目的 针对当前可逆视频水印隐蔽性和篡改定位能力不足问题,提出一种新颖的基于帧内预测模式的可逆视频水印算法。方法 首先,深入分析I帧亮度分量的预测模式对不同类型篡改的敏感性,提取每个帧内编码宏块的预测模式,通过预测模式生成特征码。然后,结合H.264/AVC编码特性和误差补偿算法,在每个亮度4×4残差块中筛选出误差最小系数。最后,运用差值扩展的方法将特征信息作为水印可逆的嵌入到所选系数。结果 在含水印视频未受到篡改时,解码端提取水印后可对原始视频进行无损恢复。当视频受到篡改时,算法能精确定位篡改区域并且篡改定位精度达到4×4子块级。由于水印嵌入在误差最小的系数中,能够有效地降低水印嵌入对于视频质量的影响,嵌入水印后图像的PSNR值比现有的基于H.264/AVC可逆水印方案平均提高10%,测试序列的码率增量平均降低了22%左右。结论 本文算法较现有算法具有更好的嵌入率、隐蔽性、篡改检测精度, 适用于医学、军事、卫星等领域。

Objective To solve the inadequate imperceptibility of reversible video watermarking and lacking of tamper localization, we present a novel reversible watermarking algorithm based on an intra-prediction mode. Method The proposed algorithm elaborately analyzes the sensitivity of the luminance prediction mode to different types of tampering of the I frame, extracts the prediction mode of each intra macro block, and generates a signature with the prediction mode. According to the features of a H.264/AVC codec, the minimum error coefficient in each 4×4 luminance residual block is selected with an error compensation method. Finally, feature information is embedded as watermarks in the selected coefficient by employing a difference expansion. Result Experimental results show that the original video can be recovered without any distortion if the watermarked video is not tampered; otherwise, the tampered region can be localized accurately, and the tamper localization accuracy is 4×4 blocks. Selected minimum error coefficients embedded with watermarks effectively reduce their impact on video quality. Compared with existing methods, the proposed algorithm improves the PSNRs of watermarked images by an average of 10%. Furthermore, the bit increase rate of the test sequence decreases by an average of 22%. Conclusion Experimental results show that compared with previous reversible watermarking schemes for H.264/AVC, the proposed method not only achieves higher embedding capacity and better imperceptibility but also features greater accuracy in tampering detection. The proposed method can thus be applied in many fields, including the areas of medicine, military, and satellites.