Non-linear Uniform Colour Space Considering Non-linearity and Non-symmetry in Opponent colour Response Mechanisms.

Abstract

A new non-linear uniform colour space NC-IIIC is developed for colour specification. First, NC-IIC space is derived by applying non-linearity at the receptor level to linear colour space NC-I composed of linear transformations of tristimulus values X, Y and Z. Then, NC-IIIC space is constructed by further introducing non-linear and non-symmetric functions in Y-B and R-G opponent colour response mechanisms to NC-IIC space. For colours aligned on a plane of constant value in Munsell space, coefficients of the above non-linear response functions are optimized by computer numerical analyses to make hue circles shape as close as possible to uniform circles in the new space. The uniformity of the space is significantly improved, and the average deviation between hue circles and uniform circles in the new space is reduced to about 1/10-1/20 of those in conventional L*a*b* and L*u*v* uniform colour spaces by applying appropriate non-linear opponent transformations. Hue, lightness and chroma can be represented independently as mutually orthogonal attributes with proper correspondences of hue with hue angle, lightness with metric lightness and chroma with metric chroma in the new colour space NC-IIIC.