Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
2001-01-26
2003-08-26
Garcia, Gabriel (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C382S167000
Reexamination Certificate
active
06611357
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to printing machines and, more particularly, relates to a method of stipulating values for use in connection with the open-loop or closed-loop control of a printing machine.
In the production of printed products it is known to register the application of ink quantitatively on measurement elements which are additionally printed at the same time or at measurement points in the actual printed image. Widespread use is made of the so-called color density measurement, in which measurement points having one or more printing inks are measured using appropriate filters in order to determine the ink film thickness. It is likewise known to measure measurement points, i.e., printing control strips or measurement points in the image, calorimetrically, in order, via the actual color loci thus obtained in conjunction with prescribed, desired color loci, including appropriate color offset (vector) formation, to derive the necessary actuating variables for the correction of the printing process. Furthermore, spectral measuring methods are known in which reflectances are determined over a multiplicity of reference points or continuously, for example, within the visible spectrum. In this case, the registered actual spectrum of a sample point of the printed product is compared with a prescribed desired spectrum, for example, a sample sheet or original, in order to derive therefrom the appropriate actuating commands for the ink feed. Spectral measurement and control methods of this type are typically used in gravure printing, since, in the case of this printing process, the additions to be fed to a color for the purpose of reaching a desired reflectance can be determined in a simple way from a registered spectral difference.
By way of example, DE 4 311 132 A1 discloses a method for effectuating closed-loop/open-loop control in a printing machine. In the disclosed method, the density spectra of sample prints of the individual printing inks with a stipulated area coverage, as well as the paper whiteness, are stored, the density spectra of a least one measurement point per inking zone on an original and corresponding measurement points on the printed product are determined, and the measured density spectra of the original and the printed product are represented as a linear combination of the density spectra weighted with the degrees of area coverage of the sample prints of the individual printing inks and of the paper whiteness. Subsequently, the degrees of area coverage are calculated in such a way that the density spectra are approximated in an optimum manner by the linear combination. In this manner, the ink feed is changed, in the event of a deviation of the degrees of area coverage of printed product and original, until an equalization of the density spectra is achieved. What is disadvantageous in the case of this method is that the factors in the formulation of the linear combination in order to represent the overall density spectrum, i.e., the combined print of the image points, are formulated from the density spectra of the individual colors as degrees of area coverage. A formulation of this type with respect to the factors presents problems at high degrees of area coverage of a color at an image point and ultimately fails during the printing of one or more colors in full-tone. The reason for this is that if, for example, one color of the original is printed as a full-tone area, the corresponding color in the printed copy can likewise be printed only as a full-tone and, moreover, not more intensely. Furthermore, this method presupposes that there already exists an original which was produced exactly with the printing inks used in the subsequent print, and on which the spectral reflectances are then determined at the corresponding image points.
By way of further example, DE 4 343 905 C2 discloses a method of determining the necessary change in the ink feed in a multicolor printing machine, in particular, an offset printing machine. In this method, the color density spectra of at least one colored image point and, simultaneously, the individual printing inks involved in the color at the point are recorded with regard to an original copy. In the case of each following printed copies, the color density spectra of the original and the printed copy are represented as a linear combination of the color density spectra of the individual colors, which are weighted with degrees of area coverage and paper whiteness. The degrees of area coverage of the individual colors are determined by linear regression. Based upon a comparison of the color density spectra, the derivation of an ink feed adjustment is performed in order to equalize the inking of the product copy to that of the original copy.
The comparison is accomplished by a differential color density spectrum which is determined from the color density spectra of corresponding image points of the original and of the printed copy and, in addition, the color density spectra of the printing inks (colored inks+black) involved in the print of the colored image. The differential color density spectrum between the original and printed copy is then represented as a linear combination of the color density spectra of the printing inks (colored inks+black) involved in the print of the printed copy, the coefficients of this linear combination being determined with the aid of linear regression. The coefficients which are determined from the linear combination then give a measure as to how the individual colors (colored inks+black) involved in the print of the printed copy must be changed in terms of their proportions. In the case of this method, it is irrelevant whether the original has been printed with the printing inks used later, or whether the original has even been produced using a quite different reproduction process. This color control method also operates using theoretically stipulated desired color density spectra.
Further methods disclosed in DE 4311 132 A1 and DE 4 343 905 C2 require that the desired color density spectra be determined at a multiplicity of image points of an original. A multiplicity of the printed products produced is set up as an original on image processing computers. Known art additionally permits the image data obtained in this manner, following appropriate color separation and subsequent raster image processing, to be further processed directly in order to generate the necessary printing forms, i.e., printing plates in offset printing. In the case of a purely digital workflow between the generation of the printing original and of the printing forms/printing plates to be used for printing, it is possible to dispense entirely with the production of originals in the form of sample prints, proofs or the like. In this case, it is even possible to stipulate desired colored loci of the digital original in the strictly calorimetric sense, since, by using color management systems, the characteristics of the color change between the output devices and the monitor of an image processing station/printing machine can be taken into account.
In DE 4 343 905 C2 yet another method for determining the necessary change of the ink feed in a multicolor printing machine is disclosed which has decisive advantages with regard to the convergence of the actual color density spectra of the printed copies which are to be guided to the desired color density spectra. However, this process presupposes previously known desired color density spectra and is in no way integrated into the color management systems which are known at present since color loci, i.e., desired color locus, actual color locus, are not used in this method.
EP 0 142 470 B1 discloses still a further method and device for assessing the print quality of a printed product which is preferably produced on an offset printing machine. In order to assess the print quality, the printed product and an original are each divided into image elements and measured photoelectrically image element by image element. The desired and actu
Schramm Peter
Wendt Karsten
Garcia Gabriel
Leydig , Voit & Mayer, Ltd.
MAN Roland Druckmaschinen AG
Poon King Y.
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