Block artifact
Block artifacts , also called blocks , building blocks or cubes , are rectangular and often multicolored visual disturbances in digitally transmitted images (e.g. JPEG and MPEG videos ), which are an undesirable side effect of image compression , but also in the event of data loss due to reading errors ( e.g. in Form of dropouts on digital video tapes ). They are caused by the technology used, so-called artifacts .
These disturbances arise at the edges of 8 × 8 pixel blocks, into which the image is divided in lossy compression methods such as JPEG , due to the inaccuracies that result from the quantization of the image data (more precisely: the DCT coefficients from the discrete cosine transformation ) are essential for data reduction during compression. Blocking artifacts cannot always be avoided, as a compromise has to be found between the highest possible image quality and the highest permissible memory requirement.