结合均值调整整数变换的迭代自适应可逆图像水印算法

Iterative adaptive reversible image watermarking algorithm combined with mean-adjustable integer transform

现有的均值调整整数变换可逆水印算法的阈值需人工选择,位置图生成策略不完备可能导致压缩后位置图数据过大,对嵌入矢量强制划分可能导致容量足够却无法嵌入。针对以上问题,提出一种结合均值调整整数变换的迭代自适应可逆图像水印算法。首先,根据负载数据大小以及整数矢量对峰值信噪比(PSNR)的影响,采用迭代自适应算法选择调整平移量以达到水印嵌入容量和嵌入载体视觉质量的平衡;然后,结合邻近像素值相近原则给出了完备位置图生成策略以提高位置图压缩性能;最后,采用分层有序嵌入策略将负载数据依次嵌入到最低、次低和第3低有效位以避免容量足够却无法嵌入的情况。实验结果表明,与传统均值调整整数变换可逆水印算法相比,所提算法无需预先设定阈值,但依然能保持大的嵌入容量,嵌入水印后掩体视觉质量更优,位置图生成策略性能优于传统均值调整整数变换可逆水印算法生成策略且压缩后的位置图数据更小,从而间接提高了嵌入容量,在实验样例上相对于比较算法,PSNR平均提高14.4%。

In the existing reversible watermarking algorithm based on mean-adjustable integer transform, there are following defects such as non-adaptive threshold selecting, incomplete location map building strategy which may lead to poor compression performance and compulsive partition strategy for embedded vectors which may lead to a failure embedding even if embedding capacity is enough. To address these problems, an iterative adaptive reversible image watermarking algorithm combined with mean-adjustable integer transform was proposed. Firstly, according to Peak Signal-to-Noise Ratio （PSNR） affected by the payload data size and integer vector, an iterative adaptive algorithm was used in selecting mean-adjustable offsets to balance the watermarking embedding capacity and the visual quality of embedded carrier; Secondly, based on the strategy that adjacent pixels have similar pixel values, a complete location map generating strategy was proposed to improve location map compression performance; Finally, to avoid failure embedding, the proposed reversible watermarking algorithm adopted hierarchical order embedding strategy to embed payload data in order from the first least significant bits to the third least significant bits. The experimental results show that the proposed algorithm has a big embedding capacity and does not need to preset threshold. Location map building strategy has a better performance in making location map data in smaller size and increasing the capacity indirectly compared with the reversible watermarking algorithm based on mean-adjustable integer transform, and the PSNR increases by 14.4% averagely in experimental sample.