Editing Lossy compression (section)

{{Short description|Data compression approach that reduces data size while discarding or changing some of it}}
[[File:Comparison of JPEG and PNG.png|thumb|Composite image showing JPG and PNG image compression. Left side of the image is from a low-quality JPEG image, showing lossy artefacts; the right side is from a PNG image.]]

In [[information technology]], '''lossy compression''' or '''irreversible compression''' is the class of [[data compression]] methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size for storing, handling, and transmitting content. Higher degrees of approximation create coarser images as more details are removed. This is opposed to [[Lossless compression|lossless data compression]] (reversible data compression) which does not degrade the data. The amount of data reduction possible using lossy compression is much higher than using lossless techniques.

Well-designed lossy compression technology often reduces file sizes significantly before degradation is noticed by the end-user. Even when noticeable by the user, further data reduction may be desirable (e.g., for real-time communication or to reduce transmission times or storage needs). The most widely used lossy compression algorithm is the [[discrete cosine transform]] (DCT), first published by [[N. Ahmed|Nasir Ahmed]], T. Natarajan and [[K. R. Rao]] in 1974.

Lossy compression is most commonly used to compress [[multimedia]] data ([[Sound recording and reproduction|audio]], [[video]], and [[image]]s), especially in applications such as [[streaming media]] and [[VOIP|internet telephony]]. By contrast, lossless compression is typically required for text and data files, such as bank records and text articles. It can be advantageous to make a [[Master recording|master lossless file]] which can then be used to produce additional copies from. This allows one to avoid basing new compressed copies on a lossy source file, which would yield additional artifacts and further unnecessary [[Lossy compression#Information loss|information loss]].