Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41F—PRINTING MACHINES OR PRESSES
  • B41F33/00—Indicating, counting, warning, control or safety devices
  • B41F33/0036—Devices for scanning or checking the printed matter for quality control
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41P—INDEXING SCHEME RELATING TO PRINTING, LINING MACHINES, TYPEWRITERS, AND TO STAMPS
  • B41P2233/00—Arrangements for the operation of printing presses
  • B41P2233/50—Marks on printed material
  • B41P2233/51—Marks on printed material for colour quality control

Definitions

• Test element based controls provide information about the Printing process. An overview of the current state of the art can be found in the IFRA report reproduced (Ifra, 2001).
• the MiniTarget measuring system described by kunzli et al pursues the second method (Brunzli, 1998). It represents a big step in the direction of miniaturization of quality control devices. With its dimensions of 7mm x 10mm, it is possible to capture the entire image information of the MiniTarget by single measurement with a CCD camera and derive the printing parameters mathematically.
• the MiniTarget concept is understood as a continuation of an idea that is already used in conventional print control strips. In particular, it is analogous to how print control strips are constructed on test elements which are arranged on a small area. With the existing dimensions, the MiniTarget still appears disturbing to the reader. In order to be invisible, or more appropriately "imperceptible", a size is required which is significantly less than 1mm 2 .
• the invention relates to a pattern of recording dots, such as lines and Surfaces with polygonal or circular boundaries, which is reduced so that it as Part of the printed image for the observer is not or almost not visible.
• This test target is magnified microscopically and preferably via CCD camera detected.
• the signal to noise ratio of the measurement is advantageously increased, which by averaging over several consecutive print patterns. through sophisticated image analysis, it is possible to directly print out the printing parameters to determine the miniaturized patterns.
• the measures for the reduction of the Test targets are described. Then, by way of example, the application to the type outlined a process control, which is essentially exemplary of the geometric features of a particular dot pattern.
• the dot pattern or test target is so small that it is virtually imperceptible to the naked eye by the observer.
• the dot pattern is formed by a plurality of dot clusters in a typical arrangement, preferably without point closure of the dot clusters with each other.
• the arrangement of the point clusters is typical in the sense that the dot pattern is identifiable as such in the print copy.
• the arrangement of the point clusters in the test target, ie the dot pattern is preferably periodic.
• the test target has a total area, ie area of the point clusters + area of the spaces, of at most one square millimeter and is preferably square. Preferably, its area is less than 0.5 mm 2 .
• the size specifications with respect to the area advantageously also apply if a virtual frame is drawn around the entirety of the point clusters of the test target, ie the size specification applies to the area within the frame.
• Each of the dot clusters is preferably printed in exactly one printing ink and is preferably formed from at least two recording dots in the X direction and two recording dots in the Y direction, ie, preferably at least four recording dots immediately adjacent in the X and Y directions.
• the X and Y directions correspond to the circumferential and lateral directions.
• the printed pixel can advantageously be understood as a recording point.
• the point clusters are at least so large that they can be analyzed planimetrically.
• the Evaluation is advantageously carried out in the printing press during printing.
• the TestTarget (Dot Pattern) for determining color densities and color locations in the overprinting of several Colors, the TestTarget (Dot Pattern) according to the invention with a complementary TestTarget (Trapping Pattern).
• the supplementary target preferably the same size and shape as the dot pattern based TestTarget. in the Four-color printing, for example, the supplementary TestTarget, depending on the color order, The following four color patches are included: C / M, C / Y, M / Y and C / M / Y.
• the Trapping Pattern can either side by side to the Dot Pattern or even independently on the Page of the printed copy.
• the invention can be used advantageously in offset printing, in particular in wet offset printing.
• a particularly preferred field of application is newspaper printing Fed rotary printing presses.
• An inventive test target can advantageously in the image or on non-image areas, in particular on a side edge, printed copy of the newspaper edition.
• the biggest advantages offers the invention in multi-color printing, although they also with advantage in monochrome Pressure can be used.
• test target is based on a specific dot pattern as shown in Figure 1.
• C, M, Y and K in Figure 1a symbolize clusters of recording points in the corresponding colors.
• n is the total number of point clusters in horizontal or vertical direction.
• the clusters are preferably equal in number to the x and y directions, i.e. 1x1, 2x2, 3x3, ..., p x p adjacent recording points.
• the Point size corresponds to the addressability of the output device, which in dpi (dots pro inch).
• the unprinted space in the TestTarget is q pixels both in the x and y directions.
• the point clusters are written in matrix notation by elements with the indices (i, j) designated.
• the dot pattern shown in the case of four-color printing is multi-color printing transferable.
• the arrangement of the colors is preferably such that the from top left to bottom right diagonal point clusters have the same color and in the top one Line in turn, all primary colors are arranged.
• a fictitious framework is preferably used in the Way defines that a cell results in a periodic regularity. This Measure is taken with regard to the evaluation, which is not of the Positioning of the measuring aperture should depend. On this topic is below received.
• control method is characterized by the fact that in Figure 1 at a Example test patterns described both the registration errors as well as the printing parameters can be removed.
• Area coverage can be determined, but point cluster-based parameters can be determined, which in conventional densitometry or spectrophotometry are not accessible.
• the presented type of point clusters is characterized by another noteworthy Property off.
• the dot patterns correspond to small-area halftone dots, which include characteristic information of the printing process.
• Small-scale point clusters As shown in Figure 1, process-related deviations of the pressure react significantly more sensitive than halftone dots in conventional control strips or in the MiniTarget.
• the most important influencing factor is the tone gain, which manifests itself in that points in comparison to the theoretical surface occupancy usually too large be reproduced.
• the effect is visualized in Figure 1b / c.
• the tone gain increases the point by a fixed amount, which is not the point diameter depends. As a result, the effect increases in inverse proportion to the dot radius.
• the Type of dot patterns as shown in Figure 1 will respond as a result in particular sensitive to process fluctuations.
• the page length at 635 dpi output is 0.56 mm.
• the area is 0.31 mm2. This is more than a hundred times smaller than that MiniTarget after Rienzli, 1998.
• a supplementary test target was developed especially for the density and color measurements.
• This test target preferably has the same size and shape as that on a Dot pattern based target. It is in four quadrants in the case of four-color printing divided, which contain printed swatches. These are in the case of Four color printing, depending on the color order, for example, C / M, C / Y, M / Y, and C / M / Y.
• the target may be side by side with the dot pattern based target, or else be placed independently. It is specially used to increase the color densities in the Overprint and determine the ink acceptance. This is a procedure applied, which is presented in (Rienzli, 2000).
• the components of the image analysis system preferably close a 3-CCD camera, a microscope, a frame grabber card and an image analysis software.
• measurement must be done by correctly adjusting the microscope, the lighting and the camera to be taken to get a stable and high-contrast image becomes. Too high amplification of the measurement signal results in a strong noise of the Image.
• the image analysis system can be used instead of one after the Tristimulus camera working, even with one, according to the spectral method working, spectrophotometer.
• the size of the orifice as well as its positioning on the sample to be measured. If the orifice is set small, only a few Point cluster detected. It must therefore be risked that the sample is not representative is, i. the differently colored point clusters not according to their proportionate Occurrence in the sample to be considered. This results in a systematic Measurement error (Romano, 1999). This is especially great when the ratio of Orifice size and the point cluster period has a low value and between two consecutive integers, e.g. 1.5 is. That's why the captured image section is adapted by software to the fictitious image frame, which represents an integer multiple of a period. This will get parameters which are independent of the measuring aperture setting. Basically, that's enough a single point cluster per ink to characterize the printing process. Out However, for sample preparation and metrology, it is recommended that for the measurement at least four point clusters per ink are provided.
• the two test fields presented are suitable despite the extremely small dimensions, to perform color and density measurements.
• the measurement of the solid density and the Color values of the individual colors are made at point clusters.
• For the measurements of overprinted colors becomes the color field based supplementary test field used, which is described earlier. This requires that the Measuring ranges are calculated by software.
• For the measurements is a calibration the 3 chip CCD camera required (Rienzli, 2000).
• the assessment of the digitized images takes place by means of image analysis (Demant Ch., 1998; Jahn B., 1997).
• the image analysis is based on the RGB image of the test pattern, which in sufficiently high resolution is shown.
• the diameter of a point cluster should be be recorded by at least 30 pixels. Most measurements will be for each ink made separately. In this case, the channel becomes one with Color evaluated, which is complementary to the observed ink.
• the determination Threshold is a basic image analysis process to obtain the point clusters from Paper white to distinguish (Barratte Ch., 1995). In the gray value histogram of the Gray value image, the signals of paper white and the ink are determined. As Threshold will be the arithmetic mean of the modal values of paper white and the Ink taken. Artifacts are eliminated during measurement by: small-area structures outside the point cluster positions are removed by image analysis become.
• the threshold value method converts the gray value image into a binary one Rendered to separate the point clusters from the paper white.
• the percentage area coverage is a determining factor in the printing process.
• the image-analytical surface measurement is based on the principle of planimetry. First, the areas of the point clusters become individual certainly. Then the dot cluster areas are summed for all colors and divided by the area of the fictitious aperture. The resulting value corresponds to the percentage area coverage.
• the parameter E describes the geometry of the point cluster with respect to an ellipse shape. This parameter is used below to determine push and duplicate.
• factor R is a measure of the smoothness of the edge course of point clusters (Haberffener, 1995), which is a characteristic variable of the printing process.
• Pushing and doubling are two typical effects in the printing process, which in one indicate disturbed litigation (Romano F., 1998). Can push through different rotational speeds of the two cylinders are caused and manifests itself in broadened lines across the printing direction. The effect manifests itself visually in vertical lines, which are widened and therefore darker appear.
• Duplication is caused by register problems between different printing units of Multicolor printing machines cause and express themselves in that the point is sideways shifted and attenuated appears again. Visually, you can see the effect of that Line fields in one direction appear darker as a result of the broadening. In contrast Duplication can occur in any orientation for pushing.
• Figure 4 shows a computer simulation of the effect.
• a presence of pushing is calculated according to equation (4) from the factor E in Connection derived with the position angle of the point clusters. From the statistical Treatment trends are visible. A preferred direction is then proven when the standard deviation of the angle is sufficiently small.
• Figure 2 shows a three-dimensional plot of a point cluster before and after the averaging.
• Relief representation of a point cluster printed by electrophotographic (left: 126 ⁇ m ⁇ 126 ⁇ m) and in newspaper printing (right: 250 ⁇ m ⁇ 250 ⁇ m).
• the vertical axis represents gray values.
• Relief of average dot clusters printed electrophotographically (left: sample size 36, 126 ⁇ m x 126 ⁇ m) and newsprint (right: sample size 41, 250 ⁇ 250 ⁇ m ⁇ m).
• the vertical axis represents gray values.
• Figure 3 shows grayscale images of dot clusters before and after the threshold process.
• Gray value images of four point clusters printed by electrophotography. (left: 250 ⁇ m ⁇ 250 ⁇ m) and in newspaper printing (right: 500 ⁇ m ⁇ 500 ⁇ m).
• the area coverage of the test sample of sample 1 is 8.7%.
• the sample size is 36 point clusters.
• the standard deviation of 0.8% results from random process and material variations, which result in point clusters of different sizes.
• Orientative measurements show that densitometric area measurements generally give larger values. This is justified by the optical light capture, which is not taken into account in the image analysis.
• the accuracy of the measurements depends significantly on the lighting as well as the choice of the threshold. It is therefore important to pay particular attention to reproducible measurement conditions.
• the following parameters refer to geometric point clusters and parameters obtained numerically from the surfaces of the point clusters.
• the dot circumference is 159 ⁇ m , which is slightly smaller than the specified value of 169 ⁇ m due to the smaller area coverage.
• the ellipsoid factor E is 87%, from which a roundish geometry is concluded. This finding is confirmed from the averaged structure in Figure 2. This also explains that the angle scatters strongly and thus can not recognize a preferred direction.
• the mean is 73 degrees and has a standard deviation of 59 degrees.
• the factor R of 0.72 indicates an uneven edge structure. This finding is visually consistent with the relief representation in Figure 2a and the gray scale images in Figure 3. The results of the newspaper print patterns show a similar behavior as Sample 1.
• Density and color measurements can be made equally on the test pattern in Figure 1 be performed.
• the image analysis system is calibrated according to a method which is described in the literature (Rienzli, 1998). It allows the conversion from RGB values to colorimetric and density values.
• diaphragms which determines the point clusters selectively.
• Figure 4 shows the computer simulation of pushing and doubling.
• testTarget can be used in conjunction with the described evaluation methodology for the control of multicolor printing.
• the process is especially popular where process control is required, but for reasons of space, no control strips can be used.
• a test pattern area that is well below 1mm 2 .
• an almost unlimited use is possible.
• a targeted positioning can now be made close to selected image locations.
• the limits of what was possible were rigorously explored. They culminate in the statement that the parameters relevant to printing technology can ultimately be taken from a test pattern which is made up of one point cluster per printing ink. However, an averaging over a plurality of successively printed print patterns is advantageous. All of the described measures, which in their entirety allow such a miniaturization of the test target, were tested experimentally or by simulation.

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• Engineering & Computer Science (AREA)
• Quality & Reliability (AREA)
• Facsimile Image Signal Circuits (AREA)
• Accessory Devices And Overall Control Thereof (AREA)
• Printing Methods (AREA)
• Non-Metallic Protective Coatings For Printed Circuits (AREA)
• Image Analysis (AREA)

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• 2001
  • 2001-09-07 DE DE10143942A patent/DE10143942A1/de not_active Withdrawn
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