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Compression artifact
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<p>A compression artifact (or artefact) is a noticeable distortion of media (including <a href="/facts/Image/hbjEdTXK">images</a>, <a href="/facts/Sound_recording/BMbpAWkE">audio</a>, and <a href="/facts/Video/F1AV8ben">video</a>) caused by the application of <a href="/facts/Lossy_compression/jHW7DDv3">lossy compression</a>. Lossy <a href="/facts/Data_compression/gMFuY4FT">data compression</a> involves discarding some of the media's data so that it becomes small enough to be stored within the desired <a href="/facts/File_size/nd3d84MN">disk space</a> or <a href="/facts/Data_stream/57yDhBCd">transmitted</a> (<i>streamed</i>) within the available <a href="/facts/Bandwidth_(computing)/lY6Tb4gX">bandwidth</a> (known as the data rate or <a href="/facts/Bit_rate/ppUNMmVd">bit rate</a>). If the compressor cannot store enough data in the compressed version, the result is a loss of quality, or introduction of artifacts. The <a href="/facts/Compression_algorithm/gMFuY4FT">compression algorithm</a> may not be intelligent enough to discriminate between distortions of little subjective importance and those objectionable to the user. </p><p>The most common digital compression artifacts are DCT blocks, caused by the <a href="/facts/Discrete_cosine_transform/gPpDhPwP">discrete cosine transform</a> (DCT) compression algorithm used in many <a href="/facts/Digital_media/QLXzDrhL">digital media</a> standards, such as <a href="/facts/JPEG/HQ8QS3uB">JPEG</a>, <a href="/facts/MP3/yrBpxUSD">MP3</a>, and <a href="/facts/MPEG/ygmT7JBB">MPEG</a> video file formats. These compression artifacts appear when heavy compression is applied, and occur often in common digital media, such as <a href="/facts/DVD/7fJsHJrN">DVDs</a>, common computer file formats such as JPEG, MP3 and MPEG files, and some alternatives to the <a href="/facts/Compact_disc/g51GRloc">compact disc</a>, such as Sony's <a href="/facts/MiniDisc/yF3LYCqL">MiniDisc</a> format. Uncompressed media (such as on <a href="/facts/Laserdisc/nU4WJhDM">Laserdiscs</a>, <a href="/facts/Red_Book_(audio_CD_standard)/FDMqNLw5">Audio CDs</a>, and <a href="/facts/WAV/ptUfKleW">WAV</a> files) or <a href="/facts/Lossless_compression/LS702KsN">losslessly compressed</a> media (such as <a href="/facts/FLAC/TbqpHlWy">FLAC</a> or <a href="/facts/Portable_Network_Graphics/mwgK6xw5">PNG</a>) do not suffer from compression artifacts. </p><p>The minimization of perceivable artifacts is a key goal in implementing a lossy compression algorithm. However, artifacts are occasionally <i>intentionally</i> produced for artistic purposes, a style known as <a href="/facts/Glitch_art/yCs2CdUX">glitch art</a> or datamoshing. </p><p>Technically speaking, a compression artifact is a particular class of data error that is usually the consequence of <a href="/facts/Quantization_(signal_processing)/fddS3BE2">quantization</a> in lossy data compression. Where <a href="/facts/Transform_coding/JGJISRFW">transform coding</a> is used, it typically assumes the form of one of the <a href="/facts/Basis_function/Bt7jqjY2">basis functions</a> of the coder's transform space. </p>