A Comparison between Block-Based and Non Block-Based Watermarking Schemes Based on DWT

In recent years, invisible digital watermarks have been proposed as a method for protecting copyrighted materials such as digital images. Due to its characteristics, one of the problems in digital image watermarking is to decide which technique should be used to hide in an image as many bits of information as possible while ensuring that the embedded watermark can be correctly extracted at the detecting stage, even after various attacks. In this paper we study the effect of dividing the image into blocks and applying a watermarking scheme to each block as an individual image (block-based), and compare it with applying the same watermark to the entire image (non-block-based). Digital wavelet transform (DWT) combined with a proper quantization method is used in this paper and normalized correlation (NC) is used to compare between the two cases after applying number of standard attacks. The results show that block-based watermarking has slightly better performance than non-block-based watermarking.