다중화 복호화 키들을 이용한 실질적인 영상 워터마크

Practical Image Watermark Using Multi-Decoding Keys

In this paper, we propose a practical image watermark method using multi-level decoding keys. A zero-padded original images are Fourier transformed and its real-valued data denotes an encoded image in the embedding process. The multiplication between the spreaded encrytion image and Walsh code image is used as a hidden image. Here, this spreaded hidden image is the same size and shape of the walsh code. A host image is then made from the linear superposition of weighted hidden image and a cover image. The original image is simply obtained by the inverse-Fourier transform and a despread process of the product of the host image and multi-level decoding keys which are generated by Walsh code and the imaginary part of encoded image in the reconstruction process. The embedding process and the reconstruction process are performed digitally. Computer simulations demonstrate the efficiency of the proposed technique that can be decryped with only one hierarchical decryption key image and a good robustness to the external attacks such as cropping.