bibkey: cie2020grassmann authors: International Commission on Illumination year: 2020 title: Grassmann’s laws, CIE S 017 International Lighting Vocabulary, entry 17-23-033 doi: null url: https://cie.co.at/eilvterm/17-23-033 claim: The entry describes three-variable colour matching and additive mixture under specified observing conditions, and explicitly says the laws do not hold for all observing conditions. strata_touched: [] license: citation-only triage: anchor

Colour matching is a conditional observation contract

The official CIE e-ILV entry 17-23-033 is titled “Grassmann’s laws” and identifies CIE S 017:2020, second edition. It states that three independent variables are necessary and sufficient to specify a colour match, that only tristimulus values matter for additive mixtures, and that gradual stimulus changes give gradual tristimulus changes. Note 1 explicitly restricts the observing conditions.

The FIB boundary volume §10 separately assumes three independent linear matching functionals on its chosen spectral vector space. Its quotient calculation does not assert that all physical spectra fill that vector space, that the nonnegative spectral image is the whole three-dimensional output space, or that colour matching establishes a spatial cross product or a displacement map.