colourfulness of an area judged as a proportion of the brightness of a similarly illuminated area that appears grey, white or highly transmitting
Note 1 to entry: For given viewing conditions and at luminance levels within the range of photopic vision, a colour stimulus perceived as a related colour, of a given chromaticity and from a surface that has a given luminance factor, exhibits approximately constant chroma for all levels of illuminance except when the brightness is very high. In the case of unrelated colours, at a given level of illuminance, if the luminance factor is increased, the chroma usually increases.
Note 2 to entry: This entry was numbered 845-02-42 in IEC 60050-845:1987.
Note 3 to entry: This entry was numbered 17-139 in CIE S 017:2011.