (the specific examples of yttrium and europium as red phosphor was a story told to me by a physicist friend, and it stuck)