A compression artifact (or artefact) is a noticeable distortion of media that includes images, audio and video caused by the application of lossy data compression that involves discarding some of the media's data so that it becomes simplified enough to be stored within the desired disk space or be streamed within the bandwidth limitations. At low bit rates, any lossy block-based coding scheme introduces visible artifacts in pixel blocks and at block boundaries. These boundaries can be transforming block boundaries, prediction block boundaries, or both, and may coincide with macroblock boundaries. Because this quantization process is applied individually in each block, neighboring blocks quantize coefficients differently. This leads to discontinuities at the block boundaries. These are most visible in flat areas, where there is little detail to mask the effect.