KEY SIGNAL GENERATING DEVICE, PICTURE PRODUCING DEVICE, KEY SIGNAL GENERATING METHOD, AND PICTURE PRODUCING METHOD

摘要

A key signal ( alpha ) is generated so that an expression C'=(F-B) alpha ' is satisfied where F, B, and C respectively represent the foreground of a picture which is the part for which the signal ( alpha ) is generated, the background (B) which is the other part than the former part and the value of a picture element constituting the picture and the prime "'" means that the variable marked with "'" is the derivative thereof. A change detecting section (10) calculates the change (C') of the picture element value between picture elements constituting the picture and an F-B detecting section (30) calculates the difference F-B between the foreground (F) and background (B). Then an integrating section (40) finds the key signal ( alpha ) by dividing the change (C') by the difference F-B and integrating the divided results. Therefore, accurate key signals can be obtained by this invention.