This paper proposes a watermarking scheme allowing desired image-quality exactly and automatically. The proposed scheme considers the finite word-length of a pixel, e.g., (1) the luminance of a pixel is represented as an integer, (2) the luminance of a pixel has the range-limitation, to generates a watermarked image of the exact desired quality. This proposed scheme embeds a watermark into the dc values of an image in the spatial domain. This embedding mechanism corresponds to that in which a watermark is embedded into dc components and simultaneously ac components are changed to achieve the desired image quality in the discrete cosine transform domain. Simulation results shows that a) this proposed scheme generates a watermarked image of the exact desired quality, b) the proposed scheme generates a high-quality watermarked image, e.g., a peak signal-to-noise ratio over 50 dB, c) proposed scheme has JPEG resilience in practical use. From these advantages, this proposed method is useful for applications that require i) an embedding a watermark into huge number of images automatically, ii) a generating a watermarked image of the exact desired quality, such as a management of contents in a broadcast station and a digital museam.
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