Editing Compression artifact (section)

{{Short description|Distortion of media caused by lossy data compression}}
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[[File:Sego lily cm-150.png|thumb|right|Original image, with good text edges and color grade]]
[[File:Sego lily cm-150.jpg|thumb|right|Loss of edge clarity and tone "fuzziness" in heavy [[JPEG]] compression]]

A '''compression artifact''' (or '''artefact''') is a noticeable distortion of media (including [[Image|images]], [[Sound recording|audio]], and [[video]]) caused by the application of [[lossy compression]]. Lossy [[data compression]] involves discarding some of the media's data so that it becomes small enough to be stored within the desired [[File size|disk space]] or [[Data stream|transmitted]] (''streamed'') within the available [[Bandwidth (computing)|bandwidth]] (known as the data rate or [[bit rate]]). If the compressor cannot store enough data in the compressed version, the result is a loss of quality, or introduction of artifacts. The [[compression algorithm]] may not be intelligent enough to discriminate between distortions of little subjective importance and those objectionable to the user.

The most common digital compression artifacts are DCT blocks, caused by the [[discrete cosine transform]] (DCT) compression algorithm used in many [[digital media]] standards, such as [[JPEG]], [[MP3]], and [[MPEG]] video file formats.<ref name="Katsaggelos">{{cite book |last1=Katsaggelos |first1=Aggelos K. |last2=Babacan |first2=S. Derin |last3=Chun-Jen |first3=Tsai |title=The Essential Guide to Image Processing |date=2009 |publisher=[[Academic Press]] |isbn=9780123744579 |pages=349–383 |chapter=Chapter 15 - Iterative Image Restoration}}</ref><ref name="Alikhani"/><ref name="pcmag"/> These compression artifacts appear when heavy compression is applied,<ref name="Katsaggelos"/> and occur often in common digital media, such as [[DVD]]s, common computer file formats such as JPEG, MP3 and MPEG files, and some alternatives to the [[compact disc]], such as Sony's [[MiniDisc]] format. Uncompressed media (such as on [[Laserdisc]]s, [[Red Book (audio CD standard)|Audio CDs]], and [[WAV]] files) or [[lossless compression|losslessly compressed]] media (such as [[FLAC]] or [[Portable Network Graphics|PNG]]) do not suffer from compression artifacts.

The minimization of perceivable artifacts is a key goal in implementing a lossy compression algorithm. However, artifacts are occasionally ''intentionally'' produced for artistic purposes, a style known as [[glitch art]]<ref>{{cite web|last=Geere |first=Duncan |url=https://www.wired.co.uk/news/archive/2010-08/17/glitch-art-databending |title=Glitch art created by 'databending' |publisher=Wired |date=2011-12-13 |access-date=2011-12-23}}</ref> or datamoshing.<ref>{{cite web |last=Baker-Smith |first=Ben |url=http://bitsynthesis.com/2009/04/tutorial-datamoshing-the-beauty-of-glitch/ |title=Datamoshing&nbsp;– The Beauty of Glitch |publisher=Bitsynthesis.com |date=2009-04-28 |access-date=2009-04-28 |archive-url=https://web.archive.org/web/20101116143835/http://bitsynthesis.com/2009/04/tutorial-datamoshing-the-beauty-of-glitch/ |archive-date=2010-11-16 |url-status=dead }}</ref>

Technically speaking, a compression artifact is a particular class of data error that is usually the consequence of [[Quantization (signal processing)|quantization]] in lossy data compression. Where [[transform coding]] is used, it typically assumes the form of one of the [[basis function]]s of the coder's transform space.