A colorimetric look at the RHS Chart—Perspectives for an instrumental determination of colour codes

Abstract

SummaryFrom their special reflectance curves, the colours of the 808 chips in the RHS colour Chart have been measured in the CIELab system using the L*C*h notation (Lightness, Chroma, hue) with respect to the CIE D65/10° Illuminant/Observer condition; three spectrocolorimeters and two copies of the Chart were used. Standardized conditions for visual observation are proposed, matching those used for colour calculations in the perspective of an objective instrumental assessment of colour codes. An important heterogeneity in colour, reaching an impairing level for a reproductible RHS codification was detected over the surface of all the chips printed by the half-tone screen process. For most of those printed in solid colours the non-uniformity of colour remains below the threshold of visual perceptibility colour in a single copy. Colour variations between patches of two copies (one recent and brand new, the other seven years old but rarely used) are more important but, in most cases, cannot be considered lar...