lossy compression - technical definition

Referring to compression techniques that tend to produce artifacts, which are unintended and unwanted distortions or aberrations that result in a degraded signal, but supports very high compression rates. In video systems and communications, the artifacts often show up as jagged blockings or tiling effect known as aliasing, banding of colors, white spots, and even dropped frames. Although the picture is degraded as a result, the compression ratios can be as high as 200:1. The MPEG standards, for example, specify lossy compression in the form of discrete cosine transform (DCT). See also artifact, compression, DCT, lossless compression, MPEG, and signal.