A Blind and Robust Image Watermarking Algorithm in the Spatial Domain using Two-level Partition

To improve the performance of the blind image watermarking technique, a novel blind and robust image watermarking scheme in the spatial-domain by applying a two-level partition is proposed in this work. Specifically, the host image is firstly partitioned into non-overlapping 4 × 4 sub-blocks, and the standard deviations of all sub-blocks are computed in the meanwhile. Then, the sub-blocks with lower standard deviation are selected, and each selected block is partitioned into four non-overlapping 2 × 2 sub-blocks. Thereafter, the direct current coefficients of three 2 × 2 sub-blocks (i.e., top-left, top-right, and bottom-left sub-blocks) are computed in the spatial-domain without carrying out the two-dimensional discrete cosine transform. Lastly, utilizing the correlation principle between adjacent 2 × 2 sub-blocks, two bits of watermark are embedded into a 4 × 4 sub-block via adjusting the direct current coefficients of the three 2 × 2 sub-blocks. Experimental results show that the proposed image watermarking scheme is suitable for gray-scale and color images, and possesses a good performance in terms of invisibility and robustness. In particular, all peak signal noise ratios are greater than 42 dB, all structural similarity index measures are more than 0.96, and the normalized correlations are greater than 0.85 under various attacks.