JP2000326649A - Method and device for evaluating printing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printing plate evaluating device and a method thereof for sensing defects of the half-tone dot quality on a printing plate without actually printing. SOLUTION: A screen tint chart formed on a printing plate to be evaluated is read by an image read section 10 to obtain an image. A plurality of screen tints of different area ratio are set on the screen tint chart. The image obtained from the screen tint chart is processed by an image processing section 20, and then given inspection items are analyzed by an image analysis section 3, and the analysis value as a result is computed. The analysis value thus obtained is compared with the preset evaluation reference by a comparison section 45 of the evaluation section 40, and whether the printing plate is good or not is judged by a judgement section 47 based on the comparison result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing plate evaluation apparatus and a printing plate evaluation method for determining the quality of halftone dots or printing durability of a printing plate (hereinafter sometimes simply referred to as "printing plate").

[0002]

2. Description of the Related Art Conventionally, in a printing process, a plate is made by exposing a continuous tone original to a film and printing the film on a raw printing plate (a printing plate before exposure). Then, printing is performed by applying ink to the plate that has been made and transferring it to paper.

In general, when a printing plate is created from a continuous tone original, halftone dots that represent gray scale in a pseudo manner are used. When the printing target is a color image, a printing plate is created using a halftone dot for each color of Y (yellow), M (magenta), C (cyan), and K (black). At this time, a different screen angle is set for each YMCK in order to prevent the moire phenomenon caused by the overlapping of the net films. Is set.

[0004] Here, when trying to obtain a screen having a desired screen ruling without causing overlapping unevenness when overlapping halftone films of different colors, a difference in size and a shape difference occurs between individual halftone dots. Since unevenness may occur due to the difference in size or shape between the individual halftone dots, a method of determining the halftone dot shape to reduce the unevenness has been proposed (Japanese Patent Application Laid-Open No. 9-148712). According to such a method, even if there is a difference in size or shape between individual halftone dots, the halftone dot shape is controlled so as not to cause unevenness.

Conventionally, a printing plate has been subjected to a burning process after exposure and development in order to increase the image strength (printing durability) of the printing plate. The burning process is a process for increasing the strength of a layer on a printing plate by performing post-exposure. This burning process increases the number of printable plates.

[0006]

In the process of manufacturing a printing plate as described above, it is ideal that the photosensitive material characteristics (γ characteristics) do not differ for each printing plate lot. The light-sensitive material characteristics of each lot are slightly different, so that even when exposure is performed with the same exposure amount, the size of the halftone dot may not be fixed. As a result, the size of the halftone dots on the printing plate after exposure and development may be different from that designed by the above halftone dot shape control method.

Further, in a printing site where printing is performed using a prepressed printing plate, an image portion (a portion on which ink is applied on the printing plate) and a non-image portion (a portion on the printing plate) as printing is repeated. The size of the portion where the ink does not cover) gradually fluctuates. Along with this, the halftone dot size on the printing plate also gradually changes and differs from the size immediately after development.

As described above, the dot size on the printing plate may vary from an ideal state (an optimum state for printing). FIG. 15 is a diagram illustrating a change in halftone dot size.
(A) shows the dot size in the ideal state, and (b) shows the dot size after the change. As shown in FIG. 15, the halftone dot size is smaller due to fluctuations compared to the ideal state. It should be noted that the variation in the dot size in the figure includes both a case where the variation occurs due to the characteristics of the photosensitive material and a case where the variation occurs due to repeated printing.

When the dot size changes in this way, the dot quality on the printing plate naturally changes. Specifically, the following degradation of dot quality occurs.

First, when the halftone on the printing plate is a flat halftone (where halftone dots of the same size are arranged), if the halftone dot size fluctuates, the designated area ratio cannot be obtained. If the halftone on the printing plate has gradation (gradation gradually changes), a tone jump (a phenomenon in which gradation changes discontinuously) may occur. Further, even when the halftone dot shape is controlled so as not to cause the unevenness as described above, "graininess" may occur if the halftone dot size changes. The influence of such a change in dot size is more susceptible to a longer dot perimeter. For example, in FIG. 15, in an ideal state, the areas of the upper half, the lower half, and the left halftone dot are the same, but when the halftone dot size is reduced due to the fluctuation, the upper halftone dot having the shortest halftone dot circumference is obtained. The size has the smallest degree of area reduction.

Therefore, in order to maintain the quality of the printed matter, it is important to control the quality of the halftone dots of the printing plate. However, in the halftone dots on the printing plate, the contrast between the image portion and the non-image portion is important. Therefore, even if the dot quality is degraded, it is difficult to find it by visual inspection, and there is a problem that it cannot be determined without actually printing.

Further, the printing plate deteriorates with time due to use, and even if the printing plate is subjected to a burning process, there is a certain limit to the number of printable plates. Conventionally, the number of printable sheets of a printing plate is sometimes indicated, but this is not a value corresponding to the image quality required for a printed matter. That is, even if the printing is performed within the number of printable sheets indicated in advance, the printed matter of the printing plate may not satisfy the required image quality.

Therefore, the life of the printing plate can be known only when the printing is actually performed up to its printing limit, and a large amount of ink, paper, and labor are required at the printing site.
Further, since the evaluation of the printing limit of the printing plate itself was also judged by human psychological evaluation, there were many variations and the judgment was often ambiguous.

As a method for solving this problem, Japanese Patent Laid-Open No.
In 574, a method is provided for ascertaining the print limit number of a printing plate by associating the mass reduction of the plate material of the plate with the print limit number, but this method also directly evaluates the image quality itself. It was not.

In other words, conventionally, the life expectancy of a printing plate (a value indicating how many good prints on the printing plate can be printed) is objectively and quantitatively determined from the viewpoint of image quality. Could not.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a printing plate evaluation apparatus and method capable of detecting a dot quality defect on a printing plate without actually printing. Aim.

It is another object of the present invention to provide a printing plate evaluation apparatus and method capable of accurately determining the life expectancy of a printing plate.

[0018]

According to a first aspect of the present invention, there is provided a printing plate evaluation apparatus which reads an evaluation flat screen provided on a printing plate to be evaluated and converts the evaluation image into an evaluation image. Evaluation image acquisition means for acquiring, analysis means for analyzing the evaluation image for a predetermined inspection item, and evaluation means for evaluating the printing plate based on the analysis result by the analysis means, ing.

According to a second aspect of the present invention, in the printing plate evaluation apparatus according to the first aspect of the present invention, the analysis means calculates an analysis value for the evaluation image. The printing apparatus includes a comparing unit that compares the analysis value with a preset inspection reference value, and a determining unit that determines whether the printing plate is good or bad based on a comparison result by the comparing unit.

According to a third aspect of the present invention, a printing plate evaluation apparatus reads a flat screen for regression calculation provided on a printing plate for regression calculation which has been subjected to a predetermined number of printing processes to obtain a regression calculation image. Regression calculation image acquisition means, an evaluation image acquisition means for reading an evaluation screen provided on a printing plate to be evaluated to obtain an evaluation image, and a predetermined inspection of the regression calculation image. First analysis means for analyzing the item, second analysis means for analyzing the evaluation image for the inspection item, and regression calculation based on the analysis result by the first analysis means; Regression calculation means for obtaining a regression curve indicating the correlation of the above, and determining the remaining life of the printing plate to be evaluated based on the regression curve, the analysis result by the second analysis means and a preset inspection reference value And that the determination unit, and a.

According to a fourth aspect of the present invention, in the printing plate evaluation apparatus according to any one of the first to third aspects of the present invention, the evaluation image acquisition unit includes a printing plate mounted on a printing machine during execution of printing. The evaluation image is obtained by reading the evaluation flat screen provided on the printing plate.

According to a fifth aspect of the present invention, there is provided a printing plate evaluation method comprising the steps of: setting a flat screen for evaluation on a printing plate to be evaluated; and reading the evaluation image by reading the flat screen for evaluation. An evaluation image acquisition step of acquiring, an analysis step of analyzing the evaluation image for a predetermined inspection item, and an evaluation step of evaluating the printing plate based on an analysis result in the analysis step. ing.

According to a sixth aspect of the present invention, in the printing plate evaluation method according to the fifth aspect of the present invention, in the analyzing step, an analysis value for the evaluation image is calculated. A comparison step of comparing the analysis value with a preset inspection reference value, and a determination step of performing a pass / fail determination of the printing plate based on the comparison result obtained in the comparison step,
It has.

According to a seventh aspect of the present invention, there is provided a printing plate evaluation method, comprising: a regression calculation flat screen setting step of setting a regression calculation flat screen on the regression calculation printing plate; An evaluation flat screen setting step of setting a flat screen, and a regression calculation for reading the regression calculation flat screen provided on the regression calculation printing plate subjected to a predetermined number of printing processes and acquiring a regression calculation image An image obtaining step for reading, an evaluation image obtaining step for reading the evaluation screen and obtaining an evaluation image, a first analysis step for analyzing the regression calculation image for a predetermined inspection item, A regression calculation based on the analysis result obtained in the second analysis step of analyzing the image for the inspection item and the analysis result obtained in the first analysis step, and forming a regression curve showing a correlation between the inspection item and the number of printed sheets. Regression calculation process to get and before Regression curve, and a, a determination step of determining life expectancy of the printing plate to be the evaluation target, based on the obtained analysis result and a preset inspection reference value in the second analysis step.

According to an eighth aspect of the present invention, in the printing plate evaluation method according to any one of the fifth to seventh aspects, the evaluation image acquiring step includes the step of: The step of reading an evaluation flat screen provided on the printing plate to obtain an evaluation image.

[0026]

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

<1. First Embodiment> First, a schematic configuration of a printing plate evaluation apparatus according to the present invention will be described. FIG.
1 is a functional block diagram illustrating a configuration of a printing plate evaluation device according to a first embodiment. The printing plate evaluation apparatus includes an image reading unit 10 that reads a screen on a printing plate to obtain an image, an image processing unit 20 that performs predetermined image processing on the read image, and an image analysis unit that analyzes the image. A unit 30, an input unit 60 for inputting an inspection item, an inspection standard, and the like; an inspection item storage unit 35 and an inspection standard storage unit 37 for storing the inspection item and the inspection standard, respectively; An evaluation unit 40 for performing the evaluation and a display unit 50 for displaying the result of the evaluation are provided.

The image reading unit 10 is configured by using a scanner, reads a net formed on a printing plate, converts the net into an electric signal, and executes an image represented by the electric signal, that is, a computer process. It has the function of acquiring possible images. It is preferable that the scanner constituting the image reading unit 10 has a resolution higher than the exposure scanning line density of the mesh formed on the printing plate. In this specification, the term “image” refers to an image digitized by the image reading unit 10, and an image represented by halftone dots on a printing plate is referred to as a “dot”.

The image processing section 20 has a function of performing image processing such as noise removal processing, averaging processing, and level correction on the image acquired by the image reading section 10. In the printing plate evaluation apparatus according to the present invention, the image processing unit 20 is not essential, and the image acquired by the image reading unit 10 may be directly transmitted to the image analysis unit 30.

The input unit 60 is constituted by using a keyboard or the like, so that an operator can input various commands to the printing plate evaluation apparatus, and also can set and input inspection items and inspection standards to be described later. it can.

Each of the inspection item storage unit 35 and the inspection standard storage unit 37 is configured by using a memory, and stores the inspection item and the inspection standard set and input, respectively.

The image analysis unit 30 has a function of analyzing the image transmitted from the image processing unit 20 with respect to the inspection items stored in the inspection item storage unit 35. Evaluation section 4
0 evaluates the quality of the halftone dots formed on the original printing plate based on the analysis result of the image analysis unit 30. Evaluation unit 40
Includes a comparison unit 45 and a determination unit 47. When evaluating the quality of a halftone dot, the comparison unit 45 checks the inspection criteria stored in the inspection criteria storage unit 37 and the analysis result by the image analysis unit 30. And the determination unit 47 determines the quality of the halftone dot quality of the printing plate based on the comparison result. In addition,
The processing contents of the image analysis unit 30 and the evaluation unit 40 will be described later in detail.

In the present embodiment, each of the image processing section 20, the image analysis section 30, and the evaluation section 40 is constituted by an electric circuit (noise removal / averaging processing circuit, comparison circuit, etc.) for executing the processing contents thereof. ing. However,
The image processing unit 20, the image analysis unit 30, and the evaluation unit 40
The present invention is not limited to the configuration using an electric circuit, and may be realized by causing a CPU to execute processing software.

The display unit 50 has a function of displaying a result of the pass / fail judgment by the evaluation unit 40 and transmitting the result to the operator of the apparatus.

Next, a printing plate evaluation processing procedure in the printing plate evaluation apparatus having the above configuration will be described. FIG.
6 is a flowchart showing a printing plate evaluation processing procedure in the printing plate evaluation apparatus.

First, an operator of the apparatus sets inspection items for evaluating a printing plate (step S31). As the inspection items, for example, the above-described “area ratio”, “roughness”, “tone jump”, and the like are set. The setting of the inspection items is performed by the operator via the input unit 60, and the set inspection items are stored in the inspection item storage unit 35.

Next, the operator sets inspection criteria for each of the set inspection items (step S3).
2). The operator also sets the inspection standard via the input unit 60, and the set inspection standard is stored in the inspection standard storage unit 37. In the present embodiment, the worker has “area ratio”,
Inspection criteria are set for each of "roughness" and "tone jump", and specific contents thereof will be described later.

Then, the operator prepares a printing plate and sets a flat screen chart (evaluation flat screen) on the printing plate (step S33). FIG. 6 is a diagram illustrating a printing plate on which a flat-screen chart is set. As shown, the printing plate PL is provided with a printing net PR and a flat net chart CH. The printing net PR is a net for a printing target to be obtained as a printed matter.

FIG. 7 is a diagram for explaining the flat screen chart CH. The flat screen chart CH is a screen composed of a plurality of gray screens, and is composed of 256 flat screen areas. Each of the plurality of flat screen areas has a flat screen of a different gradation. That is, a flat screen for 256 gradations is provided in the flat screen chart CH, and each flat screen is 0%.
The area ratio of 256 steps is set in the range of 100% or less. Specifically, in FIG. 7, a flat screen having a set area rate of 0% is provided in the flat screen area CH1, a flat screen having a set area rate of 0.39% is provided in the flat screen area CH2, and a flat screen area CH3. Is provided with a flat screen with a set area ratio of 0.78%. Similarly, a gray scale n (n =
0 to 255) flat screen (set area ratio is nx100 / 25)
5%). Here, the “set area ratio”
Does not indicate the area ratio of the flat screen actually formed on the flat screen chart CH, but the ideal area ratio specified for the flat screen of the flat screen chart CH.

When printing is performed using the printing plate of FIG. 6, ink is applied to both the printing screen PR and the flat screen chart CH, and printing is also performed on the flat screen chart CH. However, when the final printed matter is to be printed, the portion printed by the flat screen chart CH is cut and the printing screen PR is used.
Only the part printed by is available for use.

Returning to FIG. 3, the image reading section 10 of the printing plate evaluation apparatus reads the printing plate chart CH of the printing plate shown in FIG. 6 and acquires the image (evaluation image) (step S3).
4). Here, the higher the reading resolution of the image reading unit 10 is, the higher the accuracy of the image particularly in the area around the halftone dot is. In the present embodiment, the exposure scanning line density of the printing plate is 2
The flat screen chart CH is read at a resolution twice or more fine. For example, when the printing plate is exposed at 2400 dpi, the resolution read by the image reading unit 10 is 4800 dpi.
i or more. The printing plate read by the image reading unit 10 may be a plate immediately after being created in step S33, or may be a plate used to some extent in the printing process.

Next, the process proceeds to step S35, where the image processing unit 20 performs image processing such as noise removal, averaging, and level correction on the image acquired by the image reading unit 10. These processes are for adjusting the image quality of the image acquired by the image reading unit 10. The surface of the printing plate has irregularities, and the mesh on the printing plate has a small contrast between the image area and the non-image area, and the range of the image obtained by the image reading unit 10 is narrow. In order to do so, such image processing is performed. However, the image processing in step S35 is not essential, and is omitted, and the next step S3
6 may be performed.

Next, the image analysis unit 30 analyzes the image subjected to the image processing (step S36). Image analysis unit 3
“0” analyzes the image for each of the inspection items stored in the inspection item storage unit 35. In this embodiment,
Since the three inspection items “area ratio”, “roughness”, and “tone jump” are stored in the inspection item storage unit 35, the analysis is performed for each of these items. explain.

First, as for the inspection item “area ratio”, the pixel value (density value) of a pixel included in an image corresponding to one flat halftone area of the flat halftone chart CH (hereinafter, referred to as “flat halftone area image”). The image analysis unit 30 calculates the average value of ()). FIG. 8 is a diagram showing an image corresponding to one flat screen region,
FIG. 9 is an enlarged view of a part of FIG. Here, it is assumed that the flat halftone area image PC3 shown in FIG. 8 is an image corresponding to the flat halftone area CH3 (FIG. 7) of the flat halftone chart CH of the printing plate.

As shown in the figure, the flat halftone area image PC3 includes a plurality of halftone images of equal size (hereinafter, referred to as "halftone images"). The flat halftone area image PC3 itself has 40,000 pixels of 200 pixels vertically × 200 pixels horizontally. The pixel value of each pixel included in the flat halftone region image PC3 is an index indicating the ratio of the halftone image at that pixel. Therefore, the average value of the values obtained by normalizing the pixel values of 40,000 pixels included in the flat halftone region image PC3 from 0 to 100% corresponds to the area ratio of the halftone dot image in the flat halftone region image PC3. The average value of the normalized pixel values of the pixels included in the flat halftone area image PC3, that is, the area ratio AR of the halftone dot image in the flat halftone area image PC3 may be calculated as in the following Expression 1.

[0046]

(Equation 1)

Here, a (x, y) means that the pixel value of the pixel P (x, y) at the coordinates (x, y) in the flat halftone region image PC3 as shown in FIG. The value is normalized by Then, the flat halftone region image P obtained by Expression 1
The area ratio AR of the halftone dot image in C3 is an analysis value for the inspection item “area ratio”.

Since the flat-screen chart CH has 256 flat-screen areas, the image acquired by the image reading unit 10 also includes 256 flat-screen areas, and the image analysis unit 30 The area ratio is calculated for each of the 256 flat screen region images included in the obtained image.

For the inspection item “roughness”, the image analysis unit 30 calculates the maximum / minimum difference between the values obtained by performing the descreening process on one flat halftone region image. The descreening process is a process of averaging pixel values of a plurality of peripheral pixels including a pixel to be processed by a Gaussian filter, and using the obtained value as a pixel value of the pixel to be processed. Such processing is performed by the image analysis unit 30 for the entire single halftone region image. Then, the image analysis unit 30 calculates the maximum and minimum differences between the pixel values of the pixels included in the flat screen area image after the descreening processing.

FIG. 10 is a diagram for explaining the maximum and minimum differences between the pixel values of the pixels included in the flat screen area image after the descreening process. In the figure, the vertical axis indicates pixel values, and the horizontal axis indicates pixel coordinates. Here, the pixel coordinates are indices indicating the arrangement of the pixels, and the arrangement of one pixel row in the target flat screen area image may be used. For example, the pixel P in the flat screen area image PC3 shown in FIG.
One column from (1,1) to pixel P (1,200) (or one column from pixel P (1,1) to pixel P (200,1))
Column). The coordinates of the pixels are not limited to using one pixel row in the flat halftone area image, and the pixel rows included in the flat halftone area image are sequentially connected and arranged. May be used as the coordinates of the pixels.

The image analysis unit 30 calculates a difference DF between the maximum value and the minimum value of the pixel values of the pixels arranged in this way. Then, the difference D between the calculated maximum value and minimum value is calculated.
F is an analysis value for the inspection item “roughness”.

As for the inspection item “roughness”, similar to the inspection item “area ratio”, the flat-screen chart CH has 256 flat-screen areas. The image analysis unit 30 calculates the difference between the maximum value and the minimum value for each of the 256 flat halftone region images included in the acquired image.

For the inspection item “tone jump”,
The image analysis unit 30 calculates the increment of the area ratio of the halftone dot image for each gradation of the 256 flat halftone region images, and calculates the ratio of the maximum value to the minimum value of the increment. Each gradation n (n = 0 to
The area ratio of the halftone dot image in the flat halftone region image of 255) may be obtained in accordance with the above-described Expression 1. The halftone area image having the gradation n is a halftone area image corresponding to the halftone area provided with the halftone having the gray level n in the flat screen chart CH set for the printing plate.

If the area ratio of the halftone dot image in the flat halftone area image of the gradation n is AR _n , each gradation n (n = 1 to 1)
Increment INC _n of the area ratio of the halftone image in 255) are obtained as the following equation (2).

[0055]

(Equation 2)

That is, the increment from the area ratio of the halftone dot image in the flat halftone region image of one less gradation is calculated as the increment of the area ratio of the halftone dot image at each gradation.
The image analysis unit 30 calculates the ratio of the maximum value to the minimum value of the increment of the area ratio of the halftone image in each gradation obtained in this way.

FIG. 11 is a diagram for explaining the ratio of the maximum value to the minimum value of the increment of the area ratio of the halftone image in each gradation. In the figure, the vertical axis indicates the increment of the area ratio of the halftone dot image, and the horizontal axis indicates the gradation. Note that it is impossible to calculate the increment of the area ratio of the halftone dot image having the gradation 0, and thus the value does not exist.

The image analyzer 30 calculates the maximum value / minimum value of the increment in FIG. Then, the ratio of the maximum value to the minimum value of the increment calculated in this manner becomes the analysis value for the inspection item “tone jump”.

Referring back to FIG. 3, when the image analysis is completed, the process proceeds to step S37, where the inspection reference stored in the inspection reference storage unit 37 is compared with the analysis value which is the analysis result of the image analysis. This comparison processing is performed by the comparison unit 45 of the evaluation unit 40. In the present embodiment, since the analysis values are obtained for each of the three inspection items “area ratio”, “roughness”, and “tone jump”, the inspection standard is compared with the analysis value for each inspection item. .

Then, the quality of the original plate PL is determined based on the comparison result of the comparison section 45 (step S3).
8). This pass / fail judgment processing is performed by the judgment unit 47 of the evaluation unit 40. In the present embodiment, comparison results are obtained for each of the three inspection items “area ratio”, “roughness”, and “tone jump”. If one of the inspection items is determined to be defective, The printing plate PL is determined to be defective as an overall evaluation. Below, 3
A specific comparison / judgment method for each of the inspection items “area ratio”, “roughness”, and “tone jump” will be described.

First, as for the inspection item “area ratio”, the analysis value of the flat halftone region image corresponding to the flat halftone region (the flat halftone region image) Of the area ratio of the halftone dot image in
If it is not less than%, it is determined that the halftone dot size of the flat halftone area varies and the halftone dot quality is degraded. That is,
The inspection standard for the inspection item “area ratio” is set to a variation of 5%. For example, when the set area ratio in a certain halftone area of the flat halftone chart CH is 50%, the analysis value of the flat halftone area image corresponding to the flat halftone area is 45% or less or 55%.
If it is not less than%, it is determined that halftone dot quality is degraded in the flat halftone area.

Since the set area ratio in the flat halftone region is the area ratio specified as the flat halftone of the flat halftone chart CH, the fluctuation of the analysis value of the flat halftone region image if the halftone dot quality is ideal. Should be 0%. Therefore, when the variation of the analysis value is 5% or more, it is considered that the area ratio of the flat halftone region is excessively large or small depending on the magnitude of the variation, and the dot quality is degraded.

As described above, 256 charts are included in the flat screen chart CH.
The evaluation unit 40 has 256
Such determination is made for each of the flat screen areas.
Then, if there is a variation of 5% or more and the ratio of the flat halftone area determined to have deteriorated halftone dot quality is equal to or more than a predetermined value, the plate PL for the inspection item “area ratio” is It is determined to be defective.

Next, regarding the inspection item “roughness”,
If the analysis value (difference between the maximum value and the minimum value) of the flat halftone region image corresponding to a certain halftone region in the flat halftone chart CH is 1% or more, the halftone dot size of the flat halftone region varies, It is determined that the dot quality has deteriorated. That is, the inspection standard for the inspection item “roughness” is set to a difference of 1%. For example, when the maximum value after the descreening process of the flat screen area image corresponding to a certain flat screen area in the flat screen chart CH is 51% and the minimum value is 49%, the dot quality in the flat screen area is determined. Is determined to have deteriorated.

Since one flat halftone area is a flat halftone area, that is, an area that should be constituted by an array of halftone dots of the same size, ideally, the maximum value of the flat halftone area image after descreening processing is equal to the maximum value. The difference from the minimum should be 0%.
That is, in FIG. 10, a straight line parallel to the horizontal axis should be obtained. Therefore, when the difference between the maximum value and the minimum value, which are the analysis values, is 1% or more, the size of the halftone dots forming the flat halftone region is biased in accordance with the magnitude of the difference,
It is considered that the dot quality has deteriorated.

Similarly to the above, the inspection item “roughness” is provided with 256 flat screen areas in the flat screen chart CH, so the evaluation unit 40 makes such a judgment for each of the 256 flat screen areas. Do. If there is a maximum / minimum difference of 1% or more and the ratio of the plain halftone area determined to have deteriorated halftone dot quality is equal to or more than a predetermined value, the plate PL for the inspection item “roughness” is obtained. Is determined to be defective.

Next, for the inspection item “tone jump”, if the analysis value (the ratio of the maximum value to the minimum value of the increment) of the image obtained from the flat screen chart CH is 2 or more,
It is determined that the dot size of the flat dot chart CH varies and the dot quality is degraded. That is, the inspection standard for the inspection item “tone jump” is set to the ratio 2. For example, in FIG. 11, when the minimum value of the increment of the area ratio of the halftone dot image is 0.2% and the maximum value is 0.5%, the ratio of the maximum value to the minimum value is 2.5,
It is determined that the dot quality has deteriorated in the flat dot chart CH.

256 provided in the flat screen chart CH
Since the set area ratio of the flat halftone region is specified in an equal manner, the increment of the area ratio of the halftone dot image should ideally be a constant value (about 0.39%). . That is, FIG.
At 1, a straight line parallel to the horizontal axis should be obtained.
When the increment of the area ratio of the halftone dot image is smaller than this value, it is considered that there is not much change in gradation at that gradation. Conversely, when the increment is larger than this value, it is considered that a large gradation change occurs at that gradation. Therefore, when the ratio of the maximum value to the minimum value of the increment of the area ratio of the halftone dot image is 2 or more, it is considered that the gradation is discontinuously changed as the whole flat dot chart CH.

Therefore, when the ratio of the maximum value to the minimum value of the increment of the area ratio of the halftone dot image is 2 or more, it is determined that the printing plate PL is defective for the inspection item “tone jump”.

As described above, in this embodiment, if one of the three inspection items “area ratio”, “roughness” and “tone jump” is also judged to be defective, the plate PL is determined to be defective as an overall evaluation. Then, the result of the determination is displayed on the display unit 50 and transmitted to the operator.

As described above, in the first embodiment, the flat plate chart CH is provided on the printing plate PL, an image is obtained by reading the flat plate chart CH, and the original image is analyzed by analyzing the image. The printing plate PL is evaluated. A plurality of flat screens having different area ratios are set in the flat screen chart CH, and the area rates set for the respective flat screens are assumed to be equal. Therefore, the image obtained from the flat screen chart CH is suitable for statistical processing, and a quantitative and objective evaluation of the dot quality of the printing plate PL is performed through such a flat screen chart CH. It is. In this way, it is possible to accurately detect a dot quality defect on the printing plate without actually printing, and it is possible to reduce waste of time, cost, and labor in the printing process.

<2. Second Embodiment> Next, a second embodiment of the present invention will be described. FIG. 2 is a functional block diagram illustrating the configuration of the printing plate evaluation device according to the second embodiment. This printing plate evaluation apparatus is different from the printing plate evaluation apparatus of the first embodiment in that it does not include the evaluation unit 40, but also determines the printing endurance number determination unit 70 and the printing number / analysis value table storage unit 75.
And a regression curve calculation unit 80. The other configuration is the same as that of the printing plate evaluation apparatus of the first embodiment, and thus the same reference numerals are given and the description is omitted.

The print number / analysis value table storage unit 75
It is configured using a memory, and stores an analysis value analyzed by the image analysis unit 30 for a printing plate for regression calculation, which will be described later, and the number of printed sheets when the analysis is performed.

The regression curve calculation unit 80 has a function of performing a regression analysis based on the analysis value stored in the number-of-printed-numbers / analysis-value table storage unit 75 and the number of printed sheets, and obtaining a regression curve showing a correlation between them. The obtained regression curve is stored in the printed sheet / analysis value table storage unit 75 as a table.

The printing endurance number judging section 70 judges the image analysis section 30 for the flat screen chart provided on the printing plate to be evaluated.
, The inspection criteria stored in the inspection criteria storage unit 37, and the number of printed sheets / analysis value table storage unit 75
Has the function of determining the life expectancy of the printing plate based on the regression curve table stored in. As described above, the life expectancy of a printing plate is a value that indicates how many good printed images of the printing plate can be printed.

In the second embodiment, both the number-of-printed-sheets determination section 70 and the regression curve calculation section 80 are constituted by electric circuits (regression curve calculation circuit or the like) for executing the processing contents. , These are not limited to the configuration using an electric circuit,
May be realized by causing the processing software to execute.

Next, a printing plate evaluation processing procedure in the printing plate evaluation apparatus of the second embodiment will be described. FIG.
It is a flowchart which shows the evaluation processing procedure of the printing plate in the printing plate evaluation apparatus of 2nd Embodiment.

First, the operator of the apparatus sets inspection items for printing plate evaluation (step S41), and sets inspection standards for the inspection items (step S42). This setting operation is performed in the same manner as in the first embodiment, and is input by the operator via the input unit 60. The inspection item and the inspection standard set and input are stored in the inspection item storage unit 35 and the inspection standard storage unit 37, respectively. In the second embodiment, “roughness” is set as the inspection item, and a maximum / minimum difference of 1% is set as the inspection criterion. In the second embodiment, the set inspection items and inspection standards may be other than those described above, for example, “tone jump”.

Next, a regression curve is calculated, and its table is created (step S43). FIG.
9 is a flowchart illustrating a procedure of calculating a regression curve and creating a table thereof according to the embodiment. First, the operator sets a plurality of print sheets for calculation (step S51). The number of prints to be set is arbitrary, but the more the set number is, the more accurate regression analysis can be performed.

Next, a printing plate for regression calculation is prepared, and a flat-screen chart for regression calculation is set on the printing plate (step S52). The printing plate for regression calculation created here is
It is not a printing plate for obtaining printed matter, but a printing plate only for regression calculation. Therefore, the printing plate for regression calculation does not necessarily need to be the one shown in FIG. 6, and may be a printing plate provided with only a flat-screen chart for regression calculation. Note that the configuration of the flat-tone chart for regression calculation itself is the same as that of the flat-tone chart CH of the first embodiment, and a detailed description thereof will be omitted.

Then, the flow advances to a step S53 to perform printing using the printing plate for regression calculation. This printing is performed in step S5.
The ink is actually applied to the number of printed sheets for calculation set in step 1. Then, when the printing of the predetermined number of prints is completed, the image reading unit 10 reads the regression calculation flat screen chart and acquires the regression calculation image (step S5).
4) Image processing unit 2 for the acquired regression calculation image
0 performs image processing such as noise removal, averaging, and level correction (step S55). The processing contents of these reading and image processing are the same as in the first embodiment.

Next, the process proceeds to step S56, where the image analysis unit 30 analyzes the regression calculation image. Image analysis unit 30
Performs image analysis on the inspection item stored in the inspection item storage unit 35, that is, the inspection item “roughness” in the present embodiment. The image analysis method is the same method as described in the first embodiment. That is, in the second embodiment, the image analysis unit 30 performs the descreening process on the flat-tone region image included in the regression calculation image, and determines the maximum and minimum difference between the pixel values of the pixels included in the processed flat-tone region image. Calculate,
Analysis value. In the second embodiment, it is not necessary to calculate the analytic values for all the halftone region images included in the regression calculation image, and it is only necessary to calculate the analytic values only for a predetermined predetermined halftone region image. good.

Next, the flow proceeds to step S57, in which the number of printed plates of the regression calculation plate subjected to the analysis and the analysis value as the analysis result are stored in the printed number / analysis value table storage unit 75. Then, it is determined whether or not the processing from step S54 to step S57 has been performed for all the number of printed sheets set in step S51 (step S5).
8). This determination may be made, for example, by the image analysis unit 30 or the regression curve calculation unit 80. If it is determined that the processing has not been performed for all the set numbers, step S53
And printing is further performed, and the processing from step S54 to step S57 is repeated. Therefore, for all the print numbers set in step S51, the print number and the analysis value of the print number are stored in the print number / analysis value table storage unit 75.

On the other hand, if it is determined in step S58 that all the set number of sheets have been processed, step S59 is performed.
The regression curve calculation unit 80 performs a regression analysis based on the data stored in the number of printed sheets / analysis value table storage unit 75 to show a regression curve indicating a correlation between the number of printed sheets and the analysis value at the number of printed sheets. And create a table of the regression curve. Then, the regression curve calculation unit 80 stores the obtained regression curve in the number of printed sheets / analysis value table storage unit 75 in the form of a table.

FIG. 12 is a diagram showing a regression curve showing a correlation between the number of printing plates and the analysis value at the number of printing plates. In the present embodiment, an analysis value for the number of printed sheets up to 140,000 for every 10,000 sheets is calculated, and a regression curve as shown in FIG. The printing plate evaluation apparatus stores this regression curve in the form of a table in the printed sheet / analysis value table storage unit 75.

After the calculation of the regression curve is performed as described above, returning to FIG. 4, a printing plate to be evaluated is prepared, and an evaluation flat chart is set on the printing plate. (Step S44). The printing plate created here is
This is a printing plate for obtaining printed matter. The flat-tone chart for evaluation is the same as the flat-tone chart CH of the first embodiment. That is, the printing plate of the second embodiment is the same as the printing plate PL shown in FIG.

Next, the flow proceeds to step S45, where printing is performed using the printing plate. When a final printed matter is obtained, the portion printed by the evaluation flat screen chart is cut and is not used.

At an appropriate point in time when a certain amount of printing has been performed, the image reading unit 10 reads the evaluation halftone chart to obtain an evaluation image (step S46), and performs image processing on the obtained evaluation image. The unit 20 performs image processing such as noise removal, averaging, and level correction (Step S47). The processing contents of these reading and image processing are the same as in the first embodiment.

In the second embodiment, the image reading unit 10
Read both the regression calculation flat dot chart and the evaluation flat dot chart, but a dedicated image reading unit may be provided for each of the regression calculation flat dot chart and the evaluation flat dot chart. .

Then, the process proceeds to a step S48, wherein the image analyzing section 30 analyzes the evaluation image. The image analysis unit 30 performs image analysis on the same inspection item that created the regression curve, that is, the inspection item “roughness” in the present embodiment.
The method of image analysis is the same as that described in the first embodiment. The image analysis unit 30 performs a descreening process on the flat-screen area image included in the evaluation image, and executes the processed flat-screen area image. Is calculated as an analysis value. Here, it is not necessary to calculate the analysis values for all the screen halftone region images included in the evaluation image, and if the analysis values are calculated for the flat halftone region images corresponding to the flat halftone region images used for creating the regression curve, good.

In the second embodiment, the image analysis unit 30
Reads both the regression calculation image and the evaluation image, but a dedicated image analysis unit may be provided for each of the regression calculation image and the evaluation image.

When the analysis on the evaluation image is completed,
Proceeding to step S49, the analysis value, the regression curve table for the evaluation image stored in the number of printed sheets / analysis value table storage unit 75 and the inspection standard stored in the inspection standard storage unit 37 are set as evaluation targets. Seeking the life expectancy of a printing plate. This process is performed by the printing number determination unit 70.

FIG. 13 is a diagram for explaining a technique for determining the life expectancy of a printing plate to be evaluated. From the regression curve table and the inspection standard (maximum / minimum difference 1%), it is possible to determine the maximum printable number a of the printing plate. That is,
It is considered that the halftone dot quality deterioration characteristic of the printing plate for regression calculation and the halftone dot quality deterioration characteristic of the printing plate are almost the same. And
On the basis of the same concept as in the first embodiment, a printing plate having a maximum / minimum difference of 1% or more is regarded as a defective product. This can be considered as the maximum printable number a of the plate.

Further, from the regression curve table and the analysis value of the evaluation image, the number of prints b at the time when the printing plate is evaluated can be determined. This is also based on the idea that the dot quality deterioration characteristic of the printing plate for regression calculation and the dot quality deterioration characteristic of the printing plate are almost the same. The number of prints (ab) obtained by subtracting the number of prints b at the time of evaluation from the maximum printable number a becomes the remaining life of the printing plate at that time.

The printing endurance number determination unit 70 determines the remaining life of the printing plate in this way, and transmits it to the display unit 50. The display unit 50 displays the life expectancy of the printing plate to notify the operator. The printable sheet number determination unit 70 may determine the life expectancy of the printing plate comprehensively from the analysis results of all the plain halftone region images analyzed by the image analysis unit 30.

As described above, in the second embodiment, a regression calculation flat plate chart is provided on a regression calculation plate different from the printing plate, and the regression calculation flat plate chart is read. A regression curve between the number of prints and the analysis value is created by performing statistical analysis on the calculation image. A printing halftone chart is also provided on the printing printing plate, and a result obtained by analyzing the evaluation image obtained by reading the evaluation flat halftone chart is compared with a regression curve to obtain a printing halftone chart. Life expectancy is determined. That is, the life expectancy of the printing plate is determined based on the two flat charts. As described above, the flat screen chart is an evaluation standard of halftone dot quality suitable for statistical processing, and by determining the life expectancy of a printing plate via such a flat screen chart, In addition, a quantitative and objective determination can be made from the viewpoint of image quality, and the life expectancy of the printing plate can be accurately determined. As a result, waste of time, cost, and labor in the printing process can be reduced.

<3. Modifications> While the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described examples. For example, in the first embodiment, the inspection items to be set are not limited to three of “area ratio”, “roughness”, and “tone jump”, and it is sufficient if at least one is set. May be set.

Further, the inspection criteria to be set are not limited to those shown in the first embodiment, and other criteria may be set. For example, instead of uniformly setting the inspection standard for the inspection item “area ratio” to 5%, a highlight halftone region image (gradations 0 to 6) is used.
In 3), a 5% change, a halftone flat area image (gradation 64 to
191), the fluctuation may be 7%, and the fluctuation may be 5% for the shadow halftone area image (gradations 192 to 255). This is because the change in the area ratio of halftone dots is conspicuous in a highlight portion or a shadow portion.

Further, as the inspection standard, a different standard may be provided for each color plate. For example, instead of setting the inspection criterion for the inspection item “roughness” to be 1% of the difference between the maximum value and the minimum value for all the color plates, the maximum and minimum differences are 1.5% for the cyan and magenta plates, and May be 1% maximum / minimum difference. This is because the "grain" is less noticeable in the cyan and magenta plates than in the black plate.

In the first and second embodiments,
If "tone jump" is not set as the inspection item, it is not necessary to provide a flat screen for 256 gradations in the flat screen chart. For example, only a highlight and shadow flat screen may be provided. Only a flat screen having an area ratio of 50% may be provided. That is, it is sufficient to provide only a flat screen according to the characteristics of the screen formed on the printing plate to be evaluated.

The reading of the flat-screen chart by the image reading unit 10 is not limited to being performed in a state where the printing plate is not mounted on the printing press. May be read from a flat chart provided on the printing plate.

FIG. 14 is a diagram showing a flat-screen chart provided on a printing plate, which is mounted on a printing machine and is performing printing, by the image reading unit 10.
FIG. 4 is a diagram for explaining how the image is read. The printing plate is a plate cylinder 90
It is attached to. The paper 94 to be printed includes a rotating blanket cylinder 92 and an impression cylinder 9 as indicated by arrows in the figure.
1 and sent while being sandwiched. The ink placed on the printing plate is transferred to the blanket cylinder 92 and printed on the paper 94 via the blanket cylinder 92 (offset printing).

Then, the image reading section 10 reads a printing plate mounted on the rotating plate cylinder 90 to obtain an image. Specifically, the image reading unit 10 includes a CCD
A line sensor is provided, light is emitted from the light source 93 to the plate cylinder 90, and the reflected light is received by the CCD line sensor to acquire an image. In this way, the printing plate is transferred to the plate cylinder 90.
Since it is not necessary to remove the printing plate from the printer and the image can be obtained in real time, the plate can be evaluated easily and quickly.

[0104]

As described above, according to the first and fifth aspects of the present invention, an evaluation image is obtained by reading an evaluation flat screen provided on a printing plate to be evaluated. Since the printing plate is evaluated based on the analysis result obtained by analyzing the evaluation image for a predetermined inspection item, it is possible to detect a dot quality defect on the printing plate without actually printing. .

According to the second and sixth aspects of the present invention, an analysis value is calculated for an evaluation image, and the analysis value is compared with a preset inspection reference value based on a comparison result. Since the quality of the printing plate is determined, the quality can be determined based on an objective numerical value, and the dot quality defect on the printing plate can be accurately detected without actually printing.

According to the third and seventh aspects of the present invention, a regression calculation flat screen provided on a regression calculation printing plate subjected to a predetermined number of printing processes is read to obtain a regression calculation image. Then, the regression calculation image is regression-calculated based on the analysis result obtained by analyzing a predetermined inspection item to obtain a regression curve indicating a correlation between the inspection item and the number of prints, and a printing target to be evaluated. An evaluation image is obtained by reading the evaluation flat screen provided on the plate, an analysis result obtained by analyzing the evaluation image for the inspection item, an evaluation target based on a predetermined inspection reference value and the regression curve, and Since the remaining life of the printing plate is determined, the remaining life of the printing plate can be accurately determined based on an objective numerical value.

According to the fourth and eighth aspects of the present invention, an evaluation image is obtained by reading an evaluation flat screen provided on a printing plate, which is mounted on a printing press and is being printed. Therefore, the effect according to any one of claims 1 to 3 and the effect according to any one of claims 5 to 7 can be obtained easily and quickly.

[Brief description of the drawings]

FIG. 1 is a functional block diagram illustrating a configuration of a printing plate evaluation apparatus according to a first embodiment.

FIG. 2 is a functional block diagram illustrating a configuration of a printing plate evaluation apparatus according to a second embodiment.

FIG. 3 is a flowchart illustrating a printing plate evaluation processing procedure in the printing plate evaluation apparatus according to the first embodiment.

FIG. 4 is a flowchart illustrating a printing plate evaluation process performed by a printing plate evaluation apparatus according to a second embodiment.

FIG. 5 is a flowchart showing a procedure for calculating a regression curve and creating a table thereof in the second embodiment.

FIG. 6 is a diagram illustrating a printing plate on which a flat-screen chart is set.

FIG. 7 is a diagram for explaining a flat screen chart;

FIG. 8 is a diagram illustrating an image corresponding to one flat halftone area.

FIG. 9 is an enlarged view of the flat halftone region image of FIG. 8;

FIG. 10 is a diagram illustrating the maximum and minimum differences between pixel values of pixels included in a flat screen area image after descreening processing.

FIG. 11 is a diagram illustrating the ratio of the maximum value to the minimum value of the increment of the area ratio of the halftone image in each gradation.

FIG. 12 is a diagram showing a regression curve representing a correlation between the number of printed plates and an analysis value at the number of printed plates.

FIG. 13 is a diagram for explaining a method of a life expectancy determination process of a printing plate.

FIG. 14 is a diagram illustrating a state in which an image reading unit reads a flat-screen chart provided on a printing plate that is mounted on a printing press and that is performing printing.

FIG. 15 is a diagram illustrating a change in halftone dot size.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image reading part 20 Image processing part 30 Image analysis part 40 Evaluation part 45 Comparison part 47 Judgment part 50 Display part 70 Number of prints endurance judgment part 80 Regression curve calculation part 90 Plate cylinder

Claims (8)

[Claims] 1. An evaluation image acquisition means for reading an evaluation screen provided on a printing plate to be evaluated and acquiring an evaluation image, and an analysis for analyzing the evaluation image for a predetermined inspection item A printing plate evaluation apparatus, comprising: means for evaluating the printing plate based on an analysis result by the analysis unit. 2. The printing plate evaluation apparatus according to claim 1, wherein the analysis unit calculates an analysis value for the evaluation image, and the evaluation unit calculates the analysis value and a preset inspection reference value. A printing plate evaluation apparatus comprising: a comparing unit that compares the printing plate; and a determining unit that determines whether the printing plate is good or bad based on a comparison result by the comparing unit. 3. A regression calculation image acquisition means for reading a regression calculation flat screen provided on a regression calculation printing plate subjected to a predetermined number of printing processes and acquiring a regression calculation image, and an evaluation target. An evaluation image acquisition unit that reads an evaluation flat screen provided on a printing plate to obtain an evaluation image; a first analysis unit that analyzes the regression calculation image for a predetermined inspection item; A second analysis unit that analyzes an image for the inspection item; a regression calculation unit that performs a regression calculation based on an analysis result by the first analysis unit and obtains a regression curve indicating a correlation between the inspection item and the number of printed sheets. Determining means for determining the remaining life of the printing plate to be evaluated based on the regression curve, the analysis result by the second analyzing means, and a preset inspection reference value. Printing plates evaluation device. 4. The printing plate evaluation device according to claim 1, wherein the evaluation image acquisition unit is provided on a printing plate that is mounted on a printing machine and is performing printing. A printing plate evaluation apparatus, which reads a flat screen to obtain an evaluation image. 5. A flat screen setting step of setting an evaluation flat screen on a printing plate to be evaluated, an evaluation image obtaining step of reading the evaluation flat screen and obtaining an evaluation image, and the evaluation image. A printing plate evaluation method, comprising: an analysis step of analyzing a predetermined inspection item for an inspection item; and an evaluation step of evaluating the printing plate based on an analysis result in the analysis step. 6. The printing plate evaluation method according to claim 5, wherein in the analysis step, an analysis value for the evaluation image is calculated, and in the evaluation step, the analysis value and an inspection reference value set in advance are set. A printing plate evaluation method, comprising: a comparison step of comparing the printing plate; and a determination step of determining whether the printing plate is good or bad based on the comparison result obtained in the comparison step. 7. A regression calculation flat screen setting step of setting a regression calculation flat screen on a regression calculation printing plate, an evaluation flat screen setting step of setting an evaluation flat screen on a printing plate to be evaluated. A regression calculation image acquisition step of reading the regression calculation screen provided on the regression calculation printing plate subjected to a predetermined number of printing processes to obtain a regression calculation image; and reading the evaluation screen. Obtaining an evaluation image by performing a first analysis step of analyzing the regression calculation image for a predetermined inspection item; and a second analysis step of analyzing the evaluation image for the inspection item. A regression calculation step of performing a regression calculation based on the analysis result obtained in the first analysis step to obtain a regression curve indicating a correlation between the inspection item and the number of printed sheets; and Obtained in 2 analysis steps Printing evaluation method characterized by and a determination step of determining life expectancy of the printing plate to be the evaluation target analysis result and based on a preset inspection reference value. 8. The printing plate evaluation method according to claim 5, wherein the evaluation image acquiring step includes an evaluation provided on a printing plate that is mounted on a printing machine and is performing printing. A printing plate evaluation method, comprising a step of reading a flat screen to obtain an evaluation image.