A Study Of Key Technologies In Color Management

With the development of computer science and color input-output technology,color image as a media of information is applied more and more widely in such areas as press, imaging, advertisement, movie, e-business and digital entertainment et al and people raise a higher request for the quality of color reproduction. While factors like imaging mechanism, color space, apparatus capability, material peculiarity and machining precision make the IO devices'color characteristics quite different. So it is hard to achieve a platform or media-cross conformable color reproduction. To accomplish WYSIWYG (what you see is what you get) people have to measure, control and manage color. As a result, many color management systems(CMS) are developed which is far from each other. Among those, ICC color management system is the most famous one. ICC 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. Since color management system frameworks available can not render images adaptively to get a best reproduction, this paper focus on color management framework improvement and such core technologies as color characterization, color gamut description and gamut mapping is discussed. Then on the basis of the theoretic research, an application software of color management based on extended ICC specification is developed.Many shapes of CMS have come forth: close-looped, ICC-based, PostScript, sRGB-based, color appearance involved as well as spectrum based reproduction system. So far, ICC which is made of profile and color management module is in fact the standard of color industry. While theoretical analysis and applications show that ICC can not render images adaptively to get a best reproduction. So an extended framework whose kernel part is a CMM with adaptive color gamut mapping ability is proposed, the CMM will render color corresponding to image characteristics. Though on the contrary that ICC lays particular stress on profile than CMM, the proposed CMS has the same interface of ICC color management system. Among the computer peripherals, printer is the device that has most serious color nonlinearity. Focus on CMYK ink jet printers, this paper researches on color characteristic calculation with emphasis on gamut description and color calibration. Experiments show that ink colorants are quite non-linear to produce colors, so B-spline is introduced to account for the nonlinearity. Then a spine tensor-product based color calibration algorithm and a surface data sampling with spline interpolation gamut calculation method are given. Experiments show that the proposed calibration method can get an equivalent precision with much less measure samples, and the gamut description gained by the proposed algorithm is quite close to the real one. At the last of this chapter, we propose a multi-channel ink jet printer calibration algorithm by printer color gamut partition and subspace characterization. Partition reduces the data dimension and eliminates color redundancy.Different devices have different color gamuts, and gamut mapping which can map all colors to the destination gamut must be done in advance when color information is to be reproduced. In view of the limitation of the present ICC color management system, a further study is made on adaptive color gamut mapping .Two image content relevant gamut mapping algorithms are proposed. The first one classify images into different groups and each group assign a proper matching method; the second algorithm is based on human vision system, which can preserve image colors as well as image gradients as much as possible.In view of the situation that so far there is few native color management application software, we design and accomplish the ICC-extended CMS. It is composed of a profile creator and a CMM with adaptive color management. The profile creator adopts all research results of the device characterization and the CMM aggregate the adaptive gamut mapping technique. Besides, the CMM conforms to windows image color management specification and it is a 3rd-part CMM working on the operation system level. Experiments show that the adaptive color rendering is superior to the windows default color management.