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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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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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(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 (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
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