CIELAB(1976), CIE L*a*b*

CIELAB(1976), CIE Lab* device-independent color space defined for the evaluation of small color differences, with perceptually equidistant structure, defined in 1976 by the CIE together with the trivial color difference formula ΔEab (Delta E = Euclidian distance in space) on the basis of the Hunter-Lab color space (1948). The luminance axis L stands vertically on the achromatic point of the a*;b* chromaticity chart and forms a rotational solid. Brightness L*, red-green chrominance a* and yellow-blue chrominance b* are therefore cylinder coordinates that are supplemented by the intuitive CIELCH interpretation – see inside of back cover. CIELAB is based on the colorimetric values X and Y of the CIE colorimetric system CIEXYZ (1931). Although the color difference formula was improved several times – see CMC (CIELCH84), CIE94, CIEDE2000 inside of back cover – the 1976 CIELAB definitions still form the basis for all international image data exchange standards (printing process in accordance with ISO 12647 incl. process standard offset printing, ICC profile linking color space beside CIEXYZ) and various color ordering system (e.g. RAL). The suggestions for improvement of the CIELAB color model itself – CIELAB-ND(1978), LABHNU(1979- 1/-2), LABJNDS(1984) and DIN99 (DIN 6176:2001-03) by Klaus Richter (BAM) – did not gain acceptance either.