Standard Codecs: Image compression to advanced video coding (3rd Edition)
A substantially updated edition of Video Coding: An introduction to standard codecs (IEE 1999, winner of IEE Rayleigh Award as the best book of 2000), this book discusses the growth of digital television technology, from image compression to advanced video coding. This third edition also includes the latest developments on H.264/MPEG-4 video coding and the scalability defined for this codec, which were not available at the time of the previous edition (IEE 2003). The book highlights the need for standardisation in processing static and moving images and extensively exploits the ITU and ISO/IEC standards defined in this field. The book gives an authoritative explanation of pictures and video coding algorithms, working from basic principles through to the advanced video compression systems now being developed. It discusses the reasons behind the introduction of a standard codec for a specific application and its chosen parameters. Each chapter is devoted to a standard video codec, and chapters are introduced in an evolutionary manner complementing the earlier chapters. This book will enable readers to appreciate the fundamentals needed to design a video codec for any given application and should prove a valuable resource for managers, engineers and researchers working in this field.
Inspec keywords: data compression; wavelet transforms; video coding; teleconferencing; storage media; video communication; digital storage; codecs; media streaming
Other keywords: digital storage media; JPEG2000; H.263; MPEG-1; subband coding; H.261; image compression; content-based advanced video coding; video compression; MPEG-4 visual; H.264; high-quality moving picture; MPEG-2; standard codec; bit rate communication; videoconferencing; wavelet transform; MPEG-21; MPEG-7
Subjects: Multimedia communications; Video signal processing; Image and video coding; Integral transforms; Teleconferencing; Digital storage; Integral transforms
- Book DOI: 10.1049/PBTE054E
- Chapter DOI: 10.1049/PBTE054E
- ISBN: 9780863419645
- e-ISBN: 9781849191135
- Page count: 504
- Format: PDF
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Front Matter
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1 History of video coding
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In this book, we start by reviewing briefly the basics of video, including scanning, formation of colour components at various video formats and quality evaluation of video. At the end of each chapter, a few problems have been designed, either to cover some specific parts of the book in greater depth or for a better appreciation of those parts. Principles of video compression techniques used in the standard codecs are given in Chapter 3. These include the three fundamental elements of compression: spatial, temporal and intersymbol redundancy reductions. The DCT, as the core element of all the standard codecs, and its fast implementation is presented. Quantisation of the DCT coefficients for bit rate reduction is given. The most important element of temporal redundancy reduction, namely motion compensation, is discussed in this chapter. Two variable length coding techniques for reduction of the entropy of the symbols, namely, Huffman and arithmetic coding, are described. Special attention is paid on the arithmetic coding, because of its role and importance in recent video codecs. The chapter ends with an overview of a generic interframe video codec, which is used as a generic codec in the following chapters to describe various standard codecs.
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2 Video basics
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In this chapter characteristics of video signals are discussed which will help in understanding how they can be exploited for bandwidth reduction without actually introducing perceptual distortions. Image formation and colour video are discussed. Interlaced/progressive video is explained, and its impact on the signal bandwidth and display units is discussed. Representation of video in digital form and the need for bit rate reductions are addressed. Finally, the image formats to be coded for various applications and their quality assessments are analysed.
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3 Principles of video compression
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The statistical analysis of video signals indicates that there is a strong correlation both between successive picture frames and within the picture elements themselves. Theoretically, decorrelation of these signals can lead to bandwidth compression without significantly affecting image resolution. Moreover, the insensitivity of the human visual system to loss of certain spatio-temporal visual information can be exploited for further reduction. Hence, subjectively lossy compression techniques can be used to reduce video bit rates while maintaining an acceptable image quality. For coding still images, only the spatial correlation is exploited. Such a coding technique is called intraframe coding and is the basis for Joint Photographic Experts Group (JPEG) coding. If temporal correlation is exploited as well, then it is called interframe coding. Interframe predictive coding is the main coding principle that is used in all standard video codecs, such as H.261, H.263, H.264 and Motion Picture Experts Group (MPEG)-l, -2 and -4.
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4 Subband and wavelet
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Coding of still images under MPEG-4 and the decision by the JPEG committee to recommend a new standard under JPEG2000 have brought up a new image compression technique. The committee have decided to recommend a new way of coding of still images based on the wavelet transform, in sharp contrast to the discrete cosine transform (DCT) used in the other standard codecs, as well as the original JPEG. In this chapter, we introduce this wavelet transform and show how it can be used for image compression.
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5 Coding of still pictures (JPEG and JPEG2000)
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In the mid-1980s, joint work by the members of the International Tele communication Union (Telegraphy section) (ITU-T) and the International Standards Organisation (ISO) led to a standardisation for compression of greyscale and colour still images [1]. This effort was then known as the Joint Photographic Experts Group (JPEG). As it is apparent, the word joint refers to the collaboration between the ITU-T and ISO. The JPEG encoder is capable of coding full colour images at an average compression ratio of 15:1 for subjectively transparent quality [2]. Its design meets special constraints, which make the standard very flexible. For example, the JPEG encoder is parametrizable so that the desired compression/ quality trade-offs can be determined based on the application or the wishes of the user [3]. JPEG can also be used in coding of video, on the basis that video is a succession of still images. In this case, the process is called motion JPEG. Currently, motion JPEG has found numerous applications. The most notable one is video coding for transmission over packet networks with unspecified bandwidth or bit rates (UBR). A good example of UBR networks is the Internet where, because of unpredictability of the network load, congestion may last for a significant amount of time. Since in motion JPEG, each frame is independently coded, it is an ideal encoder of video for such a hostile environment.
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6 Coding for videoconferencing (H.261)
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The aim of this book is the introduction to the fundamentals of video coding standards, rather than giving instructions on the details of a specific codec, we concentrate on the reference model (RM) codec. The RM is a software-based codec, which is devised to be used in laboratories to study the core elements as a basis for the design of flexible hardware specifications. During the development of H.261, from May 1988 to May 1989, the RM underwent eight refinement cycles. The last version, known as reference model eight (RM8) [2], is in fact the basis of the current H.261. However, the two may not be exactly identical (though very similar), and the manufacturers may decide on a dif ferent approach for better optimisation of their codecs. Herein we interchangeably use RM8 for H.261. Before describing this codec, we will first look at the picture format, and spatio-temporal resolutions of the images to be coded with H.261.
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7 Coding of moving pictures for digital storage media (MPEG-1)
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MPEG-l is the first generation of video codecs proposed by the Motion Picture Experts Group (MPEG) as a standard to provide video coding for digital storage media (DSM), such as compact disc (CD), digital audio tape (DAT), Winchester discs and optical drives. This development was in response to industry needs for an efficient way of storing visual information on storage media other than the conventional ana logue video cassette recorders (VCRs). At the time the CD-ROMs had the capability of 648 Mbytes, sufficient to accommodate movie programmes at a rate of approximately 1.2 Mbit/s, and the MPEG standard aimed to conform roughly to this target. Although in most applications the MPEG-l video bit rate is in the range of 1-1.5 Mbit/s, the international standard does not limit the bit rate, and higher bit rates might be used for other applications.
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8 Coding of high-quality moving pictures (MPEG-2)
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Following the universal success of H.261 and Motion Picture Experts Group (MPEG)-l video codecs, there was a growing need for a video codec to address a wide variety of applications. Considering the similarity between H.261 and MPEG-1, ITU-T and ISO/IEC made a joint effort to devise a generic video codec. Joining the study was a special group in ITU-T, Study Group 15 (SGI5), who were interested in coding of video for transmission over the future broadband integrated services digital networks (BISDN) using asynchronous transfer mode (ATM) transport. The devised generic codec was finalised in 1995 and takes the name of MPEG-2/H.262, though it is more commonly known as MPEG-2.
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9 Video coding for low bit rate communications (H.263)
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The H.263 recommendation specifies a coded representation that can be used for compressing the moving picture components of audio-visual services at low bit rates. Detailed specifications of the first generation of this codec under the test model (TM) to verify the performance and compliance of this codec were finalised in 1995. The basic configuration of the video source algorithm in this codec is based on the ITU-T recommendation H.261, which is a hybrid of inter picture prediction to utilise temporal redundancy and transform coding of the residual signal to reduce spatial redundancy. However, during the course of the development of H.261 and the subsequent advances on video coding in MPEG-1 and -2 video codecs, substantial experience was gained, which has been exploited to make H.263 an efficient encoder. In this chapter, those parts of the H.263 standard that make this codec more efficient than its predecessors are explained.
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10 Content-based video coding (MPEG-4 visual)
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MPEG-4 is another ISO/IEC standard developed by Moving Picture Experts Group (MPEG), the committee that also developed the Emmy Award winning standards of MPEG-1 and MPEG-2. While MPEG-1 and MPEG-2 video aimed at devising coding tools for CD-ROM and digital television, respectively, MPEG-4 video aims at providing tools and algorithms for efficient storage, transmission and manip ulation of video data in multimedia environments. The main motivations behind such a task are the proven success of digital video in three fields of digital television, interactive graphics applications (synthetic image content) and the interactive multimedia (World Wide Web, distribution and access to image con tent). The MPEG-4 group believe these can be achieved by emphasising the functionalities of the proposed codec, which include efficient compression, object scalability, spatial and temporal scalability, error resilience, etc.
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11 Advanced video coding (H.264)
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The ITU-T video coding experts group, after successful completion of their H.263 video codec in 1995, started to work on the advanced video coding (AVC) project. Their long-term objective was to recommend a video codec to be at least twice better than the existing video codec, such as H.263. The project was initially called H.26L, with L standing for long-term objectives [1]. However, H.263 was under constant improvement. Its improved version under H.263+ was finalised in 1997, and in 2000, the H.263H-\specification was ratified, where each + is an indication of major improvement. Most of the innovations in H.263+ in the forms of options or annexes were also fed to H.26L. ITU-T submitted H.26L to MPEG call for proposals in 2001. MPEG-4 experts group of ISO/IEC, who were not very happy with their content-based video codec (due to high complexity the codec could not be marketed), and its frame-based counterpart had a similar performance to H.263, showed an interest in this new codec. They joined the AVC project and worked closely with the ITU-T team. The project's name was then changed to joint video team (JVT).
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12 Content description, search and delivery (MPEG-7 and MPEG-21)
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The main aim of this chapter is the standards that specify how various elements for content creation fit together, and when a gap exists, MPEG-21 will recommend which new standards are required. The MPEG standard will then develop new standards as appropriate, while other bodies may develop other relevant standards. These spe cifications will be integrated into the 'multimedia framework' through collabora tion between MPEG and these bodies. The result is an open framework for multimedia delivery and consumption, with both the content creators and content consumers as the main beneficiaries. The open framework aims to provide content creators and service providers with equal opportunities in the MPEG-21 enabled market. It will also be to the benefit of the content users, providing them access to a large variety of data in an interoperable manner. In summary, MPEG-7 is about describing and finding contents, and MPEG-21 deals with the delivery and consumption of these contents. As we see, none of these standards are about the video compression, which is the main subject of this book. However, for the completeness of the book on the standard codecs, we briefly describe these two new standards that are incidentally developed by the ISO/IEC MPEG standard bodies.
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Appendix A: A 'C' program for the fast discrete cosine transform
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This appendix tackles the C program for the fast discrete cosine transform.
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Appendix B: Huffman tables for the DC and AC coefficients of the JPEG baseline encoder
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This appendix talks about the application of Huffman tables for the DC and AC coefficients of the JPEG baseline encoder.
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Appendix C: Huffman tables for quad tree shape coding
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This appendix discusses the Huffman tables for quad tree shape coding: table_012.dat is used at levels 0,1 and 2 and table_3.dat is used at level 3.
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Appendix D: Frequency tables for the CAE encoding of binary shapes
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This appendix presents the frequency tables for intra and inter blocks, used in the context-based arithmetic encoding (CAE) method of binary shapes.
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Appendix E: Channel error/packet loss model
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This appendix talks about the channel error and packet loss modelling.
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Appendix F: Solutions to the problems
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This appendix discusses the solutions to the video coding standard codecs problem to every chapter in the book.
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Appendix G: Glossary of acronyms
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This appendix provides a glossary of acronyms.
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Back Matter
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