Process and apparatus for the evaluation of the printing quality of a printed product by an offset printing machine
AssigneeGretag Aktiengesellschaft
InventorHans Ott
Life of this patent
Estimating the term…
Abstract
Printed products and their respective corresponding printing plates are divided into a plurality of image elements. For each image element the surface coverage is determined by photoelectric measurements; a reference reflectance value is then calculated from these measurements, taking into consideration such parameters as the printing characteristic. These reference reflectance values are compared with the actual reflectance values measured on the printed products and the results of the comparison are evaluated to form a quality measure and to calculate control values for the ink feed devices of the printing machine. In this manner, the use of special color measuring strips may be eliminated.
Claims34
A process for evaluating the printing quality of a printed product produced on an offset printing machine having a printing plate prepared from a photographic master, in which the printed product and a reference are each divided into image elements and photoelectrically measured, in which for each image element, a respective reference reflectance value and an actual reflectance value are determined and the respective reference and actual reflectance values of corresponding image elements compared with each other, and in which a quality measure Q is determined from said comparisons, comprising the steps of:
- determining, for each printing ink color, the reference reflectance value R.sub.s and the actual reflectance value R.sub.i and comparing them;
- assigning to each image element at least one of the following associated factors:
- a perception weighting factor H.sub.e which forms a measure of the perception of color deviations, and a full tone weighting factor G.sub.e which forms a measure of the effect of full tone density on the reflectance as a function of surface coverage;
- and weighting the differences between the reference reflectance values R.sub.s and the corresponding actual reflectance values R.sub.i with said at least one of the associated perception weight factor H.sub.e and full tone weight factor G.sub.e.
An apparatus for evaluating the printing quality of a printed product made on an offset printing machine having means for photoelectrically scanning printed products and a reference, by image elements, and having computing means, connected to said scanning means, for comparing the differences between printed products and the reference, by image elements, and for forming a quality measure from the results of the comparison, wherein the computing means assigns to each image element at least one of the following factors:
- a perception weighting factor H.sub.e, forming a measure of color deviations and a full tone weighting factor G.sub.e, describing the effect of full tone density on reflectance as a function of its surface coverage and color, and wherein the computing means further weights the differences between the printed product and the reference with at least one of the associated perception weight factor and full tone weight factor, respectively.
An offset printing machine, comprising:
- an apparatus for evaluating the printing quality of a printed product made on said offset printing machine, said apparatus having means for photoelectrically scanning printed products and a reference, by image elements, and having computing means, connected to said scanning means, for comparing the differences between printed products and the reference, by image elements, and for forming a quality measure from the results of the comparison, wherein the computing means assigns to each image element at least one of the following factors:
- a perception weighting factor H.sub.e forming a measure of color deviations, and a full tone weighting factor G.sub.e describing the effect of full tone density on reflectance as a function of its surface coverage and color, and wherein the computing means further weights the differences between the printed product and the reference with at least one of the associated perception weight factor and full tone weight factor, respectively.
Dependencies are inferred from the claim text.