Lossy and Lossless
In information
technology, "lossy" compression is a data encoding method which
compresses data by discarding (losing) some of it. The procedure aims
to minimize the amount of data that needs to be held, handled, and/or
transmitted by a computer.
Lossy compression is most commonly used to compress multimedia data
(audio, video, still images), especially in applications such as
streaming media and internet telephony. By contrast, lossless
compression is required for text and data files, such as bank records,
text articles, etc. In many cases it is advantageous to make a master
lossless file which can then be used to produce compressed files for
different purposes; for example a multi-megabyte file can be used at
full size to produce a full-page advertisement in a glossy magazine,
and a 10 kilobyte lossy copy made for a small image on a web page.
It is possible to compress many types of digital data in a way which
reduces the size of a computer file needed to store it or the bandwidth
needed to stream it, with no loss of the full information contained in
the original file. A picture, for example, is converted to a digital
file by considering it to be an array of dots, and specifying the color
and brightness of each dot. If the picture contains an area of the same
color, it can be compressed without loss by saying "200 red dots"
instead of "red dot, red dot, ...(197 more times)..., red dot".
Lossy compression formats suffer from generation loss: repeatedly
compressing and decompressing the file will cause it to progressively
lose quality. This is in contrast with lossless data compression, where
data will not be lost via the use of such a procedure.
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