Combined DWT-DCT Based Digital Image Watermarking Technique for Copyright Protection

Abstract

A combined DWT and DCT based watermarking

technique with low frequency watermarking with weighted

correction is proposed. DWT has excellent spatial localization,

frequency spread and multi-resolution characteristics, which are

similar to the theoretical models of the human visual system

(HVS). DCT based watermarking techniques offer compression

while DWT based watermarking techniques offer scalability.

These desirable properties are used in this combined

watermarking technique. In the proposed method watermark

bits are embedded in the low frequency band of each DCT block

of selected DWT sub-band. The weighted correction is also used

to improve the imperceptibility. The extracting procedure

reverses the embedding operations without the reference of the

original image. Compared with the similar approach by DCT

based approach and DWT based approach, the experimental

results show that the proposed algorithm apparently preserves

superior image quality and robustness under various attacks

such as JPEG compression, cropping, sharping, contrast

adjustments and so on.