PRN Based Watermarking Scheme for Color Images
Ersin Elbaşı, Ahmet M. Eskicioğlu · DergiPark (Istanbul University) · 2006
Robust image watermarking is the process of embedding an invisible watermark in an image in order to make it very difficult to remove the watermark after intentional attacks and normal audio/visual processes. A recent DWT-based semi-blind image watermarking scheme leaves out the low pass band, and embeds the watermark in the other three bands into the coefficients that are higher than a given threshold T 1. During watermark detection, all the high pass coefficients above another threshold T 2 (T 2 > T 1) are used in correlation with the original watermark. In our extension to the DWT-based approach, we embed the same watermark in two bands (LL and HH) using different scaling factors for each band. In the watermark detection algorithm, the watermarked RGB (and possibly attacked) image is converted to the YUV model. After computing the DWT of the luminance layer, all the DWT coefficients higher than a given threshold T2 in the LL and HH bands are selected. The next step is to compute the sum Z, where i runs over all DWT coefficients higher than a given threshold T2 in the LL and HH bands. In each band, if Z exceeds T, the watermark is present. Experimental results indicate that detection in the LL band is robust for one group of attacks, and detection in the HH band is robust for another group of attacks.