Method and apparatus for registering color separation film

Abstract

A method and apparatus for registering the halftone color separation films used in color picture processing. A digital picture is taken of two register points on each separation film, and the pictures (which may contain register marks) are analyzed by algorithmic processes in order to calculate the movement necessary to register the halftone picture details (or register marks). Based on the calculations, the films are punched to provide a pair of register holes in each film at locations which result in registration when the register holes are aligned on register pins during the final reproduction process. The algorithmic process involves determining the halftone screen angle, average interdot spacing and fractional area occupied by each halftone dot within its halftone cell and using this data to construct a continuous tone picture. Interpolation techniques are used to interpolate the continuous tone picture to a registration picture which is a 150 line screen picture square with the raw data picture. Edge enhancement and tone normalization algorithms are used prior to registration. The final machine movements to achieve registration are computed from an algorithm that registers all points of the pictures from translational move data at two points.