Method and apparatus for preparing picture masks

A method and apparatus for preparing a fine mask of a boundary on a picture of an area of interest to be separated from the remainder of the picture by: storing a digitized representation of the picture, and of a rough mask defining the approximate boundary of the area of interest; and then sequentially selecting regions of search on the rough mask to identify boundary segments, each subsequent region of search being selected by extrapolation from the preceding region of search in the direction of boundary segments identified by the preceding region of search, until the first region of search is met or until a boundary segment is not found in the region of search, whereupon the next region of search is selected by interpolation between the preceding region of search and the closest point on the approximate boundary defined by the rough mask.