3 upvotes, 2 direct replies (showing 2)
View submission: Ask Anything Wednesday - Engineering, Mathematics, Computer Science
I assume you're talking about the chart with the parabola and triangle shown here?
https://en.wikipedia.org/wiki/CIE_1931_color_space
You maybe know that light has a wavelength/frequency that determines its color. Red has a long wavelength, blue has a short one. This is 100% true - a specific wavelength will always correspond to exactly one color. That's what the full parabola is for: the border of it maps out each wavelength to a certain color.
The thing that's getting you here is that human eyes cannot do the reverse - *we cannot calculate wavelength if we only know the color*. We can give an approximation, but we can't say for sure because our eyes do a terrible job with the hues of blue-green.
So if you look at that chart and focus on the triangle portion, you'll notice that every color inside the triangle is unique. If you look outside the triangle, you'll actually find that every color out there is not unique, and in fact has an equivalent inside the triangle. The parabola is every combination of wavelengths and what color we see. The triangle is showing the range of our RGB vision.
If you want to know more, the Wikipedia page honestly does a pretty good job of explaining it. Please feel free to read further and come back with questions.
Comment by BlueRajasmyk2 at 25/07/2024 at 05:48 UTC*
2 upvotes, 1 direct replies
If you look outside the triangle, you'll actually find that every color out there is not unique, and in fact has an equivalent inside the triangle.
This is only true when viewing the diagram on an RGB display? The point is that the RGB color space cannot represent every color that can be seen by human eyes. This is because the different color-cones in the eyes have overlapping activation ranges, so eg. pure red light will also significantly trigger the green cones. This results in some activation combinations which are possible with other wavelength-combinations but impossible with only RGB. *(It also means some activation combinations are just straight up impossible - see impossible colors[1])*
1: https://en.wikipedia.org/wiki/Impossible_color
The range of colors that can be accurately represented by a color-space is called its gamut[2]. There are in fact other color spaces with a wider gamut - see this diagram[3] for example.
2: https://en.wikipedia.org/wiki/Gamut
3: https://en.wikipedia.org/wiki/RGB_color_spaces#/media/File:CIE1931xy_gamut_comparison.svg
To answer OP's question of "what does this look like" - if you take a picture with your phone of a bright pink neon sign, or one of those painfully bright yellow safety vests, or a brilliant orange sunset, and then hold the screen next to the thing, you'll notice the picture always looks less brilliant than the real thing. The colors look muted because they cannot be accurately represented using RGB, so the nearest possible color is chosen instead.
Comment by Tripsel2 at 24/07/2024 at 19:50 UTC
1 upvotes, 2 direct replies
Thanks! I didn’t realise human perception was so key to the analysis.
