Research On Digital Watermarking Algorithm For Color Still Images Based On DWT

With the vigorous development of information and network technology, digital technology has been so widely popular that the copying and distribution of digital multimedia products is becoming increasingly easy. Due to its low cost and difficult identification, the piracy of digital products becomes more and more serious. How to effectively prevent piracy and safeguard the legitimate rights and interests of the copyright holder is the problem to be solved. To solve this problem, the researchers used a digital watermark technology. With further research, this technology has become more and more mature gradually and a lot of sophisticated algorithms have been formed, especially the digital watermarking algorithm for image copyright protection.After the study of image watermarking algorithm, it is found that the discrete wavelet transform is chose in many algorithms, which is because the discrete wavelet transform is compatible with JPEG compression standard and can be used in conjunction with the human visual system. Most algorithms have better transparency and robustness of attacks, such as the anti-low-pass filtering, adding noise, blurring and sharpening and so on, but are weak in the ability to resist the attacks of shear and JPEG compression. To solve this problem, a digital watermarking algorithm for color still images based on DWT is put forward. First, in order to ensure the security of the watermarking system, the watermark image is scrambled by Arnold transformation. The three primary colors of the color image are separated. Then the blue component and green component are respectively transformed by DWT at level two. Energy value radio of the low-frequency sub-band of the two color components transformed by DWT is calculated. If the energy value ratio is greater than one, watermark scrambled is embedded in sub-band of the blue component after DWT, otherwise, embedded in the sub-band of the green component. Finally the watermarked color image is synthesized by the blue component and the green component transformed by IDWT at level two and the red component of the original image.The algorithm is simulated to verify it validity. Experimental results show that:the algorithm has good transparency and strong robustness of attacks from the common image processing, such as median filtering, adding noise, shear, JPEG compression, blurring and sharpening and so on.