Read/Search this Article
The visual experiment on perceived colour difference is conducted using 160 colour chips of various hues arranged on a closed hue circle of constant chroma C = 6 and of constant value V=6. Correspondence between perceived colour difference and predicted colorimetric colour difference obtained by various colour difference formulae in several colour spaces is examined. The examination is conducted on uniform colour spaces CIELUV, CIELAB, NC-IIIC and L^*a^*b^*-N, colour appearance model CIECAM97s, and colour difference formulae CMC, CIEDE94 and CIEDE2000. Results obtained are as follows : 1) In uniform colour spaces NC-IIIC and L^*a^*b^*-N, predicted colour difference has good correspondence to perceived colour difference. These two uniform colour spaces are implemented with proper non-linear compensation in opponent response process and thus they are significantly superior to other colour spaces in the geometrical uniformity of colour specification. 2) In uniform colour spaces CIELUV and CIELAB, it can be stated that non-uniformity in hue difference is caused by the fact that hue and chroma axes are not perpendicular and the fact that hue and chroma are not independent, both of the above facts originating from the lack of compensation mechanism in opponent response process. 3) The revised colour difference formulae based on the uniform colour space CIELAB, namely CMC, CIEDE94 and CIEDE2000, do not create an improvement to colour difference characteristics compared to the original colour space CIELAB. 4) When designing a uniform colour space or a colour difference formula that ensures accurate colour difference evaluation, it is essential to construct the uniform colour space in which hue, lightness and chroma axes cross at right angles so that all elements (hue, lightness and chroma) can be independently evaluated and attached weight by introducing proper non-linear opponent response functions.