A DWT-based Image Watermarking Approach using Quantization on Filtered Blocks

In this paper, the authors propose a digital water-marking scheme for gray-scale images, in which, coefficients of a host image are quantized in the wavelet domain. In particular, the binary watermark image is embedded into the wavelet-blocks that can be obtained by grouping four coefficients at different sub-bands at corresponding coordinates. The modification of only two coefficients at the LH4 and HL4 sub-bands is decided by the value of watermark bit and the significant difference of them. In order to improve the performance, these blocks are filtered by sorting in the difference as the reparation before applying an embedding algorithm. The improvement reduces the degradation in the output image. The method is evaluated for many samples under various types of attack including the geometric and non-geometric attacks. Moreover, the comparison of the proposed method and recent others is also represented at the same payload.