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Contourlet based image watermarking using QR decomposition

The paper presents an image watermarking algorithm based on Contourlet Transform (CT) and QR factorization method. Contourlet Transform is used to transform both the cover and watermark image into subbands. The watermarking is applied to the Contourlet Transform as the human visual system is comparatively less sensitive to edges of the image. The low frequency coefficients of an image contain the highest energy. Thus the lowest frequency coefficients of the contourlet transformed original and watermark image are selected for watermarking. The selected coefficients are then decomposed using QR factorization method. The QR factorized coefficients of watermark image is embedded into the QR factorized original image values. Inverse QR and inverse CT is then applied on the watermark embedded coefficients of image to obtain the watermarked image. Experimental results show that the proposed algorithm is a better technique as compared to other watermarking schemes based on Contourlet Transform. The proposed watermarking scheme is imperceptible and robust against image processing attacks such as Gaussian noise, scaling, compression, salt and pepper noise.