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Protecting of image data
Nováček, Aleš ; Přinosil, Jiří (referee) ; Číka, Petr (advisor)
Bachelor´s thesis is about protection of digital images, especially about modern watermarking techniques. It consists of three main parts. The first one is the theoretical part, that describes watermarking terminology, techniques of embeding and detection of watermark, watermarking applications and watermarking requirements such as robustness and impercebility. The second and third part compares two methods of watermarking. Both methods are based on the transformation of image to the frequency domain. The first method uses discrete cosine transformation and the second one discrete wavelet transformation. Method using DCT embeds watermark by swaping DCT coefficients. The second method embeds watermark by modifying some coefficients of DWT decomposition according to the equation vi´= vi (1+sxi ), where vi´ is a coefficient of watermarked image, vi is a coefficient of original image, xi is pixel of watermark and s is scale factor, constant, that affects robustness of watermark.
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