Closed Loop Color Control in the Work

Fifteen years ago, closed loop color control systems were introduced for commercial web offset presses. These systems soon became standard equipment. This generation of color control systems utilized color bars. The ink keys were adjusted so as to maintain proper color characteristics of the patches in the color bar. The advancement of technology has just recently made the next generation of color control systems possible. These systems do not rely on color bars but rather control color based on measurements of the printed images. Controlling color bars is relatively easy to understand, at least in principle. A measurement is made of a patch with a single color of ink. If the color is too weak, inking levels are increased. If the color is too strong, inking levels are decreased. Gray balance control is a bit more complicated, but the strategy is similar. There are two features of these control systems that simplify the task. First, the color bars are a known shape and size. Second, the color bars are a known that do not change from one job to the next. For Color Control In the Work (CCIW), the control system must be able to adapt to whatever is printed. Such a system must be able to decide how to adjust color for any ink combination. How this might be done is not entirely obvious. For this paper, I have reviewed a number of patents to understand a number of ways that CCIW might be performed. These methods are described. I also show the results of tests performed on a CCIW system that we have developed.