Gretag Aktiengesellschaft

Heidelberger Druckmaschinen Ag

Gretag-macbeth Ag

Heidelberger Druckmaschinen

Heidelberger Druckmaschinen Aktiegesellschaft

Gretag Atkiengesellschaft

Gretak Aktiengesellschaft

Hans Ott

Helmut Kipphan

Nikolaus Pfeiffer

Gerhard Loffler

Manfred Schneider

Guido Keller

Thomas Senn

Bruno Zimmermann

Kurt Ruegg

Rolf Boegli

Willi Jeschke

Markus Berner

Fortunat Schrammli

Tino Celio

Wilhelm H Koch

Ulrich Birch

Andreas Spiess

Markus Weidmann

Jean-Pierre Graf

The device for the pixel-by-pixel photoelectric measurement of a planar measured object includes projection means for the imaging of the measured object onto a two-dimensional CCD image sensor, filter means provided in the imaging light path for the wavelength selective filtering of the measuring light impinging on the image sensor, signal processing means for the processing of the electrical signals produced by the image sensor and for the conversion thereof into corresponding digital raw measured, as well as data processing means for the processing of the raw measured data into image data representing the colors of the individual image elements of the measured object. Furthermore, illumination means are provided which include a Fresnel lens, which illuminate the measured object with at least one essentially parallel light bundle under an angle of incidence of essentially 45&#xb0;+/&#x2212;5&#xb0;. The projection means which include at least one tele-lens constructed as a Fresnel lens, are constructed as tele-centrical imaging optics, which image each point of the measured object under essentially the same angle of observation of essentially 0&#xb0; and with essentially the same aperture angle of essentially maximally&#xb0; onto the light converter element array. The data processing means carry out extensive correction measures.

Device for the pixel-by-pixel photoelectric measurement of a planar measured object

The device for the pixel-by-pixel photoelectric measurement of a planar measured object includes projection means for the imaging of the measured object onto a two-dimensional CCD image sensor, filter means provided in the imaging light path for the wavelength selective filtering of the measuring light impinging on the image sensor, signal processing means for the processing of the electrical signals produced by the image sensor and for the conversion thereof into corresponding digital raw measured data, as well as data processing means for the processing of the raw measured data into image data representing the colors of the individual image elements of the measured object. Furthermore, illumination means are provided which include a Fresnel lens, which illuminate the measured object with at least one essentially parallel light bundle under an angle of incidence of essentially 45&#xb0;+/&#x2212;5&#xb0;. The projection means which include at least one tele-lens constructed as a Fresnel lens, are constructed as tele-centrical imaging optics, which image each point of the measured object under essentially the same angle of observation of essentially 0&#xb0; and with essentially the same aperture angle of essentially maximally 5&#xb0; onto the light converter element array. The data processing means carry out extensive correction measures.

To obtain colorimetric values intended for regulating inking on a printing press ( ) from a printed image ( ) produced by the printing press ( ), the printed image is measured calorimetrically in a plurality of pixels ( ) with respect to a selected color coordinate system. The color vectors thus obtained for each pixel ( ) are used to calculate color difference vectors to predetermined reference color vectors based on the same color coordinate system or reference color vectors determined from a reference printed sheet ( ). The color difference vectors are multiplied by a weighting factor determined from the ink coverage of the pixels ( ) and/or the color differences between the pixels ( ) and their neighboring pixels ( ). The color difference vectors weighted in this way can then be used as colorimetric values for regulating the inking on the printing press ( ).

Method of obtaining colorimetric values

The invention relates to the use of a spectrophotometer connected with a computer to measure and store a solid color atlas in the computer. The halftone percentage values necessary for the adjustment of a given color are calculated by determining the desired color coordinates of the color involved and entered into the computer. The latter calculates from them, using the stored color atlas and a regression method, the halftone percentage values sought. In the process, with the aid of printing characteristics, stored color adaptations to prevailing printing conditions can be brought up to date without the need for the preparation of a new solid color atlas.

Process and apparatus for the determination of halftone percentage values

To improve the control of the inking process in an offset printing machine, color measuring fields provided on printed sheets are evaluated not as heretofore densitometrically but colorimetrically by means of spectral measurements. Spectral reflections are used to match colors, or color coordinates are calculated from them and compared with corresponding set reflections or set color coordinates. The color deviations obtained in this manner are used to control the inking process. For the stabilization of printing runs the spectral reflections are converted into filter color densities and the inking process is controlled on the basis of these color densities in a conventional manner. The control of the inking process using color deviations and control using color density may be superposed upon each other. The process makes it possible to adapt color impressions in delicate locations of importance for the image in the print to the corresponding locations of the proof. Color deviations due to different material properties and other error sources may also be equalized to some extent.

Process and apparatus for controlling the inking process in a printing

The scanning device comprises a measuring table (T) to which measured object B can be fixed for measurement, measurement carriage (W) with a photoelectric scanning device (100) which can be linearly moved over the surface of the measuring table by means of a drive unit (A), a control unit (S) for the measuring carriage (W), the scanning device (100) and the drive unit (A), and a processing unit (C) for processing and analyzing the measuring signals generated by scanning device (100) from scanned pixels (8) of measured object (B). Scanning device (100) in turn comprises a plurality of measuring heads (120) for pixel-by-pixel measurement of a corresponding plurality of pixels (8) of measured object (B) lying in a row one behind the other and along a corresponding plurality of scanning tracks (5a, 5b) which are parallel to motion direction (X) of measuring carriage (W) such that measured object (B) is sequentially scanned, pixel by pixel, in a grid-like scanning pattern.

Scanning device for pixel-by-pixel photoelectric measurement of a

Method and apparatus for the determination of the color value gradients of a picture element of a printed image when there are changes in the layer thicknesses of the inks used in the printing, the picture element (4) is photo-electrically scanned in the visible range of the spectrum and also in the near infrared range. From the scanning signals thereby obtained, color coordinates or an approximated subjectively equidistant color system and at least one infrared value is formed. The color value gradients are then calculated from these color coordinates and the at least one infrared value.

Method for controlling the inking of a printing press by determining

For determining the ink coverages of printing inks involved in printing in one pixel of a print image, the pixel is scanned photoelectrically in the visible range of the spectrum and also in the near infrared range. Color coordinates of a perceptually approximately equidistant color system and at least one infrared value are formed from the scanned signals thus obtained. The ink coverages of the printing inks involved in the printing are then calculated from these color coordinates and from the minimum of one infrared value and are allocated to the pixel.

Method of determining ink coverage in a print image

In order to control ink application in a printing press, a sheet (3) printed by the printing press (1) is colorimetrically measured in a number of pixels (4) with respect to a selected color coordinate system that has been expanded to be four-dimensional by also taking into account an infrared component. Color difference vectors with respect to the desired color vectors, predefined or determined from a reference sheet (3) and referred to the same color coordinate system, are computed from the color vectors obtained for each pixel (4). A sensitivity matrix is determined for each measured pixel (4) of the sheet (3). The pixels (4) are classified by sensitivity class. The color difference vectors and sensitivity matrices of the pixels (4) pertaining to the same sensitivity class are averaged for each sensitivity class, and input parameters, in particular film thickness modification vectors, are computed from the averaged color difference vectors and averaged sensitivity matrices of all sensitivity classes for a control unit (9) of the inking mechanisms of the printing press (1). The inking of the printing press (1) is then controlled on the basis of the input parameters thus computed.

Method controlling ink application in a printing press

Hand held unit for determining photometric data

A microcomputer controlled manual densitometer for the analysis of print control fields has a manual and an automatic operating mode. In the manual mode the measuring functions desired are selected by the operator, while in the automatic mode the measuring function is selected automatically on the basis of the type of the print control field measured. The densitometer is able to recognize the color of the print control field including overprint situations, and to distinguish between solid-tone fields including overprint situations, and to distinguish between full-tone fields and half-tone fields with two different nominal dot areas. For solid-tone fields the color and the solid-tone density, for overprint fields the ink trap and the overprint color and for half-tone fields the dot gain, the color and the nominal dot area, are detected and displayed. The color recognition is based on the relative variables of grayness and color hue error. Solid-tone and half-tone fields are distinguished by continuously updated, solid-tone density dependent dot area limits for corresponding density limits.

Apparatus for the analysis of print control fields

To improve the control of the inking process in an offset printing machine, color measuring fields provided on printed sheets are evaluated not as heretofore densitometrically but colorimetrically by means of spectral measurements. Spectral reflections are used to match colors, or color coordinates are calculated from them and compared with corresponding set reflections or set color coordinates. The color deviations obtained in this manner are used to control the inking process. For the stabilization of printing runs the spectral reflections are converted into filter color densities and the inking process is controlled on the basis of these color densities in a conventional manner. The control of the inking process using color deviations and control using color denisty may be superposed upon each other. The process makes it possible to adapt color impressions in delicate locations of importance for the image in the print to the corresponding locations of the proof. Color deviations due to different material properties and other error sources may also be equalized to some extent.

In a process for the evaluation of the quality of prints and for the color control or ink regulation of a printing machine, half tone fields, preferably gray balance fields, are scanned by a densitometer. The half tone density differences obtained by comparative measurements are transformed by an experimentally determined transform matrix into colorimetric measure differences of a color space uniformly graduated relative to perception, so that on the one hand the advantages resulting from quality evaluations in a true colorimetric system instead of a densitometric measure system may be utilized, and on the other, the use of regulation strategies requiring a colorimetric measuring system, such as for example the L*a*b* system or the LUV system, becomes possible. The transform matrix system is determined experimentally by producing a reference calibrating print and several addition calibrating prints, each containing one gray balance field and three full tone fields. In the case of each addition calibrating print the layer thickness of another full tone field is increased. By detecting the colorimetric measure differences and the half tone density differences and substituting them into a system of equations expressing the relationship between the half tone density differences and the colorimetric measure differences, the elements of the transform matrix describing the relationship between the half tone density variations and the associated colorimetric variations, may be determined.

Process for the determination of colorimetric differences between two

In a process for the ink control or regulation of a printing machine the actual color coordinates of measuring fields are compared with the desired color location. If the desired color location is found outside the correction color space defined by the boundary values of the full tone densities of the printing inks, as a substitute for the given desirable color locations, attainable desired color locations are determined on the surface of the correction color space by finding the point on the surface of the color correction space that is nearest to the given desired color location. The search for the nearest point may also be carried out in a manner such that the nearest point on the surface of the correction color space is sought in the direction of the brightness axis of the color space. If in the process, a boundary value of the brightness error is reached, the attainable desired color location is determined beginning at the desired color location displaced along the brightness axis to the maximum permissible brightness error.

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Regensdorf, Switzerland

Hans Ott