Theoretical determination of Optimum Split-Filter Exposures for Color-Correction Masks

A split-filter mask made by consecutive exposures through red, green, and blue filters provides better color correction than a mask exposed through a single filter. Nevertheless, split-filter masking has never been adopted in the direct screen separation method. This may be due to the difficulty in determining the optimum red:green:blue split-filter exposures. Optimum exposure ratios were determined with the assistance of a digital computer by systematically trying out 231 different combinations of red, green and blue exposures using the improved Yule-Pollack equation for calculating the effect of split-filter exposures. It was found that a red-blue and a red-green split-filter mask are sufficient for the green and blue separations respectively. For the red separation, a red-green-blue, three-filter split mask provides improved color correction.