Editing Data compression (section)

== Lossy ==
{{Main|Lossy compression}}

[[File:Comparison of JPEG and PNG.png|thumb|Composite image showing JPG and PNG image compression. Left side of the image is from a JPEG image, showing lossy artifacts; the right side is from a PNG image.]]
In the late 1980s, digital images became more common, and standards for lossless [[image compression]] emerged. In the early 1990s, lossy compression methods began to be widely used.<ref name="Wolfram"/> In these schemes, some loss of information is accepted as dropping nonessential detail can save storage space. There is a corresponding [[trade-off]] between preserving information and reducing size. Lossy data compression schemes are designed by research on how people perceive the data in question. For example, the human eye is more sensitive to subtle variations in [[luminance]] than it is to the variations in color. JPEG image compression works in part by rounding off nonessential bits of information.<ref name="Arcangel"/>  A number of popular compression formats exploit these perceptual differences, including [[psychoacoustics]] for sound, and [[psychovisual]]s for images and video.

Most forms of lossy compression are based on [[transform coding]], especially the [[discrete cosine transform]] (DCT). It was first proposed in 1972 by [[N. Ahmed|Nasir Ahmed]], who then developed a working algorithm with T. Natarajan and [[K. R. Rao]] in 1973, before introducing it in January 1974.<ref name="Ahmed">{{cite journal |last=Ahmed |first=Nasir |author-link=N. Ahmed |title=How I Came Up With the Discrete Cosine Transform |journal=[[Digital Signal Processing (journal)|Digital Signal Processing]] |date=January 1991 |volume=1 |issue=1 |pages=4–5 |doi=10.1016/1051-2004(91)90086-Z |bibcode=1991DSP.....1....4A |url=https://www.scribd.com/doc/52879771/DCT-History-How-I-Came-Up-with-the-Discrete-Cosine-Transform}}</ref><ref name="DCT"/> DCT is the most widely used lossy compression method, and is used in multimedia formats for images (such as JPEG and [[HEIF]]),<ref name="JPEG"/> [[Video compression|video]] (such as [[MPEG]], [[H.264/AVC|AVC]] and HEVC) and audio (such as [[MP3]], [[Advanced Audio Coding|AAC]] and [[Vorbis]]).

Lossy image compression is used in [[digital camera]]s, to increase storage capacities. Similarly, [[DVD]]s, [[Blu-ray]] and [[streaming video]] use lossy [[video coding format]]s. Lossy compression is extensively used in video.

In lossy audio compression, methods of psychoacoustics are used to remove non-audible (or less audible) components of the [[audio signal]]. Compression of human speech is often performed with even more specialized techniques; [[speech coding]] is distinguished as a separate discipline from general-purpose audio compression. Speech coding is used in [[internet telephony]], for example, audio compression is used for CD ripping and is decoded by the audio players.{{cn|date=May 2025}}

Lossy compression can cause [[generation loss]].