The CIECAM02 color appearance model

The CIE Technical Committee 8-01, color appearance models for color management applications, has recently proposed a single set of revisions to the CIECAM97s color appearance model. This new model, called CIECAM02, is based on CIECAM97s but includes many revisions1-4 and some simplifications. A partial list of revisions includes a linear chromatic adaptation transform, a new non-linear response compression function and modifications to the calculations for the perceptual attribute correlates. The format of this paper is an annotated description of the forward equations for the model

Uniform color spaces based on CIECAM02 and IPT color difference equations

Color difference equations based on the CIECAM02 color appearance model and IPT color space have been developed to fit experimental data. There is no color space in which these color difference equations are Euclidean, e.g. describe distances along a straight line. In this thesis, Euclidean color spaces have been derived for the CIECAM02 and IPT color difference equations, respectively, so that the color difference can be calculated as a simple color distance. Firstly, the Euclidean line element was established, from which terms were derived for the new coordinates of lightness, chroma, and hue angle. Then the spaces were analyzed using performance factors and statistics to test how well they fit various data. The results show that the CIECAM02 Euclidean color space has performance factors similar to the optimized CIECAM02 color difference equation. To statistical significance, the CIECAM02 Euclidean color space had superior fit to the data when compared to the CIECAM02 color difference equation. Conversely, the IPT Euclidean color space performed poorer than the optimized IPT color difference equation. The main reason is that the line element for the lightness vector dimension could not be directly calculated so an approximation was used. To resolve this problem, a new IPT color difference equation should be designed such that line elements can be established directly

The Effects of Neighboring Colors on Color Appearance

Department of Human and Systems EngineeringEvery day, people don???t perceive one color independently, but perceive many neighboring colors simultaneously. Most color studies regarding color appearance were done based on a single color. There are also earlier studies conducted on neighboring colors. However, it is not sufficient to focus on the effect of neighboring colors which color attribute affect the color appearance. Therefore, the effects of neighboring colors on color appearance need to be investigated. The research aimed to investigate how neighboring colors effect on color appearance. Color appearance experiment was carried out in the dark room by using a viewing booth. Total of 5 different neighboring color conditions were used in the experiment and those were ???Reference Condition???, ???Desaturated???, ???Saturated???, ???Dark???, and ???Light???. Total of 20 participants were invited to each neighboring color condition. Each participant evaluated Hue, Colorfulness, and Lightness of 22 test colors by using magnitude estimation method. To analyze the data, all participants??? responses were averaged by using arithmetic mean. Then the experiment results were analyzed according to neighboring color conditions. Furthermore the results were compared with the estimated results of two different color appearance models, CIELAB and CIECAM02, respectively. As for the findings of the experiment, Hue, Colorfulness, and Lightness tended to be affected by neighboring colors. First, Colorfulness was evaluated higher when neighboring colors were desaturated. Both Colorfulness and Lightness of test colors tended to be evaluated lower when neighboring colors were lighter. Hue was affected when neighboring colors were light. The results were compared with estimated color appearance values of CIELAB and CIECAM02. In overall, CIECAM02 showed better performance than CIELAB. The performances of both models tended to be worse as the neighboring color condition became extreme in a specific color attribute, especially when estimating Colorfulness and Lightness. The degree of color appearance changes was compared between experimental results and CIECAM02 values of ???Reference Condition??? and ???Light???. In the result, CIECAM02 model could not estimate the Colorfulness and Lightness changes according to neighboring color conditions sufficiently and it estimated the changes less than experimental results in both Colorfulness and Lightness. Therefore, further research regarding color appearance should be considered more in regards to surrounding environment.ope

Repairing Gamut Problems in CIECAM02: A Progress Report

The color-appearance model CIECAM02 has several problems, which can result in mathematical instabilities, due to the relation of the chromatic-adaptation primaries to the spectrum locus and to the presumed physiological cone primaries. To keep a corresponding color within the positive gamut given by the chromatic adaptation primaries, that gamut must lie within the cone primary octant. To contain a color that is already outside the gamut, it suffices to algebraically prevent adaptation from moving a test color outside the positive octant of the physiological cone space. Such modifications may be needed to avoid the mathematical problems in CIECAM02

Modelling of chromatic contrast for retrieval of wallpaper images

Colour remains one of the key factors in presenting an object and consequently has been widely applied in retrieval of images based on their visual contents. However, a colour appearance changes with the change of viewing surroundings, the phenomenon that has not been paid attention yet while performing colour-based image retrieval. To comprehend this effect, in this paper, a chromatic contrast model, CAMcc, is developed for the application of retrieval of colour intensive images, cementing the gap that most of existing colour models lack to fill by taking simultaneous colour contrast into account. Subsequently, the model is applied to the retrieval task on a collection of museum wallpapers of colour-rich images. In comparison with current popular colour models including CIECAM02, HSI, and RGB, with respect to both foreground and background colours, CAMcc appears to outperform the others with retrieved results being closer to query images. In addition, CAMcc focuses more on foreground colours, especially by maintaining the balance between both foreground and background colours, while the rest of existing models take on dominant colours that are perceived the most, usually background tones. Significantly, the contribution of the investigation lies in not only the improvement of the accuracy of colour-based image retrieval, but also the development of colour contrast model that warrants an important place in colour and computer vision theory, leading to deciphering the insight of this age-old topic of chromatic contrast in colour science

Color Appearance Study under Two Lightings Having Different Illuminance Levels

Department of Human Factors EngineeringColor appearances of the objects are changing, depending on light sources. In everyday life, it is common to see a scene having two or more light sources together, or to look at an object that is shadowed by other objects. However, these situations might not be interpreted by current color appearance models, which are based on a single light source. With increasing interest in color reproduction of high dynamic scenes, color appearance research that can explain these multi illumination situations is necessary. In this research, it was intended to explain color appearance phenomena in the context where observers alternately saw two light sources having largely different illuminance levels (7005 lux and 376 lux, respectively) being present at the same time. This study also attempted to identify the observer's state of adaptation in the presence of multiple lightings, by exploring how color appearance in terms of hue, brightness and colorfulness changes in complex multiple lighting conditions, as opposed to single lighting conditions. Psychophysical experiment based on magnitude estimation technique was conducted to estimate color appearance and was composed of four sessions according to 1) illuminance of lighting either high or low, and 2) observer's adaptation to the lighting conditions for either single lighting or multiple lightings. Seven observers who were skillfully trained for color appearance estimation participated in the experiment and evaluated the color appearance of 50 color patches in terms of hue, colorfulness and brightness throughout the four sessions. As for the analyses of the results, human color perception data regarding hue, brightness and colorfulness of all observers were averaged and compared across sessions, based on the illuminance of lighting and the observer???s adaptation to the lighting conditions. Also, the color appearance model CIECAM02 performance was evaluated in terms of hue, brightness and colorfulness by comparing model prediction data with color perception data. As a result, through the color appearance study under two lightings with different illuminance levels, it turned out that hue appearance was not affected by the illuminance level of lighting and the observer???s adaptation to the lighting conditions. Perceived brightness and colorfulness were increased under higher illuminance level, but not affected by the observer's adaptation to the lighting conditions, explaining that observers locally adapted to the lighting where the color was directly shown. It was also found that the CIECAM02 H adeptly predicted hue appearance regardless of the illuminance level of lighting and the observer's adaptation to the lighting conditions. However, the CIECAM02 Q and the CIECAM02 M were overestimated under high illuminance lighting. The modification of the luminance-level adaptation factor, FL, by lowering the value from 1.20 to 0.67, helped the model not to overestimate Q and M. These results are based on color appearance perception when there are only two lightings having 19 times the illuminance difference. Consequently, it cannot be firmly concluded that these phenomena are common color appearance in multiple lighting environments. Therefore, it is necessary to conduct additional color appearance estimation research in multiple lighting conditions having more diverse illuminance level differences or having different configurations of lightings.clos

Image appearance modeling

Traditional color appearance modeling has recently matured to the point that available, internationally-recommended models such as CIECAM02 are capable of making a wide range of predictions to within the observer variability in color matching and color scaling of stimuli in somewhat simplified viewing conditions. It is proposed that the next significant advances in the field of color appearance modeling will not come from evolutionary revisions of these models. Instead, a more revolutionary approach will be required to make appearance predictions for more complex stimuli in a wider array of viewing conditions. Such an approach can be considered image appearance modeling since it extends the concepts of color appearance modeling to stimuli and viewing environments that are spatially and temporally at the level of complexity of real natural and man-made scenes. This paper reviews the concepts of image appearance modeling, presents iCAM as one example of such a model, and provides a number of examples of the use of iCAM in still and moving image reproduction