Color matching that improves image quality on mobile phone displays

Abstract

With digital convergence, color reproduction technology for mobile phones continues to improve. Camera technology now enables users to take both still and moving pictures, store them as digital files, and then display or project them anywhere. Color fidelity remains a challenge, however, and LCDs on mobile phones require real-time color matching between camera and cellular screen to ensure image quality. Our proposed color-matching system, shown schematically in Figure 1, comprises three steps: characterization of LCD and camera, gamut mapping, and application of a 16bit-based lookup table (LUT) design.? Device characterization defines the relationship between the tristimulus values (color spaces CIEXYZ or CIELAB) and RGB (red, green, blue) digital values. In general, characterization is modeled by polynomial regression, and as the polynomial order increases, performance improves.? However, for higher-order polynomials, most estimated tristimulus values exceed the boundary of maximum lightness and chroma. This makes implementation difficult because the relationship between tristimulus and digital RGB values has not been analyzed. We suggest a polynomial order based on investigating the relation between RGB digital values, then transformed using opponent color theory and CIELAB values. Meanwhile, for the mobile LCD characterization, we use a sigmoid function instead of a conventional method such as the GOG or S-curved model, to estimate the luminance curve made by the system designer.? This aims at better color reproduction and improved contrast. Additionally, characterization is based on the 16bit processing that controls the mobile LCD, in contrast to digital TVs or monitors, with 24bit data. Figure 1. Block-diagram of the proposed color-matching system.