COMPARATIVE ANALYSIS OF THE QUANTIZATION OF COLOR SPACES ON THE BASIS OF THE CIELAB COLOR-DIFFERENCE FORMULA

摘要

This article discusses the CIELAB color space within the limits of optimal colors including the complete volume of object colors. A graphical representation of this color space is composed of planes of constant lightness L* with a net of lines parallel to the a* and b* axes. This uniform net is projected onto a number of other color spaces (CIE XYZ, tristimulus RGB, predistorted RGB, and YCC color space) to demonstrate and study the structure of color differences in these spaces on the basis of CIELAB color difference formulas. Two formulas are considered: the CIE 1976 formula Delta E-ab and the newer CIE 1994 formula Delta E-94*. The various color spaces considered are uniformly quantized and the grid of quantized points is transformed into CIELAB coordinates to study the distribution of color differences due to basic quantization steps and to specify the areas of the colors with the highest sensitivity to color discrimination. From a threshold value for the maximum color difference among neighboring quantized points searched for in each color space, concepts for the quantization of the color spaces are derived. The results are compared to quantization concepts based on average values of quantization errors published in previous work. In addition to color spaces bounded by the optimal colors, the studies are also applied to device-dependent color spaces limited by the range of a positive RGB cube or by the gamut of colors of practical print processes (thermal dye sublimation, Chromalin, and Match Print). For all the color spaces, estimations of the number of distinguishable colors are given on the basis of a threshold value for the color difference perception of Delta E-ab = 1 and Delta E-94* = 1. [References: 21]