Pixel Value Adjustment for Digital Watermarking Using Uniform Color Space

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In this chapter, we propose a pixel adjustment procedure for digital watermarking methods using uniform color space. Many digital watermarking methods use uniform color space due to the convenience of controlling image quality (Yoshiura & Echizen, 2006). However, there is the problem that watermarked RGB integer pixel values in such methods are not quite corresponding to the watermarked real-number pixel values in uniform color space because the color transform between RGB space and uniform color space is non-linear, where we assume that the watermarked RGB integer pixel values are obtained by rounding off the RGB real pixel values transformed from the real pixel values in uniform color space. Note that RGB space means sRGB color space in this chapter. In sRGB color space, each color component is stored as an integer value and the range of pixel values is [0, 255]. This problem often causes erroneous extraction.