Region-of-interest scrambling for scalable surveillance video using JPEG XR


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Region-of-interest scrambling for scalable surveillance video using JPEG XR.

Paper presented at ACM Multimedia 2009 in Beijing, China.

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Region-of-interest scrambling for scalable surveillance video using JPEG XR

  1. 1. Region-of-Interest Scrambling for Scalable Surveillance Video using JPEG XR Hosik Sohn, Wesley De Neve, and Yong Man Ro Image and Video Systems Lab, Department of Electrical Engineering, KAIST, Daejeon, Korea I. INTRODUCTION In this paper, we discuss a privacy-protected video surveillance • Contains more transform coefficients than a DC subband, but less system that makes use of the JPEG XR standard. This standard transform coefficients than an HP subband. offers a low-complexity solution for the scalable coding of high- • Random Permutation (RP) was applied to the different transform resolution images. To address privacy concerns, face regions are coefficients in the LP subband. detected and subsequently scrambled in the transform domain, taking into account the scalability features of JPEG XR. 3) HP and Flexbits Subbands II. IMAGE CODING USING JPEG XR • Visual effect of scrambled HP 1. Scalable Intra Coding subbands can hardly be seen at 4CIF resolution. • Low computational complexity, while offering a high image quality • Even at a low spatial resolution, and spatial and quality scalability provisions. face regions with a sufficiently • Frequency domain in JPEG XR (4 subbands) : DC (1), low pass (15), high resolution cannot be high pass (240), and Flexbits (256) subband. Fig 3. Visual impact of scrambled HP subbands: concealed adequately. (a) QCIF resolution and (b) 4CIF resolution. 2. ROI Representation • For this reason, we propose not to scramble HP subbands and Flexbits subbands. • Uniform tile layout : each tile has the same width and height. IV. EXPERIMENTAL RESULTS • Non-uniform tile layout : tiles may have 1. Visual Results different widths and heights. III. SCRAMBLING Fig 1. ROI representation 1. Proposed Encoder Architecture Secret key DC Fig 4. Privacy-protected surveillance video: (a) DC, (b) DC + LP, (c) DC + LP + HP, and (d) DC + LP LBT LBT Q Pred. Scrambling + HP + Flexbits. • Adaptive Low pass entropy 2. Bit Stream Overhead Analysis Adaptive coding Q Pred. Scrambling Table 1. Bit stream overhead according to the tile size scan • Fixed High pass/Flexbits length Tile grid 1x1 MB 5x5 MB 10x10 MB 9 tiles Adaptive coding Bit rate (Kbit/s) (%) (%) (%) Q Pred. scan 629 10.6 771.9 72.2 16.5 955 7.3 482.1 47.6 11.2 Fig 2. Architecture of our modified JPEG XR encoder 1348 4.5 323.0 32.8 7.4 2. Subband-Adaptive Scrambling 1964 2.8 207.9 21.5 4.6 Important factors for scrambling 2809 1.9 135.5 14.2 3.2 4404 1.2 86.8 8.9 1.9 • Visual importance of the subband. 5791 0.5 54.4 5.0 0.6 • Available amount of coded data in the subband. 8158 0.2 35.0 3.0 0.2 Fig. 5. Bit stream overhead introduced by scrambling • Level of security offered by the scrambling technique . 3. Security Considerations • Effect on the coding efficiency. • DC subband in one MB • Computational complexity of the scrambling technique.  2N+1 combinations 1) Scrambling for DC Subbands (N: the number of bits used to represent the fixed length part of Random Sign Inversion (RSI): the DC coefficient) where D denotes the data to be scrambled and where De denotes the • LP subband in one MB pseudo-randomly sign-flipped data.  15! Combinations Random Bit Flipping (RBF) is applied to the DC refinement bits and • Total number of combinations the level refinement bits: Fig. 6. Average number of bits used to represent  2N+1 + 15! the fixed length part of a DC coefficient B denotes the data to be encrypted while Be denotes the encrypted V. CONCLUSIONS data. Further, bi denotes the ith bit of B and R denotes the set of This paper discussed an approach for scrambling privacy-sensitive pseudo-random bits. face regions in scalable surveillance video coded using JPEG XR. Our Each DC coefficient is partitioned into a significant part and a approach is the result of a trade-off between the visual importance of refinement bits. The significant part is again partitioned into a level subbands, the amount of coded data in the subbands, the level of value and level refinement bits. security offered by a particular scrambling technique, the effect of 2) Scrambling for LP Subbands scrambling on the coding efficiency, and the computational complexity of the scrambling technique used. The results show that privacy- • LP subband : visually less important than a DC subband, but sensitive regions can be successfully concealed with a feasible level of visually more important than an HP subband. protection.