METHOD AND DEVICE FOR BORDERING, IN DIGITAL OPTICAL IMAGE FORMATION, A SUBJECT INCRUSTED ON A BACKGROUND

For every point of an image in a special effects digital optical image formation method and apparatus the value of a border key signal is obtained by conducting a search for the maximum value of the subject's key signal in an analysis window centered on this point. The subject's key signals of the points in the window are delayed so as to make them simultaneous and are supplied to the same comparator which may be controlled in order to inhibit some of its inputs so as to define, for example, a circular analysis window; such a process makes it possible to obtain a regular border.