Image fusion based visible watermarking using dual-tree complex wavelet transform

Digital watermarking has been researched extensively due to its potential use for data security and copyright protection. Much of the literature has focused on developing invisible watermarking algorithms. However, not much has been done on visible watermarking. A visible watermark is apparently needed for copyright notification. This work proposes a new framework of visible watermarking based on image fusion, a common technique used in combining images acquired from different modalities. To better protect the host features and increase the robustness of the watermark, the dual-tree complex wavelet transform (DT-CWT) is used. A new classification strategy is proposed to classify complex wavelet coefficients into 6 classes with different perceptual significance. The embedding decision can be made based on the classification information. Small watermark coefficients are prohibited from embedding. In the host edges, the insertion of watermark energy is controlled by using the inversely proportional embedding scheme to better preserve the sensitive region, while in other regions, the embedding strength becomes stronger as texture activity increases. This work also addresses the problem of low-pass subband watermark embedding, which is a special issue of visible water-marking. Experimental results show that the proposed algorithm yields significantly superior image quality than the current DCT-based method.