The concept of a clean aperture in a digital system defines an inner picture area (within the production aperture) within which the picture information is subjectively uncontaminated by all edge transient distortions (SMPTE 260M). Filtrations for bandwidth limitation, multiple digital blanking, cascaded spatial filtering, etc., introduce transient disturbances at the picture boundaries, both horizontally and vertically. It is not possible to impose any bounds on the number of cascaded digital processes that might be encountered in the practical post-production system.

Hence, the clean aperture is defined to represent an acceptable (and practical) worst-case level of production.