一种多变换结合的图像水印加载技术研究

Digital Image Watermarking Using Multiple Transforms

研究了图像中数字水印加载的问题;针对以往基于空间域或者频率域水印图像加载保密性差,对原始图像造成破坏等缺陷,提出了一种综合利用不同变换域的优势,从而实现水印加载与提取的算法;首先利用图像乱序算法对需要加载的水印进行乱序编码操作;然后将图像分别进行离散小波变换和离散余弦变换,变换时特别针对小波系数的中频区域进行;再将乱序后的水印图像通过两组随机数添加到小波系数之上,实现水印的加载;由于利用多种变换域内的不同频率特点,因此能较其他单一的变换域或者空间域水印加载方法提供更为稳定有效的加载结果;试验结果显示文章方法能在不影响原始图像的观感条件下实现水印的有效添加,并且所添加的水印图像能有效地防止噪声、缩放、压缩及截取等图像预处理操作所造成的影响。

We suggest a new algorithm to embed watermark into a digital image by using DCT and DWT. The first step of proposed method is to scramble the watermark. Then the DWT is carried out for original image for three levels which only for middle frequency sub- band on the last two levels. The DCT is implemented on the middle frequency sub--band of final DCT results. After that, we embed the watermarks on the DCT coefficient. Prior to embedding, two pseudo--random sequences are generated to represent the binarized watermark. This will make sure the watermarks are secure and robust to noise. The experiments show that the proposed algorithm is invisible to the orig inal image and is robust against to noise and other image processing procedure.