05A Compression

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    .Mhlhuser Multimedia-Systems:

    Compression

    Prof. Dr.-Ing. Ralf SteinmetzProf. Dr. Max Mhlhuser

    MM: TU Darmstadt - Darmstadt University of Technology,

    Dept. of of Computer Science

    TK - Telecooperation, Tel.+49 6151 16-3709,

    Alexanderstr. 6, D-64283 Darmstadt, Germany, max@informatik.tu-darmstadt.de Fax. +49 6151 16-3052

    RS:TU Darmstadt - Darmstadt University of Technology,

    Dept. of Electrical Engineering and Information Technology, Dept. of Computer Science

    KOM - Industrial Process and System Communications, Tel.+49 6151 166151,

    Merckstr. 25, D-64283 Darmstadt, Germany, Ralf.Steinmetz@KOM.tu-darmstadt.de Fax. +49 6151 166152

    GMD -German National Research Center for Information Technologyhttc - Hessian Telemedia Technology Competence-Center e.V

    http://goback/
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    Scope

    Usage Applications

    Learning & Teaching Design User Interfaces

    Services Content

    Process-

    ing

    Docu-

    mentsSecurity ...

    Synchro-

    nization

    GroupCommuni-

    cations

    System

    s Databases Programming

    Media-Server Operating Systems Communications

    Opt. Memories Quality of Service Networks

    Basics Computer

    Archi-tectures

    Compression

    Image &

    GraphicsAnimation Video Audio

    http://goback/
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    Contents

    1. Motivation2. Requirements - General

    3. Fundamentals - Categories

    4. Source Coding

    5. Entropy Coding:

    6. Hybrid Coding: Basic Encoding Steps

    7. JPEG

    8. H.261 and related ITU Standards

    9. MPEG-1

    10. MPEG-2

    11. MPEG-4

    12. Wavelets13. Fractal Image Compression

    14. Basic Audio and Speech Coding Schemes

    15. Conclusion

    http://goback/
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    1. Motivation

    Digital video in computing means for

    Text:

    1 page with 80 char/line and 64 lines/page and 2 Byte/Char

    80 x 64 x 2 x 8 = 80 kBit/page

    Image:

    24 Bit/Pixel, 512 x 512 Pixel/image 512 x 512 x 24 = 6 MBit/Image

    Audio:

    CD-quality, samplerate44,1 kHz, 16 Bit/sample

    Mono: 44,1 x 16 = 706 kBit/s

    Stereo: 1.412 MBit/s Video:

    full frames with 1024 x 1024 Pixel/frame, 24 Bit/Pixel, 30 frames/s1024 x 1024 x 24 x 30 = 720 MBit/s

    more realistic360 x 240 Pixel/frame = 60 MBit/s

    Hence compression is NECESSARY

    http://goback/
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    2. Requirements - General

    high quality

    compression

    low delay

    low complexity (e.g., ease of decoding)efficient implementation (e.g., memory req.)

    intrinsic scalability

    http://goback/
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    Requirements

    DIALOGUE AND RETRIEVAL mode requirements:

    Independence of frame size and video frame rate

    Synchronization of audio, video, and other media

    DIALOGUE mode requirements:

    Compression and decompression in real-time(e.g. 25 frames/s)

    End-to-end delay < 150ms

    RETRIEVAL mode requirements:

    Fast forward and backward data retrieval

    Random access within 1/2 s

    Software and/or hardware-assisted implementation requirements

    http://goback/
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    3. Fundamentals - Categories

    entropy encodingsource coding

    - based on semantic of the data

    - often lossy

    channel coding

    - adaptation to communication channel

    - introduction of redundancy

    hybrid

    coding

    - entropy

    and

    source

    coding

    entropy coding

    - ignoring semantics of the data

    - lossless

    http://goback/
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    Categories and Techniques

    EntropyCoding

    Run-Length CodingHuffman Coding

    Arithmetic Coding

    Source

    Coding

    Prediction DPCM

    DM

    TransformationFFT

    DCT

    Layered Coding

    Bit Position

    Subsampling

    Sub-Band Coding

    Vector Quantization

    Hybrid

    Coding

    JPEG

    MPEG

    H.261, H.263

    proprietary: Quicktime, ...

    http://goback/
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    Categories & Techniques, Cont. (1)

    Two principal possibilities

    1. Entropy Coding: Eliminate Redundancy (thus, lossless)

    2. Reduction Coding: Eliminate Irrelevance / Low-Relevance (lossy)

    Preparatory Step: Decorrelation - Eliminate Interdependencies this is the essence of source coding

    changes "representation" of media

    goal usually: reduce dependencies between data

    as such, is a preparatory step!!

    usually, does not compress

    Steps in hybrid coding (often): decorrelation - reduction - entropy coding

    often: reduction by quantization

    last step: additional compresion without harm

    note: literature usually uses terms as in last slide!!

    note: reduction coding is "smart deletion", not really "compression"

    http://goback/
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    Categories and Techniques, Cont. (2)

    Major distinction: Symmetric / Asymmetric

    Asym. (usually): more effort for compression

    o.k. if compression non real-time, "only once" (movie!)

    may involve number-crunchers (...owned by content provider)

    Symmetric: "required" for real-time, e.g., videoconferencing

    in reality, often not 100% symmetricFurther considerations include, e.g.,

    Adjustable compression rate? ...quality?

    "smooth" bit stream ("isochronous")?

    terms: CBR (const. bit rate) vs. VBR (variable bit rate)

    may be "over time": e.g., packet size BigSmallSmall BigSmallSmall...

    may be simulated w/ loop-back filter plus buffer

    "progressive" (mainly: non-continuous media): display-while-download

    "streaming": ~ same for video (here, rather an issue of software)

    more subtle issues "open" standard?

    good "performance" (ratio, speed) for all kinds of media?

    bullet-proof, well-understood?

    ...

    http://goback/
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