JP2010262012A - Method for measuring area ratio of printing plate pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for measuring an area ratio of a printing plate pattern, by which the area ratio of the printing plate pattern drawn by a laser can be measured with high accuracy. <P>SOLUTION: As the printing plate pattern drawn by the laser, a dot close pattern surrounded only by laser irradiation regions or by laser unirradiation regions is used and the dot close pattern is imaged by an image taking-in sensor 3 while using direct motivation mechanisms 6a, 6b which can move to a predetermined position. At this time, the dot close pattern is taken-in as image data at a position where the dot close pattern can be housed inside a measurement extent. Even when a measurement position of the image taking-in sensor 3 toward the printing plate pattern changes, calculated area ratio does not vary, thereby achieving measurement with high accuracy. Moreover, comparison with reference dot data suppresses influence of distortion aberration of a lens to achieve measurement with higher accuracy. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for measuring an area ratio of a printing plate pattern of a printing plate drawn with a laser.

  2. Description of the Related Art In recent years, printing presses for printing printed materials such as newspapers create a printing original by converting digitized document image data into highly directional light such as a laser beam and writing it directly onto a recording medium. CTP (Computer to plate) technology is employed.

  In this CTP, a drum around which a sheet-like recording medium is wound is rotated to move the recording medium in the main scanning direction, and the optical recording head is moved in the sub-scanning direction orthogonal to the drum rotation direction (main scanning direction). An image is formed on the recording medium by moving and irradiating the recording medium with a laser beam from the optical recording head.

  In order to obtain high productivity without increasing the drum rotation speed with the CTP, it is necessary to increase the number of laser beams applied to the recording medium from the optical recording head. If the output of each laser varies at this time, even if an attempt is made to draw with the same output, an actual image will have image unevenness according to variations in the output of the laser. For this reason, in order to ensure high quality drawing performance, it is indispensable to uniform the output of each laser.

  Conventionally, as a method for adjusting the output of a laser, for example, a method described in (Patent Document 1) can be given. In this method, a printing plate is printed with a laser based on predetermined data, printing is performed with the plate, a printed image is taken in, and a ratio of printed halftone dots in a predetermined range is calculated. Based on the obtained halftone dot ratio, the laser output is calculated from the relationship between the halftone dot ratio and the laser output whose correlation is known in advance, thereby adjusting the output of each laser. Is possible.

JP 2000-89473 A

  In recent years, it has been demanded to print high-definition images with higher reproducibility. In this case, it is necessary to prepare a printing plate with higher quality than before, and for this purpose, it is indispensable to make the outputs of the respective lasers more uniform. According to the above adjustment method, it is possible in principle to adjust the output of the laser. However, since the image data to be measured actually includes various variations, the dot ratio is calculated with high accuracy. It is very difficult to do.

  For example, the ratio of halftone dots is measured by reading an image drawn according to predetermined data with a measuring device. However, the ratio of halftone dots obtained varies depending on which part of the image is measured, and causes variation. It becomes. This variation will be described with reference to FIGS. 6 (a) to 6 (c). In FIG. 6A, reference numeral 101 denotes a square image drawn with a laser. This square has a side length of √2 and is inclined 45 degrees with respect to the X and Y axes. A plurality of squares are drawn in the X and Y directions so that the vertices of the squares are in contact. Reference numeral 102 denotes a halftone dot measurement range. In this measurement range, the length of one side is 5, and the square is parallel to the X and Y axes. Since one side of the square 101 is a hypotenuse of a right triangle whose length is 1 in the X and Y axis directions, each side of the measurement range 102 is a position in contact with the apex of the square 101 in FIG. The ratio of the halftone dots calculated here is the ratio of the area of the square 101 existing inside the measurement range 102 to the area of the measurement range 102. At this time, since the area of the measurement range 102 is 25 and the area of the square 101 existing inside the measurement range 102 is 12.5, the ratio of halftone dots in FIG. Next, a case where the measurement range 102 is moved by -0.5 from the position of FIG. 6A with respect to the X and Y axes will be described with reference to FIG. The area of the measurement range 102 is 25 as before, but since the area of the square 101 existing inside the measurement range 102 is 10, the ratio of the halftone dots in FIG. 6B is 0.4. Further, the case where the measurement range 102 is moved by +0.5 from the position of FIG. 6A with respect to the X and Y axes will be described with reference to FIG. Similarly, the area of the measurement range 102 is 25, but since the area of the square 101 existing inside the measurement 102 is 15, the ratio of the halftone dots in FIG. 6B is 0.6. As described above, since the ratio of halftone dots changes depending on which part is measured even in the same printing plate pattern, variation also occurs here.

  This variation due to the position of the measurement range can be eliminated by setting the length of one side of the measurement range 102 to an integral multiple of the drawing pitch of the square 101 (2 in FIG. 6). Since it is necessary to measure an image with a large drawing pitch, it is difficult in practice.

  Further, the captured image is captured by a CCD or the like, which is an image capturing sensor, through the lens. However, since the lens generally has distortion aberration, there is a slight distortion of the image from the center of the measurement range to the outside. For this reason, even if the same printing plate pattern is taken in, the ratio of halftone dots varies depending on the measurement position.

  The present invention solves these problems, and an object of the present invention is to provide a measurement method capable of measuring the area ratio of a printing plate pattern of a printing plate drawn with a laser with high accuracy.

  In order to solve the conventional problem, the method of measuring the area ratio of the printing plate pattern of the present invention includes a step of imaging the printing plate pattern, a region where the laser irradiation and non-irradiation of the imaged printing plate pattern are mixed, Identify the boundary with only the laser irradiation or non-irradiation region surrounding this, determine the inside of this boundary as a halftone dot closed pattern, and determine whether the halftone dot closed pattern is within the measurement range, If it is not within the range, move the imaging means to re-image, and if the halftone dot closed pattern is surrounded by the laser irradiation area, calculate the area ratio of the laser non-irradiated part of the measurement range, and the halftone dot closed pattern In the case of being surrounded by a laser non-irradiation region, the method includes a step of calculating the area ratio of the laser irradiation portion of the measurement range.

  In order to measure with higher accuracy, a step of imaging the reference printing plate pattern and the printing plate pattern, a region where laser irradiation and non-irradiation of the imaged reference halftone dot pattern and printing plate pattern are mixed, and a laser surrounding the region are included. Identifying the boundary with only the irradiated or non-irradiated area, setting the inside of this boundary as the reference halftone dot pattern and halftone dot closing pattern, and the reference halftone dot closing pattern and halftone dot closing pattern for the measurement range A step of calculating a position; a step of moving the imaging means again when the position shift of the halftone dot closed pattern with respect to the position of the reference halftone dot closed pattern is outside a predetermined range; If the dot-closed pattern is surrounded by the laser irradiation area, calculate the area ratio of the dot-closed pattern with respect to the reference dot-closed pattern from the laser non-irradiated part of the measurement range, and If the turn and Amiten閉 pattern is surrounded by the laser non-irradiation region has a step of calculating the area ratio of the halftone dots closed pattern with respect to the reference dot closed pattern from the laser irradiated portion of the measurement range.

  According to the present invention, by using a halftone dot closed pattern as a printing plate pattern, the area ratio of the printing plate pattern can be calculated with high accuracy. In addition, by moving the position of the image capture sensor and lens so that the position of the halftone dot closed pattern relative to the measurement range matches the position of the reference halftone dot closed pattern, it is not affected by the distortion of the lens and is highly accurate. It is possible to measure the printing plate pattern.

The figure which shows the measuring machine of the area ratio of the printing plate pattern of this invention Block diagram of measuring machine control system for area ratio of printing plate pattern of the present invention The flowchart which shows the measuring method of the area ratio of the printing plate pattern of this invention The flowchart which shows the method of measuring the area ratio of the printing plate pattern of this invention with higher precision Detailed view showing the printing plate pattern of the present invention Detailed view showing an explanatory diagram showing a change in the area ratio of the printing plate pattern due to a difference in measurement position

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a view showing a measuring device for the area ratio of the printing plate pattern of the present invention, FIG. 2 is a block diagram of a control system for the measuring device of the area ratio of the printing plate pattern of the present invention, and FIG. FIG. 4 is a flowchart showing a method for measuring the area ratio of the printing plate pattern of the present invention with higher accuracy, and FIG. 5 is a detailed diagram showing the printing plate pattern of the present invention.

  First, a measuring apparatus for measuring the area ratio of the printing plate pattern of the present invention will be described.

  As shown in FIG. 1, a predetermined halftone dot closing pattern 1a is drawn on the printing plate 1 by a laser as a printing plate pattern. As shown in FIG. 5A, the halftone dot closing pattern 1a is composed of a laser irradiated portion (colored portion in FIG. 5A) and a laser non-irradiated portion (uncolored portion in FIG. 5A). One halftone dot closed pattern is drawn by one laser, and a printing plate pattern drawn by one laser is drawn so as not to overlap with a printing plate pattern drawn by another laser. For example, in the halftone dot closing pattern 1a in FIG. 5A (portion surrounded by a one-dot chain line), 16 squares 1b inclined by 45 degrees with respect to the X and Y directions are drawn by one laser, and another laser is drawn. The square is not overlapped. In order to reduce the influence of variation when drawing with a laser, it is preferable to make the range of the halftone dot closed pattern 1a as large as possible. However, the measurement range 12 (solid line), which is a measurable range of the image capturing sensor described later. It is necessary to make it smaller than the part surrounded by. Further, the printing plate pattern drawn by the laser is not limited to the printing plate pattern that selectively irradiates the laser only inside the halftone dot closing pattern as shown in FIG. 5A. For example, the halftone dot closing as shown in FIG. The outside of the pattern may be irradiated with a laser so as to surround the halftone dot closed pattern.

  Further, as shown in FIG. 1, a lens 2 is attached to the image capturing sensor 3, and the lens can be moved in the X direction and the Y direction by linear motion mechanisms 6a and 6b. An example of the image capturing sensor 3 is a CCD. The lens 2 can be selected from various magnifications, but is selected in consideration of a necessary measurement range and resolution determined by the combination with the image capturing sensor 3.

  Image data captured by the image capture sensor 3 is sent to the control unit 5. The control unit 5 performs processing of the captured image data, control of the linear motion mechanisms 6a and 6b, transfer of the image data to the display device 4, and the like. Furthermore, the function of calculating the area ratio of the halftone dot closed pattern from the captured image data and feeding it back to the output of a predetermined laser based on the relationship between the area ratio of the halftone dot closed pattern and the laser output that has been grasped in advance. Have.

  In the display device 4, the feedback amount of each laser output calculated from the image data sent from the control unit 5, the area ratio of the halftone dot closed pattern, the position of the halftone dot closed pattern with respect to the reference, and the area ratio of the halftone dot closed pattern It is possible to display various information.

  Next, a method for measuring the area ratio of the printing plate pattern using the measuring device will be described with reference to FIGS. First, the image capturing sensor 3 to which the lens 2 is attached is moved by the linear motion mechanisms 6a and 6b to a predetermined printing plate pattern drawn by a laser whose output is to be adjusted (S1). The plate pattern at a predetermined position is captured as image data by the image capturing sensor 3 (S2).

  Next, in the captured image data, the range of the halftone dot closing pattern is specified by the image data processing unit 5c (S3). For example, when the printing plate pattern shown in FIG. 5A is captured, the area surrounded by the boundary between the area where the laser irradiation and the non-irradiation part coexist and the area where only the laser non-irradiation part is present is the range of the halftone dot closed pattern 1a. Judge. Note that the boundary of the halftone dot closing pattern 1a does not need to be determined strictly for the reason described later.

  Next, it is determined whether the halftone dot closing pattern of the captured image data is within the measurement range (S4). Specifically, if the outer fixed range is all the laser non-irradiated part or all the laser irradiated part, the main control unit 5a determines that the halftone dot closed pattern is within the measurement range 12. If not, the linear motion mechanisms 6a and 6b are finely moved through the main controller 5a to a position within the measurement range (S5). For example, in the case of FIG. 5A, the halftone dot closing pattern 1 a may be located at any position in the measurement range 12 as long as it is within the predetermined range of the measurement range 12. As a result, it is estimated that at least the halftone dot closing pattern 1a is within the measurement range 12 even if the boundary of the halftone dot closing pattern 1a is not strictly determined. In addition, by displaying the captured image data on the display device 4, it can be visually determined whether the region of only the laser non-irradiation portion described above surrounds the halftone dot closing pattern 1a. As a result, whether or not the halftone dot closing pattern is within the measurement range can be determined visually by the operator without using the main controller 5a.

  Next, the image data of the halftone dot closed pattern that falls within the measurement range 12 is stored in the image data storage unit 5b (S6). Then, white / black binarization processing is performed on the image data by the image data processing unit 5c (S7). Specifically, the stored image data is processed based on an optimal threshold value set in advance so that the laser non-irradiated portion is white and the laser irradiated portion is black.

  Next, based on the binarized image data, the image data processing unit 5c calculates the area ratio of the drawing portion of the halftone dot closed pattern. (S8) For example, in the case of the printing plate pattern shown in FIG. 5A, the measurement range 12 includes the outside portion of the halftone dot closed pattern 1a, but the outside of the halftone dot closed pattern 1a is all white by binarization processing. It has become. That is, the area of the black portion of the measurement range 12 becomes the area of the drawing portion of the halftone dot closed pattern 1a. For this reason, using the area inside the halftone dot closed pattern when drawing with a laser as a reference, the area ratio of the halftone dot closed pattern drawing portion is obtained by dividing the halftone dot closed pattern drawing portion area by this reference area. Can do. In the case of the image of FIG. 5B, on the contrary, the area of the white portion is calculated, and the area ratio of the drawing portion of the halftone dot closed pattern can be obtained from the area of the measurement range and the reference area. Up to this point, the printing plate pattern drawn by the next laser is also checked as one step, and the area ratio is measured for all printing plate patterns (S9).

  With the above measurement method, it is possible to easily and accurately determine the area ratio of the drawing portion of the halftone dot closed pattern without being affected by the boundary position of the halftone dot closed pattern. A measuring method will be described with reference to FIG.

  In general, since the lens has distortion, the image is slightly distorted from the center to the outside of the measurement range. For this reason, if the printing plate patterns are taken in different positions on the basis of the lens, even if the printing plate pattern is the same, the ratio of halftone dots will be different due to image distortion. As a method for solving this, in the present invention, first, a reference printing plate pattern similar to the printing plate pattern to be measured is imaged in advance using the above-described measuring device (S11). Next, the range of the reference halftone dot closing pattern is specified by the same method as S3 described above (S12). Then, the position of the reference halftone dot closing pattern with respect to the measurement range is calculated (S13). At this time, it is desirable to adjust the position of the image capturing sensor 3 so that the position of the reference halftone dot closing pattern is substantially the center of the measurement range for the reason described later. At this time, the image data of the reference printing plate pattern and the position of the reference halftone dot closing pattern are stored in the reference image data storage unit 5d shown in FIG.

  Next, also for the printing plate pattern to be measured, the range of the halftone dot closed pattern is specified by the same method as S1 to S3 described above (S14 to S16), and the position of the halftone dot closed pattern is determined by the same method as S13. Is calculated (S17).

  Next, the positional deviation between the reference halftone dot closing pattern and the halftone dot closing pattern is calculated (S18), and it is determined whether the positional deviation is within an allowable range (S19). If the positional deviation deviates from the allowable value, the linear motion mechanisms 6a and 6b are moved slightly to fall within the allowable value (S20). As a result, the reference halftone dot closing pattern and the halftone dot closing pattern capture images at substantially the same position with respect to the measurement range. That is, by using the reference halftone dot pattern as a reference, the influence of image distortion can be relatively suppressed. In addition, the halftone dot closed pattern is aligned with the center of the measurement range, so the area close to the outside of the measurement range where image distortion is likely to occur is irradiated with a halftone dot pattern laser that is not directly used for area ratio calculation. Or only non-irradiation exists, and the influence of image distortion is further reduced. Although the plate pattern is imaged by calculating the position of the reference halftone dot closed pattern this time, the range and the position of both may be specified by calculating the plate pattern first.

  Thereafter, the image data of the halftone dot closed pattern is stored in the image data storage unit 5b (S21), and white and black binarization processing is performed in the same manner as the measurement method described above (S22). Further, the binarization process is similarly performed for the reference halftone dot closing pattern (S23), and the area ratio of the halftone dot closing pattern with respect to the reference halftone dot closing pattern is calculated (S24). The steps up to this point are sequentially confirmed, and the area ratio with respect to the reference halftone dot closing pattern is calculated for all halftone dot closing patterns (S25). With the measurement method described above, the relationship between the area ratio of the halftone dot closed pattern and the laser output without the influence of image distortion can be derived from the relationship between the area ratio of the reference halftone dot closed pattern and the laser output.

  According to the method for measuring the area ratio of the printing plate pattern of the present invention, the area ratio of the printing plate pattern can be calculated with high accuracy by using a halftone dot closed pattern as the printing plate pattern. In addition, by moving the position of the image capture sensor and the lens so that they match the pre-stored reference halftone dot closed pattern position, it is not affected by the distortion of the lens, and the area ratio of the printing plate pattern is more accurate. Can be calculated. This makes it possible to measure even subtle changes in the printing plate pattern due to differences in laser output, which is useful for laser output adjustment.

DESCRIPTION OF SYMBOLS 1 Printing plate 2 Lens 3 Image acquisition sensor 4 Display apparatus 5 Control part 6a, 6b Linear motion mechanism

Claims (2)

A method for measuring an area ratio of a printing plate pattern of a printing plate drawn with a laser, the step of imaging the printing plate pattern, and a region where laser irradiation and non-irradiation of the imaged printing plate pattern are mixed are surrounded by the step. Identify the boundary with the laser-irradiated or non-irradiated region only, determine whether the inside of this boundary is a halftone dot closed pattern, and determine whether the halftone dot closed pattern is within the measurement range. If this is the case, move the imaging means to capture the image again, and if the halftone dot closed pattern is surrounded by the laser irradiation area, calculate the area ratio of the laser non-irradiated part in the measurement range, and the halftone dot closed pattern is not laser-irradiated. A method for measuring the area ratio of a printing plate pattern, comprising a step of calculating the area ratio of a laser irradiation portion of a measurement range when surrounded by a region. A method of measuring an area ratio of a printing plate pattern of a printing plate drawn with a laser, imaging a reference printing plate pattern and the printing plate pattern, and laser irradiation and non-imaging of the picked reference halftone pattern and printing plate pattern Identifying the boundary between the region where the irradiation is mixed and the region surrounding only the laser irradiation or non-irradiation surrounding this, and setting the inside of this boundary as a reference halftone dot pattern and a halftone dot closed pattern, The step of calculating the reference halftone dot closing pattern and the position of the halftone dot closing pattern, and when the positional deviation of the halftone dot closing pattern with respect to the position of the reference halftone dot closing pattern is outside the predetermined range, the imaging means is moved to take an image again. And when the reference halftone dot closing pattern and the halftone dot closing pattern are surrounded by the laser irradiation area, the halftone dot from the laser non-irradiation part of the measurement range When the area ratio of the pattern is calculated and the reference halftone dot closing pattern and the halftone dot closing pattern are surrounded by the laser non-irradiated area, the area ratio of the halftone dot closing pattern to the reference halftone dot closing pattern is determined from the laser irradiation portion of the measurement range. A method for measuring the area ratio of a printing plate pattern, comprising calculating steps.

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