motion estimation and compensation for very low bitrate video coding

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24 Chapter 1. Digital Video Coding at Very-Low BitRate of pels on the image border is then reproduced (for more details, see Section 2.5.1). Arithmetic coding [60]: instead of Hu man codes [38], a more sophisticated entropy coding can be used. Advanced prediction mode: if necessary, a motion vector can be assigned to every 8 8 block. In addition, the motion reconstruction is achieved with overlapping (cf. Section 2.5.2). PB-frames: a PB-frame consists in two pictures being coded as one unit. A predicted (P) frame is a normal inter-coded one, while a bi-directionally predicted (B) frame is computed on the basis of both the previous frame and the next P frame (which is located in the future of B along the time axis). 1.4.1.4 Future Improvements: H.263+ Thanks to its ne tuning, H.263 already achieves very good results, combined with low complexity and fast computation. A software coder able to treat 5 frames of 144 176 pels per second and a decoder working faster than 30 frames=s are provided by Telenor Corp. at http://www.nta.no/brukere/DVC/. Moreover Bjontegaard [9] made a few improvements that are to be added to the existing standard in order to de ne a new one: H.263+. 1.4.2 \COMIS", the UCL Approach Initially developed by M.P. Queluz, B. Simon and B. Macq in the context of the European COST 211ter research group [112], and further rened by C. Devleeschouwer, T. Delmot, X. Marichal and B. Macq [70], the UCL has proposed an original scheme for VLBR video coding in which spatial information and temporal changes are encoded using similar tools: binary trees are used to transcribe a multiscale decomposition of the information, which explains the name of the algorithm: \COding on Multiscales Image Sequences" (COMIS). A complete description of the algorithm may be found in [65, 68]. Designed as a VLBR codec, COMIS tries to combine the cheap blockbased picture description provided by the multiscale representation and a region-oriented understanding of the pictures in order to improve the analysis and the reconstruction stages. Figure 1.4 presents the codec
1.4 Some (Very-) Low BitRate Codecs 25 scheme. One can notice that a \region model" box is present in both the encoder and the decoder. Therefore, no object information needs to be transmitted: the object detection can be simultaneously generated on both sides (for instance, via a morphological watershed procedure [134]), every time the decoder receives additional picture information. preprocessing CODER DECODER region model optional communication region model Figure 1.4: Scheme of the COMIS codec reconstruction user’s interaction An original bitrate regulation scheme [19] gives then the priority tothe regions that are considered subjectively more important. The following sections aim at presenting the way images are coded and the peculiarity of COMIS that voluntarily simpli es images (both in intra and inter mode) in order to reach VLBR with a good subjective quality. 1.4.2.1 Intra Images Figure 1.5 describes the way a picture is treated in the intra-mode. The following paragraphs provide explanations about the di erent parts. All the images presenting intermediate results will always refer to a letter (A to F) of the diagram. Tree decomposition. The objective of the spatial segmentation is to identify the regions with uniform luminance or with random textures. At rst, the image is split into non-overlapping 16 16 blocks 4 . Starting from such large blocks, the aim is to obtain homogeneous block 4 Any size 2 x would be convenient: if 16 16 is used, it is because analysis of test images [128] has shown that larger blocks are always inhomogeneous in a QCIF (144 176 pixels) picture.
Page 1: LABORATOIRE DE TELECOMMUNICATIONS E
Page 5: Avant-propos Mener a bien une these
Page 8 and 9: Resume L'estimation du mouvement re
Page 10 and 11: x 2.1.1 Apparent versus Real Motion
Page 12 and 13: xii A VLBR-like video sequences 167
Page 14 and 15: 2 Introduction Ancient Greece initi
Page 16 and 17: 4 Introduction Meanwhile, the desir
Page 18 and 19: 6 Introduction However, one can que
Page 20 and 21: 8 Introduction compensation in a vi
Page 22 and 23: 10 Introduction Once the proposed s
Page 25 and 26: Chapter 1 Digital Video Coding at V
Page 27 and 28: 1.2 Video Coding 15 These di erence
Page 29 and 30: 1.2 Video Coding 17 { The redundanc
Page 31 and 32: 1.2 Video Coding 19 exhaustive use
Page 33 and 34: 1.4 Some (Very-) Low BitRate Codecs
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Page 49: 1.5 Discussion 37 1.5 Discussion Th
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74 Chapter 2. Motion in the Framewo
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76 Chapter 2. Motion in the Framewo
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78 Chapter 3. Multiscale Block Matc
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Chapter 4 Image Pre-Processing for
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4.1 Intuitive Rationale 97 (a) (b)
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4.1 Intuitive Rationale 99 (a) (b)
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4.2 Rate Distortion Conditions 101
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4.3 Experimental Results 107 Pre-pr
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4.3 Experimental Results 109 Mean P
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4.3 Experimental Results 111 From t
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4.3 Experimental Results 113 Origin
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4.4 Conclusion 119 4.4 Conclusion T
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122 Chapter 5. Mesh-Based Motion Co
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162 Conclusion so as to adapt the s
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164 Conclusion gain is not as obvio
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Appendix A VLBR-like video sequence
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VLBR-like video sequences 169 Coast
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Appendix B Rate Distortion theory A
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B.1 Information Theory 173 B.1 Info
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B.2 Discrete Memoryless Sources and
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B.3 Rate Distortion Function 177 B.
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B.4 Extension to Moving Pictures 17
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B.4 Extension to Moving Pictures 18
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184 Chapter C. Markov Random Fields
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186 Chapter C. Markov Random Fields
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Appendix D Complements to Chapter 5
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D.2 Pseudo-code of the implementati
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Bibliography [1] COST 211ter Simula
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Bibliography 205 [21] E. Decenciere
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Bibliography 207 [41] R.M. Gray. Ve
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Bibliography 209 [65] B. Macq, M.P.
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Bibliography 211 [86] H.G. Musmann,
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Bibliography 213 [110] M.P. Queluz
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Bibliography 215 [132] F. Vermaut,
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