Exposure control process and photographic copying apparatus

Claim 1

Process for exposure control of photographic copies comprising the steps of: scanning a copy master by areas in a measuring station with a measuring light beam; detecting measuring light transmitted or reflected by the copy master with a detection device; converting the detected measuring light into electrical measuring signals corresponding to densities of the scanning areas; evaluating the electrical measuring signals in a computing and evaluating unit to determine density and color correction values; determining quantities of copying light and exposure times based on said density and color correction values; controlling a source of copying light in an exposure station in response to said determined exposure times; attenuating the intensity of the copying light impacting the entire copy master by areas in accordance with predetermined criteria, said step of attenuating being performed with a mask having locally different light permeabilities and further including the steps of: correlating individual densities of the copy master with spatial coordinates of scanning areas in a transport plane of the copy master; intermediately storing said individual densities in said computing and evaluating unit; determining a density range of the copy master from the individual densities; comparing said density range with a predetermined limit value; comparing a location dependent density variation of the copy master with a location dependent density variation of the mask if said density range exceeds said predetermined limit value; selecting a partial area of the mask having a location dependent density variation closest to an inverse location dependent density variation of the copy master; passing spatial coordinates of said partial area density variation relative to the copying light beam path to an x-y control device of a mask displacing device; and displacing said mask such that the partial area is entirely exposed to the copying light.