Image Watermarking

Abstract

Watermarking is a possible solution for content authentication and copyright protection. Imperceptibility and robustness are two contradictory requirements for watermarking. In this thesis three approaches of watermarking to ful_ll both the requirements are pre- sented. In the _rst approach a non-blind color image watermarking scheme using principle compo- nent analysis, discrete wavelet transform and singular value decomposition is proposed. The color components are uncorrelated using principle component analysis. The wa- termark is embedded into the singular values of discrete wavelet transformed sub-band associated with principle component containing most of the color information. In the second approach a robust color image watermarking scheme is proposed, in which a color watermark is embedded into a color image. Principle component analysis is used to un-correlate the R, G and B channels of both the images. Each channel of color wa- termark is embedded into singular values of corresponding channel of cover image after discrete wavelet decomposition. As original image is required at the time of extraction of watermark so given scheme is non-blind. In the third approach a robust gray image watermarking scheme based on human visual system is proposed. The perceptual quality of the watermarked image is controlled by determining adaptive scaling factor for each individual pixel value. To determine the adaptive scaling factor, human visual system (luminance masking, texture masking) and fuzzy inference systems were used. Peak signal to noise ratio is used to measure the imperceptibility whereas similarity between original and extracted watermark is measured using normalized correlation co- e_cient. These schemes were tested against various attacks (including histogram equal- ization, rotation, Gaussian noise, scaling, cropping, JPEG compression, Y-shearing, X- shearing, median _ltering, a_ne transformation, translation, sharpening, blurring, aver- age _ltering), to check the robustness. The results of proposed schemes are compared with state-of-the-art existing color watermarking schemes. The simulation results show that proposed schemes are robust and imperceptible, as compared to existing schemes.