METHOD FOR QUALITATIVELY EVALUATING MATERIAL

摘要

The invention relates to a method for qualitatively evaluating material with at least one identification characteristic whose position can vary within an expectation range designated by tolerance limits. The evaluation involves the use of at least one illuminating device, at least one photoelectric sensor and an evaluating device that interacts therewith. At least one background reference value and at least one mask reference are stored in the evaluating device, whereby the background reference value represents the characteristics of the printed image, particularly the gray scale value, in at least one portion of a surrounding area around the identification characteristic. In addition, the mask reference represents the geometrical contour of the identification characteristic and/or the relative arrangement of several identification characteristics among themselves. When inspecting the imprinted material, differential image data is formed, at least for the expectation range, from the actual image data and from the background reference value in the evaluating device. The actual position of the identification characteristic is subsequently derived in the evaluating device based on the comparison of the differential image data with the mask reference.