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Computational Colour Science Using MATLAB, 2nd Edition by Vien Cheung, Caterina Ripamonti, Stephen Westland

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Chapter 5

CIELAB and Colour Difference

5.1 Introduction

Although the system of colour specification introduced in 1931 by the CIE and augmented in 1964 has served the colour industry well, there remain a number of problems. One of the main problems is that in terms of visual perception it is very nonuniform. Equal changes in x, y or Y at various points in the colour space do not correspond to perceived differences of equal magnitude. Most attempts to develop more uniform spaces sought to find linear or nonlinear transforms of the tristimulus values or chromaticity coordinates to give a more uniform colour space. In 1976 the CIE recommended two new colour spaces for general use (CIE, 1986b): CIE L*a*b* and CIE L*u*v* also known as CIELAB and CIELUV respectively. CIELUV tends to be used to specify the colours of lights and other self-luminous sources whereas CIELAB tends to be used for the specification of surface colours. It is possible to compute a colour difference for two stimuli in CIELAB space by calculating the Euclidean distance in the space between the two points that represent the stimuli in the space (Equation 1.7). The CIELAB colour-difference formula has been used extensively for quality control in industry but its application is limited because although CIELAB space is more perceptually uniform than the tristimulus space on which it is based, it is still far from being perfectly uniform. The consequence of this is that for equal perceptual colour differences between ...

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