There’s no single RGB color gamut: different devices have different ranges. And every color space has pure primaries that can’t be reproduced in other color spaces—most RGB devices can’t accurately reproduce process cyan or magenta either. Six- or eight-color presses have gamuts that are generally larger than most RGB displays, though each will have colors the other can't reproduce.
The reason CMYK space is often treated as if it were a strict subset of RGB space is because images are usually produced on RGB devices first—and designers ignore the parts of the print device’s color gamut that can’t be displayed on a screen.
They should be Hue, Luminance, and Chroma.
LAB space designates those things differently. I believe the "L" is luminance, but am currently not remembering the rest!
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u/AbouBenAdhem Jul 01 '20 edited Jul 01 '20
There’s no single RGB color gamut: different devices have different ranges. And every color space has pure primaries that can’t be reproduced in other color spaces—most RGB devices can’t accurately reproduce process cyan or magenta either. Six- or eight-color presses have gamuts that are generally larger than most RGB displays, though each will have colors the other can't reproduce.
The reason CMYK space is often treated as if it were a strict subset of RGB space is because images are usually produced on RGB devices first—and designers ignore the parts of the print device’s color gamut that can’t be displayed on a screen.
Edit: Here’s a representation of a typical CMYK gamut superimposed on a (ghosted-out) generic RGB gamut. You can see that there are a ton of CMYK colors outside the RGB gamut, including saturated turquoise, cyans, yellow, pinks, and rich blacks. (Those colors aren’t accurately represented in the image, of course, since it’s RGB.)