Image watermarking using dual-tree complex wavelet by coefficients swapping and group of coefficients quantization
In this paper, we present two watermarking schemes for images using the low-pass frequency coefficients and high-pass complex frequency coefficients of the Dual-Tree Complex Wavelet Transform (DT-CWT) of the image, the distinctive characteristics of the two schemes can lead to different applications. We investigate the problem of embedding binary watermark sequence in DT-CWT domain, which is a challenging problem. The coefficients swapping is done by carefully selecting those 2×2 blocks with high-energy in the low frequency and swap the coefficients that lie in the median range in the block to embed the watermark. Whereas the group of coefficients quantization quantizes a group of high-pass complex frequency coefficients to make the quantized coefficients lie in the middle of the quantization range and distribute the changes among the coefficients. Experimental results conducted on 100 standard images achieve about 96% and 92% detection rate for the low-pass and high-pass frequency coefficients-based schemes, respectively. Robustness tests against some common signal processing attacks such as additive noise, median filtering and lossy JPEG compression confirm the superior performance of the proposed schemes.