Generator
The 1976 uniform chromaticity diagram, with the unreachable region marked
The u′v′ diagram: the same spectral locus and the same sRGB primaries as the 1931 picture, projectively transformed. Straight lines stay straight, so mixtures and the gamut triangle survive; what changes is the distribution of area, and the green region that dominates the 1931 diagram is much reduced. 8% of the cells sampled inside the locus are reachable at Y = 0.55; the rest are hatched.
Drawn at its defaults, in colour in practice.
It reads 5 options and
no others: obs, step, Y, primaries, ellipses.
Called by 2 essays
the blast radius of changing it
Matching and measuring
Most of this diagram cannot be shown
The chromaticity horseshoe is the canonical illustration of colour science, and nearly every printed copy is filled edge to edge with colours the page cannot produce. The honest version marks them, and the marking covers most of the picture.
Matching and measuringThe diagram was replaced in 1976
The CIE knew the 1931 diagram was badly distorted and published a better one. Half a century later almost every chromaticity plot in print is still the old one, and both are still printed filled edge to edge with colours no display can show.