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Human trichromacy means any color sensation can be described by three numbers

Fact L1Foundations L · Visual foundations

The human retina contains three types of cone photoreceptors (S, M, L — roughly blue, green, red). Because there are only three independent detector types, any color stimulus producing the same S/M/L responses is perceptually identical regardless of the actual spectrum. This is why RGB with three primaries covers the full range of human color experience (with the caveat that extreme colors need ‘negative’ primary weights). It is the biological basis for the existence of three-channel color spaces and RGB displays.

Examples

A spectral yellow (570 nm single wavelength) and a red+green light mix produce identical S/M/L cone responses and look identical — this is metamerism.

Assessment

If humans had four cone types (tetrachromacy), would three-channel RGB still be sufficient to reproduce all colors? Explain why or why not.

Prerequisites — understand these first

Color theory must address both objective physical laws and subjective individual perception — neither alone is sufficient

Sources

“a human retina has three different types of photoreceptive [cones](https://en.wikipedia.org/wiki/Cone_cell), any color sensation can be matched using three fixed colors with varying intensities.”

corpus · color-spaces-bartosz-ciechanowski-interactive-article · chunk 8

Taught in modules

Encoding Color Numerically: RGB, color spaces, and gamma

Unlocks (8) — atoms that build on this