Over the years, many CATs (chromatic adaptation transform), typically based on the von Kries coefficient rule, have been developed to predict the corresponding colors under different illuminants. However, these CATs were derived for uniform stimuli surrounded by a uniform adapting field. To investigate the adaptation state under spatially complex illumination, an achromatic matching experiment was conducted under dual lighting conditions with three color pairs and two transition types. It has been found that the transition type has an impact on both the equivalent chromaticity and degree of adaptation. These results can help build a comprehensive von Kries based CAT model, with considering the spatial complexity of illumination.
Recent data has shown that the process of chromatic adaptation might be asymmetrical, or irreversible, and that this effect might be more than simply a manifestation of the time course of adaptation. This paper introduces a simple modification of the von Kries chromatic adaptation transform, referred to as vK20, that can account for the asymmetry in chromatic adaptation through inclusion of previous adapting conditions. Also introduced is a new reference chromaticity (∼15000K) for degree of adaptation that seems more physiologically plausible than the commonly used equal-energy (EE) illuminant or CIE illuminant D65.
A 'consistent colour appearance' is hard to achieve between different substrates or display systems. A chromatic adaptation transform or substrate adjustment strategy is typically used, but for this present paper a dynamically scaled ICC Media Relative transform was utilised. A soft-proofing system with a method of adjustment was used, allowing simultaneous viewing and adjustment of a reproduction colour image relative to a reference on different simulated substrates under P2 viewing conditions. The degree of adjustment was found to be highly correlated to the image content's lightness and to lesser extent its chromaticity, and was not consistent with the complete adaptation assumed by a media-relative rendering. Other aspects of the experimental setup, including accuracy, observer strategies, and the application of soft proofing for media relative adjustments are discussed.
The performance of Color Prediction Methods CAT02, KSM2, Waypoint, Best Linear, MMV center, and relit color signal are compared in terms of how well they explain Logvinenko & Tokunaga [1] asymmetric color matching results. In their experiment, given a Munsell paper under a test illuminant, 4 observers were asked to determine (3 repeats) which of 22 other Munsell papers made the least-dissimilar match under a match illuminant. Given this data, we address the following four questions. Question 1: Are observers choosing the original Munsell paper under the match illuminant? If they are, then the average (12 matches) color signal (cone response triple or XYZ) made under a given illuminant condition should correspond to that of the Munsell paper's color signal under the match illuminant. Computation shows that in 274 of the 400 cases, the relit color signal is close to the mean color signal of the matches. Question 2: How do algorithm predictions compare to the average observer prediction of the actual color signal of the relit paper? The Wilcoxon signed-rank test shows that KSM2, Waypoint, and Best Linear perform equally, and that both slightly outperform the observer average, which, in turn, significantly outperforms CAT02, and MMV (metamer mismatch volume) center. Question 3: Which method most closely predicts the observer average? We found that the color signal of the relit reflectance is a better predictor of the average observer than Best Linear, which in turn is marginally better than Wpt and KSM2, both of which outperform CATO2 and MMV center. Question 4: Do the observers agree with one another? Using a leave-one-observer-out comparison shows that individual observers predict the average matches of the remaining observers somewhat better than the relit color signal, which in turn slightly outperforms Best Linear, Wpt and KSM2, which then all significantly outperform CATO2 and MMV center.