Data Compression Part 2
A very simple compression method is run-length encoding, which replaces the same continuous data with simple data-length encoding, which is an example of lossless data compression.
This method is often used on office computers to make better use of disk space, or to make better use of bandwidth on a computer network. Losslessness is a very important requirement for symbolic data such as spreadsheets, text, executables, etc., because in most cases even a single bit of data change is unacceptable, except in some limited cases.
For video and audio data, some level of quality degradation is acceptable as long as a significant portion of the data is not lost. Taking advantage of the limitations of the human perception system, a lot of storage space can be saved and the quality of the results obtained does not differ significantly from the quality of the original data. These lossy data compression methods generally require a trade-off between compression speed, compressed data size, and quality loss.
Lossy image compression is used in digital cameras to dramatically increase storage capacity with little degradation in image quality. Video compression with lossy MPEG-2 codec for DVD implements a similar function.
In lossy audio compression, psychoacoustic methods are used to remove inaudible or hard-to-hear components of a signal. Human speech compression often uses more specialized techniques, so “speech compression” or “speech coding” is also sometimes distinguished from “audio compression” as a separate field of study. Different audio and speech compression standards fall under the category of audio codecs. For example, voice compression is used for Internet telephony, while audio compression is used for ripping and decoding CDs using MP3 players.
theory
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Compression theory (which is closely related to algorithmic information theory) and rate distortion theory, research work in this area was established primarily by the American academic Claude Elwood Shannon, who in the late 1990s In the 1940s and 1950s, fundamental articles were published on the subject. in the early 1900s. Doyle and Carlson wrote in 2000 that data compression “is one of the simplest and most elegant design theories in all engineering fields.” Cryptography and coding theory are also closely related disciplines, and the idea of data compression and statistical inference also have deep roots.
Many lossless data compression systems can be viewed as a four-step model, and lossy data compression systems generally contain more steps, such as prediction, frequency transformation, and quantization.
