From lower to higher colour metrics: a historical account

'Lower colour metrics' describes the laws of colour mixture as manifest in trichromatic colour space and best known in its two-dimensional projection, the chromaticity diagram. 'Higher colour metrics' describes how distance in this colour space translates into perceptual difference. It is higher in the sense that it builds on the fundamentals of lower colour metrics.

A historical account is given of the development of higher colour metrics, with many ups and downs, since Helmholtz started it at the end of the 19th Century.

Despite long periods of silence, Helmholtz's basic ideas have survived by successfully extended modelling, which could also account for seemingly paradoxical effects of luminance and saturation on colour discrimination.

The subject theme, which presently is at a low tide of interest, deserves the renewed interest of colour vision researchers.