Colour Science & Perception
what the eye settles, and what it cannot
Concept

The Judd–Vos correction — where it appears

A correction to the 1931 observer's short-wave end, which is known to be too low. It gives better agreement with matching data below about 460 nanometres and is not what any colour specification is written in, so it exists as a known repair nobody applies.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

The CIE 1931 colour-matching functions. The three functions that turn a spectrum into three numbers. They are all positive, which is why XYZ exists — the RGB functions they were derived from are not. ȳ is by construction the luminous efficiency function, which is why luminance comes out of Y.

Seventeen observers in 1931

The standard observer that governs every colour specification in industrial use is an average over seventeen young British men, measured with equipment from the 1920s. It is known to be wrong in the blue, the correction has existed since 1951, and it has never been adopted.

limits · Limits How far a match comes apart when the observer changes. A broad source and a three-primary source, solved at each primary width so the pair is an exact tristimulus match for the CIE 1931 observer. The pair is then handed to the 1964 observer, and the gap between them is plotted. For the observer they were built for the gap is arithmetic noise at every width. For the other it grows as the primaries narrow, reaching 0.012 at 10 nm — and displays have been getting narrower for twenty years.

Two degrees or ten

This site names the observer on every figure it draws, which was supposed to be the point. Measuring what it had actually done found two hundred and four figures naming the same observer, three naming the other, and sixty-two of sixty-four generators printing a string that had never once varied.

limits · Limits

Named alongside it

The objects these essays reach for when they reach for this one.

Colour-matching functionsMacular pigmentObserver metamerismStandard observerXYZChromaticityThe CIE 1931 2° observerThe CIE 1964 10° observerCone fundamentalsIndividual variationPrimariesWhite point

All concepts