T.Sharon-A.Frank1

Multimedia

Size of Data Frame

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Major Issues

1. Size of Data Frame

2. Need High Bandwidth

3. Digital vs. Analog Representation

4. Multi-Modality Integration/Blending

5. Soft Real-Time Constraints

6. Need Group Communication

7. Need Synchronization

8. Need for Standards

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1 .Size of Data Frame

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Storage Requirements

580 MB 1 GB

1 GB 500 MB 100 MB

100 MB 6.4 MB

10 MB 1 MB

1 MB

500 pages 100 fax line 100 color 10 min of 10 min of 1 hour of

of text images images animation video video

(uncompr.) (compr. 15:1) (compr. 15:1) (compr. 30:1) (compr. 200:1)

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Use Compression

Use Smaller Frame Size

Solutions

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(Smaller )Frame Sizes

640x480 352x288 174x144

PAL CIF QCIF

(Q)CIF – (Quarter) Common Interchange Format

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What is Compression?

• Process of reducing the amount of data required to represent a given quantity of information.

• Same amount of information represented using fewer bits – relies on the notion of data redundancy.

• Sometimes called packing, coding, encoding or zipping.

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Compression Necessity (1)

Network

2. Bus

1. Storage

3. Communications

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Compression Necessity (2)

1. Storage – data is compressed before being stored, decompressed before being retrieved.

2. Bus – compressed data transfer requires reduced bandwidth.

3. Communications – sender compresses data before sending it over line, receiver decompresses it after receiving it.

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Compression Characteristics

• (A)Symmetrical Compression

• Lossless/Lossy Compression

• Spatial/Temporal Compression

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Types of Compression

• Entropy encoding – lossless. Data considered a simple digital sequence and semantics of data are ignored.

• Source encoding – lossy. Takes semantics of data into account. Amount of compression depends on data contents.

• Hybrid encoding – combination of entropy and source. Most multimedia systems use these.

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Compression Schemes (1)

Lossless Compression Method files are packed and unpacked without losing original data.

Run Length Encoding (RLE): Algorithm – redundant information replaced with run length code.

Symmetrical Lossy Compression Method – some loss of original data.

Joint Photographic Expert Group (JPEG): Uses DCT algorithm, works best on images without sharp edges or detail. Spatial Compression – redundancies in images are compressed.

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Compression Schemes (2)

Asymmetrical Lossy Compression – some loss of original data.

Motion Picture Expert Group (MPEG): applies predictive inter-frame coding techniques.

Combination of Spatial and Temporal compression – checks for redundancies within frame and from frame to frame.

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Compression Standards (1)

• Joint Photographic Experts Group (ISO)• International Standard for Continuous-Tone Still

Image Compression (Color Pictures, Slides)• Recommended in 1991JPEG

P*64

Multiple of 64 Kbps Coding (CCITT)International Standard for Video Telephony, Conferencing and CollaborationRecommended in Q4 1990

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Compression Standards (2)

Motion Pictures Experts Group (ISO)

International Standard for Compression of Addressable Video

Recommended in Q2 1992MPEG-1

MPEG-2

International Standard for Digital Broadcast Quality TV

Recommended in Q4 1994

International Standard for Narrowband Digital Broadcast of Media ObjectsRecommended in Q4 1998

MPEG-4

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Compression Standards (3)

• High Definition Television (FCC)

• Next Generation Standard for High Resolution Broadcast TV

• Recommended in Q4 1995 (ATSC DTV)

HDTV

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Video Coding Techniques

• MPEG1: standard for storage and retrieval of moving pictures and audio (VCR quality) on storage media (CD-ROM, WORM).

• MPEG2: standard for digital TV quality.

• MPEG4, H.261: standard for multimedia applications at very low bit-rate.

• MPEG7: multimedia content representation standard for information search.

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Emerging Market Segments (1)

Market Standard Transmission Medium

Analog Videophone In ProgressPOTS

NetworkDesktopCollaboration/Videotelephony

P*64Basic Rate ISDN

Switched Digital ServicesLAN

Business Conferencing P*64Primary Rate ISDN

Switched Digital ServicesLAN, ATM

Interactive Multimedia MPEG I CD-ROM, LAN, ATM

Digital Television (NTSC) MPEG II DBS, Cable, ATM

High Definition Television FCC DBS, Cable, Terrestrial

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Emerging Market Segments (2)

Market Bandwidth Image Size Frame Rate

Analog Videophone 8K-28K up to 170x128 3-5

DesktopCollaboration/Videotelephony

56K-128KQCIF 176x144CIF 352x288

5-15

Business Conferencing 384K+ 352x288 15-30

Interactive Multimedia 1M-2M up to

352x288 30

Digital Television (NTSC) 4M-15M 720x480 30

High Definition Television 17M+up to

1080x192030/60