Researches Of Meaningful Watermark Based On Wavelet-packet Transform

In recent years, with the development of network technique and the rapid increase of digital media application, right protection for digital media has been the hotspot of researches. Traditional encryption technique only protects data during transferring period. Once data has been received, the protection will disappear, while the digital watermark technique can protect right information all the time. So it's very important of researches in this field. Most of the former watermark techniques usually use pseudo-random sequence as watermark, which produce a sequence randomly in arithmetic for embedding. It only can detect whether the watermark is still remaining or not. The modern network products and e-commerce require watermark carrying right information such as author, publishing house and publish date and etc. In order to satisfy the new requires to digital watermark, we propose a new uniform watermark arithmetic based on wavelet-packet transform and spread spectrum in this paper. Taking wavelet domain as transform domain, our method can deal with multi-kind watermark such as string and logo. Consulting the idea of the second watermark technique, we divide wavelet domain coefficients by characters of image to decide the embedding regions and intension. Channel capacity in information theory is used to analysis how many characters can be embedded in a certain size image on the base of zero error probability. Then watermark will be embedded into the origin image in wavelet domain after be processed by spread spectrum technique. Examinations show that our arithmetic can make good use of HVS system, and is robust to common image processing such as noise, mean-filter, sub-sample and JPEG compress. String-type watermark is more robust.