A DWT-based robust semi-blind image watermarking algorithm using two bands

Robustness of an image watermarking scheme is the ability to detect the watermark after intentional attacks and normal audio/visual processes. A DWT image watermarking paper embeds a PRN sequence as a watermark in three bands, excluding the low pass subband, using coefficients that are higher than a given threshold T1. During watermark detection, all the coefficients higher than another threshold T2 (T2 ≥ T1) are chosen for correlation with the original watermark. In this paper, we extend the idea to embed the same watermark in two bands (LL and HH). Our experiments show that for one group of attacks (i.e., JPEG compression, resizing, adding Gaussian noise, low pass filtering, and rotation), the correlation with the real watermark is higher than the threshold in the LL band, and for another group of attacks (i.e., histogram equalization, contrast adjustment, gamma correction, and cropping), the correlation with the real watermark is higher than the threshold in the HH band. As the DWT coefficients in the LL band are higher than the DWT coefficients in the HH band, we use a smaller scaling factor for the lower of the two bands.