lect909h

lect909h - Video Phones Application of Structure from...

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1 Video Phones Application of Structure from Motion Video Compression Mubarak Shah
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2 What is Compression? • Compression is a process of converting data into a form requiring less space to store or less time to transmit, which permits the original data to be reconstructed with acceptable precision at a later time. Orange Juice Analogy! • Freshly squeezed orange juice (uncompressed) • Remove water (redundancy), convert it to concentrate (encoding) • Shipped, stored, and sold. • Add water to concentrate (decoding), tastes like freshly squeezed!!!
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3 Why is compression necessary? • Storage space limitations • Transmission bandwidth limitations. Resolution • QCIF: 180 x 144 • MPEG: 352 x 288 • VGA: 640 x 480 • NTSC 720x486 • Workstation 1280x1024 • HDTV: 1920 x 1080 • 35mm slide: 3072 x 2048
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4 Floppy Disk • Floppy disk capacity = 1.44 MB • A single 1280x1024x24 image= 3.9 MB • A single 640x480x24=922kB • Floppy disk holds only one VGA image! CD-ROM • Capacity=600 MB • A 1280x1024x24 @30 fps=118MB/s • CD-ROM would hold only about 5 sec of video! • A 160x120x16 image @30 fps=1.15MB/sec • CD-ROM now holds 8.7 minutes of video
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5 DVD-ROM • Capacity 2.4 GB to 15.9 GB • Single side/single layer Double side/dual layers • 4.4 to 25 times capacity of CD ROM • 20 sec to 2 minutes of 1280x1024x24 @30 fps • 3 hours of 160x120x16 image @30 fps Bandwidth • 160X120=1.15 MB/sec • Quad-speed CD-ROM drive delivers 600 KB/sec (half of the required speed) • DVD ROM delivers from 4Mbs to 9.8Mbs • “T1” line delivers 1.54 Mb/sec (192KB/sec) • Ethernet delivers 10Mb/sec (1.25 MB/sec) (barely fast enough, will use up entire bandwidth, 2-way video not possible)
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6 Digital TV • Networks started broadcasting limited DTV programs in Nov 98. • All commercial stations are supposed to switch to DTV by 2002 • All stations are supposed to switch to DTV by 2003 • Govt wants broadcasters’ NTSC channels returned by 2006 for auctioning! Digital TV • CBS carried few NFL games last year • CBS and ABC plans – evening news – movies – rest of the day up-convert standard TV • NBC – no broadcast yet – plans for “Tonight Show” this fall!
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7 Digital TV • CBS and NBC use 1080i (1920X1080), which is 995Mb/s at 30 fps • ABC and Fox use 720p (1280X720), which is 424Mb/s at 30 fps • 6 MHz channel assigned to each network can carry 19.4Mb/s • Need 50:1 compression ratio! Why is compression acceptable?
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lect909h - Video Phones Application of Structure from...

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