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.
A compression technique that does not decompress digital data back to 100% of the original. Lossy methods can provide high degrees of compression and result in smaller compressed files, but some number of the original pixels, sound waves or video frames are removed forever. Examples are the widely used JPEG image, MPEG video and MP3 audio formats. The greater the compression, the smaller the file. However, a high image compression loss can be observed in photos printed very large, and people with excellent hearing can notice a huge difference between MP3 music and high-resolution audio files (see audiophile). Typically, the moving frames of video can tolerate a greater loss of pixels than still images. Lossy compression is never used for business data and text, which demand a perfect restoration (see lossless compression). See data compression, codec examples, JPEG, MPEG and MP3.