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

摘要

In this invention, when the portion from which a key signal alpha is to be generated of picture is caused to be foreground F, the portion except for the above is caused to be background B, and pixel value of pixels constituting that picture is designated at C, the key signal alpha is generated so as to satisfy the relational expression C' = (F-B) alpha ' (' (prime) represents differentiation). In more practical sense, a change detecting section 10 calculates change C' of pixel value between pixels constituting picture, and an F-B detecting section 30 calculates difference F-B between the foreground and the background. In addition, an integral value calculating section 40 divides the change C' by the difference F-B to integrate the result obtained by divisional operation to thereby determine key signal alpha . As a result, precise key signal can be obtained in this invention. <IMAGE>