Referring to compressed video formats, particularly DVD and direct broadcast satellite using MPEG-2 compression, an artifact is a visual anomaly or error created when the compression system is not able to keep up with fast action or complex scenes in a video image. Artifacts are rare with direct broadcast satellite and rarer still with DVD, and when they occur they disappear in less than a second. Most artifacts take place in a single frame or a few frames resulting in errors lasting a fraction of a second. Artifacts tend to appear as clumps of colored blocks or pixels that obscure part of an image. n artifact may occur, for example, when two jet planes cross quickly in front of one another with a large explosion in the background. Since MPEG-2 compression uses as part of its compression technique a method of eliminating data that does not change from frame to frame, fast moving images may cause compression problems. If everything in the image changes rapidly from frame to frame, the compression scheme will not be able to eliminate redundant data since there would be none (or very little). In the jet plane example, the explosion is a rapid, changing background. The jets themselves are also moving quickly. This results in frames that contain little carryover or little redundancy. If the compression cannot keep up with the vast amounts of motion and the need to completely redraw each frame, artifacts may appear. In the jet planes example, the explosion may disintegrate into a blur of red and orange blocks resulting in a jagged appearance. Little can be done by the consumer to avoid artifacts, but they are of little concern in most systems due to their infrequent appearance and quick dissipation.