Process for assessing the quality of a printed product

Abstract

The differences between the scanned values of corresponding image points of a specimen and an original are formed by point-by-point scanning and comparison with an original. The difference values are subjected to a tone or shade correction, and then a weighting process and a minimum threshold correction. In the shade or tone correction, a mean value formed from the difference values in a specific surrounding area of the associated image point is subtracted from each difference value. The weighting process is effected individually for each image point and results in systematic errors and critical image zones not producing faulty assessments. The weighting factors are determined by statistical analysis of specimens which are assessed as good visually. The minimum threshold correction eleminates all those pre-treated difference values which are below a certain minimum threshold. The difference values of the points surrounding each image point are added algebraically with distance-dependent weighting to the remaining difference values of each image point. The resulting values are compared with a threshold value for each image point. If these values exceed the threshold value at least at one image point, the specimen is assessed as faulty.

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