US 4,649,502 A · Process and apparatus for evaluating printing quality and for regulating the ink feed controls in an offset printing machine

Abstract

The printed sheets are scanned, by image elements, immediately behind the last printing mechanism, with one or several measuring heads. Suitable dimensions of an image element range from approximately 1.times.1 mm.sup.2 to 10.times.10 mm.sup.2. In each image element the reflectance is measured in four spectral ranges (infrared for black, red for cyan, green for magenta and blue for yellow). The measured reflectance values are converted by means of Neugebauer equations into surface coverages in a demasking step and inputted to a computer for evaluation. With the same measuring device, both the reference values associated with OK sheets, and the actual values associated with continuous printing, are measured. The computer compares the measured data, weights them with respect to such factors as surface coverage, foreign color component and the environment of a respective image element, and produces a regulating signal to control the ink feed elements. The color coordinates (X,Y,Z) may be determined from the surface coverage values of the four colors in a parallel computer program. Image elements which are important for the visual appearance of an image are given a high weight. A quality measure may be determined from the weighted comparison of reference and actual values to change the visual appearance. With this process it is possible to control the ink feed elements of a multicolor printing press by direct on-line measurement of the printed image, without using color measuring strips.

Claims42

Dependent claims

A process for evaluating printing quality and for regulating ink feed controls in an offset printing machine by photoelectric measurement, by image elements, of both the printed products and a reference, in which the comparison, by image elements, of the printed products to the reference is the basis for the determination of a quality measure and of setting values for the ink feed control elements, comprising the steps of:

dividing a reference for the individual printing colors into a plurality of image elements, and for each image element, determining the reference surface coverage for the individual printing colors, the reference being in the form of at least one of a printing plate upon which the printing process is based, and a printed product which has previously been determined to be satisfactory, assigning to each image element, for each printing color, a weighting factor indicating a measure of the assurance with which the prevailing surface coverage may be determined, dividing the printed product into image elements in the same manner as is the reference, measuring the reflectance for each printed product image element, calculating the actual surface coverage for each of the printing colors from the respective reflectances, determining, for each image element and the individual printing colors, deviations of the actual surface coverages from the reference coverages, weighting the deviations with the assigned weighting factors, and determining at least one of the quality measure, and the setting values for the ink feed control elements, from said weighted deviations.

Dependencies are inferred from the claim text.

Process and apparatus for evaluating printing quality and for regulating the ink feed controls in an offset printing machine

Life of this patent

Process and apparatus for evaluating printing quality and for regulating the ink feed controls in an offset printing machine

Life of this patent

Abstract

Claims42