Abstract: Radiation pulses are directed at a measuring spot on a rotating printing-image carrier in an offset printing press. The intensity of the radiation returned from the measuring spot outside of the angle of reflection of the pulse is measured for a predetermined wavelength. A pulse is directed at the measuring spot before printing and while the measuring spot is dry, and a signal representing the intensity of the returned radiation is stored in a working memory. During a subsequent printing operation, a dampening agent is applied to the printing-image carrier. In order to determine the amount of dampening agent on the printing-image carrier, radiation pulses are directed at the measuring spot as the printing-image carrier rotates during printing. The intensity of the returned radiation in the predetermined wavelength is converted into damp signals which represent the amount of dampening agent since the predetermined wavelength approximates or equals an absorption wavelength of the dampening agent.

Abstract: 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.

Abstract: A printing plate is secured to the printing cylinder of an offset printing machine by clamping bars which are installed in the cylinder channel and carry gripping strips serving to hold the edges of the printing plate. The front edge of the printing plate is provided with cutouts for the tips of feelers forming part of electronic measuring devices which are mounted on the guide strips of the printing cylinder. The cutouts have a fixed relationship relative to images on the printing plate. The clamping bar for the front edge of the printing plate is adjustable with reference to the printing plate by tightening screws until the measuring devices indicate that the front edge is in zero position. The measuring devices thereupon indicate any deviations of the position of the printing plate from zero position with reference to the printing cylinder.