Lecture-7 - 1 Lecture-7 Video Compression Mubarak Shah 2 What is Compression • Compression is a process of converting data into a form requiring

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1 Lecture-7 Video Compression Mubarak Shah 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!!! 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 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 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) 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 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! 7 Why is compression acceptable? • Limitations of visual perception – Number of shades (colors, gray levels) we can perceive – Reduced sensitivity to noise in high- frequencies (e.g. edges of objects) – Reduced sensitivity to noise in brighter areas • Ability of visual perception – Ability of the eye to integrate spatially – Ability of the mind to interpolate temporally Why is compression acceptable? • Some type of visual information is less important than others • Goal is to throw away bits in psycho- visually lossless manner • We have been conditioned to accept imperfect reproduction • Limitations of intended output devices 8 Why is compression possible?...
View Full Document

This note was uploaded on 06/12/2011 for the course CAP 6411 taught by Professor Shah during the Spring '09 term at University of Central Florida.

Page1 / 38

Lecture-7 - 1 Lecture-7 Video Compression Mubarak Shah 2 What is Compression • Compression is a process of converting data into a form requiring

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online