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Contribution of Non-Scrambled Chroma Information in Privacy-Protected Face Images to Privacy Leakage Hosik Sohn 1, Dohyoung Lee 2, Wesley De Neve 1, Konstantinos.

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Presentation on theme: "Contribution of Non-Scrambled Chroma Information in Privacy-Protected Face Images to Privacy Leakage Hosik Sohn 1, Dohyoung Lee 2, Wesley De Neve 1, Konstantinos."— Presentation transcript:

1 Contribution of Non-Scrambled Chroma Information in Privacy-Protected Face Images to Privacy Leakage Hosik Sohn 1, Dohyoung Lee 2, Wesley De Neve 1, Konstantinos N. Plataniotis 2, and Yong Man Ro 1 1 Korea Advanced Institute of Science and Technology (KAIST), Image and Video Systems Lab. 2 University of Toronto, Multimedia Lab October th International Workshop on Digital-forensics and Watermarking (IWDW 2011)

2 Contents Introduction 2. Layered Scrambling for Motion JPEG XR 3.1 Objective Assessments 3.2 Subjective Assessments 3. Assessment of Chroma-induced Privacy Leakage 4. Discussion and Conclusion

3 INTRODUCTION -3-

4 1. Introduction  Present-day video surveillance systems often come with high-speed network connections, plenty of storage capacity, and high processing power  The increasing ability of video surveillance systems to identify people has recently raised several privacy concerns  To mitigate these privacy concerns, scrambling can be leveraged to conceal the identity of face images in video content originating from surveillance cameras -4- Privacy protected surveillance videos

5 1. Introduction  The past few years have witnessed the development of a wide range of content-based tools for protecting privacy in video surveillance systems  Dependent on the location where scrambling (or encryption) is applied, three different approaches of scrambling can be distinguished Uncompressed domain scrambling Transform domain scrambling Compressed bit stream domain scrambling  One of the main challenge is to concealment of privacy-sensitive regions by making use of invertible transformation of visual information at a low computational cost -5-

6 1. Introduction  Content-based tools for privacy protection need to find a proper balance between the level of security offered and the amount of bit rate overhead  In general, altering the visual information present in privacy-sensitive regions typically breaks the effectiveness of coding tools  To limit bit rate overhead, many content-based tools for privacy protection only scramble luma information, leaving chroma information unprotected -6- Coding efficiency Security level

7 1. Introduction  In this paper, we investigate the contribution of non-scrambled chroma information to privacy leakage  To that end, we study and quantify the influence of the presence of non- scrambled chroma information on the effectiveness of automatic and human FR  Objective assessment: we apply automatic FR techniques to face images have been privacy-protected in the luma domain  Subjective assessment: we investigate whether agreement exists between the judgments of 32 human observers and the output of automatic FR -7-

8 1. Introduction  FR vs. Perception-based security metrics for assessing privacy level  Luminance Similarity Score (LSS), Edge Similarity Score (ESS), and Local Feature-based Visual Security Metric (LFVSM) [1,2]  However, these metrics are general in nature and are thus not able to take advantage of domain-specific information (e.g., face information) -8- [1] Tong, L., Dai, F., Zhang, Y., Li, J. “Visual security evaluation for video encryption,” in: Proceedings of ACM International Conference on Multimedia, 835–838 (2010) [2] Mao Y., Wu M., "A joint signal processing and cryptographic approach to multimedia encryption," IEEE Transactions on Image Processing, 15(7), (2006),

9 LAYERED SCRAMBLING FOR MOTION JPEG XR -9-

10 2. Layered scrambling for Motion JPEG XR  The video surveillance system studied makes use of Motion JPEG XR to encode surveillance video content  Motion JPEG XR offers a low-complexity solution for the intra coding of high-resolution video content, while at the same time offering quality and scalability provisions  Layered scrambling for JPEG XR [3]  Modified JPEG-XR encoder -10- [3] Sohn, H., De Neve, W., Ro, Y.M., “Privacy Protection in Video Surveillance Systems: Analysis of Subband-Adaptive Scrambling in JPEG XR,” IEEE Transactions on Circuits and Systems for Video Technology, 21, 170–177 (2011)

11 2. Layered scrambling for Motion JPEG XR  Overview of layered scrambling technique N denotes the number of MBs, L denotes the RLS parameter, K denotes the number of non-zero LP coefficients in a MB, and M denotes the number of non-zero HP coefficients in a MB Random level shift (RLS) for DC subbands - Random permutation (RP) for LP subbands - Random sign inversion (RSI) for HP subbands

12 ASSESSMENT OF CHROMA-INDUCED PRIVACY LEAKAGE -12-

13 3.1. Objective assessments  Experimental setup  FR technique used: PCA, FLDA, LBP  Face images: 3070 frontal face images of 68 subjects from CMU PIE (68 gallery, 340 training, and 2662 probe face images) Probe face images represent privacy-protected face images that appear in video content originating from surveillance cameras.  Performance evaluation: Cumulative Match Characteristic (CMC) curve  Notations -13- NotationExplanation DC, LP, and HPDC, LP, and HP subband S3S3 DC+LP+HP S2S2 DC+LP S1S1 DC Subscripts (Y, Co, Cg)Luma and chroma channels (Y, Co, and Cg) Prime (′)Scrambled image data

14 3.1. Objective assessments  Influence of distance measurement on FR effectiveness  Distance metric: Euclidean, Mahalanobis, Cosine, and Chi-square distance  In the remainder of our experiments, we make use of the Euclidean distance metric for PCA- and FLDA-based FR, and the Chi-square distance metric for LBP-based FR -14- D E : Euclidean distance D M : Mahalanobis distance D C : Cosine distance D H : Chi-square distance

15 3.1. Objective assessments  Scrambled luma information  Assumes that an adversary is not able to take advantage of the possible presence of non-scrambled chroma information in the privacy-protected probe face images -15-

16 3.1. Objective assessments  Scrambled luma and non-scrambled chroma information  We investigate whether layered scrambling is still effective when the scrambled luma channel and the non-scrambled chroma channels are simultaneously used for the purpose of automatic FR  Assuming that an adversary has access to the compressed bit stream structure, and thus to the non-scrambled chroma information  To take advantage of non-scrambled chroma information, we adopted feature-level fusion -16-

17 3.1. Objective assessments  Scrambled luma and non-scrambled chroma information -17-

18 3.1. Objective assessments  Non-scrambled chroma information -18-

19 3.2. Subjective assessments  Experimental setup  Number of observer: 32  We presented three scrambled probe face images of different subjects to the human observers for each experimental condition  Assessment method Human observers were asked to select the gallery face image that is most similar to the given probe face image human observers were also able to study the probe face images at different zoom levels -19- Gallery face images use for subjective assessment

20 3.2. Subjective assessments  Non-scrambled chroma information -20-

21 3.2. Subjective assessments  Scrambled luma and non-scrambled chroma information -21-

22 DISCUSSION & CONCLUSION -22-

23 4. Discussion  For video surveillance applications requiring a high level of privacy protection, both the luma and the chroma channels need to be scrambled at the cost of a higher bit rate overhead  Layered scrambling to both the luma (Y) and the chroma channels (Co and Cg) -23-

24 4. Discussion  Bit rate overhead  Security (ideal case)  Sub-sampling decreases the level of privacy protection, given the lesser amount of data available for scrambling  Total number of combinations required to break the protection of 10 MBs reduces from 3.6× (4:4:4) to 1.7× (4:2:0) -24-

25 5. Conclusions and future work  This paper studied and quantified the influence of non-scrambled chroma infor- mation on the effectiveness of automatic and human FR  Our results show that, when an adversary has access to the coded bit stream structure, the presence of non-scrambled chroma information may significantly contribute to privacy leakage  For video surveillance applications requiring a high level of privacy protection, our results indicate that both luma and chroma information needs to be scrambled at the cost of an increase in bit rate overhead  In order to compile a benchmark for privacy protection tools, future research will focus on identifying additional worst case scenarios -25-

26 Thank you for your attention! -26-

27 APPENDIX  Effectiveness of general-purpose visual security metrics  Visual security metric used Luminance Similarity Score (LSS), Edge Similarity Score (ESS), and Local Feature- based Visual Security Metric (LFVSM)  Lower the values computed by the visual security metrics, the higher the visual security -27-


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