JP2011176559A - Image reading device and image reading method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce image noise by the flicker of a light source. <P>SOLUTION: In adjustment, a selection means 1c specifies one setting table to be stored in a setting table storage means 1d, and an image reading means 1a reads a picture image of an adjustment medium based on the specified setting table. An evaluation means 1b calculates luminance distribution of the picture image to calculate an evaluated value of the image noise included in the picture image based on characteristics of the luminance distribution. The selection means 1c collates the calculated evaluated value with a criterion, and when the evaluated value satisfies the criterion, selects the setting table as for reading of an object medium. When the evaluated value does not satisfy the criterion, similar processing is performed in the next setting table. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image reading apparatus that reads an image from a target medium and an image reading method thereof.

  2. Description of the Related Art Conventionally, as an image reading device that reads an image image such as a character or an image from a target medium such as a paper sheet, there is a stand-type image reading device in which an image sensor unit is disposed at a height away from a base on which the target medium is placed. . Such a stand-type image reading apparatus has an advantage that, for example, the target medium such as a thick form can be read because the target medium and the image sensor unit are separated from each other.

  However, the stand-type image reading apparatus is affected by the lighting environment of the installation location due to its structure. In many cases, the light source is a ceiling lamp or the like that is turned on by a commercial AC power supply, and a flicker phenomenon of brightness corresponding to the frequency of the commercial AC power supply occurs in the light source. In an image reading apparatus that obtains a two-dimensional image image of a target medium with an area image sensor, the exposure timing for each field is different, so that a stripe pattern is generated due to a periodic change in luminance level. In general, the striped image noise is determined for each image reading device in accordance with the frequency of a commercial AC power source that turns on the light source. Therefore, there is a method of preparing a setting table for adjusting the setting state of the image sensor in advance according to the frequency of the commercial AC power source, and appropriately selecting the setting table to prevent image image deterioration due to light source flicker. is there. In addition, there is a technique in which a phase detector that detects the phase of flicker is provided and correction calculation processing is performed in synchronization with the phase of flicker (see, for example, Patent Document 1). Furthermore, there is a technique of providing a flicker sensor and correcting the brightness of the image based on the relationship between the flicker sensor output and the image brightness (see, for example, Patent Document 2).

JP 2001-203864 A JP 2000-244706 A

However, the conventional image reading apparatus has a problem that it is not easy to adjust the image reading apparatus in accordance with the flicker cycle of the light source.
As described above, image noise due to flickering of the light source can be reduced by adjusting the setting at the time of image reading using the setting table corresponding to the frequency of the commercial AC power source that turns on the light source. However, if a separate sensor is not provided, the image reading apparatus cannot detect the frequency of the commercial AC power supply. For this reason, the selection of the setting table is often left to the user, and the selected setting table often does not match the frequency of the commercial AC power supply in the installation environment. When the setting table does not match the frequency of the commercial AC power supply, it is not possible to remove striped image noise due to light source flicker from the image image. For example, when an image of a seal is read from a form using this image reading device at a financial institution and collated with a pre-registered seal image, if image noise in a striped pattern occurs in the read image, There was a problem that the verification rate at the time of verification decreased.

On the other hand, if a flicker phase detector or flicker sensor is separately provided in the image reading apparatus, there is a problem that the apparatus is increased in size and cost.
In view of the above, an object of the present invention is to provide an image reading apparatus and an image reading method thereof that can reduce image noise caused by flicker of a light source without increasing the size and cost of the apparatus.

  In order to solve the above-described problems, an image reading apparatus that includes a setting table storage unit, an image reading unit, an evaluation unit, and a selection unit and reads an image image from a target medium is provided. The setting table storage unit stores a setting table in which reading settings for reducing image noise due to the flicker phenomenon included in the read image image are registered in association with the flicker cycle of the light source having the flicker phenomenon. The image reading means performs image image reading processing based on the reading setting of the designated setting table. The evaluation unit obtains the image image data of the adjustment medium from the image reading unit at the time of adjustment, and calculates the luminance distribution of the pixels included in the image image. Then, an evaluation value of image noise included in the image image is calculated based on the feature of the luminance distribution. The setting table stored in the setting table storage unit at the time of adjustment is sequentially designated to the image reading unit. In addition, an evaluation value for an image image read based on the designated setting table is obtained from the evaluation unit and collated with a determination criterion. When the evaluation value satisfies the determination criterion, the setting table is read as an image image of the target medium. Choose for.

  According to such an image reading apparatus, at the time of adjustment, the selection unit designates the setting table stored in the setting table storage unit to the image reading unit. The image reading means performs image image reading processing with settings based on the specified setting table. The evaluation unit acquires the image image data read by the image reading unit, and calculates the luminance distribution of the pixels included in the image image. Further, an evaluation value of image noise included in the image image is calculated based on the feature of the luminance distribution. The selection unit acquires an evaluation value for the image data read based on the designated setting table from the evaluation unit, and collates it with a determination criterion. When the evaluation value satisfies the criterion, the setting table at this time is selected for reading the image of the target medium. If not, specify the next setting table and repeat the same procedure.

  In addition, in order to solve the above-described problem, an image reading method for executing a processing procedure similar to that of the image reading apparatus is provided.

  According to the disclosed image reading apparatus and image reading method, a setting table suitable for the flicker cycle of the light source can be selected based on the characteristics of the luminance distribution of the read image. As a result, it is possible to reduce the influence of light source flicker without increasing the size and cost of the apparatus.

It is a conceptual diagram of the invention applied to embodiment. It is a figure which shows an example of a structure of the image reading apparatus of embodiment. It is a block diagram which shows the hardware structural example of a control apparatus. 3 is a diagram illustrating a software configuration example of the image reading apparatus according to the first embodiment. FIG. It is the figure which showed an example of the relationship between an exposure table and the luminance distribution of image image data. It is the figure which showed an example of the criterion of exposure table. It is an example of the flowchart which showed the procedure of the exposure table selection process. It is a block diagram of the image reading apparatus of 2nd Embodiment. It is a figure explaining shading correction. It is a block diagram of the image reading apparatus of 3rd Embodiment. It is a figure explaining a line emphasis process. It is the figure which showed an example of the change of the luminance distribution before a line emphasis process and after a line emphasis process. It is the figure which showed the example of the determination threshold value table according to exposure time. It is a block diagram of the image reading apparatus of 4th Embodiment. It is the figure which showed the line sampling process.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram of the invention applied to the embodiment.
The image reading apparatus 1 includes an image reading unit 1a, an evaluation unit 1b, a selection unit 1c, and a setting table storage unit 1d, and performs image image reading processing using illumination lighted by a commercial AC power source as a light source. A flicker phenomenon of brightness occurs in the light source according to the frequency of the commercial AC power source that turns on the light source (hereinafter referred to as the power frequency). Further, in the image reading apparatus 1, before reading the target medium, adjustment is performed to match the setting state of the image reading unit 1 a with the installation location of the image reading apparatus 1. At the time of adjustment, an image medium is read using an adjustment medium having a uniform reflectance throughout the medium, for example, plain white paper, and various settings for image reading are adjusted.

  The image reading means 1a has an image sensor and reads a two-dimensional image image of a target medium such as a form or a booklet. The exposure at the time of reading is determined based on the setting table designated by the selection means 1c.

  At the time of adjustment, the evaluation unit 1b acquires image image data read from the adjustment medium by the image reading unit 1a using the setting table designated by the selection unit 1c. Then, the luminance distribution of the acquired image image is calculated, and the evaluation value of the image noise included in the image image is calculated based on the characteristic of the luminance distribution. In general, when an image image of a plain white adjustment medium is read, ideally, the luminance of each pixel of the image image is distributed higher and has the same luminance. Accordingly, when the image noise is not included in the image image data, the variation in the luminance distribution of the pixels is reduced. On the other hand, when image noise (appears as a pixel with low luminance) is included in the image image, the luminance of the image image varies, and the variation increases as more image noise is included. Therefore, the variation (scattering degree) of the luminance distribution is used as an evaluation value of image noise included in the image image. For example, the standard deviation of the luminance distribution is calculated. Note that the evaluation unit 1b may not only perform evaluation on the image data of the entire adjustment medium, but also may perform evaluation on a part of a predetermined adjustment medium (this is a sampling area). Good.

  At the time of adjustment, the selection unit 1c selects one of the setting tables stored in the setting table storage unit 1d and designates it to the image reading unit 1a. Based on this setting table, the evaluation value of the image noise included in the image read by the image reading unit 1a is acquired from the evaluation unit 1b. Then, the acquired evaluation value is collated with a determination criterion when the image noise included in the image image is recognized to be equal to or less than the reference value. When it is determined that the evaluation value satisfies the determination criterion, the setting table used at this time is selected for reading the target medium. When it is determined that the evaluation value does not satisfy the determination criterion, the next setting table is designated to the image reading unit 1a, and the same procedure is repeated. In this way, a setting table is selected that can reduce the image noise due to the flicker of the light source to a reference value or less.

The setting table storage unit 1d stores a setting table for reducing image noise due to the flicker phenomenon in association with the flicker cycle of the light source.
The operation of the image reading apparatus 1 having such a configuration will be described.

  When adjusting the image reading apparatus 1, the adjustment medium is set on the document table of the image reading apparatus 1. The selection unit 1c designates one of the setting tables stored in the setting table storage unit 1d to the image reading unit 1a. The setting table is a table in which reading settings for reducing image noise due to the flicker phenomenon of the light source are registered. The setting table is set in advance according to the power supply frequency for turning on the light source and is stored in the setting table storage unit 1d. The image reading unit 1a reads an image on the adjustment medium according to the settings registered in the specified setting table, and generates image image data. The evaluation unit 1b acquires image image data and calculates an evaluation value, for example, a standard deviation, of image noise included in the image image based on the characteristics of the luminance distribution. The selection unit 1c acquires the evaluation result of the evaluation unit 1b, and checks whether the calculated evaluation value satisfies the determination criterion. When the determination criterion is satisfied, it is determined that the image noise when this setting table is used is equal to or less than the reference value, and this setting table is selected for reading the image of the target medium. Otherwise, the next setting table is designated and the above processing is repeated until the setting table is selected.

Thus, the adjustment is completed, and the image of the target medium can be read using the selected setting table.
According to such an image reading apparatus 1, an optimum setting table that reduces image noise due to light source flicker can be selected based on the read image. Since a sensor such as a flicker phase detector is not used, the influence of light source flicker can be reduced without increasing the size and cost of the apparatus.

  In the above description, the characteristic of the luminance distribution is expressed using the standard deviation, but the present invention is not limited to this. For example, dispersion, average deviation, coefficient of variation, etc. are known in addition to standard deviation as the degree of dispersion representing the degree of variation of a certain data group, and the characteristics of the luminance distribution can be captured using these dispersion degrees as appropriate. .

Hereinafter, the invention will be described in detail with reference to the drawings, taking as an example the case where the invention is applied to an image reading apparatus that selects an exposure table and reduces image noise due to light source flicker.
FIG. 2 is a diagram illustrating an example of the configuration of the image reading apparatus according to the embodiment.

  The image reading apparatus includes a control device 10 that controls reading of an image of a target medium and an image reader 20 that reads an image, and reads an image using a light source 30 having a predetermined power supply frequency.

  The control device 10 is connected to the image reader 20 via the communication path 24 and acquires the image image data of the target medium read by the image reader 20. Normally, processing such as displaying the acquired image and storing it in the storage device is performed. In addition, for example, character recognition processing, collation processing with an image registered in advance such as collation of a seal image, or the like can be performed. At the time of adjustment, various reading parameters are adjusted, and an exposure table matching the power supply frequency of the light source in the installation environment is selected and designated to the image reader 20.

  The image reader 20 includes an image generation unit 21, a pedestal 22, and a stand 23, and is connected to the control device 10 via a communication path 24. The image generation unit 21 is fixed to a height of a predetermined distance from the pedestal 22 by the stand 23, and reads an image of a target medium placed on the pedestal 22 under the light source 30. The image generation unit 21 has an area image sensor in which imaging elements are two-dimensionally arranged in a matrix. For example, a CCD (Charge Coupled Device) is used as the image sensor. In the example of FIG. 2, the pixel corresponding to the first field 40 is read from the entire image at timing 1. At the next timing 2, pixels in the second field are read out from the entire image. Similarly, a two-dimensional image is obtained from the target medium by reading the number of field lines. In the two-dimensional image image output from the image generation unit 21, the periodic brightness of the image image due to the flicker of the light source 30 appears in a striped pattern. Hereinafter, this is referred to as vertical line noise. As described above, the period of the vertical line noise appearing in the two-dimensional image is generally determined according to the power supply frequency for turning on the light source 30. Therefore, the image reader 20 is provided with a setting table for adjusting the exposure value at the time of image image reading for each power supply frequency. Hereinafter, this setting table is referred to as an exposure table. The exposure value is a parameter for adjusting the amount of light hitting the CCD, and an exposure value pattern corresponding to the period of vertical line noise is registered in the exposure table in association with the power supply frequency. Although the exposure time is determined by the exposure value, if the exposure time is not a multiple of the flicker cycle, the amount of light received varies depending on the exposure timing even if exposure is performed for the same time, and vertical line noise occurs. In the exposure table, an exposure value pattern is set so that an appropriate exposure time can be obtained so that the amount of light received by the CCD is the same regardless of the timing of exposure at the power frequency.

In the above configuration example, the control device 10 and the image reader 20 are separate devices, but both functions may be incorporated in the same device.
Here, the hardware configuration of the control device 10 will be described. FIG. 3 is a block diagram illustrating a hardware configuration example of the control device.

  The entire control apparatus 10 is controlled by a CPU (Central Processing Unit) 101. A random access memory (RAM) 102, a hard disk drive (HDD) 103, a graphic processing device 104, an input interface 105, and a communication interface 106 are connected to the CPU 101 via a bus 107.

  The RAM 102 temporarily stores at least part of an OS (Operating System) program and application programs to be executed by the CPU 101. The RAM 102 stores various data necessary for processing by the CPU 101. The HDD 103 stores the OS and application programs. A monitor 108 is connected to the graphic processing device 104, and an image is displayed on the screen of the monitor 108 in accordance with a command from the CPU 101. A keyboard 109 a and mouse 109 b are connected to the input interface 105, and signals sent from the keyboard 109 a and mouse 109 b are transmitted to the CPU 101 via the bus 107. The communication interface 106 is connected to the image reader 20 via the communication path 24, and transmits / receives data to / from the image reader 20 via the communication path 24.

With such a hardware configuration, the processing function of the control device 10 can be realized.
Next, software configurations of the control device 10 and the image reader 20 will be described. First, as a first embodiment, a configuration in which a plurality of sampling areas are set in an image image and an exposure table is selected based on image image data in the sampling area will be described. FIG. 4 is a diagram illustrating a software configuration example of the image reading apparatus according to the first embodiment.

  The image reader 20 includes an image acquisition unit 210, an exposure table adjustment unit 220, and an exposure table storage unit 230. The image acquisition unit 210 controls the image generation unit 21 to read the image of the target medium or the adjustment medium placed on the pedestal 22. The read image data is output to the control device 10. The exposure table adjustment unit 220 reads the exposure table specified by the exposure table selection unit 120 from the exposure table storage unit 230, and performs exposure adjustment of the image acquisition unit 210 based on the read exposure table. The exposure table storage unit 230 stores an exposure pattern that reduces vertical line noise due to flicker of the light source 30 in association with the power supply frequency for turning on the light source 30. Here, it is assumed that an exposure pattern when the power supply frequency is 50 hertz (hereinafter referred to as Hz) and an exposure pattern when the power supply frequency is 60 Hz are stored.

  The control device 10 includes an evaluation unit 110 that calculates an evaluation value of vertical line noise included in an image, and an exposure table selection unit 120 that selects an optimal exposure table based on the evaluation value calculated by the evaluation unit 110. . Then, when executing a calibration process for adjusting the exposure setting according to the installation location, a process for selecting an exposure table suitable for the installation location is performed using an adjustment medium having a uniform reflectance. Here, the adjustment medium used for calibration is a plain white paper (hereinafter referred to as a calibration sheet).

  The evaluation unit 110 includes a sampling data extraction unit 111 that extracts image image data in the sampling region, and a standard deviation calculation unit 112 that calculates a standard deviation of the luminance distribution in the sampling region. The sampling data extraction unit 111 acquires the image data of the calibration sheet read by the image acquisition unit 210, extracts the image image data of a predetermined sampling area, and uses it as sampling data. The sampling area can be set at an arbitrary position of the image, but it is preferable to set so that vertical line noise corresponding to the flicker cycle of the light source can be detected in each sampling area. Here, in order to grasp the characteristics of the entire image image, sampling areas are set at five locations on the upper left, upper right, center, lower left, and lower right of the image image. The standard deviation calculator 112 calculates the standard deviation of the luminance distribution of the pixels included in the image image of the sampling area for each sampling area. When no image noise is included in the image image of the sampling area, the luminance of the pixels becomes uniform and the standard deviation becomes small. When image noise is included in the image image data in the sampling area, the luminance of the pixels is not uniform and the standard deviation is large. The exposure table selection unit 120 designates an exposure table to the image reader 20 and causes the image image data of the calibration sheet to be read. Then, the exposure table to be selected is determined based on whether or not the evaluation value calculated by the evaluation unit 110 for the acquired image data satisfies the determination criterion. The determination criterion is, for example, “based on the standard deviation for each sampling region, when the standard deviation of four or more sampling regions in five sampling regions is smaller than the determination threshold, the acquired image image data has no vertical line noise”. And Then, the exposure table when this determination criterion is satisfied is selected. This criterion is defined as criterion 1. When the calculated standard deviation of the luminance distribution does not satisfy the determination criterion 1, it is compared with the determination criterion 2 that is the second determination criterion. As the determination criterion 2, for example, the average of the standard deviation of all sampling regions of 50 Hz is compared with the average of standard deviation of all sampling regions of 60 Hz, and the most suitable one is selected. Details of the selection method will be described later. Thus, the selected exposure table is designated to the image reader 20 as an exposure table for normal reading processing, and thereafter, image reading processing is performed using this exposure table.

Next, the operation of the image reading apparatus having the above configuration will be described in detail.
The image reader 20 is greatly affected by the image quality of the read image depending on the lighting environment of the installation location. Therefore, calibration is performed when the installation location or lighting environment changes. When the calibration sheet is set on the base 22 and a calibration instruction is issued, the control device 10 controls the operation of the image reader 20 and starts the calibration process. In the calibration process, an exposure table selection process for configuring magnification correction, exposure setting, and the like based on the image of the calibration sheet read by the image reader 20 and selecting an exposure table according to the power supply frequency of the light source 30. Is done. Hereinafter, the exposure table selection process will be described.

  The exposure table selection unit 120 selects one from the exposure tables corresponding to the power supply frequency of the light source 30 stored in the exposure table storage unit 230 and designates it to the exposure table adjustment unit 220. Here, it is assumed that an exposure table of 50 Hz is designated. The exposure table adjustment unit 220 reads an exposure table of 50 Hz from the exposure table storage unit 230 and sets it in the image acquisition unit 210. In this way, the image acquisition unit 210 reads the image of the calibration sheet according to the exposure setting of the exposure table of 50 Hz, and outputs it to the evaluation unit 110. In the evaluation unit 110, the sampling data extraction unit 111 extracts the image data of the sampling area from the acquired image data of the calibration sheet, and outputs it to the standard deviation calculation unit 112. The standard deviation calculation unit 112 calculates the standard deviation of the luminance distribution of the pixels included in each sampling area. The exposure table selection unit 120 acquires the standard deviation of each sampling area and determines whether the exposure table is appropriate.

  FIG. 5 is a diagram showing an example of the relationship between the exposure table and the luminance distribution of the image image data. (A) shows the luminance distribution when the exposure table is correct, and (B) shows the luminance distribution when the exposure table is different. Note that “correct exposure table” means when the power frequency of the light source and the power frequency of the exposure table match, and “different exposure table” means that the power frequency of the light source and the power frequency of the exposure table are Say when they do not match.

  (A) The luminance distribution at the correct exposure table shows an example of an image image and the luminance distribution when the power source frequency of the light source and the power source frequency of the exposure table match. In the image image 400, sampling areas 401, 402, 403, 404, and 405 are installed. When the exposure table is correct, vertical line noise due to flicker of the light source 30 is removed from the image image by exposure setting based on the exposure table. For this reason, no vertical line noise is generated in any of the sampling areas 401, 402, 403, 404, and 405. A distribution diagram 500 is a luminance distribution of the sampling areas 401, 402, 403, 404, and 405. The horizontal axis represents the luminance of the pixels included in the sampling areas 401, 402, 403, 404, and 405, and the luminance increases (becomes brighter) toward the right side. The vertical axis represents the number of pixels, and the number of pixels increases as it goes upward. The standard deviation 501 indicates variations in luminance of pixels in the sampling areas 401, 402, 403, 404, and 405, and is an evaluation value that increases as noise increases in the image. When there is no vertical line noise as in the image image 400, the luminance of each pixel is uniform and the standard deviation is small.

  (B) The luminance distribution at different exposure tables shows an example of an image image and its luminance distribution when the power supply frequency of the light source and the power supply frequency of the used exposure table are different. Sampling regions 411, 412, 413, 414, and 415 are installed in the image image 410. These are at the same positions as the sampling areas 401, 402, 403, 404, and 405 of the image 400. In the case of different exposure tables, the exposure setting based on the exposure table and the flicker cycle of the light source 30 are shifted, so that vertical line noise due to the flicker of the light source 30 is not removed. For this reason, vertical line noise 419 occurs in any of the sampling regions 411, 412, 413, 414, and 415. A distribution diagram 510 is a luminance distribution of the sampling regions 411, 412, 413, 414, and 415. The horizontal axis and the vertical axis are the same as in the distribution diagram 500. The standard deviation 511 is an index indicating variations in luminance of pixels in the sampling areas 411, 412, 413, 414, and 415. When the vertical line noise 419 is generated as in the image image 410, the intensity of the brightness is generated in the sampling region, and the luminance varies. Therefore, the standard deviation 511 is larger than the standard deviation 501 of the distribution diagram 500 when there is no vertical line noise 419.

  The exposure table selection unit 120 acquires the standard deviation of each sampling region, and determines whether there is vertical line noise based on the determination criterion 1. In the determination criterion 1, a determination threshold value for determining whether or not there is vertical line noise and a number of sampling regions in which no vertical line noise is determined when the standard deviation does not exceed the determination threshold value are determined in advance. . The exposure table selection unit 120 compares the standard deviation of each sampling region with a determination threshold value, and determines whether or not the determination threshold value is exceeded. Of the five sampling areas, for example, when the standard deviation of the four sampling areas is smaller than the threshold value, it is determined that no vertical line noise has occurred. At this time, it is determined that the exposure table designated for reading the image is correct, and is selected as the exposure table for reading the target medium in the normal process. The selection result is notified to the exposure table adjustment unit 220, and the exposure table selection process is terminated. As shown in the image image 410, the vertical line noise 419 is periodically generated in the entire area from the upper end to the lower end in the vertical direction of the image image 410. For this reason, occurrence of vertical line noise 419 can be detected in at least a part of the sampling region.

  On the other hand, it is assumed that among the five sampling areas, the standard deviation smaller than the threshold is not enough for the prescribed number of four. In this case, it is determined that vertical line noise has occurred, and it is determined that the exposure table set at this time is not correct. Then, the exposure table is specified as the other (50 Hz is specified, so the next is the 60 Hz exposure table), and the same procedure is repeated. When it is determined that the other exposure table is correct, this is selected as the exposure table for reading the target medium.

  If the exposure table is not determined in any of the determinations, either the 50 Hz or 60 Hz exposure table is selected based on the determination criterion 2. In the selection based on the criterion 2, when the difference between the standard deviations obtained using the respective exposure tables is larger than the determination threshold and the standard deviation on the smaller side is within the allowable range based on the criterion 1, the smaller side Select the exposure table that was the standard deviation. If the difference in standard deviation is greater than a certain value, a difference in vertical line noise reduction by the exposure table is recognized. In addition, depending on the allowable range, it is also possible to select one having a lower degree of vertical line noise reduction than the criterion 1. In the selection based on the criterion 2, the average values of the standard deviations of all sampling areas calculated by the exposure tables of 50 Hz and 60 Hz are calculated and compared. The difference between the average value of the standard deviation at 50 Hz and the average value of the standard deviation at 60 Hz is larger than a predetermined threshold value, and the average value of the standard deviation on the smaller side is smaller in the average standard deviation Select. Then, the exposure table adjustment unit 220 is notified of the selection, and the exposure table selection process ends.

Here, the criteria for selecting the exposure table will be described. FIG. 6 is a diagram showing an example of the criteria for determining the exposure table.
In the determination criterion 600, the determination criterion is determined in two stages of determination criterion 1 and determination criterion 2. If the criterion 1 is satisfied, the exposure table is selected based on the criterion 1. When the criterion 1 is not satisfied, the exposure table is selected based on the criterion 2.

  The determination condition of determination criterion 1 is “4 out of 5 sampling regions have a standard deviation“ 4.0 ”or less”. If the exposure table set in the image reader 20 when this condition is satisfied is 50 Hz, the 50 Hz exposure table is selected. If it is 60 Hz, an exposure table of 60 Hz is selected. The standard deviation “4.0” that is a determination condition is a numerical value that is recognized as not including vertical line noise in the sampling data of the sampling region, and is appropriately set for each image reading apparatus. Also, the condition of “4” or more locations can be set as appropriate.

  The determination condition of the determination criterion 2 is “Comparing the standard deviation average of 50 Hz and the standard deviation average of 60 Hz, the difference is“ 0.5 ”or more and the smaller one is“ 4.5 ”or less”. . This does not satisfy the criterion 1, but when there is a difference in standard deviation when using exposure tables of 50 Hz and 60 Hz, it can be estimated that the exposure table with the smaller standard deviation is more correct. by. When this condition is satisfied, if the standard deviation average when the 50 Hz exposure table is used is smaller than the standard deviation average when the 60 Hz exposure table is used, the 50 Hz exposure table is selected. When the standard deviation average when the 60 Hz exposure table is used is smaller than the standard deviation average when the 50 Hz exposure table is used, the 60 Hz exposure table is selected. Note that the numerical values of the difference “0.5” and the smaller standard deviation “4.5”, which are determination conditions, are set as appropriate for each image reading apparatus. Alternatively, the determination criterion 2 may be a determination condition of selecting an exposure table on the side that satisfies the determination criterion 1 in more sampling regions. In this way, the determination criterion can be set as appropriate.

Next, the process procedure of the control apparatus 10 is demonstrated using a flowchart. FIG. 7 is an example of a flowchart showing the procedure of the exposure table selection process.
When a calibration sheet is placed and calibration is started, exposure table selection processing is also started.

  [Step S01] The exposure table selection unit 120 selects an exposure table of 50 Hz as an initial value and designates it to the exposure table adjustment unit 220. The exposure table adjustment unit 220 performs exposure setting on the image acquisition unit 210 based on the 50 Hz exposure table.

  [Step S02] The evaluation unit 110 acquires the image image data of the calibration sheet read by the image acquisition unit 210 using the 50 Hz exposure table specified in step S01, and extracts the image image data of the sampling region. Then, a standard deviation is calculated for each sampling region.

  [Step S03] The exposure table selection unit 120 determines whether the criterion 1 is satisfied when the 50 Hz exposure table is used, that is, whether there is vertical line noise in the image (the exposure table is the power frequency of the light source 30). To match). The standard deviation calculated for each sampling region is compared with the determination threshold value of the determination criterion 1, and it is checked whether the standard deviation of the sampling region equal to or larger than the specified number is equal to or smaller than the threshold value. If the number of sampling areas is equal to or less than the determination threshold value, it is determined that no vertical line noise is detected, and the process proceeds to step S04. Otherwise, the process proceeds to step S05 as suspicion of vertical line noise.

  [Step S04] When the exposure table selection unit 120 determines that vertical line noise is not detected in the image image of the sampling region, the exposure table of 50 Hz is determined to be correct (matches the power supply frequency of the light source 30). . Then, an exposure table of 50 Hz is designated for the exposure process adjustment unit 220 for normal processing, and the exposure table selection process is terminated.

  [Step S05] When there is a suspicion of vertical line noise, the exposure table selection unit 120 temporarily stores the value of the standard deviation of each sampling area in the storage unit calculated by the evaluation unit 110 for the 50 Hz exposure table. Keep it. Next, a 60 Hz exposure table is selected and designated to the exposure table adjustment unit 220. The exposure table adjustment unit 220 performs exposure setting on the image acquisition unit 210 based on the 60 Hz exposure table.

  [Step S06] The evaluation unit 110 acquires the image image data of the calibration sheet read by the image acquisition unit 210 using the 60 Hz exposure table specified in step S05, and extracts the image image data of the sampling region. Then, a standard deviation is calculated for each sampling region.

  [Step S07] The exposure table selection unit 120 determines whether the criterion 1 is satisfied when the 60 Hz exposure table is used, that is, whether there is vertical line noise in the image image (the exposure table is the power frequency of the light source 30). To match). The standard deviation calculated for each sampling region is compared with the determination threshold value of the determination criterion 1, and it is checked whether the standard deviation of the sampling region equal to or larger than the specified number is equal to or smaller than the threshold value. If the number of sampling areas is equal to or less than the determination threshold value, it is determined that no vertical line noise is detected, and the process proceeds to step S08. Otherwise, the process proceeds to step S09 as suspicion of vertical line noise.

  [Step S08] When the exposure table selection unit 120 determines that the vertical line noise is not detected, the exposure table selection unit 120 determines that the 60 Hz exposure table is correct (matches the power frequency of the light source 30). Then, a 60 Hz exposure table for normal processing is designated to the exposure table adjustment unit 220, and the exposure table selection processing is terminated.

  [Step S09] When there is a suspicion of vertical line noise in step S07, the exposure table selection unit 120 uses the criterion 2 to determine which exposure table is suitable for the power supply frequency of the light source 30. The average value of each standard deviation is calculated. An average value of standard deviations when using the 60 Hz exposure table calculated in step S07 is calculated. Similarly, the average value is calculated from the standard deviation when the 50 Hz exposure table stored in the storage means in step S05 is used.

  [Step S10] The exposure table selection unit 120 determines whether or not the criterion 2 is satisfied based on the average value of the standard deviation of the sampling area when the exposure tables of 50 Hz and 60 Hz calculated in step S09 are used. . That is, the difference between the average value of the standard deviation at 50 Hz and the average value of the standard deviation at 60 Hz is larger than a predetermined threshold value, and the smaller standard deviation is larger than the determination threshold value of the criterion 2. Is also determined whether it is too small. When determination criterion 2 is satisfied, the process proceeds to step S11. If determination criterion 2 is not satisfied, the process proceeds to step S14.

  [Step S11] When the criterion 2 is satisfied, the exposure table selection unit 120 determines which exposure table the average value of the standard deviation of the sampling area is smaller. If the average value of the standard deviation of the sampling area when using an exposure table of 60 Hz rather than 50 Hz is small, the process proceeds to step S12. Otherwise, the process proceeds to step S13.

  [Step S12] When the average value of the standard deviation of the sampling area when the 60 Hz exposure table is used is smaller than the case of 50 Hz, the exposure table selection unit 120 determines that 60 Hz is a correct exposure table. Then, a 60 Hz exposure table for normal processing is designated to the exposure table adjustment unit 220, and the exposure table selection processing is terminated.

  [Step S13] When the average value of the standard deviation of the sampling area when the 50 Hz exposure table is used is smaller than the case of 60 Hz, the exposure table selection unit 120 determines that 50 Hz is a correct exposure table. Then, an exposure table of 50 Hz is designated for the exposure process adjustment unit 220 for normal processing, and the exposure table selection process is terminated.

  [Step S14] When the average value of the standard deviation of the sampling area when each exposure table is used is smaller than the threshold value, the exposure table selection unit 120 cannot determine which one is suitable. Therefore, the exposure table of 50 Hz that is the initial value is designated to the exposure table adjustment unit 220 for normal processing, and the exposure table selection processing is ended.

  By executing the above processing procedure, it is possible to select an exposure table that matches the power frequency of the light source based on the image data read based on each exposure table.

In step S01, the initial value may be an exposure table of 60 Hz. In this case, the subsequent processing procedure 50 Hz and 60 Hz are interchanged.
As described above, according to the image reading apparatus of the first embodiment, since the exposure table is selected based on the image reading result using the calibration sheet, a sensor for detecting the flicker cycle of the light source is separately provided. There is no need to provide it. In addition, since an exposure table that reduces image noise is selected based on the actually read image, an optimal exposure table can be selected.

  Next, a case where the image acquired from the image acquisition unit 210 is corrected before the evaluation by the evaluation unit 110 will be described as a second embodiment. FIG. 8 is a configuration diagram of an image reading apparatus according to the second embodiment.

  The control device 10a of the image reading apparatus of the second embodiment has a configuration in which a shading correction unit 130 is added to the components of the first embodiment shown in FIG. 4, and the other components are the first. It is the same as the component of the embodiment. The components of the processing function that the image reader 20 has are the same as the components of the first embodiment shown in FIG. Therefore, the operations of the control device 10a and the image reader 20 will be described using the reference numerals of the components shown in FIG. 4 for the same components as those in the first embodiment.

  The shading correction unit 130 acquires the image data of the calibration sheet read by the image acquisition unit 210 using the exposure table specified by the exposure table selection unit 120. Then, the obtained image data is subjected to shading correction that corrects uneven brightness of the entire image and is output to the evaluation unit 110.

  The operation of the control device 10a will be described. In the control device 10a, the shading correction unit 130 performs shading correction of the image image data before the evaluation unit 110 evaluates the image image data. FIG. 9 is a diagram for explaining shading correction. (A) is an image before shading correction, (B) is a diagram showing an example of an image after shading correction.

  The image image 420 before shading correction in FIG. 9A has no vertical line noise, but has a shadow portion below the image. Sampling areas 421 and 422 exist in the bright part without shadow above, and sampling areas 424 and 425 exist in the shadow part below. In addition, the sampling area 423 includes a bright portion and a shadow portion. The brightness of the pixels above the sampling areas 421 and 422 and the sampling area 423 in the bright part is relatively high, and the brightness of the pixels below the sampling areas 424 and 425 and the sampling area 423 in the shadow part is relatively low. Become. For this reason, in the luminance distribution of the entire sampling region shown in the distribution diagram 520, two peaks occur in the luminance distribution, and the standard deviation 521 is relatively larger than that in the case of one peak. For this reason, there is a possibility that it is determined that there is vertical line noise even though there is no vertical line noise. Therefore, shading correction is performed so that the brightness of the shadow portion is the same as that of the portion without the shadow. The shading correction may be performed when unevenness of brightness different from the periodic change in brightness level due to the flicker of the light source is detected in the image image 420 shown in the image image.

  An image image 430 shown in FIG. 9 (B) after the shading correction is an image after the shading correction is performed on the image 420. The sampling areas 431, 432, 433, 434, and 435 correspond to the sampling areas 421, 422, 423, 424, and 425 of the image 420, respectively. The shaded portion of the image 430 is removed by the shading correction, and the uneven brightness of the sampling areas 431, 432, 433, 434, and 435 is eliminated. In the luminance distribution after shading correction shown in the distribution diagram 530, there is no peak corresponding to the shadow portion, and there is only one peak. Also, the standard deviation is smaller than before the shading correction.

  The exposure table selection process is the same as that in the first embodiment shown in FIG. In the evaluation by the evaluation unit 110, a correct standard deviation can be calculated even when a shadow portion is removed from the image image data and there is a shadow in the sampling area. As described above, it is possible to prevent the standard deviation from being increased even when there is no vertical line noise due to the influence of the shadow part, and to prevent the shadow part from being recognized as the vertical line noise. Thereby, in the exposure table selection part 120, possibility that an incorrect exposure table will be selected can be reduced.

Next, a case where the image acquired from the image acquisition unit 210 is corrected by a method different from that of the second embodiment before the evaluation by the evaluation unit 110 will be described as a third embodiment.
FIG. 10 is a configuration diagram of an image reading apparatus according to the third embodiment.

  The control device 10b of the third embodiment has a configuration in which the line enhancement processing unit 140 is added to the components of the first embodiment shown in FIG. 4, and the other components are the same as those of the first embodiment. It is the same as the component of a form. The components of the processing function that the image reader 20 has are the same as the components of the first embodiment shown in FIG. Therefore, for the same components as those in the first embodiment, the operations of the control device 10b and the image reader 20 will be described using the reference numerals of the components shown in FIG.

  The line enhancement processing unit 140 acquires the image data of the calibration sheet read by the image acquisition unit 210 using the exposure table specified by the exposure table selection unit 120. Then, based on the acquired image image data, a vertical line is detected from the image image, and a line emphasis process for emphasizing the vertical line is performed. The vertical line is a line in which pixels with low luminance are arranged vertically or horizontally, and is highly likely to be vertical line noise due to the flicker phenomenon of the light source 30. In the line enhancement process, a line is detected by comparing the luminance difference between the pixel and the surrounding pixels for each direction. For a certain pixel, a difference in luminance from the peripheral pixels in the horizontal direction and a difference in luminance from the peripheral pixels in the vertical direction are detected, and the smaller difference is regarded as a part of the line. When a part of the line is continuously detected, it is determined that the line is formed. Then, a correction process for emphasizing the detected line portion is performed, and the image data subjected to the line emphasis is output to the evaluation unit 110.

  The operation of the control device 10b will be described. In the control device 10b, the line enhancement processing unit 140 performs line enhancement processing of the image image data before the evaluation unit 110 evaluates the image image data. FIG. 11 is a diagram for explaining line enhancement processing. (A) is an image before line emphasis processing, (B) is a figure showing an example of an image image after line emphasis processing.

  An image image (part) 440 shown in the image image before the line enhancement process in FIG. 11A is a diagram showing the target pixel and its peripheral pixels included in the image image before the line enhancement process. For the target pixel 441, there are an upper peripheral pixel 442, a lower peripheral pixel 443, a left peripheral pixel 444, and a right peripheral pixel 445. The line enhancement processing unit 140 is close to the color of the upper peripheral pixel 442 and the lower peripheral pixel 443 in the vertical direction with respect to the target pixel 441 and the color of the target pixel 441, and is lateral to the target pixel 441. The left peripheral pixel 444 and the right peripheral pixel 445 are compared with the color closeness of the target pixel 441. Then, it is determined that the target pixel 441 is a part of a line in a direction in which colors are close. For example, in the example of FIG. 11, the colors of the peripheral pixels 442 and 443 in the vertical direction are closer to the target pixels 441 than the colors of the peripheral pixels 444 and 445 in the horizontal direction. Therefore, it is determined that the target pixel 441 is a part of a vertical line. Subsequently, the same determination is performed with the peripheral pixel 443 below the target pixel 441 as the target pixel. Here, it is assumed that it is determined to be a part of the vertical line. Thus, when it is determined that a predetermined number of target pixels are continuously part of a vertical line, it is determined that a vertical line is formed, and a column of pixels on this line is determined. Replace with black (lowest brightness color). The left and right pixel rows are replaced with white (the color with the highest luminance). A vertical line is detected by such a procedure and the detected vertical line is emphasized. Similarly, when a horizontal line is detected, the pixel column on the horizontal line is replaced with black, and the upper and lower pixel columns are replaced with white.

  An image image (part) 450 shown in the image image after line enhancement processing in FIG. 11B is a diagram showing the target pixel and its peripheral pixels included in the image image after line enhancement processing. The target pixel 451 corresponds to the target pixel 441, and the peripheral pixels 452, 453, 454, and 455 correspond to the peripheral pixels 442, 443, 444, and 445, respectively. In the image (part) 450 after the line enhancement process, the pixels 451, 452, and 453 detected as vertical lines are replaced with black, and the left and right pixels 454 and 455 are replaced with white. Thereby, a vertical line or a horizontal line with a high possibility of vertical line noise is emphasized.

  The exposure table selection process is the same as that in the first embodiment shown in FIG. In the evaluation by the evaluation unit 110, the vertical line or horizontal line that has a high possibility of vertical line noise in the image image data is emphasized, so that the difference in standard deviation between when there is vertical line noise and when there is no vertical line noise can be increased. it can. As a result, the exposure table selection unit 120 reduces errors in determining whether there is vertical line noise, and makes it easier to select the correct exposure table. In the above description, the closeness of the colors of the target pixel and the peripheral pixels is determined, but the same processing can be performed using luminance.

  In the above process, the line enhancement process detects lines based on the similarity in color between the target pixel and surrounding pixels. However, the binarization process is performed on the image image data acquired from the image acquisition unit 210. You may go and emphasize the lines. In the binarization process, image data obtained by reading the calibration sheet acquired from the image acquisition unit 210 is acquired, and binarized with a predetermined threshold. By the binarization processing, pixels whose luminance is lower than a predetermined threshold value of the image image data are replaced with black. In addition, pixels brighter than a predetermined threshold are replaced with white. For this reason, a part with a line is emphasized as vertical line noise. Thereby, in the evaluation by the evaluation unit 110, the difference in standard deviation between when image image data has vertical line noise and when there is no vertical line noise can be increased. In addition, the exposure table selection unit 120 reduces errors in determining whether there is vertical line noise, and makes it easier to select the correct exposure table.

  FIG. 12 is a diagram illustrating an example of a change in luminance distribution before and after the line enhancement process. (A) is a change in luminance distribution due to line enhancement processing when there is noise, and (B) is a change in luminance distribution due to line enhancement processing when there is no noise. Note that the change in the luminance distribution due to the line enhancement process is the same in the case of line detection based on the color similarity between the target pixel and the peripheral pixels and in the case of the binarization process of the image image data.

  FIG. 12A shows changes in luminance distribution due to line enhancement processing when there is noise, a distribution diagram 550a showing luminance distribution before line enhancement processing when image image data includes vertical line noise, and after line enhancement processing. And a distribution diagram 560a showing the luminance distribution of. When there is vertical line noise, the vertical line noise recognized as a line by the line enhancement process is replaced with a black pixel. Therefore, the peak of the black pixel is higher in the luminance distribution after the line enhancement processing shown in the distribution diagram 560a than the standard deviation 551a in the luminance distribution before the line enhancement processing shown in the distribution diagram 550a. growing.

  FIG. 12B shows a change in luminance distribution due to line enhancement processing when there is no noise, a distribution diagram 550b showing luminance distribution before line enhancement processing when there is no vertical line noise in the image image data, and after line enhancement processing. And a distribution diagram 560b showing the luminance distribution of. When there is no vertical line noise in the image image data, since there is no vertical line noise recognized as a line in the line enhancement process, only a few pixels are replaced with black pixels, and many are replaced with white pixels. For this reason, in the luminance distribution after the line enhancement processing shown in the distribution diagram 560b, the white pixel has a higher peak and the standard deviation 561b is smaller than the standard deviation 551b in the luminance distribution before the line enhancement processing shown in the distribution diagram 550b. Become.

  As described above, when the standard deviation is calculated by the evaluation unit 110 for the image image data subjected to the line enhancement processing by the line enhancement processing unit 140, the standard deviation of the image image data having vertical line noise (for example, FIG. 12). The difference between the standard deviation 561a of the distribution map 560a) and the standard deviation of the image data without vertical line noise (for example, the standard deviation 561b of the distribution map 560b of FIG. 12) is compared with the case where no line enhancement processing is performed. , Get bigger. Thereby, the exposure table selection unit 120 can reduce the possibility of erroneously selecting an exposure table suitable for the power supply frequency of the light source 30.

  By the way, the image quality of the image image data read by the image reader 20 is greatly affected by the installation environment, particularly the light source 30, but not only the flicker of the light source 30 but also the brightness of the light source 30 itself. Receive. Accordingly, by appropriately setting the value of the determination criterion used for determining whether or not it is suitable for the exposure table according to the brightness of the light source 30, it is possible to perform the determination at the time of selecting the exposure table more accurately. FIG. 13 is a diagram illustrating an example of a determination threshold value table according to the exposure time.

  Since the brightness distribution of the image image read in the environment where the light source 30 is bright is more strongly changed in brightness level, the range of the pixel brightness distribution (in the horizontal axis direction of the distribution diagram) tends to be widened. On the other hand, the range of luminance distribution of an image read in an environment where the light source 30 is dark tends to be narrow. In other words, in an environment where the light source 30 is bright, even when there is no vertical line noise, the luminance of the pixels varies and the standard deviation tends to increase. On the other hand, in an environment where the light source 30 is dark, even if vertical line noise is generated, there is little variation in the luminance of the pixels, and the standard deviation tends to be small. For this reason, in the exposure table selection unit 120, for example, as shown in FIG. 6, when the determination criterion 1 that “4 or more out of 5 sampling areas are standard deviation“ 4.0 ”or less” is used, In an image image read in a bright environment 30, even if the image image has no vertical line noise, the condition may not be satisfied. On the other hand, in an image image read with the light source 30 dark, there is a risk that the condition may be satisfied even if the image data has vertical line noise. In addition, the difference between the standard deviation of an image image in the presence of vertical line noise and the standard deviation of an image image in the absence of vertical line noise also tends to increase when the light source 30 is bright and decreases under a dark environment. It is in.

Therefore, as shown in the determination threshold table 610, the correct exposure table is selected by changing the setting of the determination reference value according to the exposure time.
The determination threshold table 610 includes an exposure time 611, a determination criterion 1 (612), a determination criterion 2 (difference) 613, and a determination criterion 2 (threshold) 614, and an optimum determination threshold corresponding to the exposure time is registered. . The exposure time 611 is classified into “short”, “standard”, and “long” exposure times determined by the calibration process. The exposure time is determined according to the brightness of the light source 30, and “short” exposure time indicates a bright environment. An exposure time of “long” indicates a dark environment.

  The criterion 1 is a criterion value for determining the standard deviation in the criterion 1 shown in FIG. 6, “4 or more points out of 5 sampling areas have a standard deviation“ 4.0 ”or less”. When the exposure time is “short”, “6.0”, which is larger than “4.0” in standard time, is used. When the exposure time is “long”, “2.0” smaller than the standard time is used. Judgment standard 2 is the difference in “standard difference average of 50 Hz and standard deviation average of 60 Hz compared with the standard deviation average of 60 Hz shown in FIG. And the threshold criterion value. When the exposure time is “short”, the difference is set to “0.7” which is larger than “0.5” at the standard time, and the threshold is set to “6.5” which is larger than “6.0” at the standard time. When the exposure time is “long”, the difference is set to “0.3” smaller than the standard time, and the threshold is set to “2.5” smaller than the standard time.

As described above, the selection accuracy of the exposure table selection unit 120 can be improved by selecting the most suitable determination threshold according to the environment in which the image reader 20 is installed.
Next, a case where the sampling area is formed in a line shape will be described as a fourth embodiment. FIG. 14 is a configuration diagram of an image reading apparatus according to the fourth embodiment.

  The control device 10c of the fourth embodiment has a configuration in which the evaluation unit 110 of the component of the first embodiment shown in FIG. 4 is replaced with an evaluation unit 150, and other components are the first implementation. It is the same as the component of the form. The components of the processing function that the image reader 20 has are the same as the components of the first embodiment shown in FIG. Therefore, the operations of the control device 10c and the image reader 20 will be described using the reference numerals of the components shown in FIG. 4 for the same components as in the first embodiment.

  The evaluation unit 150 includes a line sampling extraction unit 151 and a standard deviation calculation unit 152. The line sampling extraction unit 151 acquires the image image data of the calibration sheet read by the image acquisition unit 210 using the exposure table specified by the exposure table selection unit 120. Then, according to the number of field lines of the area image sensor of the image generation unit 21, field lines scanned at the same timing are combined to form one line block. And it outputs to the standard deviation calculation part 152 for every same line block. For each line block extracted by the line sampling extraction unit 151, the standard deviation calculation unit 152 calculates the standard deviation of the luminance distribution for the pixels included in the image image data of this block.

  The exposure table selection unit 160 acquires the standard deviation of the luminance distribution calculated for each line block, and examines the difference. When the difference in the standard deviation of the luminance distribution of each line block is smaller than a predetermined criterion, it is determined that there is no vertical line noise in the image image data. When the difference is larger than the determination criterion, it is determined that there is vertical line noise in the image image data. When vertical line noise is not generated, the luminance of the pixels included in the image image data is substantially uniform, so that the standard deviation of each line block has the same value. On the other hand, since the vertical line noise is generated at a constant cycle, that is, every fixed line block, the standard deviation is large in the line block where the vertical line noise is generated. Therefore, the presence or absence of vertical line noise can be detected by comparing the standard deviation of each line block.

  The operation of the control device 10c will be described. In the control device 10c, in the evaluation unit 150, the line sampling extraction unit 151 acquires the image image data of the calibration sheet from the image acquisition unit 210 and divides it into line blocks, and the standard deviation calculation unit 152 performs the processing for each line block. Calculate the standard deviation.

FIG. 15 is a diagram showing line sampling processing. The image sensor in the example shown in FIG.
In the example of FIG. 15, in the period a, the images in the fields 482, 485, and 488 are read. Similarly, the images of the fields 483, 486, 489 in the period b, and the fields 481, 484, 487 are read in the period c. Therefore, the line sampling extraction unit 151 collects the pixels included in the fields 482, 485, 488 of the period a into one line block and outputs it to the standard deviation calculation unit 152. Similarly, the pixels included in the fields 483, 486, and 489 of the period b are collected and output to the standard deviation calculation unit 152. Similarly for the period c, the pixels included in the fields 481, 484, and 487 are combined into a line block and output to the standard deviation calculation unit 152. The standard deviation calculator 152 calculates the standard deviation of each line block.

  The exposure table selection unit 120 compares standard deviations calculated for the line blocks of the periods a, b, and c. When the difference between the three standard deviations exceeds the reference value, it is determined that there is vertical line noise. If the reference value is not exceeded, it is determined that there is no vertical line noise. When there is no vertical line noise, the luminance of the pixels in each line block is almost uniform, so that the standard deviation has the same value. Since the vertical line noise is generated for each fixed line block, the standard deviation of the line block in which the vertical line noise is generated is a large value as compared with other line blocks. In the example of FIG. 15, vertical line noise is generated in the period c, and the number of pixels with lower luminance is larger than the luminance of the pixels of the other line blocks, and thus the standard deviation is also larger. The exposure table selection unit 120 determines that there is vertical line noise when a line block having a larger standard deviation than other line blocks is detected.

  As described above, by performing sampling for each line block in accordance with the feature of the vertical line noise generated for each fixed line block, it becomes possible to detect the vertical line noise with high accuracy. As a result, the exposure table selection unit 120 can select an optimum exposure table.

  The above processing functions can be realized by a computer. In that case, a program describing the processing contents of the functions that the image reading apparatus should have is provided. By executing the program on a computer, the above processing functions are realized on the computer. The program describing the processing contents can be recorded on a computer-readable recording medium.

  When distributing the program, for example, portable recording media such as a DVD (Digital Versatile Disc) and a CD-ROM (Compact Disc Read Only Memory) on which the program is recorded are sold. It is also possible to store the program in a storage device of a server computer and transfer the program from the server computer to another computer via a network.

  The computer that executes the program stores, for example, the program recorded on the portable recording medium or the program transferred from the server computer in its own storage device. Then, the computer reads the program from its own storage device and executes processing according to the program.

DESCRIPTION OF SYMBOLS 1 Image reading apparatus 1a Image reading means 1b Evaluation means 1c Selection means 1d Setting table storage means

Claims (9)

In an image reading device that reads an image from a target medium,
A setting table storage unit that stores a setting table in which reading settings for reducing image noise due to the flicker phenomenon included in the read image image are registered in association with a flicker cycle of a light source having a flicker phenomenon;
An image reading means for performing an image image reading process based on the specified reading setting of the setting table;
At the time of adjustment, image image data of an adjustment medium is acquired from the image reading unit, a luminance distribution of pixels included in the image image is calculated, and evaluation of image noise included in the image image is performed based on characteristics of the luminance distribution An evaluation means for calculating a value;
The setting table stored in the setting table storage unit at the time of adjustment is sequentially specified to the image reading unit, and an evaluation value for the image image read based on the specified setting table is acquired from the evaluation unit and determined. When the evaluation value satisfies the determination criterion by collating with a criterion, a selection unit that selects the setting table for reading the image of the target medium;
An image reading apparatus comprising: The evaluation means sets a plurality of the sampling areas as a sampling area as a partial area of the image image, extracts the image image data of the sampling area from the image image data acquired from the image reading means, Using the extracted image data of the sampling area to calculate an evaluation value for each sampling area,
The selection means collates an evaluation value for each sampling region with the determination criterion, and determines whether to select the setting table based on a collation result.
The image reading apparatus according to claim 1. When the setting table that satisfies the determination criterion cannot be detected, the selection unit compares the evaluation values calculated for the setting tables and selects one of the setting table selection candidates. If the difference between the evaluation value of the candidate and the evaluation value of the other setting table is larger than a predetermined threshold, and the evaluation value of the selection candidate of the setting table is within the predetermined allowable range of the determination criterion, Select the setting table;
The image reading apparatus according to claim 1. The selection unit varies a determination threshold value of the determination criterion to be compared with the evaluation value according to the brightness of the light source.
The image reading apparatus according to claim 1. The image data acquired from the image reading unit is subjected to shading correction for reducing non-periodic luminance unevenness of the image image, and the image image data subjected to the shading correction is output to the evaluation unit. 1 correction means,
The image reading apparatus according to claim 1, further comprising: Among the pixels of the image image data acquired from the image reading means, a pixel having a luminance lower than a predetermined luminance is set as a target pixel, and a luminance difference between the target pixel and peripheral pixels is calculated in the vertical direction and the horizontal direction. When a pixel row in a direction with a small difference is estimated as a part of the line and a part of the line is detected in the same direction continuously from the target pixel in the same direction, a part of the line is detected. It is determined that there is a line in the detected direction, the pixel included in the line is replaced with a pixel having a low luminance determined in advance, and the line is corrected to be emphasized, and the line is corrected to be emphasized Second correction means for outputting image image data to the evaluation means;
The image reading apparatus according to claim 1, further comprising: Performing the binarization process on the image image data acquired from the image reading means, replacing pixels whose luminance is lower than a predetermined threshold with pixels having a low luminance determined in advance, and performing correction for emphasizing the image data; Third correction means for outputting to
The image reading apparatus according to claim 1, further comprising: The evaluation unit is configured such that the image reading unit moves a partial image image while moving an image sensor in which an image sensor is two-dimensionally arranged in a predetermined reading direction relative to the target medium and the adjustment medium. When reading the image data by sequentially reading the image data, the area to be read in the same cycle as a line block, the evaluation value is calculated for each line block,
The selection unit compares the evaluation value for each of the line blocks calculated by the evaluation unit, compares the evaluation value difference with a predetermined criterion for the evaluation value difference, and the difference between the evaluation values is When the determination criterion is satisfied, the setting table is selected for reading the image of the target medium.
The image reading apparatus according to claim 1. In an image reading method for reading an image from a target medium,
A setting in which the selection unit registers reading settings for reducing image noise caused by the flicker phenomenon included in the read image image in association with the flicker cycle of the light source having the flicker phenomenon stored in the setting table storage unit during the adjustment. Specify the setting table from the table group,
The image reading means performs image image reading processing based on the specified reading setting of the setting table,
The evaluation unit obtains image image data of the adjustment medium from the image reading unit, calculates a luminance distribution of pixels included in the image image, and image noise included in the image image based on the characteristic of the luminance distribution Calculate the evaluation value of
The selection means acquires an evaluation value for the image read based on the designated setting table from the evaluation means and collates it with a determination criterion, and when the evaluation value satisfies the determination criterion, the setting When the table is selected for reading the image of the target medium and does not satisfy the determination criteria, the procedure from the setting table is repeated for the setting table group excluding the setting table,
An image reading method characterized by the above.

Images