Quantifying and Evaluating Colour Appearance Models based on Helmholtz Kohlrausch Effect

Abstract

The brightness sensation of a colour source depends in part on colour purity, and this colour appearance phenomenon is defined as the Helmholtz-Kohlrausch effect. With the recent advancement in HDR and WCG displays, greater brightness and contrast will make the Helmholtz-Kohlrausch effect more noticeable. An experiment using magnitude estimation was conducted to evaluate the Helmholtz-Kohlrausch effect. Twenty-one observers participated in the experiment and judged the brightness of the test colour samples in relation to achromatic samples. Saturated colour samples were judged by the observers with high brightness values as compared to less saturated colour samples with the same luminance, and a small deviation in observers’ predictions of lightness was observed on chromatic backgrounds. The performance of several existing colour appearance models was investigated. The lightness values predicted by CAMs on all backgrounds were lower than perceptual lightness values returned by the observers. CAMs were quantitatively assessed based on CV statistics showing higher variations between predicted lightness values and the observers’ perceptual lightness judgements. In addition to lightness, the chroma channels were also shifted in the case of CIECAM02, CAM16 and Jzazbz. However, in ICtCp chroma shift was minimal because of decorrelation between achromatic and chromatic components due to constant luminance.