chromacoördinaten

Chromacoördinaten are coordinates used to describe color independent of its brightness. In the most common form, the xy coordinates come from the CIE colorimetric system: x = X/(X+Y+Z) en y = Y/(X+Y+Z), where X, Y en Z are the tristimulus values. A third coordinate, z, can be defined as z = Z/(X+Y+Z) or simply z = 1 − x − y. The quantity Y acts as the luminance component, so colors with the same x and y but different Y have the same chromaticity but different brightness.

The set of all chromacoördinaten forms a two-dimensional chromaticity diagram, most often the CIE 1931 xyY diagram. The boundary of the diagram is the spectral locus, representing pure spectral colors; interior points correspond to mixtures or non‑spectral hues. The white point of a reference illuminant, such as D65, has a specific chromaticity (approximately x ≈ 0.3127, y ≈ 0.3290).

Chromacoördinaten are used to compare colors independent of light level, to define device gamuts as polygons within the diagram, and to support color matching and color management. They are derived from measured spectra or reflectance data using instruments like spectrophotometers or colorimeters, and can be converted to coordinates such as xy or uv' for different color spaces.

Limitations: chromacoördinaten do not encode luminance, so colors with the same chromaticity can appear equally colored at different brightness levels. For a full color description, chromaticity is combined with a luminance component, yielding spaces such as CIE xyY, CIELAB, or CIECAM02.