A Study Of Color Management Technology Based On ICC Specification

As color information is applied in relative fields more and more widely, people raise a higher request for the quality of color reproduction. The high quality reproduction of color graphic and image among different devices can be achieved by using color management technology which is predicated on the devices' color characteristic detecting and describing. The color management system introduces device independent color space (usu. CIELab or CIEXYZ) to describe the color characteristic of all the devices in a uniform space. Through gamut mapping and nonlinear calibration on the input/output characteristic of the device, this system creates a mapping between device dependent color space (RGB or CMYK) and device independent color space, which helps to transform the color information from the input device color space to the device independent color space, and finally, to the output device color space to accomplish WYSIWYG (what you see is what you get). It is not an easy job to set up the mapping because of the variety of color characteristics on different devices. This paper researches on the technologies of color characteristics detection of general device, nonlinear calibration of input/output characteristic and gamut mapping based on the mathematical modeling and analyzing of color management system. In view of the limitation of the present ICC color management system, a further study is made on adaptive color management system and the relevant adaptive color gamut mapping technique. On the basis of the theoretic research, an application software of color management based on ICC specification is developed.Through the experimental research on color characteristic of the scanner, we find that the scanner's input characteristic is nonlinear and inconsistent in device independent color space. Given this situation, an adaptive regression calibration method is proposed. When a scanned value is input, samples whose characters are consistent with that of the input are first selected from the calibration samples. Then the subset, which consists of those selected samples, is used to correct the given scanned value to colorimetric of device independent color space by multiple polynomial regression method. Experiments show that the proposed method can improve the precision of calibration and meanwhile keep the consistency and continuity of the corrected color information. To solve the problem that the output characteristic of printer is nonlinear and nonuniform in device independent color space, a new calibration method is presented. Firstly, a nonuniform individual calibration sample set should be created according to the color characteristic of the printer. When a value in device independent color space is to be output, samples whose characters are consistent with that of the value are selected from the set. Then the subset, which consists of those selected samples, is used to correct the given value to CMY value by multiple polynomial regression method. Experiments show that the proposed method improves the calibration precision obviously.Different device has different color gamut, and gamut mapping which can map all the color to the destination gamut must be done in advance when color information is to be reproduced. Gamut mapping results in the loss of color information, and ICC (International Color Consortium) defined 3 rendering intents which aim to preserve the most important color characteristic of the image after gamut mapping. This paper makes a comprehensive study on the gamut mapping algorithms and works out 3 algorithms to meet each of the 3 rendering intents. To increase the commonality, a mapping algorithm using gamut partition and variant Anchor is presented. Color space is partitioned into 5 subareas by geometric characteristics of the destination gamut. In each subarea, a different mapping strategy is selected to improve saturation and precision of colors after mapping; particularly, a method of variant anchor is used in the subarea which contains the maximum chroma to ensure the color continuity shown in mapping result. Experiment results show that the algorithm greatly enhances the saturation and precision of color reproduction, and avoids the halo artifact.An adaptive color management system is constructed based on mathematical modeling and analyzing of the color management system (CMS). First, the color information of an image is input into the system, and gamut mapping which takes the image gamut as source gamut and the device gamut as destination gamut is selected based on the image's color characteristic; then the output image is achieved after the correction against the device nonlinearity. Transforming the colors based on the image's color characteristic, this system can make the most performance of the device and significantly improves the quality of the color image reproduction. One implementation method of the system under ICC framework is given to meet the application.In accordance with the adaptive color management system, an adaptive gamut mapping algorithm based on the image's color characteristic is proposed, which uses different mapping strategies in different regions of an image according to its color characteristic. In this algorithm, a segmentation filter is constructed first, which can segment an image into areas of mutative color and pure color. Then compression mapping is performed on the areas of mutative color to keep the contrast, while clipping mapping is performed on the areas of pure color to ensure the color precision and chroma. Experimental results show that the proposed algorithm can retain the advantage of both the compression mapping and the clipping mapping, and can achieve better mapping result than traditional algorithms.Based on the theoretic research, an application software of color management in accordance with ICC specification is designed, which can realize the precise detection, description and correction of the color characteristic of input/output device. This project creates specific calibration sample set for a given device; constructs the gamut by gift wrapping algorithm; sets up the mapping between device independent color space and device dependent color space by the gamut mapping and correction methods mentioned above; and builds device profile in accordance with ICC specification finally. This ICC profile can be invoked by the standard color management module to achieve high quality image reproduction on different devices and different platforms. Directing against the high cost and low efficiency of measuring calibration sample target by spectrophotometer, a scanner-measure solution is recommended, which scans the color samples on the target and corrects the scanned RGB values to colorimetrics through the adaptive scanner calibration method. This solution can reduce the cost and increase the efficiency of target measure. The presented project which has an overall compatibility with ICC specification can be referenced and applied by the researcher, producer, user and the third party member of input/out device.