A robust colour image watermarking scheme for copyright protection using a Non-negative Matrix Factorization (NMF) in Discrete Wavelet Transform (DWT) domain is suggested. The main goal of the proposed scheme is to decompose the RGB host image into four sub-bands using DWT and then apply the NMF to the vertical detail of the host image. This is followed by scrambling and decomposition of the watermark image using Arnold transform and DWT respectively before embedding it in the host image. To test the robustness of the proposed scheme, the watermarked image is subjected to various signal processing attacks and geometrical rotation attack. The results are assessed in terms of Normalized Correlation (NC), Peak Signal to Noise Ratio (PSNR), Structural Similarity Index Measurement (SSIM). Their average numerical values without attacks for the proposed scheme are 0.8411 for NC, 0.98 for SSIM and 35.5dB for PSNR. The proposed scheme is compared to other existing schemes and the results confirm the superior robustness of the proposed scheme to the existing scheme with the same capacity.

Keywords : Arnold Transform, Colour Image Watermarking, Discrete Wavelet Transform, Non-negative Matrix Factorization.