ON THE IMPORTANCE OF COLOUR SPACE UNIFORMITY AND SAMPLESET SPECTRAL UNIFORMITY FOR COLOUR FIDELITY MEASURES

摘要

The impact of a light source's spectral power distribution on the colour appearance of surfaces has traditionally been evaluated by the CIE Colour Rendering Index (R_a). However, a growing body of evidence shows that R_a is not accurate enough when evaluating some spectral power distributions containing narrow-band features, such as with certain types of fluorescent sources and light-emitting diodes (LEDs). CIE TC1-90 is therefore developing a replacement colour fidelity index (here referred to as TC1-90 R_f) based on the metric recently released by the Illuminating Engineering Society as IES R_f. Both include two major improvements: the outdated U*V*W* space is replaced with the state-of-the-art uniform CAM02UCS colour space and the small set of test colour samples (which were all Munsell-based) is replaced with a larger set of 99 samples of various common types which are uniformly distributed in colour and wavelength space. This paper shows why these improvements are needed.