Industria Textila | 2019
Dependence of colour difference formulae on regular changes of colour coordinates in CIELAB colour space
Abstract
CIE, International Commission on Illumination, defined the CIELAB colour space in 1976 which was indented to be a visually uniform one. The space was characterized by three axes that represented the three colour coordinates which were lightness (L*), red-green (a*) and yellow-blue (b*) together with two supplementary colour related terms of chroma (C*) and hue angle (h°). After the calculation of the three tristimulus values (X, Y, and Z) under specified illumination and viewing conditions, they are used as the computing components in the calculation of colour coordinates to designate the place of the colour in CIELAB colour space. Together with the definition of CIELAB colour space, CIELAB (1976) colour difference formula was developed to calculate the colour difference between two colours in the space. However, CIELAB colour space is not truly visually uniform which means that equal colour difference magnitude appear of different visual magnitudes in different regions of the colour space. When the difference between two colours are calculated by CIELAB colour difference formula, the formula calculates the linear (Euclidean) distance between the two points in the CIELAB colour space by using the three colour coordinates of L*, a* and b*. Because of the non-uniformity of the CIELAB colour space and the setup of CIELAB (1976) formula, the colour difference obtained is free from human eye sensitivity. Human eye is sensitive to different kinds of changes in the shade(s) under observation. Human visual system perceives the differences in different magnitudes even though they may have the same colour difference calculated by CIELAB (1976) Dependence of colour difference formulae on regular changes of colour coordinates in CIELAB colour space