Robust blind image watermarking by modulating the mean of partly sign-altered DCT coefficients guided by human visual perception

A novel discrete cosine transform (DCT)-based blind watermarking scheme is proposed to embed binary information into images with substantial improvement in robustness against commonly encountered attacks. This scheme modulates the partly sign-altered (PSA) mean of selected DCT coefficients derived from an 8 × 8 image block. To enhance the imperceptibility of the watermark, the variation margin of each coefficient is regulated either by referring to a JPEG quantization table or the just noticeable distortion (JND) of the human visual system. In particular, a companding function is employed to emulate the contrast masking effect of human eyes. Compared with other DCT-based methods executed at a peak signal-to-noise ratio of approximately 40 dB, the incorporation of the JPEG quantization table into the PSA mean modulation achieves significant improvement in terms of bit error rates for attacks like JPEG & JPEG 2000 compression and noise corruption. The exploitation of JND also offers advantages in cases of median filtering, Gaussian lowpass filtering, and scaling correction.