Nonblind Watermarking for Color Images using DWT Hybrid Technique

Watermarking is the method of embedding data into multimedia content such as image, audio and video file for the purpose of copyright protection. The watermarking technique has developed greatly and became the powerful tool for protection of multimedia contents. A robust nonblind watermarking scheme has been proposed and images are exposed to various attacks. This method uses DWT-DCT combination for effective watermarking. The color image is converted to Luminance (Y), Intensity (I) and Hue (Q) components. Haar wavelet transform is used for the decomposition of luminance component. Three level decomposition of DWT is performed here. The color image of size 512x512 is taken as the cover image and watermark of size 32x32 is embedded in cover image. Robustness and imperceptibility are the two main factors influencing the quality of the watermarked image. The strength of the watermarking scheme has been evaluated in terms of metrics like PSNR and Correlation coefficient after exposing the embedded image to a wide range of aggressive image processing operations like noise, rotation, filtering, compression etc. The watermark is retrieved after each attack. The DWT provides flexibility in providing the choice of embedding location while the DCT provides the necessary robustness towards intentional and unintentional attacks. A Composite payload is used and the effect of variation of payload over the image quality is also studied.