Thursday, May 24, 2012

Data Compression

What is data compression?
It is a term for a group of technologies that encodes large files to convert them into a smaller file.
What is a data compression ratio?
 {\rm Compression\;Ratio} = \frac{\rm Compressed\;Size}{\rm Uncompressed\;Size}
 {\rm Compression\;Ratio} = \frac{\rm Compressed\;Data\;Rate}{\rm Uncompressed\;Data\;Rate}

Data compression ratio is also known as the compression power, used to count the reduction in data-representation size by a data compression algorithm.

Why is data compression an important technique for the online world?
It is important as it helps compress data to be downloaded/uploaded to anything, from anything.
What is the difference between Lossy and Lossless data compression?
Lossless compression recreates a compressed file as an identical match to its original form. All lossless compression breaks up a file into smaller pieces, for storage or transmission, later on. It uses compression algorithms which allow it to copy the data exactly while Lossy data retrieves data that may be different from the orginal but is still similar to the original without anyone noticing.

Which method offers the greatest compression ratio?
the lossy compression is the offers the greatest compression. the rate or a lossy compression is about 5-6% while the rate of lossless compression ranges from 50-60%.
Why is human psychology and perception an important factor in methods of Lossy compression?
It is an important factor as it allows us to get rid of data that no one notices.
Name Lossy file formats for audio, still image and video format.


Audio:

MP3 - .mp3

WMA - .wma


Still Image:

DjVu - .djvu .djv

JPEG - .jpg .jpeg


Video:

MPEG-1 - .mpg .mpeg .mp2 .mp3 .mpa

MPEG-2 - .mpg .mpeg .mp2 .mp3 .m2v

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