DE102010049945A1 - Method for detecting geometric errors of printed image, involves measuring reference position on substrate with measuring device - Google Patents

Abstract

The method involves measuring reference position on a substrate with a measuring device (8). The XY-position of the measuring device is determined with respect to the reference position. The pressure points of the colors are identified at the reference position. A comparing position is measured on the substrate with the measuring device. An independent claim is also included for a device for detecting geometric errors of a printed image.

Description

The present invention relates to a method and a device for detecting geometrical errors when transferring a printed image onto a printing substrate, wherein areas of a printed printing material are measured by means of a measuring device.

In methods for paper stretch compensation it is known that at least one print original is created, which is based on the print image, the print original is rasterized and at least one raster bitmap is generated, the raster bitmap is in the form of a matrix with m rows and n columns whose elements information about contain a color to be printed and the raster bitmap is manipulated by matrix manipulation so that geometric distortions of the printed image are compensated on the substrate.

In reproduction technology, print templates are created for printed pages containing all the elements to be printed, such as text, graphics and images. In the case of electronic production of the print templates, these elements are in the form of digital data. For an image, the data z. B. generated by the image in a scanner scanned point and line by line, each pixel is decomposed into color components and the color values of these components are digitized. Usually, images in a scanner are decomposed into the color components red, green and blue (RGB). For four-color printing, these components are then further transformed into cyan, magenta, yellow and black (CMYK) inks.

In the further course of work, the digitized texts, graphics and images in a processing station under visual control on a color monitor or automatically according to stored layout specifications to a printed page complained. The print page is then described in a data format, e.g. In the page description language PostScript or as PDF, and stored. In order to produce a printing plate for each printing ink, the printing page data consists of color separation data for one of the printing inks CMYK. The color separation data are recorded on a film or disk recorder in very high resolution on film or directly on printing plates. There are also digital printing machines that work without printing plates. In this case, the color separation data are transferred directly to the digital press and printed there on the substrate.

For recording on film material or printing plates, the color separation data are converted into high-resolution bitmap data in a raster image processor (RIP), whereby screen dots of different sizes are produced for the different density values of the colors. The result is a high-resolution binary image with only two brightness values per pixel (black or white). In English usage, such an image is referred to as a "bitmap" or as a raster bitmap, in the German jargon also as a "stroke image".

The raster bit map thus generated is forwarded to a printing plate setter where a printing plate is exposed based on the information of the raster bit map.

If the printing plate thus produced is used in a printing press, depending on the type of printing plate used, color is transferred from the exposed or unexposed pixels or pixels of the printing plate to a printing substrate.

The printing material is passed through a corresponding printing gap for printing, where it is acted upon by the color. The more ink is applied to the substrate, the moister it becomes and is distorted geometrically as it passes through various pressure gaps. It comes to a geometric distortion, as in 1 is shown. The substrate, z. As paper is distorted trapezoidal and with it the applied to the substrate printed image.

To compensate for these geometric errors, it is out of the DE 197 24 066 B4 It is known to supply the raster bitmap to a matrix manipulation device by which the raster bitmap itself is distorted by matrix manipulations opposite to the expected distortions of the printing material. In the matrix manipulation device, geometric error correction is performed by means of individual functions which are applied to the matrix representing the raster bitmap. With regard to a possible correction method for paper stretch compensation, the following will be referred to DE 197 24 066 B4 directed.

In order to be able to make a corresponding correction of the paper stretch in the raster bitmap, it is necessary to know the parameters which describe the elongation of the paper or, in general, of a printing material. This is in the DE 197 24 066 B4 proposed that elements for the construction of the printed image are inserted specifically for this measurement operation or already existing vernier elements and electronically evaluable position markers, which are already provided in the normal production, measured and evaluated or suitable elements in the printed image, ie measured in the subject itself. Edge elements or existing register elements are proposed here as suitable elements.

It is known to the person skilled in the art how such distortions of a printing material can be determined from special measuring elements or existing position markings or vernier elements. However, it is more problematic to measure suitable elements of the subject yourself in order to deduce the paper or substrate stretch or the geometry errors of the printed image.

The object of the present invention is therefore to present a method and a device with which a simple detection of geometrical errors of the printed image is possible even without existing or specially printed position markings.

The invention is achieved by a method according to the preamble of claim 1, wherein first a reference position on the substrate is measured with the measuring device, the XY position of the measuring device is determined with respect to the reference position, and the pressure points of the colors used in the reference position detected and their XY coordinates are determined.

This is based on a multi-color printing, which is particularly useful, since only then geometric errors caused by the printing of the substrate, which affect the overprinting of the printing inks. For the reference position, it is advantageously provided that a position is selected which has points which comprise different colors. By means of the measuring device, the XY coordinates of the pressure points of the colors used can then be recognized via the XY position of the measuring device and the position of pressure points of the different colors within the detected area. These XY coordinates can then be further stored in order to be used for the determination of the geometry errors.

Furthermore, at least one comparison position on the printing substrate is measured with the measuring device in the manner described above, such that XY coordinates are determined by determining the relative XY position of the measuring device relative to the reference position in combination with the coordinates of printing points within the detected area at this comparison position detected, determined and preferably stored for pressure points of the colors used here.

In order to obtain uniquely assignable XY coordinates in the pressure points detected at the comparison position, it is advantageously provided that a specific pressure point in the measured range of the reference position is defined here as the zero point with respect to the XY coordinate system of the pressure points. The XY coordinates of the pressure points of the different colors at the reference position and also at the comparison positions can then be determined via the respective XY positions of the measuring device and the position of the measured pressure points in the respectively recognized regions.

In this way, usable pressure ranges can be prescribed and defined together with fixed XY coordinates even without the use of special position markings. From deviations from XY coordinates of these pressure points with one another and / or to a raster bitmap on which the printed image is based, the geometric errors or paper strains to be compensated can then be determined. For this purpose, the XY coordinates of at least two pressure points of different color at the comparison position are compared with the XY coordinates associated Rasterpunkte a raster bitmap underlying the printed image and deviations are recognized or it will be the differences of the XY coordinates of the pressure points at the comparison position with differences of XY Coordinates of pressure points of the same different colors in the range of the reference position detected and determined deviations of the XY coordinates themselves or the differences as such. Hereby, it is provided in particular in a further development that pressure points are used for all printing inks used both in the reference region and in the comparison position, in particular printing dots are selected in which at least two different colors are printed one above the other. Preferably, in particular, printing dots should also be selected here, where all printing inks used are printed on top of each other. By recognizing the deviations of the individual printing inks for a printing point relative to one another in comparison with these similar differences in the reference point or in comparison to the corresponding specifications from the raster bitmap, the geometry errors can then be determined.

On the basis of the deviations thus measured, correction values are to be determined in the following, the correction values being applied to at least one object of the group, artwork, raster bitmap and control data for imaging elements. The imaging elements may be, for example, inkjet printheads or laser diodes of a printing plate imaging device.

Finally, a new printing form (also digital) is to be created and a new print image based on the new printing form to be imaged, whereby by applying the correction values for creating the new printing form the geometry errors of Print image is at least reduced in subsequent printing operations.

In a further development according to the invention, it is provided that a camera with position detection system is used as the measuring device, the resolution of the camera being so great that the XY coordinates of individual pressure points in the detection area of the camera are resolved. It is then advantageously possible to detect the position and / or the rotation of the camera at the reference position and at the corresponding comparison positions via the position detection system in order to determine the position as determined by determining the position and / or rotation of the camera together with the detected area Positions of the pressure points determine the XY coordinates of the individual pressure points of the different printing colors in a common XY coordinate system for the entire printing material.

To advantageously allow to correct geometry distortions over the entire print image, it is further provided to set a plurality of comparison positions on the substrate and at all these positions, the deviations of the XY coordinates of pressure points to XY coordinates within the raster bitmap or deviations of the To detect differences between the pressure points of different colors of comparison position to reference position and then to determine a value for the geometry distortion of the printed image relative to its bearings on the substrate for each comparison position. From these deviations data can then be calculated for the correction of the paper stretch in the print template of the raster bitmap or in all control data of the imaging device of the printing form. As already mentioned, this correction is within the raster bitmap z. B. in the DE 197 24 066 B4 described.

In particular, one edge of the printed image can be used as the reference position. Alternatively, particularly concise positions or existing register elements on the substrate can be selected. In this way, on the one hand, unambiguous XY positions of the measured pressure points on the printing substrate can be determined; on the other hand, the associated grid points can be assigned to the individual grid points of the raster bitmap by comparing this concise reference point with the raster bitmap.

On the one hand, the entire course of the geometry distortion, i. E. H. the absolute geometry distortion of the entire print image are determined, according to the invention, however, it is also provided that the calculated correction data are provided spatially resolved and taken into account locally during the correction. As a result, in particular areas in which more color is printed and thus a larger geometry distortion occurs, can be corrected locally clearly without producing incorrect corrections in the areas with little ink application.

In particular, the geometry distortions are ignored without regard to the raster bitmap, i. H. determined only on comparison of the pressure points of different colors in a comparison range with the reference range. It is further provided according to the invention a plausibility check, in particular taking into account a limited paper stretch possible. Therefore, if geometry errors are calculated in this way that are not plausible, d. H. could describe a too large or small possibly even negative distortion of the printing material, the detected geometric distortion can be adjusted or even discarded by this plausibility check, in particular it can be provided that only one comparison position is discarded and a second comparison position as a substitute for this Determining the geometry distortion is used. If a large number of comparison positions lead to implausible geometric distortions, then it may be provided in particular that instead of the original reference range a comparison position is used as the new reference range or a second position not yet measured on the printing material is to be used as the new reference position.

In order to obtain the best possible values for the deviation of the pressure points, it is advantageously also provided that positions are selected as the comparison position which have distinctive image contents in the detection range of the camera. These distinctive image contents may in particular be edge, corners and preferably also printing dots which comprise a plurality of colors printed one above the other. It can also be z. B. to act contrasting patterns in this area. In particular, a high-resolution photograph of the images should be used to determine this distinctive image content by the camera.

In order to achieve the most accurate possible picture of the geometry distortions, it is advantageously also provided that the comparison positions are distributed as possible in a grid-like manner over the entire printing material.

The most accurate possible consideration of the geometric distortions is also or additionally obtained if, as proposed by the invention, the comparison positions are selected on the printing substrate in such a way that they are distributed as far as possible lie apart and preferably also include edge regions of the printing material with.

In addition to the selection methods for the comparison items described also comparative positions, especially in problem areas of the print template, such as. B. in areas where a large paint job is expected to be selected. As a result, locally expected geometric distortions can then be determined particularly well and, if necessary, compensated.

In order to compare pressure points on the printing substrate with corresponding halftone dots of the raster bitmap of the printing original, a paper stretch determination device is provided according to the invention which determines geometric distortions of the printing material on the basis of the deviations. In this case, the deviations of the differences of the pressure points of different colors in each case in the reference region and in a comparison position are meant in particular, as well as the deviations of the pressure points in a reference region or in a comparison position with the corresponding halftone dots of the provided halftone bitmap. It is therefore provided for comparing the halftone dots with the printing dots, that at least one bitmap bit from a prepress for the comparison of the printing dots with halftone dots is passed to the paper stretch detection device.

To achieve the object of the invention, a device according to the preamble of claim 7 is further provided which comprises a camera for detecting areas on the substrate, which further comprises a drive means for adjusting and / or pivoting the cameras relative to the substrate, wherein additionally a position detection system for Determining an XY position of the camera should be provided. Furthermore, a corresponding paper stretch determination device should be provided, which can determine geometry distortions of the printing material on the basis of the detected regions and / or XY position of the camera.

As described above, in order to enable the XY coordinates of the printing dots of different colors both between the reference area comparison areas and the reference dot directly to the raster bitmap, apparatus is comparatively for comparing XY coordinates of printing dots detected by the camera and provided for determining geometrical errors of the printing substrate. In this case, in particular, the comparison device should be encompassed by the paper stretch determination device.

For comparison of the detected pressure points, a transmission device is also provided, which transmits a raster bitmap of the prepress for comparison with these pressure points to the comparison device of the paper strain detection device, wherein in particular provided that the transmission device and the comparison device or the paper strain detection device are connected to each other in the manner of a network ,

An embodiment of the invention, from which further inventive independent features may result, but to which the invention should not be limited, is shown in the following drawings.

Show it:

1 a possible geometry distortion of a paper sheet,

2 a structure for detecting geometry distortions,

3 the measuring device for determining the geometry distortions,

4 a representation of measuring points on a sheet,

5 a further detection area as comparison position,

6 a representation of the comparison of comparison position with reference position, and

7 a representation of a comparison of a comparison position with the corresponding position in a raster bitmap.

In the 1 is an example of geometry distortion of a paper sheet 1 shown as substrate.

An unprinted paper sheet 1 has a rectangular shape. When printing with color and passing through one or more printing units, the paper sheet 1 damp and pressed apart through the pressure column. In this way, a trapezoidal paper sheet 1' generated when passing through a printing press, not shown.

Other possible geometry errors of a printing material are in the DE 197 24 066 B4 listed, which are hereby incorporated by reference.

In the 2 is the construction of a device for detecting and reducing geometry errors 2 outlined. In a design process, not shown, is a print template 3 generated. This can in particular as a pdf. The artwork 3 is applied to a raster image processor (RIP) 4 which of these extracts color raster bitmaps 5 generated. Based on the raster bitmaps will be a gel 6 so controlled that he printed forms in particular printing plates according to the template 3 imaged. The imaged printing plates are transferred to a printing machine 7 passed and clamped in this. The printing press 7 imprinted paper sheet 1 . 1' , causing it to geometry distortions, as in 1 shown, comes. Within the printing press or preferably after the print job carried out, the paper sheets 1 . 1' a measuring device 8th fed. This measuring device 8th determines the XY coordinates of different pressure points 50 . 51 . 52 and 53 as they are in the 5 and 6 are shown. These XY coordinates of the different pressure points 50 to 53 be from the measuring device 8th to the paper stretch detection device 9 passed. Based on the differences 54 . 56 different colored pressure points 50 . 51 and 52 . 53 in different reference positions 57 or comparative positions 58 The paper strain detection device can use conventional mathematical calculation methods to determine the local geometry distortion of the paper sheet 1 determine. Alternatively, the paper stretch detection device can also directly the coordinates of pressure points 52 . 53 with associated grid points 62 . 63 , as in 7 displayed, compare and thus infer the geometry distortion. For comparison of pressure points 52 . 53 with grid points 62 . 63 the raster bitmap 5 It is within this alternative that the raster bitmap 5 according to the file 10 to the paper stretch detection device 9 is handed over.

Due to the paper strain detection device 9 detected geometry distortions of the substrate 1 . 1' Now, the raster bitmap is preferred 5 already during another raster process in the RIP 4 manipulated. This is a matrix manipulation device 11 in the area of the RIP 4 intended. Like in the DE 197 24 066 B4 can be described by means of the matrix manipulation device 11 the individual grid points of the raster bitmap 5 be manipulated so that the different color separations the distortions of the substrates 1 . 1' within the printing press 7 compensate or take into account.

Alternatively, correction signals can be used 12 . 13 directly to the manipulation of the artwork 3 or for manipulating the control signals of the imagesetter 6 be provided. This can be either the print template 3 be manipulated so that it already anticipates the geometry errors of the sheet in different inks, or the pressure points 50 to 53 on the bow 1 are caused by appropriately delayed or accelerated exposure points on a printing plate in the gel 6 adapted to the geometry distortions. For this purpose, a corresponding correction via a correction signal 13 at the funnel 6 intended.

The 3 shows the substrate 1 with a subject 20 , which here, for example, two differently colored picture elements 21 . 22 having. Next shows the 3 Components of the measuring device 8th , in particular a camera here 23 , which via a drive device 24 along the arrows 25 . 26 over the substrate 1 can be moved. Furthermore, here is a position detection system 27 provided, which due to the position of the camera 24 relative to the substrate 1 and by the pivoting position of the camera 24 on the location of one of the camera 24 can close the detected image area. The XY coordinates of individual pressure points 50 to 53 can then be determined by their relative position within the captured image area 28 be determined.

The 4 continues to show a bow 1 with a camera 24 , corresponding to the arrows 25 . 26 over the bow 1 is moved. Here are systematically support points 30 indicating the different image areas, such as reference area and comparison area, for detection by the camera 24 on the substrate 1 represent. The support points 30 are like a network over the arch 1 distributed. In this way, the geometry distortion of the entire sheet as such as well as local deviations thereof can be determined.

In the 5 is the camera 23 at a comparison position 31 positioned. This comparison position 31 can in particular via the position detection system 27 determined by the camera. In particular, by the position detection system 27 an actual / target comparison between desired positions of the camera 23 and the actual position of the camera 23 respectively. For this purpose, the drive device of the camera with a controller 40 connected. At the comparison position 31 captures the camera 23 an image area 28 in which the picture element 21 at least partially. The comparison position 31 is chosen so that within the image area 28 a striking area 32 of the printed image on the paper sheet 1 lies. The striking area 32 is characterized in particular by the fact that here places with high contrast or clearly defined edges or corners of the picture element 21 available. In particular, here are different inks in the picture element 21 be printed on top of each other. In the 5 is further sketchily illustrated that within the striking area 32 pressure points 52 . 53 with a difference to each other 56 available. This should be in particular to different colored pressure points 52 . 53 act, so that a location deviation of each other pressure points 52 . 53 through the difference 56 is described. This difference 56 can then use a difference resulting from the rasterized template, ie the raster bitmap 5 alternatively, directly also the positions, ie the XY coordinates of the pressure points 52 . 53 with the grid points of the raster bitmap 5 can be compared. By this comparison, then the actual actual value of the XY coordinates of the pressure points 52 . 53 or the difference 56 with the setpoints as they are from the raster bitmap 5 to be compared. This comparison is made within the paper strain detection device 9 and gives information at least about the local paper stretch in the area of the image area 28 , Be different picture areas 28 at different comparison positions 31 , as in 4 shown at the different interpolation points 30 recorded, so can for each support points 30 corresponding distortion parameters, ie geometry errors of the paper sheet as a result of overprinting, can be detected, and it can be a paper stretch profile over the entire substrate 1 to be created. Simply this can then be simplified so far in a first approximation that an absolute paper stretch in the X and Y direction, ie in the direction of the arrows 25 . 26 , relative to the substrate 1 is recognized and determined. These distortions can then be sent to the matrix manipulator 11 and either globally the raster bitmap 5 be corrected or corrected locally, so that the geometry distortions of the substrate 1 can be counteracted. This can be done by re-measuring the pressure points 52 . 53 or the difference 56 in the image area 28 be checked in a further step by an iterative process even better.

The 6 shows a sketched measurement for the recognition of the geometry error of the printing substrate 1 as a result of overprinting different colors.

First, the camera 23 to a reference position 57 especially in a corner of the substrate 1 method. Here, the camera becomes an image area 28 measure which different colored pressure points 50 . 51 having. From the XY coordinates within the image area 28 become absolute XY coordinates for the pressure points 50 . 51 determined in relation to the substrate. Here, a point within the reference range, ie within the image area 28 , at the reference position 57 as zero point of the printing material 1 construed. In particular, this is the lower left corner. About the thus determined XY coordinates of the pressure points 51 . 51 will also be a difference 54 the pressure points 50 . 51 recognized each other. The pressure points 50 . 51 should be chosen so that they should obviously be printed on each other in relation to the color register.

In a next step, the camera 23 to a comparison position 58 proceed where a picture area 28 as comparison area by means of the camera 23 measured and recognized. In this comparison area different colored pressure points 52 . 53 detected and measured with respect to the color register, and by their XY position within the comparison range in conjunction with the comparison position 58 the camera 23 their absolute XY coordinates are defined relative to the zero point of the reference range. For the inks of the pressure points 52 . 53 it should preferably be the same colors as the pressure points 50 . 51 act. By recognizing the difference 56 between the pressure points 52 . 53 in the comparison range, a deviation of the difference 56 from the difference 54 be recognized. The deviation is to a deviation caused by a geometry distortion of the substrate 1 is caused. As described, by means of the paper stretch detection device 9 based on the deviation of the differences 56 . 54 detected local or absolute geometry distortions of the substrate and by appropriate matrix manipulation in the matrix manipulation device 11 of the RIP 4 so on the raster bitmap 5 be applied to the raster bitmap 5 is changed so that the distortions of the substrate 1 counteracted.

The 7 shows more clearly a comparison between pressure points 52 . 53 in one area 28 were recognized as comparison area. Here can be absolute differences 56 be recognized by means of a comparison 70 within the paper strain detection device 9 with a raster bitmap 5 can be compared. Based on the absolute XY coordinates of the pressure points 52 . 53 with respect to the reference range at the reference position 57 the camera 23 can the corresponding grid area 71 in the raster bitmap 5 be determined. Here, at the corresponding XY coordinates, the pressure points 52 . 53 associated grid points 62 . 63 be recognized. For the grid points 62 . 63 are actual values in relation to the XY coordinate system of the raster bitmap 5 specified. These XY values are in the paper defloration detection device with the actual XY values of the pressure points 52 . 53 compared and detected deviations. The deviations are dependent on the paper stretch of the printing substrate 1 and give direct information about the size of the geometry distortion of the substrate 1 due to printing. This parameter can be used to correct the raster bitmap 5 as described in the matrix manipulation device 11 be handed over.

In the two described ways can alone by measuring the subject 20 of the substrate 1 Geometry distortions of the substrate 1 be determined without further markers together with the subject 20 on a bow 1 must be printed. In particular, local geometry distortions can be detected locally, especially at positions with a high color thickness, and in matrix manipulation in the matrix manipulation device 11 of the RIP 4 be taken into account.

LIST OF REFERENCE NUMBERS

1, 1 '

sheet of paper

2

Device for reducing geometric errors

3

master

4

Raster Image Processor (RIP)

5

raster bitmap

6

Gelichter

7

press

8th

measuring device

9

Paper stretching recognizer

10

arrow

11

Matrix manipulation device

12, 13

correction signals

20

subject

21, 22

pixels

23

camera

24

driving means

25, 26

arrows

27

Position detection system

28

image area

30

reference points

31

compared position

32

striking area

40

control

50-53

pressure points

54, 56

differences

57

reference position

58

compared position

62, 63

dots

70

comparison

71

screen range

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19724066 B4 [0009, 0009, 0010, 0021, 0044, 0046]

Claims (9)

Method for detecting geometry errors of a printed image ( 20 ), whereby by means of a measuring device ( 8th ) Areas ( 28 ) of a printed substrate ( 1 . 1' ), characterized in that first a reference position ( 57 ) on the substrate ( 1 . 1' ) with the measuring device ( 8th ), the XY position of the measuring device ( 8th ) with regard to the reference position ( 57 ), pressure points ( 50 . 51 ) at the reference position ( 57 ) detected colors and their XY coordinates are determined; at least one comparison item ( 31 . 58 ) on the substrate ( 1 . 1' ) with the measuring device ( 8th ), the XY position of the measuring device ( 8th ) with regard to the at least one comparison item ( 31 . 58 ), pressure points ( 52 . 53 ) at the at least one comparison item ( 31 . 58 ) and their XY coordinates are determined, an XY coordinate of a pressure point ( 50 . 51 ) in the measured area ( 28 ) of the reference position ( 57 ) is set as the zero point and the XY coordinates of the pressure points ( 50 . 51 . 52 . 53 ) of the different colors at the reference position ( 57 ) and the at least one comparison item ( 31 . 58 ) through the respective XY position of the measuring device ( 8th ) and the position of the pressure point ( 50 - 53 ) in the measured area ( 28 ), the XY coordinates of at least two pressure points ( 52 . 53 ) of different color at the comparison position ( 31 ) with the XY coordinates of associated grid points ( 62 . 63 ) one of the printed image ( 20 ) underlying raster bitmap ( 5 ) and differences are detected or differences ( 56 ) of the XY coordinates of the pressure points ( 52 . 53 ) at the comparison position ( 31 . 58 ) with differences ( 54 ) of the XY coordinates of pressure points ( 50 . 51 ) of the same different colors in the region of the reference position ( 57 ) and deviations of the XY coordinates themselves or the differences ( 54 . 56 ), correction values are determined on the basis of the measured deviations, the correction values are determined on at least one object of the group of artwork ( 3 ), Raster bitmap ( 5 ) and control data for imaging elements ( 6 ), a new printing form is created, a new print image ( 20 ) is imaged on the basis of the new printing form, wherein by applying the correction values for creating the new printing form the geometry errors of the printed image ( 20 ) are at least reduced in subsequent printing operations. Method according to claim 1, characterized in that the measuring device ( 8th ) a camera ( 23 ) and a position detection system ( 27 ), the resolution of the camera ( 23 ) is so large that the XY coordinates of individual pressure points ( 50 - 53 ) within the scope ( 28 ) the camera ( 23 ) are resolved via the position detection system ( 27 ) Position and rotation of the camera ( 23 ) at the reference position ( 57 ) and at least one comparison item ( 31 . 58 ), and taking into account the position and rotation of the camera ( 23 ) XY coordinates of pressure points ( 50 - 53 ) of different colors in the detection area ( 28 ) the camera ( 23 ). Method according to claim 2, characterized in that a plurality of comparison positions ( 30 . 31 . 59 ) on a printing substrate ( 1 . 1' ) at each reference position ( 30 . 31 . 58 ) Deviations of the XY coordinates of pressure points ( 52 . 53 ) to XY coordinates of grid points ( 62 . 63 ) a raster bitmap ( 5 ) or deviations from differences ( 54 . 56 ) between pressure points ( 50 - 53 ) of different colors, for each comparison position ( 30 . 31 . 58 ) a value for a geometry distortion of the printed image ( 20 ) in the respective comparison position ( 30 . 31 . 58 ) and from these deviations data ( 12 . 13 ) for the correction of paper stretch in the artwork ( 3 ), the raster bitmap ( 5 ) or the control data of the imaging device ( 6 ) of the printing form. Method according to claim 3, characterized in that the calculated correction data ( 12 . 13 ) are spatially resolved and accordingly taken into account locally during the correction. A method according to claim 3, characterized in that the deviations are first subjected to a plausibility check taking into account a limited paper stretch and possibly adjusted or discarded. Method according to claim 6 or 7, characterized in that as comparative positions ( 30 . 31 . 58 ) Positions on the substrate ( 1 . 1' ), which are widely distributed from each other and preferably also edge regions of the printing substrate ( 1 . 1' ). Device for detecting geometric errors of a printed image ( 20 ) comprising a printing machine ( 7 ) for printing a printed image ( 20 ) on a substrate ( 1 . 1' ) according to a print template ( 3 ), characterized in that a measuring device ( 8th ) comprising a camera ( 23 ) for detecting areas ( 28 ) on the substrate ( 1 . 1' ) is provided that further a drive device ( 24 ) for adjusting and / or pivoting the camera ( 23 ) relative to the printing substrate ( 1 . 1' ), the measuring device ( 23 ) a position detection system ( 27 ) for determining an XY position of the camera ( 23 ), and that further comprises a paper stretch determination device ( 9 ) is provided, which based on the deviations geometrical distortions of the printing substrate ( 1 . 1' ). Apparatus according to claim 7, characterized in that a comparison device for comparing XY coordinates of pressure points ( 50 - 53 ), which from the camera ( 23 ) and for determining geometric errors of the printing substrate ( 1 . 1' ) from the paper strain detecting device ( 9 ) is included. Apparatus according to claim 8, characterized in that a transmission device is included, which comprises a raster bitmap ( 5 ) of the prepress for comparison with pressure points ( 50 - 53 ) are transmitted to the comparison device, wherein the transmission device and the comparison device are connected to each other in the manner of a network.

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