Study Of Color Difference Vealuation For Color Dgital Images Based On ICAM Framework

With the development of various display technology, the color digital images have been widely applied into daily work and life. Therefore, the color difference evaluation of color digital images is becoming more and more important. However, due to that color digital images are composed of a large number of pixels, rather than uniform color samples, the color of digital images are difficult to be measured directly by physical instruments or computed conveniently as uniform color samples. Hence, it is a difficult issue for a long time in the field of color science and imaging technology.The main topic of this study is to discuss the application of iCAM framework on image color difference evaluation. The psychophysical experiment in Phase Ⅰ was carried out base on the categorical judgment method to test the performance of color difference formulas or models of CIELAB, CIEDE2000, S-CIELAB, S-CIEDE2000, CAM02-UCS and iCAM on image color difference evaluation. Also analysized were the relationships between the parameters of lightness, chroma, hue, resolution and sharpness, which impact the color difference of images, through the visual data. The research results indicate that the iCAM framework based on image color appearance model performs best in the color difference prediction of image, followed by S-CIELAB, and CAM02-UCS is the poorest in the prediction of image color difference.The study of Phase Ⅱ was divided into two parts, threshold and suprathreshold color difference evaluation of digital images. The threshold color difference estimation was conducted to obtain the perceptible and acceptable image color difference thresholds of lightness, chroma, hue and sharpness. Then, the perceptible thresholds were employed as the reference in the suprathreshold experiment via the magnitude estimation method to test the performance of iCAM on predicting suprathreshold color difference. The experimental data at the threshold level of image color difference show that the average perceptible and acceptable thresholds of the observers are1.85△E*ab and3.63△E*ab, respectively, with a relationship of roughly2times. And the perceptible and acceptable thresholds of lightness are greater than those of chroma, hue and sharpness. The observer accuracy of suprathreshold experiment is higher than that of Phase I, and the prediction performance of iCAM framework also shows advantage. However, for the range of small color difference at the threshold level, the calculated color difference of iCAM framework is less than the visual one, and for the large color difference of suprathreshold level, the calculated metric of iCAM framework is greater than the visual color difference.Finally, the main contents and conclusions of this study are summarized, and an outlook for the future research and exploration are made.