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정송균,김정엽,현기호 영산대학교 2003 영산논총 Vol.11 No.-
In this paper, we reviewed and compared the methods uses the key as watermark and key with watermark. And we found some methods using the key in watermarking on the frequency domain which were robust to arbitrary attack. At first, the image was transformed to frequency domain by DWT(Discrete Wavelet Transform) in the methods uses the key as watermark, and then the watermark was inserted and extracted in the high frequency region on the transformed image. The second one uses the key with watermark transforms the image into frequency domain by DCT(Discrete Cosine Transform) and inserts the watermark on the mid frequency region that is selected by human visual characteristics. This method also inserts and extracts the watermark with minimum effect to the image quality by using multiple thresholds to maximize the image quality. Experimental results shows the second method using the key with watermark has higher PSNR compared to the other method for the watermark extraction.