MiniTarget for Quality Control in Newspaper Printing

Running a printing press requires frequent measurements in order to achieve and maintain an acceptable level of print quality. Ideally, on-line measurements should be made and automatically used to adjust the inking system to achieve and maintain the desired target values. However, there are still several obstacles to this approach. As an intermediate solution, we have developed a system for quality control in newspaper printing, consisting of a miniaturized target, denoted in the following as MiniTarget, an optical device, and a three-chip CCD camera. The measurements are done off-line by a single shot. Individual prints are analyzed from which the behavior of the printing press can also be studied. The MiniTarget was minimized to approximately 0.8 cm2 , which is more than a magnitude smaller compared to control strips commonly used. The MiniTarget contains areas of solid tone and halftone, lines for register control, and elements for doubling and slurring. Due to its small dimensions it is accepted in newspaper printing. The CCD camera is a commercially available three-chip 8-bit camera. Using the camera and image analysis software that has been developed, we measure registration, solid-tone density, dot gain, doubling and slurring, and colorimetric values. A measurement is made by capturing the image of the test target in a single shot followed by image analysis.