JP3967307B2 - Image correction apparatus and method - Google Patents

Description

  The present invention relates to an image correction apparatus and method.

  As an inspection system that automatically inspects printed matter (for example, color quality inspection, inspection for presence / absence of stains, inspection for presence / absence of omission), an image to be inspected is obtained by imaging the printed matter with an imaging device. There is one that compares data with reference image data prepared in advance (in general, image data to be inspected that seems to be accurate) (for example, see Patent Document 1).

  In this inspection system, a plurality of lines obtained by imaging are picked up one by one by an imaging device including a line sensor whose scanning direction is a direction orthogonal to the conveyance direction of the printed material conveyed by the conveying device. 2D image data (inspected image data) is obtained from the image data.

  In the above inspection system, when the transport speed of the printed material is low, the resolution of the obtained image data is high, and a precise image inspection is possible. However, the higher the inspection accuracy, the higher the rate at which an acceptable range is determined to be defective. On the other hand, if the conveyance speed of the printed material is high, the obtained image is blurred in the conveyance direction, and the inspection accuracy is lowered.

As described above, since the conveyance speed of the printed matter affects the resolution of the obtained image data, the inspection accuracy varies depending on the conveyance speed.
Japanese Patent Laid-Open No. 11-207936

  SUMMARY OF THE INVENTION An object of the present invention is to make it possible to keep the accuracy of inspection of printed matter almost constant regardless of the conveyance speed of the printed matter.

  Another object of the present invention is to make the image quality (degree of blurring) of image data obtained by imaging the conveyed printed matter substantially the same regardless of the conveying speed of the printed matter.

  According to the image correction apparatus of the present invention, a plurality of filter coefficients for filtering image data (low-pass filtering or blur filtering) so that the degree of blurring increases as the conveyance speed of a printed material becomes slower, and a plurality of different conveyance speeds. The filter coefficient storage means stored corresponding to the above, the speed determination means for determining the transport speed of the printed matter, and the printed matter determined by the speed determination means from among the plurality of filter coefficients stored in the filter coefficient storage means The filter coefficient selecting means for selecting one filter coefficient corresponding to the transport speed of the image and the image data of the unit area output from the imaging device for imaging the printed matter being transported, with each unit area as the center in the transport direction For image data of multiple unit areas arranged in the direction corresponding to Those having a filtering means for filtering using a filter coefficient selected by the filter coefficient selection means (low-pass filtering means or blurring filtering means).

  The image correction method according to the present invention determines a transport speed of a printed material, and filters a plurality of filters for filtering (low-pass filtering or blur filtering) image data so that the degree of blurring increases as the transport speed of the printed material decreases. One filter coefficient corresponding to the determined conveyance speed of the printed material is selected from the coefficients, and each unit area is centered on each of the unit area image data output from the imaging device that images the conveyed printed material. As described above, filtering (low-pass filtering or blur filtering) is performed on the image data of a plurality of unit regions arranged in the direction corresponding to the transport direction using the selected filter coefficient.

  In the present invention, the image data subjected to image correction (filtering) is obtained by imaging the conveyed printed matter with an imaging device. The imaging device may include either a line sensor or an area sensor, but preferably a line sensor is used.

  In the present invention, the determination of the conveyance speed of the printed material includes both measuring the conveyance speed of the printed material and setting the conveyance speed of the printed material. Therefore, the determination of the transport speed of the printed material includes not only measuring the transport speed (moving speed, traveling speed) of the printed material being transported, but also the transport speed for transporting (moving, traveling) the printed material. It includes setting, reading or using the set transport speed.

  In the present invention, the conveyance speed includes a speed range. That is, the determination of the conveyance speed of the printed material includes not only the determination of the conveyance speed but also the determination of the conveyance speed range. Further, it includes storing a plurality of filter coefficients for a plurality of different conveyance speed ranges, or defining different filter coefficients for a plurality of different conveyance speed ranges.

  Further, in the present invention, the unit area may be a unit of pixels, or may be a unit of a region composed of a plurality of pixels.

  According to the present invention, based on the determined transport speed of the printed material, the transport speed of the printed material is selected from the plurality of filter coefficients for filtering the image data so that the degree of blurring increases as the transport speed of the printed material decreases. One filter coefficient corresponding to (including the conveyance speed range as described above) is selected. The selected filter coefficient is used to filter the image data output from the imaging device that images the conveyed printed matter. Filtering can be realized by a hardware circuit or a computer operation according to software.

  Since the filter coefficient that causes a large blurring is selected as the transport speed is slow, filtering that causes a small blurring at a high transporting speed is performed, and filtering that generates a large blurring is performed at a slow transporting speed. Each done. Since the filtering is performed on the image data of the unit areas output from the imaging apparatus, the image data of a plurality of unit areas arranged in the direction corresponding to the transport direction with each unit area as the center is subjected to the filtering. The blur corresponding to the conveyance speed occurs in the direction corresponding to the direction.

  The faster the conveyance speed of the printed material being conveyed, the more optically blurred the image obtained by imaging occurs in the direction corresponding to the conveyance direction. On the other hand, a filter coefficient that causes a large blur as the conveyance speed is slow is selected, and filtering is performed in a direction corresponding to the conveyance direction. For this reason, according to the present invention, it is possible to make the degree of blurring due to the combination of blurring that occurs optically and blurring caused by filtering the same, regardless of the conveyance speed.

  An image based on image-corrected (filtered) image data obtained by the present invention is particularly effective when used in an inspection system for inspecting a printed material by comparing the inspected image data of the printed material with reference image data. Since an image to be inspected having the same degree of blur in the transport direction can be obtained regardless of the transport speed of the printed matter, variations in determination due to differences in transport speed can be prevented in the comparison process.

  FIG. 1 is a perspective view schematically showing a part of a printed matter inspection system.

  The inspection system takes an image of a printed matter to be inspected by an imaging device including a CCD line sensor, and inspects the printed matter based on an image obtained by the imaging. Inspecting printed matter is image processing, for example, comparing inspected image data obtained by imaging and reference image data (appropriate image data of the printed matter) acquired in advance (through preprocessing of image data as necessary) The determination is made by determining whether the result satisfies a predetermined condition. The image processing checks (determines) the quality of the color tone, the presence / absence of dirt, the presence / absence of omission, and the like.

  A predetermined image (picture, character, etc.) is printed on the surface of a continuous sheet W such as paper or film by a rotary printing machine. The rotary printing press includes a rotationally driven plate cylinder 3 and a roll 4 which are arranged close to each other. The sheet W is printed and sent out in the process of passing between the plate cylinder 3 and the roll 4.

  A printed sheet (hereinafter referred to as “printed matter”) W sent from the rotary printing press is transported by a transport device. In this embodiment, the conveying device is configured such that a large number of conveying rollers 5 are arranged in parallel on the horizontal plane along the conveying path at substantially constant intervals. The plate cylinder 3 and the roll 4 of the rotary printing press are rotationally driven in synchronization with each other by a rotational drive device (not shown). An imaging device 1 including a CCD line sensor and a linear illumination light source 2 are fixedly provided above the imaging position determined on the conveyance path of the conveyance device. The linear illumination light source 2 extends in the width direction of the conveyance path (direction perpendicular to the conveyance direction) and illuminates the entire imaging position on the conveyance path. The CCD line sensor of the imaging apparatus 1 is arranged so that the width direction of the transport path is the scanning direction, and images the imaging position illuminated by the light source 2 over the entire width direction (at least the entire width of the printed matter W).

  The input shaft of the rotary encoder 6 is connected to the rotary shaft of the roll 4 of the rotary printing press. The rotary encoder 6 outputs an encoder pulse having a frequency (cycle) corresponding to the rotation speed of the roll 4 (that is, the conveyance speed of the printed material W).

  The image data obtained by the imaging device 1 and the encoder pulse output from the rotary encoder 6 are input to the image correction device 7. In the image correction device 7, image data to be described later is corrected, and image processing (inspection of the printed matter W) is performed based on the corrected image data.

  FIG. 2 is a block diagram showing an electrical configuration of the imaging device 1 and the image correction device 7. FIG. 2 also shows a block representing the rotary encoder 6.

  The imaging device 1 includes a line sensor 11 and its drive circuit 12. A scanning start pulse (start pulse) S and a pixel clock signal CL output from the drive circuit 12 are supplied to the line sensor 11. When the scanning start pulse S is given, a plurality of pixel data (image data for one line) is read out according to the pixel clock signal CL and sequentially output from the line sensor 11. It is preferable that the reading of the image data by the scanning start pulse S and the pixel clock signal CL is set so as to correspond to the fastest transport speed regardless of the transport speed of the printed material W. That is, each of the scanning start pulse S and the pixel clock signal CL has a predetermined frequency (period) regardless of the transport speed of the printed material W, and the exposure time of the line sensor 11 is a predetermined constant regardless of the transport speed. It's time.

  The image correction apparatus 7 includes a counter 13, a delay circuit 14, a filter circuit 15, a filter coefficient selection setting circuit (means) 16, a filter coefficient table 17, and an image memory 18.

  The scanning start pulse S output from the drive circuit 12 is applied to the line sensor 11 as described above and also input to the counter 13 of the image correction device 7.

  The counter 13 is a scan start pulse S input between two consecutive encoder pulses (start and reset) output from the rotary encoder 6 and applied to the counter 13 (hereinafter referred to as “encoder pulse period T”). Is counted (see FIG. 3). As described above, the scan start pulse S output from the drive circuit 12 has a constant period regardless of the conveyance speed. On the other hand, the encoder pulse period T corresponds to the rotational speed of the roll 4 (= conveyance speed of the printed product W). When the conveyance speed of the printed product W is low, the encoder pulse period T becomes long and the number of scanning start pulses S in the encoder pulse period T increases, so the count value counted by the counter 13 increases. When the conveyance speed of the printed material W is high, the encoder pulse period T is shortened, and the number of scanning start pulses S in the encoder pulse period T is reduced, so that the count value is reduced. As described above, the count value counted by the counter 13 represents the transport speed of the printed material W (more precisely, the count value is inversely proportional to the transport speed).

  The count value (conveying speed of the printed material W) counted by the counter 13 is given to the filter coefficient selection setting circuit 16. The filter coefficient selection setting circuit 16 selects and reads out the filter coefficient corresponding to the given count value (conveyance speed of the printed matter W) from the filter coefficient table 17 and gives it to the filter circuit 15.

  FIG. 5 shows an example of the contents of the filter coefficient table 17. The filter coefficient table 17 stores a plurality of filter coefficients corresponding to each of a plurality of count values (conveying speed of the printed material W). In FIG. 5, nine filter coefficients corresponding to count numbers 44, 28, 16, 10, 8, 7, 6, 5, and 4 are stored. Among these count numbers, 44, 28, 16, and 10 represent count value ranges 52 to 36, 35 to 21, 20 to 12, and 11 to 9, and the count value of the counter 13 is within these ranges. If so, the filter coefficient corresponding to the count value of the representative value is selected.

  The filter coefficients stored in the filter coefficient table 17 are set such that the greater the count value, that is, the slower the conveyance speed of the printed material W, the greater the degree of blurring in the image. Among the plurality of filter coefficients stored in the filter coefficient table 17, the count value counted by the counter 13, that is, the filter coefficient corresponding to the transport speed of the printed material W (as described above, the count number is the filter coefficient table 17). The filter coefficient selection setting circuit 15 selects an index, which represents a range of count numbers, and is a filter coefficient corresponding to a count number representing a range in which the count number is included. The selected filter coefficient is supplied to the filter circuit 15.

  The image data output from the line sensor 11 is input to the filter circuit 15 via the delay circuit 14. FIG. 4 shows the detailed electrical configuration of the delay circuit 14 and the filter circuit 15.

  The delay circuit 14 includes 37 shift registers R1 to R37 connected in series. Each of the shift registers R1 to R37 has a cell for temporarily storing image data output from the line sensor 11. The image data output from the line sensor 11 is sequentially shifted in synchronization with the pixel clock signal CL.

For ease of explanation, one cell is taken out from each of the shift registers R1 to R37 and indicated by reference numeral 21a. Although the cell 21a is shown as the rearmost one of the shift register, it may be located at any position of the shift register, but it needs to be at the same position in all shift registers. These image data stored in the cell 21a is shown in a s _-18 ~s ₀ ~s _18, these image data are the image data of one-dimensional obtained from the line sensor 11 in the longitudinal direction (conveying direction When image data arranged two-dimensionally in a corresponding direction is configured, they are arranged in a straight line in the vertical direction (see FIG. 6).

Image data of the cell 21a of the shift register R1~R37 is removed, and the luminance values represented by the respective (pixel data) of 37 pieces of the image data s _-18 ~s ₁₈ taken out, the selected filter Each of the coefficient values f _{-18 to} f ₁₈ (37 coefficient values) at the position corresponding to the coefficient F is multiplied (a multiplication circuit is indicated by reference numeral 22).

  The 37 multiplication results are added by the adder circuit 23.

Further, the coefficient values f _{-18 to} f ₁₈ of the selected filter coefficient F are added by the adding circuit 24.

The addition value obtained by the addition circuit 23 (addition value obtained by multiplying the luminance value of the pixel data and each coefficient value of the filter coefficient) is the addition value obtained by the addition circuit 24 (addition of each coefficient value of the filter coefficient). The value is divided by the divider circuit 25. This result is the pixel data (weighted average value S ₀ ) after filtering the pixel data s ₀ .

As shown in FIG. 6, if the line sensor 11 has 2048 pixels, the image data of each line includes 2048 pixel data, and the image data s ₋ of L _{−18 to} L ₁₈ for 37 lines. _The above-described weighted average processing is performed on the pixel data s ₀ of the center line L ₀ among _{18 to} s ₁₈ . Since the image data in the shift registers R1 to R37 are sequentially shifted, finally, filtering for all the image data is performed.

  By the filtering (weighted average processing) in the filter circuit 15, the image data input to the filter circuit 15 is blurred according to the conveyance speed. The filtered image data is sequentially stored in the memory 18 through a thinning process for making the image size the same, thereby forming two-dimensional image data. Two-dimensional image data constituted by filtered image data is used for image processing (inspection of the printed matter W).

  In the image data output from the line sensor 11, the higher the transport speed of the printed material W, the greater the optical blur in the direction corresponding to the transport direction of the printed material W. On the other hand, the image data output from the line sensor 11 is more blurred as the transport speed of the printed material W is slower in the filter circuit 15. That is, the image correction device 7 outputs image data having a blur of a combination of a blur generated optically and a blur generated by filtering. As described above, the degree of optical blurring in the direction corresponding to the conveyance direction of the printed matter W increases as the conveyance speed of the printed matter W increases, and conversely, the blurring in the direction corresponding to the conveyance direction of the printed matter W generated in the filter circuit 15 occurs. Is larger as the conveyance speed of the printed material W is lower. Thereby, the degree of blurring in the direction corresponding to the conveyance direction of the image data output from the image correction device 7 can be made the same regardless of the conveyance speed of the printed matter W.

  The above-described image correction processing (filtering processing) may be realized by hardware by the image correction device 7 (counter 13, delay circuit 14, filter circuit 15, filter coefficient selection setting circuit 16, filter coefficient table 17 and memory 18). It can also be realized by processing (software processing) in a programmed computer as shown below.

  FIG. 7 is a block diagram showing a hardware configuration of an inspection system including the processing device 42 when the above-described image correction processing is realized using a programmed computer (processing device 42). With reference to the flowcharts shown in FIGS. 8, 9, 10 and 11, a case will be described in which the above-described image correction processing is realized using a programmed computer (processing device 42).

  In FIG. 7, the same components as those described above are denoted by the same reference numerals, and description thereof is omitted. The scanning start pulse S of the drive circuit 12 of the imaging device 1 and the encoder pulse of the rotary encoder 6 are input to the processing device 42 via the input port 41. The counter 43 in the processing device 42 performs the same operation as the counter 13 and outputs a count value. The counter 43 may be a hardware circuit or may be realized by software as will be described later. The 37 pieces of image data output from the delay circuit 14 are sequentially input to the processing device 42 via the input port 41. The processing device 42 further includes a filter coefficient table 44 having the same content as that shown in FIG. 5 (stored in the internal memory of the processing device 42). Further, the processing device 42 includes an image memory 45.

  As shown in FIG. 8, in the processing device 42, the filter coefficient selection setting process 50 (FIGS. 9 and 10) and the filtering process 60 (FIG. 11) are performed in parallel.

  In the filter coefficient selection setting process 50 (FIGS. 9 and 10), when the scanning start pulse S is input (YES in step 51 in FIG. 9), the counter 43 counts the number of scanning start pulses S (step 52). Each time the scan start pulse S is input to the counter 43, the count value CNT of the counter 43 is incremented.

  When an encoder pulse is input (YES in step 53), the count value CNT counted between the previous encoder pulse input and the next encoder pulse input is the work area (in the internal memory of the processing unit 42) ( (Step 54). In the counter 43, the count value CNT is cleared (step 55), and the counter 43 counts the scanning start pulse S from zero again.

  The filter coefficient corresponding to the CNT value taken into the work area, that is, the filter coefficient corresponding to the transport speed of the printed material W is read out from the filter coefficient table 44 stored in the storage device of the processing device 41. (Step 56). The read filter coefficient is set to be used for the filtering process (FIG. 11) (step 27).

  In the filtering process (step 60, FIG. 11), 37 pieces of image data input to the processing device 42 via the input port 41 are used.

  37 pieces of image data to be input to the processing device 42 are taken into the work area (step 61).

Using the filter coefficient set by the above-described filter coefficient selection setting process (FIGS. 9 and 10) and image data for 37 pixels continuous in the direction corresponding to the conveyance direction, pixel data s _{0 of the} center pixel is used. A weighted average process (filtering process) is performed for (Step 62). The weighted average pixel data S ₀ is written into the memory 45 (step 63).

  The above filtering process is repeatedly executed sequentially using the image data for 37 pixels that are sequentially input, and is finally performed for all of the two-dimensionally arranged image data representing the image to be inspected. become.

  In the above-described embodiment, the filter coefficient to be used for the filtering process is selected based on the count value counted by the counter 13 (that is, based on the measured value of the conveyance speed of the printed material W). The filter coefficient to be used for filtering may be selected based on the conveyance speed of the printed material W set in the conveyance device (or the conveyance control device).

  The line sensor 11 may be a color line sensor that outputs image data of three colors of red (R), green (G), and blue (R). In this case, the above-described image correction processing (filtering) is performed on each of the three color image data output from the color / line sensor.

It is a perspective view which shows schematically the inspection apparatus of printed matter. It is a block diagram which shows the electrical structure of an imaging device and an image correction apparatus. The relationship between the scanning start pulse S and the encoder pulse is shown. The process in a filter circuit and the detailed electrical configuration of the filter circuit are shown. The contents of the filter coefficient table are shown. Indicates the target of weighted average processing. And FIG. 11 is a block diagram illustrating an electrical configuration of a computer that performs image correction processing. It is a flowchart which shows the process sequence of an image correction process. It is a flowchart which shows the process sequence of a counter process. It is a flowchart which shows the process sequence of a filter coefficient selection setting process. It is a flowchart which shows the process sequence of a filtering process.

Explanation of symbols

1 Imaging device 6 Rotary encoder 7 Image correction device
12 Drive circuit
13 counter
14 Delay circuit
15 Filter circuit
15a, 15b Adder circuit
15c Division circuit
16 Filter coefficient selection setting circuit
17, 44 Filter coefficient table
42 Processing equipment

Claims (2)

Filter coefficient storage means for storing a plurality of filter coefficients for filtering image data so as to increase the degree of blurring as the conveyance speed of the printed material is slow, corresponding to a plurality of different conveyance speeds;
Speed determining means for determining the transport speed of the printed matter;
A filter coefficient selection means for selecting one filter coefficient corresponding to the transport speed of the printed matter determined by the speed determination means from the plurality of filter coefficients stored in the filter coefficient storage means; With respect to each of the unit area image data output from the imaging device that images the printed matter, the filter coefficient selection unit targets the image data of a plurality of unit areas arranged in the direction corresponding to the transport direction centering on each unit area. Filtering means for performing filtering using the selected filter coefficient;
An image correction apparatus comprising: Determine the transport speed of the printed material,
Select one filter coefficient corresponding to the determined transport speed of the printed material from the multiple filter coefficients for filtering the image data so that the degree of blurring increases as the transport speed of the printed material decreases.
For each unit area image data output from the imaging device that captures the printed matter being conveyed, the image data of a plurality of unit areas arranged in the direction corresponding to the conveyance direction with each unit area as the center is selected. Filtering using filter coefficients,
Image correction method.

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