CONCEAL: A robust dual-color image watermarking scheme

Compared with binary and grayscale watermark, the color watermark has a larger amount of information, which makes color blind watermarking algorithms more challenging in terms of robustness, watermark capacity and computational complexity under the limitation of distortion. To better meet these challenges, a robust dual-COlor image watermarking scheme exploiting COmpressive seNsing and inter-bloCk approximatE mAximum eigenvaLue, namely CONCEAL, is proposed in this work. Specifically, the Compressive Sensing (CS) is first executed on a watermark, which can effectively compress the watermark information to one-half of the original. Secondly, the carrier image is separated into 4×4 non-overlapping pixel blocks, and the standard deviation of each pixel block is calculated. Then, the pixel blocks with smaller standard deviations are subdivided into four 2×2 non-overlapping pixel sub-blocks (the upper-left, lower-left, upper-right, and lower-right pixel sub-blocks), and the Approximate Maximum Eigenvalue (AME) of four sub-pixel blocks are directly calculated in the spatial-domain at the same time. Finally, every 3-bit watermark data is embedded in a 4×4 pixel block using the AME of the upper-left pixel sub-block and the other three pixel sub-blocks. The imperceptibility and robustness of CONCEAL are assessed experimentally. The experimental results show that all Peak Signal-to-Noise Ratios (PSNRs) are above 47 dB, Structural Similarity Index Measures (SSIMs) are above 0.98, and Normalized Correlations (NCs) are above 0.9. Compared with the state-of-the-art schemes, the proposed CONCEAL possesses large capacity, high imperceptibility, comparable robustness.