motion estimation and compensation for very low bitrate video coding

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34 Chapter 1. Digital Video Coding at Very-Low BitRate This PPD considers that Multimedia is the convergent point of three industries, i.e. computer, telecommunications and TV/ lm industries. Although focusing at rst on all the very-low bitrate applications [103], MPEG-4 has decided to extend its scope so as to be a much more open and evolutive system: exibility and extensibility are its driving forces. The following sections highlight [57] the key points of MPEG-4 motivation(s) and principle(s). More details may be found in the Image Communication Special Issue [104] that explores the various aspects of the future standard on a video point of view. 1.4.3.1 Developments to Be Supported In addition to the increasing need for audio-visual communications at very-low bitrate [103], some new trends concerning the use of audiovisual information have to be taken into account. These are mainly: The way images are produced. Computer-generated images are being very commonly used. MPEG-4 addresses both \Synthetic & Natural Hybrid Coding" (SNHC [26]). The waymultimedia content isdelivered. VLBR is needed across \Global System for Mobile communications" (GSM) networks, but the same content could also been transmitted across ADSL (Asymmetric Digital Subscriber Loop) or ATM (Asynchronous Transfer Mode) nets, at a rate of several Megabits per second. Such a large range of bitrates requires scalability. Moreover, a scalable description of the information will enable the decoder to adapt itself to the processing power of the machine. The consumption of multimedia is rapidly evolving as it is taking more and more place in the way people communicate. The main changes in consumer habits are the need for interactive supports, possibilities to re-use the information and software implementations. 1.4.3.2 A New Challenge for the Representation of Audio- Visual Information In order to ll all these needs, MPEG-4 represents an audio-visual scene in a new way [100]: rather than considering a frame-based video, it
1.4 Some (Very-) Low BitRate Codecs 35 de nes the scene as a coded representation of Audio-Visual Objects (AVO). An AVO can be a Video Object Component (VOC), or an audio one (AOC) or a combination of both. These AVOs are obeying a scenario describing their relations in space and time. The scene depicted on gure 1.12 can be interpreted as a combination of ve AVOs: the background plus four elements. 4 2 Figure 1.12: Audio-visual scene described in terms of AVOs All these objects are separately encoded and the various objects bitstreams are multiplexed before being transmitted (Figure 1.13). In addition to this object-based representation of the information, a scene compositor ensures the possibility of re-using objects and extends the interaction capabilities of the scheme. Of course, this compositor is standardized (MPEG-4, just like many image coding standards, is a decoding standard) unlike the segmentation stage prior to coding (see Section 1.5 for a brief discussion of this topic). 1.4.3.3 Video Coding in MPEG-4 H.263 was used as an anchor for the subjective tests established with all the proposed codecs. Finally, the tools used to encode and compress the video information in MPEG-4 are very similar to the ones of H.263 (cf. Section 1.4.1), with the slight di erence that they are applied to objects whose borders should also be described. 5 3 1
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
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Page 14 and 15: 2 Introduction Ancient Greece initi
Page 16 and 17: 4 Introduction Meanwhile, the desir
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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
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84 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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motion estimation and compensation for very low bitrate video coding

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