RP 157:2012 - SMPTE Recommended Practice - Key and Alpha Signals

This document describes the requirements for the key, alpha or matte signal with respect to its associated fill. In the remainder of the document the term “key” is used, but the requirements are equally applicable to all three. This description is given for digital and analog signals and is valid for all image formats, including without limitation SDTV, HDTV and UHDTV.