DE102017213262A1 - Image capture with area-wise image resolution - Google Patents

Abstract

A method for image acquisition in a substrate-processing machine (14) by means of a computer (12, 15), wherein image data (16) of a print job in the preliminary stage by the computer (12, 15) and analyzed in image areas (2, 3, 4) divided image contents are different, the different areas (2, 3, 4) are assigned different image resolutions, the printed image data (5) by means of an image sensor (9) of an image acquisition system (10) consisting of individual modules, recorded and analyzed and which thereby is characterized in that the individual modules of the image sensor (9) are able to use different image resolutions and they are controlled by the computer (15), that the different image areas with the respective different, associated image resolutions (19) recorded and to the Image Capture System (10).

Description

The invention relates to a method and a system for image acquisition in a printing machine for quality assurance of printed products.

The invention is in the technical field of automatic quality control.

Many state-of-the-art printing presses have automated image capture systems that allow print products to be examined for print quality. In the case of multicolor printing, both the target color values achieved and the register are examined. H. the overprint of the individual color separations. Also under investigation, even in monochrome printing, are the registers, d. H. the correct distance to the edge of the print substrate and the overall print quality. The latter is based on the correct representation of certain image objects, where it is important that these z. B. with respect to the edge transitions are displayed correctly. An example of this is barcodes or QR codes, in which even the slightest deviation of the printed image can lead to a change in the transported data content and thus to a printing error. Another example is leaflets of medication, where also printing errors can have a significant impact.

In particular, in larger sheetfed and web presses, the image capture systems are installed internally in the printing press, usually behind the last printing or coating unit, so as to be able to perform inline measurements during the production run. The image acquisition systems have one or more cameras or scanner strips, which are used for the corresponding inline image acquisition. From the image data recorded in this way, the data for colorimetry, for general image inspection and for registration and registration can then be obtained.

The different objectives of the image capture thereby require different quality requirements in terms of the necessary image resolution, which must provide the cameras or scanner strips used. For example, to verify register and register integrity, high image resolution, e.g. from at least 300 dpi to 600 dpi and more, while for color measurement lower image resolutions of 50 to 150 dpi are sufficient. For general image inspection, image resolutions between 100 and 300 dpi are usually enough. In addition to the image resolution is another factor that results in a requirement for the cameras used, the transport speed of the printing substrate, which depends on the type of printing machine used in each case, for. B. whether it is a sheet-fed or web-fed press depends.

Currently, CCD-based RGB cameras and scanner strips are currently used in the prior art, which, however, at the usual high transport speeds of at least 3 m / sec in sheetfed offset presses and at least 0.6 m / s in digital, or inkjet printing machines are unable to capture the entire print image with the currently used highest resolution of 600 dpi. In particular, the bottleneck relates to the data processing in the evaluation electronics of the cameras, or the interface between the camera and subsequent data processing in the image processing computer.

This therefore results in the need to use a plurality of cameras, for example, one camera monitors only the colorimeters on the print substrate, a second performs the general image inspection and a third scans only the register marks, so as to be able to perform all the objectives of image capture can. However, this has the disadvantage that thus the installation effort and thus the cost factor for the image acquisition system increases massively.

To remedy this problem, it would therefore be advantageous to have an image sensor, so a camera or scanner bar, which can monitor the entire print substrate according to the requirements mentioned. Since the simplest solution, namely the use of a camera or scanner bar, which can always capture and process the entire print substrate in the highest resolution, is not possible since such camera systems would either be too expensive or overwhelm the subsequent data processing of the image processing computer. you have to search for alternative camera systems here.

The object of the present invention is thus to find a method for image acquisition in a printing press with a camera system as part of the printing press, with which the disadvantages known from the prior art can be overcome.

The object is achieved by a method according to the invention for image acquisition in a substrate-processing machine by means of a computer, wherein image data of a print job are analyzed by the computer and divided into image areas with different image content, the different areas are assigned different image resolutions, the printed image data by means of an image sensor an image capture system consisting of individual parts, be recorded and analyzed and which is characterized in that the individual parts of the image sensor are able to use different image resolutions and they are controlled by the computer that the different image areas recorded with the respective different, associated image resolutions and transmitted to the image capture system become. It is crucial that the image sensor used for the camera system for different areas of the print image can represent different image resolutions. Thus, in the context of image capture for quality control of the generated print products for the individual areas can be detected in each case with the optimal image resolution. The image acquisition process must be adapted to these new possibilities. That is, it must be analyzed by a computer, for example, the computer of the image acquisition system, the control computer of the printing press or the computer of the prepress, based on the precursor data, which image data is currently being printed, these image data must then in corresponding image areas with the different image content and the corresponding optimal image resolutions must be assigned to these different image areas. Ideally, this can already be done directly in the preliminary stage if the precursor system used is capable of doing so. Otherwise, it is taken over by a downstream computer, such as the image processing computer, which is responsible for monitoring the image acquisition system. This division is then made available to the image acquisition system, so that the corresponding split image areas can be detected by the image sensor independently with the respectively assigned optimal image resolution and analyzed in the image processing computer.

Advantageous and therefore preferred developments of the method according to the invention will become apparent from the accompanying dependent claims and from the description with the accompanying drawings.

A preferred embodiment of the method according to the invention is that the areas with different image content, image areas for register and register measurement and / or for color measurement and / or for general image inspection include. The registration and registration marks can therefore be correspondingly recorded with the highest image resolution, the color control strips with a correspondingly lower image resolution and the areas for general image inspection with a correspondingly average image resolution.

A further preferred embodiment of the method according to the invention is that the image areas for register and register measurement, an image resolution of at least 200 dpi, the image areas for color measurement, an image resolution of at least 50 dpi and the image areas for general image inspection for the inspection of machine-readable data codes, such eg Barcodes, an image resolution of at least 200 dpi, for the inspection of other areas an image resolution of at least 100 dpi. For register and register measurement, the highest image resolution of at least 200 dpi up to 600 dpi is required for current image acquisition systems in order to be able to record the registers and registers as accurately as possible. For general image inspection, average image resolutions of at least 200 dpi are sufficient for certain data codes, such as barcodes or QR codes, while at least 100 dpi are sufficient for other areas of the inspection. The color measurement control via the acquisition of the color control strips requires the lowest image resolution from 50 dpi up to 200 dpi with current systems.

A further preferred embodiment of the method according to the invention is that the computer creates an interface specification from the image data with the differently resolved image areas, which assigns the image areas to the respective image recording location, transmits these to the image acquisition system which controls the individual parts of the image sensor in that the individual image areas are evaluated with their respective assigned image resolution. In order to provide the appropriately divided image areas with different image resolution and their image acquisition system in a correct manner, so that the image acquisition system can also do something with these data, the computer, which for example the image acquisition computer, the control computer of a printing press or the computer of the prepress can be, from the image data with the differently divided image areas an interface specification for the image capture system, more precisely, for the camera system, created, which is then transmitted to the image capture system. In this way, the individual modules of the image sensor can then be controlled in such a way that they evaluate the corresponding different image areas with their respectively assigned optimum image resolution. The control of the individual modules of the image sensor is usually implemented independently by the control electronics of the image sensor by means of the information which areas are to be detected with which image resolution. That is, the correspondingly controlled parts of the image sensors always capture their respective area visually with their maximum image resolution. However, since this leads to the problems mentioned in the data analysis, the captured image data by the so-called "binning", ie the Combine individual pixels to a common pixel, reduced.

A further preferred development of the method according to the invention is that the individual parts of the image sensor are controlled in such a way that the image information of a plurality of pixels is weighted onto a pixel in the image regions which are detected with a reduced image resolution. Since the optics of the image sensors always captures the corresponding print image or the respectively assigned split regions with the full image resolution, the desired image resolution is carried out by means of the control of the individual parts of the image sensor via their evaluation electronics. The reason for this is that the critical point of the image acquisition and image processing of the image sensor is less the optics, but that the downstream evaluation is not able to process the image data supplied by the optics with the necessary speed. And even if the evaluation of the image sensor itself may be able to process the corresponding image data, but the image acquisition system itself is overwhelmed with the transfer of the amount of data. Therefore, the corresponding control of the individual modules of the image sensor for detection with different image resolution via the image capture system to the evaluation of the image sensor.

A further preferred development of the method according to the invention is that the image areas are read out with different image resolution with full RGB color information. Since, for example, a color measurement is also carried out by means of the method according to the invention in the context of image acquisition, it must of course be possible to also capture the corresponding image areas which evaluate the color control strips with full color information. The areas for general image inspection may also require detection with full RGB color information.

A further preferred embodiment of the method according to the invention is that the image capture of the image acquisition system at a transport speed of the printing substrate of at least 3m / s in offset printing machines and at least 0.6m / s in inkjet printing machines happens. The transport speed of the printing substrate in a printing machine, which is monitored by an image acquisition system, is generally at least 3 m / sec in offset printing presses. In inkjet printing machines, the transport speed is currently much lower - currently at least 0.6 m / sec. The image capture of the image acquisition system with the different image areas with correspondingly optimal, individual image resolution must therefore also be able to capture and process the image data generated with at least 3 m / sec, or 0.6 m / sec transport speed.

A further preferred embodiment of the method according to the invention is that in the case of using the image capture system in an inkjet printing machine, a printed image is divided into several image areas, which are sequentially detected with the highest possible image resolution and then used to detect faulty print nozzles. Faulty print nozzles cause image disturbances in the image areas where the faulty print nozzle should have actually printed. For the detection of such image disturbances and thus faulty printing nozzles, a very high image resolution in the image capture of the printed image is necessary. Here too, the method according to the invention can be used in which individual regions of the printed image with the highest available image resolution are detected sequentially and then evaluated accordingly by the image acquisition system or by another component. The individual areas are sequentially, i. one after the other with the highest available image resolution recorded and evaluated until the entire print image and thus the entire print head width were checked with the highest possible image resolution.

A further preferred development of the method according to the invention is that the color resolution of the image sensor is increased to more than 8 bits when detecting the image areas for color measurement. The usual 8-bit color resolution allows a depth of color depth of 256 Color values ( 0 to 255 ) in each detected by the image sensor color range. However, it is advantageous to use a larger color value depth for color acquisition. Increasing the color resolution, for example, from 8 bits to 10 bits, the captured color value of the image sensor in 1024 Color values ( 0 to 1023 ), which allows a more accurate examination of the generated color values and thus a better color control. However, if the amount of data generated in this way becomes too high for further processing, you can reduce the image resolution from at least 50 dpi to 200 dpi and thus save on data volume. It is important, however, not to drop the image resolution below 50dpi.

Another object of the invention is to provide an image acquisition system for a sheetfed press with an inline measuring device for carrying out a method according to one of the preceding claims, which is characterized in that the image sensor is a modular CIS scanner bar based on CMOS or CCD or a CMOS camera, wherein all parts of the CIS scanner bar or the CMOS camera for image acquisition with different image resolution in sections driven and can be read out. The image acquisition system according to the invention for the sheet-fed printing machine with inline measuring device provides a modular CIS scanner strip, in which case all parts or modules for image acquisition with correspondingly different image resolution can be individually controlled. Thus, the method according to the invention can be carried out with the detection of the different image areas with correspondingly optimal image resolution. Alternatively, a modular controllable CMOS camera can be used. Where modular controllable means that the individual CMOS sensors of the CMOS camera can be individually controlled so that a partial image capture of the printed substrate in its entire width is possible. No matter whether a CIS scanner bar or a CMOS camera is used: It is important that the modular control allows a partial image capture with different image resolution. In the case of the CIS scanner bar, this means that the individual modules must be divided in such a way that it is possible to capture all image areas with an assigned optimal individual image resolution. In the case of the CMOS camera, this is anyway no problem due to the individual controllability of the individual CMOS sensors. It is quite possible to capture individual image areas with corresponding image resolution from several parts of the camera, ie CMOS sensors with the same image resolution. However, it is important that the monitoring range of a CMOS sensor is not so large that several image areas with different image resolution can only be detected by this one CMOS sensor.

A further preferred development of the image acquisition system according to the invention is that the image acquisition system can take over a changed interface at least within 20 image lines. In order to avoid the already described problem that several image areas with different image resolution can only be detected by a part of the image sensor, the image acquisition system must be able to produce a modified interface specification, ie. H. in the form of the application of another image resolution, to be able to take over within a maximum of 20 picture lines. The transfer of one image line to the next is the long-term goal, but can not be achieved with the current image sensor technology. With a takeover within a maximum of 20 image lines, however, it is ensured that each area is captured with an individual image resolution corresponding to an individual part of the image sensor.

A further preferred development of the image acquisition system according to the invention is that the image sensor ( 9 ) Sensor lines ( 8th ) having three or more color channels, wherein RGB sensor lines ( 8th ) can be used for three color channels in a trilinear arrangement, mixed arrangement of sensor lines or prism camera, as well as more than three sensor lines with individual color detection. For the application of the image acquisition system for general image inspection and especially for color measurement control via the detection of the color control strips, the image sensor must be able to capture the color information of the printed image. This is done by using sensor lines with at least three color channels. When using three color channels, for example, three RGB sensor lines can be converted. These may, for example, be classically arranged in a trilinear manner; ie one sensor line captures the R-, another the G- and another the B-color information. However, alternative mixed arrangements are also possible where, for example, one sensor row acquires R color information, but then the other two sensor rows mixedly acquire the G and B color information. Another option for RGB sensor lines is the use of a prism camera, in which the individual color channels for RGB are individually recorded and processed and then combined again in the downstream image processing of the image sensor to form a common image. For a more accurate color registration, the use of more than three color channels is also possible. In this case, sensor lines with an individual frequency range can be used in addition to the RGB sensor lines. However, alternative splits of the color channels which do not contain RGB sensor lines are possible. In this case, the frequency range to be covered by the image sensor is newly divided among the sensor lines used with their color channels.

The inventive method and functionally advantageous developments of the method will be described below with reference to the accompanying drawings with reference to at least one preferred embodiment. In the drawings, corresponding elements are provided with the same reference numerals.

• 1 einen Druckbogen mit Bildbereichen unterschiedlicher Bildauflösung
• 2 den funktionalen Aufbau einer CIS-Scannerleiste
• 3 den funktionalen Aufbau eines Bilderfassungssystems
• 4 den Ablauf des erfindungsgemäßen Verfahrens

The drawings show:

• 1 a printed sheet with image areas of different image resolution
• 2 the functional structure of a CIS scanner bar
• 3 the functional structure of an image capture system
• 4 the course of the method according to the invention

Modern imaging technologies such as scanner strips 9 from CIS sensors and CMOS cameras 9 have electronics that allow different areas of the imaging sensors. This property can be used to vary the resolution at which the image data is transferred to the connected image processing system, depending on the function of register measurement, image acquisition or color measurement. Internally, the sensors always work with the highest resolution, but the data is collected in the sensor-related electronics to the desired resolution. This can be done in the row direction as well as in the column direction by averaging image pixels of several lines. scanner strips 9 consist of several assembled sensor modules (> 100), which can be controlled independently. Individual sensor modules can also be used at high image resolutions ( 600 dpi) can be operated at high speeds (> 5 m / sec).

Generally, RGB scanner strips already consist of several RGB sensor modules with different electronic control. RGB cameras with CCD technology are usually built up from just a few RGB sensor modules that can be read out individually. The CMOS technology offers greater possibilities, but also requires a locally different control of sensor areas, so that these functions can be realized with more or less high effort or have to be developed as special configurations.

CIS scanner strips are preferred for the method according to the invention 9 , consisting of several sensor modules, used. An example of such a CIS scanner bar 9 , is in 2 shown in sections. Good to see here are the actual sensor modules 8th , as well as the LEDs 6 indicating the illumination of the printed image to be detected 5 allow and also the optics in the form of the lens 7 , Right inside the scanner bar 9 are also the signal processors 21 attached, which process the area-wise image data and, together with the signal processors of the other sensor modules, the digital print image 16 produce. This we do about the hardware interface 22 to the image processing computer 15 forwarded. These CIS scanner bars 9 prefers to use CMOS sensors 8th However, the use of CCD sensors is possible if they provide the required performance data in terms of image resolution and speed of data acquisition. For color measurement, image data of a reduced resolution 3 recorded from 50 to 200 dpi. Only in selected areas of the image will image data be recorded at a higher resolution, such as 200 or 600dpi. These image data with higher image resolution become the register measurement 2 (600dpi) or for higher resolution inspection (200dpi), eg for barcodes 4 , used.

Another particularly preferred embodiment is the use of a CMOS camera 9 , provided that the entire print image 5 can capture. For CMOS cameras 9 can the individual image sensors 8th which makes image capture even easier with area-wise image resolution than with CIS scanner bars 9 , The application of a CMOS camera 9 for the inventive method does not differ from the application of a CIS scanner bar 9 , The control of the CMOS camera 9 differs from the described control of the CIS scanner bar 9 only to the extent that constructive differences require it. The following description of the image capture system 10 and the method of the invention uses a CIS scanner bar 9 ; however, the use of a CMOS camera is 9 just as possible and stressed.

The image capture system used 10 is schematically in 3 described. It includes besides the printing press 14 even one in the printing press 14 attached CIS scanner bar 9 , an image processing computer 15 directly to the CIS scanner bar 9 is connected and with the control computer 12 the printing press 14 connected is. The control computer 12 with his display 13 provides the interface to the user 11 there. The CIS scanner bar 9 itself is inside the printing press 14 , usually mounted behind the last printing unit. It takes on the printed image to be inspected 5 on. By taking a picture of the printed, original picture 5 The print job now creates a digital overall picture 16 the pressure ranges 2 . 3 . 4 , which then in the course of further image acquisition from the image processing computer 15 is compared with a digital Solldruckbild.

4 schematically shows the sequence of the method according to the invention in a preferred embodiment. This is done by a calculator 12 . 15 , preferably the precursor computer, the printed image divided into different areas. The areas correspond to the places to be inspected 2 . 3 . 4 of the printed image 5 . 16 , Every area 2 . 3 . 4 then becomes the optimum image resolution for the intended image capture 19 assigned. Which image resolution is optimal depends on the already presented type of the respective image capture. An example of a printed print image 5 on a print substrate 1 with different image areas 2 . 3 . 4 is in 1 shown.

From the various areas of the print image in its digital form with the associated image resolutions 17 is then from the computer 12 a software interface rule 18 created, which assigns exactly, at which point of the printed image 17 the scanner bar 9 with which image resolution the respective area 2 . 3 . 4 should capture. The software interface rule 18 defines exactly which image regions 2 . 3 . 4 in the x / y direction on the printed image 17 which image resolution to use. It is then from the computer 12 to the image processing computer 15 of the image capture system 10 transmitted via software interface and allows this the targeted evaluation of the selected image regions 2 . 3 . 4 with the selected image resolution. The structure of the transmitted image data 17 So depends on this software interface rule 18 from. Thereafter, as part of the image capture the printed image data 5 captured during production. The software interface specification is used 18 Moreover, when reading out the data, the recorded image data can again be correctly assigned to the respective image recording location. The results of the image acquisition with locally optimized image resolution can then quite normal as before the user 11 via the output devices 13 from calculator 12 . 15 and / or printing machine 14 be communicated. In addition, the output or storage in a log is possible.

It is also advantageous if the image capture system 10 rapidly, ie within 20 picture lines, an amended software interface rule 18 can take over, thus capturing a printed image 5 optimized as possible on the image content 2 . 3 . 4 can be done.

The advantage of the method according to the invention is that usually the interface 22 for image processing, the transmission of high resolution ( 600 dpi) and at high speeds of printing substrate transport 1 (> 5 m / sec) limited. This disadvantage is due to the only partially, so partial, reading and transferring image areas 2 . 4 bypassed with high image resolution. Only the image areas 2 . 4 which require a high resolution are also read out at the high resolution. As a result, the limiting speed of the image recording is increased for a given bandwidth of the image data transmission and the data volume of the acquired printed image 16 reduced to the absolutely necessary level.

A drawback, on the other hand, may be that the greater hardware and software overhead on the scanner bar side 9 and in composing an overall picture 16 in image processing, possibly higher costs. If one compares the costs, however, with those for the installation of multiple cameras, as known from the prior art, where also the work of the individual cameras with high effort must be precisely matched, the invention according to the preferred embodiment is much more efficient.

LIST OF REFERENCE NUMBERS

1

printing substrate

2

Register / register mark

3

Color bar

4

Image object (barcode)

5

printed print image

6

LED for lighting

7

lens

8th

sensor module

9

CIS scanner strip

10

Image capture system

11

user

12

Control computer of the printing machine

13

Display of the control computer

14

press

15

Image processing computer

16

digital print image

17

to be inspected print image areas

18

Interface specification

19

Print image areas with assigned image resolution

20

Result of image acquisition

21

signal processor

22

Hardware interface

Claims (12)

Method for image acquisition in a substrate-processing machine (14) by means of a computer (12, 15), wherein image data (16) of a print job by the computer (12, 15) analyzed and divided into image areas (2, 3, 4) with different image content be assigned to the different areas (2, 3, 4) different image resolutions, the printed image data (5) by means of an image sensor (9) of an image acquisition system (10) consisting of individual parts, recorded and analyzed, characterized in that the individual parts of the image sensor (9) are able to use different image resolutions and they are controlled by the computer (15), that the different image areas with the respective different, associated image resolutions (19) recorded and passed to the image acquisition system (10) become. Method according to Claim 1 , characterized in that the areas (2, 3, 4) with different image content, image areas for register and register measurement (2) and / or for color measurement (3) and / or for general image inspection (4). Method according to Claim 2 , characterized in that the image areas for register and register measurement (2) an image resolution of at least 200 dpi, the image areas for color measurement (3) an image resolution of at least 50 dpi and the image areas for general image inspection (4) for the inspection of machine-readable data codes , such as barcodes, an image resolution of at least 200 dpi, for the inspection of other areas an image resolution of at least 100 dpi are assigned. Method according to one of the preceding claims, characterized in that the computer (12) from the image data with the differently resolved image areas (19) creates an interface rule (18) which assigns the image areas (2, 3, 4) to the respective image recording location , this the imaging system (10) transmitted, which controls the individual parts of the image sensor (9) such that the individual image areas are evaluated with their respective associated image resolution (19). Method according to one of the preceding claims, characterized in that the individual parts of the image sensor (9) are driven such that in the image areas (3, 4), which are detected with a reduced image resolution, the image information of a plurality of pixels weighted to a pixel becomes. Method according to one of the preceding claims, characterized in that the image areas (2, 3, 4) are read out with different image resolution with full RGB color information. Method according to one of the preceding claims, characterized in that the image capture of the image acquisition system (10) at a transport speed of the printing substrate (1) of at least 3m / s in offset printing machines and at least 0.6m / s in inkjet printing machines happens. Method according to one of the preceding claims, characterized in that in the case of using the image acquisition system (10) in an inkjet printing machine, a printed image is divided into several image areas, which are sequentially detected by the image sensor (9) with the highest possible image resolution and then used to detect faulty pressure nozzles. Method according to one of the preceding claims, characterized in that the color resolution of the image sensor (9) is increased to more than 8 bits in the detection of the image areas for color measurement (3). An image acquisition system (10) for a sheet-fed press (14) with an inline measuring device (9) for carrying out a method according to one of the preceding claims, characterized in that the image sensor (9) has a modular CIS scanner bar (9) on CMOS or CCD base or a CMOS camera (9), wherein all parts of the CIS scanner bar (9) or the CMOS camera (9) for image acquisition with different image resolution can be controlled in sections and read. Image acquisition system (10) according to Claim 10 , characterized in that the image acquisition system (10) can adopt a modified interface specification (18) within a maximum of 20 image lines. Image acquisition system (10) according to one of Claims 10 to 11 , characterized in that the image sensor (9) sensor lines (8) having three or more color channels, wherein RGB sensor lines (8) for three color channels in trilinear arrangement, mixed arrangement of sensor lines or prism camera, as well as more than three sensor lines with individual color registration can be used.

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