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(16)¡¡Digital watermarking by a holographic technique¡¡Applied Optics, Vol.41, No.5, pp. 865-873, 2002-2
¡¡A holographic technique is applied for digital watermarking by a computer. A digital watermark image to be hidden is phase-modulated in a random fashion, and its Fourier transformed hologram is superposed on a content image. The watermark is reconstructed by means of holographic reconstruction technique from the bit-map image hiding it. In the study, the construction and reconstruction processes of a digital hologram are described on a basis of the theory of Fourier Optics. The condition in superposing the hologram onto the content images is investigated in detail. The validity of the present method is verified by changing the weight of the hologram to the content image. The size effect of images is also discussed with respect to reconstruction of the watermark, and it is shown that the watermark information in a form of the diffuse-type Fourier transform hologram cannot be removed by cutting out from the host image.
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