Koenderink J J, van Doorn A J, 2000, "Mensurating the colour circle: Ostwald's 'principle of internal symmetry'" Perception 29 ECVP Abstract Supplement
Mensurating the colour circle: Ostwald's 'principle of internal symmetry'
J J Koenderink, A J van Doorn
There exist two types of 'colour atlases' that are different in kind: those based upon eye measure and those based upon colorimetric principles. The best known example of the former is Munsell's atlas, of the latter that of Wilhelm Ostwald. Both date from the early 19th century.
Eye measure is intrinsically subjective, whereas colorimetry is a fully objective discipline, involving only judgments of indistinguishability. When the aim is a subdivision of the colour circle in 'equal parts', eye measure simply leaves it up to the observer to do something (anything is -- in principle -- equally valid). The colorimetric method stands in need of some means to establish 'equal spacing' and Ostwald's 'principle of internal symmetry' provides exactly that. We show that the original principle is flawed and how it can be mended. We calculate an equally tempered colour circle based upon the principle and compare it to the Munsell (eye measure) result.
We find that the differences are small (1 to 2 steps on a 24-hue scale) and of the same order as differences between various published eye-measure results. This implies that eye measure veridically reflects the spectral differences, filtered through the fundamentals.