29-06-2012, 04:06 PM
IMAGE AND VIDEO COMPRESSION
[attachment=26151]
Why do we need to compress?
At any given time, the ability of the Internet to transfer data is fixed
Increase the rate of digital image data transfer or data rate (Megabit per second or Mb/s)
Reduce the total amount of digital storage required or data capacity (Megabyte or MByte).
Many files can be combined into one compressed document making sending easier, provided combined file size is not huge.
Why Can We Compress?
Coding redundancy
Most 2-D intensity arrays contain more bits than are needed to
represent the intensities
Spatial redundancy
Neighboring pixels are not independent but correlated
Temporal redundancy
Irrelevant information
Most 2-D intensity arrays contain information that is ignored
by the human visual system
Run Length Encoding
Run-length Encoding, or RLE is a technique used to reduce the size of a repeating string of characters.
This repeating string is called a run, typically RLE encodes a run of symbols into two bytes , a count and a symbol.
RLE can compress any type of data
RLE cannot achieve high compression ratios compared to other compression methods
It is easy to implement and is quick to execute.
Run-length encoding is supported by most bitmap file formats such as TIFF, BMP and PCX
What is MPEG ?
"Motion Picture Expert Group", established in 1990 to create standard for delivery of audio and video.
MPEG-1 : target VHS (Video Home System) quality on a CD-ROM (320 x 240 + CD audio @ 1.5 Mbits/sec) .
[attachment=26151]
Why do we need to compress?
At any given time, the ability of the Internet to transfer data is fixed
Increase the rate of digital image data transfer or data rate (Megabit per second or Mb/s)
Reduce the total amount of digital storage required or data capacity (Megabyte or MByte).
Many files can be combined into one compressed document making sending easier, provided combined file size is not huge.
Why Can We Compress?
Coding redundancy
Most 2-D intensity arrays contain more bits than are needed to
represent the intensities
Spatial redundancy
Neighboring pixels are not independent but correlated
Temporal redundancy
Irrelevant information
Most 2-D intensity arrays contain information that is ignored
by the human visual system
Run Length Encoding
Run-length Encoding, or RLE is a technique used to reduce the size of a repeating string of characters.
This repeating string is called a run, typically RLE encodes a run of symbols into two bytes , a count and a symbol.
RLE can compress any type of data
RLE cannot achieve high compression ratios compared to other compression methods
It is easy to implement and is quick to execute.
Run-length encoding is supported by most bitmap file formats such as TIFF, BMP and PCX
What is MPEG ?
"Motion Picture Expert Group", established in 1990 to create standard for delivery of audio and video.
MPEG-1 : target VHS (Video Home System) quality on a CD-ROM (320 x 240 + CD audio @ 1.5 Mbits/sec) .