Method and apparatus for monitoring and evaluating the quality of color reproduction in multi-color printing

摘要

Color control strips of sheets in a multi-color printing press are monitored by a light beam which is reflected by successive increments of the patches of the strip and passes through the filters of a filter wheel. The thus obtained color density signals are stored in memories, one for each color and each capable of storing the entire density profile of a patch. When the memories are filled to capacity, the admission of each fresh signal entails the eradication of the oldest stored signal. The stored profiles are evaluated by a microcomputer which discards certain signals and processes the remaining signals to ascertain the boundaries between neighboring patches, the center of the patch following the last-ascertained boundary, and the color density at the center of such patch. The evaluation can involve a comparison of the oldest and most recent signals in each memory and the processing of the resulting difference signals, such as a comparison of each difference signal with a fixed or variable threshold value for the purpose of ascertaining the aforementioned boundaries. The centers of the patches can be ascertained by counting the number of monitored increments of the patch following the last-ascertained boundary.