數位影音被廣泛使用於各種傳播媒體，對於畫面中的個人隱私保護成為一項重要議題。本論文提出了一個作用於H.264/AVC視訊壓縮架構上的隱私保護機制，對於欲保密區域的視訊畫面資料進行擾亂，使得隱私區域在一般使用者面前是模糊而無法被正常觀看的，只有權限使用者能將畫面完整還原成原始影像。
我們擾亂的方式是修改H.264/AVC視訊編碼串流中的資料，使得解碼端得到錯誤資訊產生擾亂效果，最後再將原始資料利用資料隱藏的方式嵌入於視訊串流中，讓具有權限的使用者藉由取出該資料而確實還原隱私畫面區域。由於H.264/AVC編碼利用空間與時間的相依性以獲得良好的壓縮效果，當我們實作區域性擾亂時，會因漂移誤差(drift error)的產生，造成非保密區域的畫面也受到影響。為了解決此一問題，本研究採取限制編碼的方式以及slice方式，藉由限制H.264/AVC編碼過程中的畫面預測，有效解決飄移誤差的發生。實驗結果顯示本方法能夠確實擾亂隱私區域，使畫面模糊讓人眼看不清楚，權限使用者能夠確實還原畫面，達到個人隱私權的保護，而且整體視訊的資料量能獲得控制，符合相關的視訊應用需求。

關鍵字—H.264/AVC、區域擾亂、隱私保護、資訊隱藏。

Protecting personal privacy on digital images and videos is important these days. In this research, we present a privacy protection mechanism in H.264/AVC videos. The private visual information on video frames is scrambled by processing the data in the compressed bitstream directly so that the private region is not visible to the regular users. Nevertheless, the scrambled region can be restored to the original content by authorized users. Basically, the scrambling is applied by extracting and removing some data from the H.264/AVC bitstream. These data will be embedded into the bitstream so that the recovery can be applied successfully by placing these data back. In other words, the de-scrambling is achieved via the methodology of information hiding. Since the H.264/AVC encoder makes use of the spatial and temporal dependency for reducing the data size, careless partial scrambling on H.264/AVC compressed bit-stream will result in drift errors. To solve this problem, the restricted H.264/AVC encoding is employed to prevent the modified data from affecting the subsequent video content. Experimental results show that our method can effectively scramble the privacy region, which can be recovered by using the hidden information. In addition, the size of partially scrambled video is kept under good control.

Index Terms—H.264/AVC, Partial scrambling, Privacy protection, Information hiding.

[1] P. Korus, W. Szmuc, and A. Dziech, “A scheme for censorship of sensitive image content with high-quality reconstruction ability,” 2010 IEEE International Conference on Multimedia and Expo (ICME), pp. 1073-1078, 2010.
[2] J. Wang, Y. Fan, T. Ikenaga, and S. Goto, “A partial scramble scheme for H.264 video,” International Conference on ASIC,2007 ASICON'07, pp. 802-805, 2007
[3] L. Tong, F. Dai, Y. Zhang, and J. Li, “ Restricted H.264/AVC video coding for privacy region scrambling,”, 2010 17th IEEE International Conference on Image Processing (ICIP), pp. 2089-2092, 2010.
[4] T. Wiegand, G.J. Sullivan, G. Bjontegaard, and A. Luthra, “Overview of the H.264/AVC video coding standard, ”IEEE Transactions on Circuits and Systems for Video Technology, vol. 13, no.7, pp. 560-576, 2003.
[5] S. Lian, J. Sun, and Z.Wang, “A novel image encryption scheme based on JPEG encoding,” Eighth International Conference on Information Visualisation, 2004. IV 2004. Proceedings, pp. 7-220, 2004.
[6] L. Krikor, S. Bab, T. Ari, and Z. Shaaban,“ Image encryption using DCT and stream cipher,” European Journal of Scientific Research, vol. 32, no.1, pp. 47-57, 2009.
[7] G. Liu, T. Ikenaga, S. Goto, and T. Baba, “ A selective video encryption scheme for MPEG compression standard,” IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, vol. 89 no. 1 pp. 194-202, 2006.
[8] B. Bhargava, C. Shi, and S.Y. Wang, “MPEG video encryption algorithms,” Multimedia Tools and Applications, vo1. 24, no. 1, pp. 57-79, 2004.
[9] LS Choon, A. Samsudin, and R. Budiarto, “Lightweight and cost effective MPEG video encryption,” 2004 International Conference on Information and Communication Technologies: From Theory to Applications, pp. 525-526, 2004.
[10] I.K. Cheong, Y.C. Huang, Y.S. Tung, S.R. Ke, and W.C. Chen, “An efficient encryption scheme for MPEG video,” International Conference on Consumer Electronics, 2005. ICCE, pp. 61-62, 2005
[11] H.J. Lee and J. Nam. “Low complexity controllable scrambler /descrambler for H.264/AVC in compressed domain,” Proceedings of the 14th annual ACM international conference on Multimedia, pp. 93-96, 2006.
[12] F. Dufaux and T. Ebrahimi, “H.264/AVC video scrambling for privacy protection,” IEEE International Conference on Image Processing (ICIP), pp. 1688-1691, 2008.
[13] L. Tong, F. Dai, Y. Zhang, and J. Li, “Prediction restricted H.264/AVC video scrambling for privacy protection,” Electronics letters, vol. 46, no. 1, pp. 47-49, 2010.
[14] A. Westfeld. ”F5-a steganographic algorithm,” In Information Hiding, pp. 289-302, 2001.
[15] F. Peng, Xiao-wen Zhu, and Min Long, “ A ROI Privacy Protection Scheme for H. 264 Video Based on FMO and Chaos,” IEEE Transactions on Information Forensics and Security, pages 1688-1699, 2013