JP2018026729A - Imaging apparatus, imaging method, and imaging program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve user convenience and productivity when scanning books and the like. An imaging unit that acquires both an image of a subject arranged in an effective image area and an image of a specific pattern via an imaging lens, and calculates a focus evaluation value based on the image of the specific pattern in the effective image area. An evaluation value calculation unit, an optimal lens position calculation unit that calculates an optimal lens position corresponding to a focus state based on the focus evaluation value, a storage unit that stores in advance an adjustment value for adjusting the optimal lens position, and imaging A switching control unit that controls switching of the operation mode of the image capturing unit, and the optimal lens position with respect to the image of the specific pattern acquired by operating the image capturing unit in the first operation mode based on the adjustment value. And a lens position correction unit that corrects the lens position to focus on the image of the subject acquired when operating in the two-operation mode. [Selection] Figure 3

Description

  The present invention relates to an imaging apparatus, an imaging method, and an imaging program.

  2. Description of the Related Art An imaging device that acquires a medium such as a book in which characters and figures are recorded as an image is known. Such an imaging apparatus is generally called a “scanner”. There are various types of scanners. As one of them, there is known a stand-type scanner that places a medium (reading target) such as a book and captures characters and figures as an image by taking an image from above the medium. The stand-type scanner includes an imaging system including a two-dimensional imaging element (area sensor) and an imaging lens.

  The stand-type scanner automatically adjusts the focus of the imaging lens to the reading target (to bring it into focus), and a live view that displays the subject image acquired via the imaging lens so that it can be viewed in real time. And an imaging system having a function. The former is called an auto focus (AF) function.

  In order to speed up the imaging lens control (AF control) in the AF function, a plurality of correction amounts of the imaging lens position corresponding to the spatial frequency of the subject are stored, and the lens position is corrected using this correction amount. An imaging device is known (see, for example, Patent Document 1).

  The technique disclosed in Patent Document 1 calculates the optimum lens position in the low resolution mode, then analyzes the spatial frequency component of the subject image acquired in the high resolution mode, and stores the lens position stored in advance based on the analysis result. Select an appropriate correction amount and correct the lens position.

  In the technique disclosed in Patent Document 1, in order to select an appropriate one of a plurality of lens position correction amounts stored in advance, a subject image is acquired in a high resolution mode and a spatial frequency component of the subject is analyzed. There is a need. That is, after obtaining the subject image in the low resolution mode and obtaining the optimum lens position, the operation mode of the image sensor is changed to the high resolution mode, and the subject image is obtained again.

  When the technique of Patent Document 1 is applied to a scanner including an area sensor, the user operates in the low resolution mode when operating the live view function in order to perform alignment of a reading target (such as a document). AF control in the image mode is performed. However, photographing based on the high resolution mode is desirable to ensure legibility after photographing the object to be read. Therefore, it is necessary to perform AF control again in the high resolution mode. In this case, the live view function is temporarily stopped and AF control in the high resolution mode is performed after the operation mode of the image sensor is switched.

  In this way, the live view function is temporarily stopped while the user is preparing for scanning such as document alignment, and the convenience of the user is reduced. In addition, since it takes time to switch the operation mode of the image sensor, productivity in the case where AF control and scan processing are continuously performed is reduced. As described above, when the conventional technique is applied to a stand-type scanner, there is a problem in performing appropriate AF control without causing a decrease in user convenience and productivity.

  The present invention has been made in view of the above problems, and an object of the present invention is to improve user convenience and productivity when scanning books and the like.

  In order to solve the above-described problem, an aspect of the present invention relates to an imaging apparatus, and an imaging unit that acquires both an image of a subject arranged in an effective image area and an image of a specific pattern via an imaging lens; An evaluation value calculation unit that calculates a focus evaluation value based on the image of the specific pattern in the effective image region, and an optimal lens position calculation unit that calculates an optimal lens position corresponding to a focus state based on the focus evaluation value A storage unit that preliminarily stores an adjustment value for adjusting the optimum lens position, a switching control unit that controls switching of the operation mode of the imaging unit, and the imaging unit that is operated in the first operation mode. Based on the adjustment value, the optimum lens position with respect to the image of the specific pattern is focused on the image of the subject acquired when the imaging unit is operated in the second operation mode. A lens position correction unit for correcting the lens position, characterized in that it comprises a.

  According to the present invention, user convenience and productivity can be improved when scanning books and the like.

1 is a cross-sectional view schematically illustrating a configuration of an image reading apparatus according to an embodiment of the present invention. 1A is a side view showing a configuration of a document scanner according to an embodiment of the present invention, FIG. 1B is a view of a part of the document scanner viewed from the bottom side, and FIG. It is a hardware block diagram of the said document scanner. It is a functional block diagram of the said document scanner. It is a flowchart which shows the flow of a process of the imaging program performed in the said document scanner. It is a flowchart which shows the flow of AF adjustment processing in the said imaging program. It is a flowchart which shows the flow of the offset measurement process performed in the said document scanner. It is a flowchart which shows the flow of the error start process performed in the said document scanner. It is a data block diagram which shows the example of the adjustment value used with the said imaging program. It is the schematic explaining the relationship between the area sensor in the said document scanner, a document, and a document stand. It is explanatory drawing explaining the principle of AF process applicable in the said document scanner. It is a figure which shows the example of the pattern for contrast detection applicable in the said document scanner. It is a flowchart which shows the flow of a process in general AF control. It is a figure which shows the difference in a defocus characteristic by the difference in the operation mode of an area sensor in general AF control.

<Summary of the present invention>
The image pickup apparatus according to the present invention has an optimum lens position for a subject including a high spatial frequency to be imaged in the high resolution mode based on the optimum lens position (focus position) by AF control of the image pickup element operated in the low resolution mode. One of the main points is to automatically acquire

<Embodiment of Imaging Device>
Hereinafter, an embodiment of an imaging apparatus according to the present invention will be described with reference to the drawings. First, an embodiment of an image reading apparatus including a scanner device configured as an imaging apparatus according to the present invention will be described.

  FIG. 1 is a schematic cross-sectional view illustrating a configuration example of an MFP 500 that is an image reading apparatus according to the present embodiment. In FIG. 1, an MFP 500 includes a paper feed unit 400, an image reading apparatus main body 300, a scanner 102, a document scanner 101 which is an embodiment of an imaging apparatus according to the present invention, and an operation panel 200.

  Inside the image reading apparatus main body 300, a tandem image forming unit 301, a registration roller 303 that supplies recording paper from the paper supply unit 400 to the image forming unit 301 via the conveyance path 302, an optical writing device 304, and the like. A fixing / conveying section 305 and a double-sided tray 306.

  In the image forming unit 301, four photosensitive drums 307 corresponding to respective colors of Y (yellow), M (magenta), C (cyan), and K (black) are arranged in parallel. Around the photosensitive drum 307, an image forming element including a charger / developer 308, a transfer device, a cleaner, and a charge eliminator is arranged. Further, an intermediate transfer belt 309 stretched between the driving roller and the driven roller is disposed between the transfer unit and the photosensitive drum 307 in a state of being sandwiched between the two nips.

  The tandem type MFP 500 configured as described above performs optical writing on the photosensitive drum 307 corresponding to each color of YMCK, develops the toner for each toner by the developing device 308, and, for example, Y, M, and C by the intermediate transfer belt 309. , K in the order of primary transfer. Thereafter, a full color image in which the four colors are superimposed by the primary transfer is secondarily transferred to the recording paper. Thereafter, by fixing the secondary transfer and ejecting it, a full-color image can be formed on the recording paper.

  Operation panel 200 is a user interface (I / F: Interface) that instructs the operation of MFP 500. The document scanner 101 described later is also operated by the operation of the user I / F included in the operation panel 200.

  The scanner 102 is a so-called flat head scanner, and is a device that scans an object to be read placed on the document table 130 with a line sensor and reads an image.

  The document scanner 101 is a stand-type imaging device that is an embodiment of the imaging device according to the present invention. The detailed configuration of the document scanner 101 will be described later.

<Overall configuration of imaging device>
Next, the document scanner 101 which is an embodiment of the imaging apparatus according to the present invention will be described. As shown in FIG. 2A, the document scanner 101 includes an area sensor 110, an illumination 120 that illuminates a document 600 that is an object to be read, a document table 130 on which the document 600 is placed, an area sensor 110, and an illumination 120. The support part 140 which supports is provided.

  The area sensor 110 is an image pickup device having an image pickup surface made up of pixels arranged in a two-dimensional manner, and is used to capture a subject image including character information and graphic information displayed on a document 600 placed on a document table 130. An image signal for generation is output. The area sensor 110 is held at the upper end of the support unit 140 in order to photograph the original 600 from above.

  FIG. 2B is a view of the area sensor 110 and the illumination 120 held at the upper end of the support portion 140 as viewed from the document table 130 side. As shown in FIG. 2B, a plurality of illuminations 120 are arranged around the area sensor 110. For example, the area sensor 110 is arranged so as to sandwich the area sensor 110 so that light is emitted in a direction in which the imaging surface of the area sensor 110 faces (a method in which the document table 130 is provided).

  FIG. 2C is a view of the document table 130 to which the lower end portion of the support portion 140 is fixed as viewed from the area sensor 110 side. As shown in FIG. 2C, the document table 130 is a planar member placed on a horizontal plane and is a base of the document scanner 101. A document placement area 132, which is an area on which the document 600 is placed, is set on the document table 130. The document placement area 132 is an area that can be imaged by the area sensor 110 and is an effective image area. The document placement area 132 is provided with a different color, for example, so that it can be easily distinguished from other areas on the document table 130.

  An AF reference pattern 131 is arranged on the document table 130. The AF reference pattern 131 is a “contrast detection pattern for low resolution mode” used for AF control described later, and is a “specific pattern” in the present embodiment. The contrast detection pattern will be described later. The AF reference pattern 131 is arranged at the base portion of the support part 140 outside the document arrangement area 132. The angle of view of the lens 150 described later is set so that the area where the AF reference pattern 131 is arranged is an area included in an image acquired by the area sensor 110. That is, the imaging optical system provided in the document scanner 101 includes an area sensor 110 that is an imaging element and a lens 150 that is an imaging lens. This imaging optical system is configured to capture a wider area in the effective pixel area of the area sensor 110 than the document placement area 132 suitable for placement of the document 600.

  Here, an outline of the operation of the document scanner 101 will be described. First, if the document 600 is a book, the document 600 is set (placed) on the document table 130 with the page to be scanned opened. When the user presses the start button on the operation panel 200, the illumination 120 is turned on and the document scanning operation is executed. After the document scanning operation is completed, if the user wants to scan another page, the user turns the page and presses the start button on the operation panel 200 again. By repeating the above operation, continuous scanning is executed.

  Further, by selecting operation from the operation panel 200, paper output can be executed for scanned image data after scanning, and data output to an external storage device such as a USB memory can be selected and executed.

  The reason why the illumination sensor 120 is turned on when the area sensor 110 captures the image of the document 600 is to eliminate external influences such as reflection of indoor lighting and reflection of the user's own shadow. Therefore, when the user operates the operation panel 200 to give a scan instruction, the illumination 120 is turned on in accordance with the instruction, and is automatically turned off when the scan operation ends.

  Here, the relationship between the area sensor 110, the document 600, and the document table 130 will be described with reference to FIG. As shown in FIG. 10, the document scanner 101 is configured to form an image of the document table 130 and the document 600 on the area sensor 110 using a lens 150 and read the image of the document 600. Here, whether or not the image of the original 600 on the imaging surface of the area sensor 110 is in focus is determined by the distance between the area sensor 110, the lens 150 and the original table 130, and the focal length of the lens 150. The lens 150 is held in a movable state along the direction indicated by the arrow A (the optical axis direction of the lens 150) by a lens driving unit that moves the lens 150 based on AF control described later. AF control can be performed so that the lens position of the lens 150 in the optical axis direction is adjusted by the lens driving means.

<The principle of AF control and the defocus characteristic of the lens 150>
Next, the principle of AF control will be described. FIG. 11 is a characteristic diagram illustrating an example of the defocus characteristic of the lens 150. The horizontal axis in FIG. 11 indicates the lens position of the lens 150 in the optical axis direction. The vertical axis represents the contrast value calculated from the subject image acquired by the area sensor 110. The contrast value is an example of a focus evaluation value calculated by performing predetermined image processing on an image acquired by the area sensor 110, and is an index value used for determining the focus state of the subject image. is there. Various definitions and calculation methods for the evaluation value of the in-focus state are known. For example, as a contrast value using the maximum pixel value Imax and the minimum pixel value Imin of an image, a method of calculating using a formula (Imax−Imin) / (Imax + Imin) is also known.

  As shown in FIG. 11, when the contrast value at each lens position is calculated while moving the lens 150 in the optical axis direction, it changes so as to have a peak at a predetermined lens position. The lens position corresponding to the peak of the contrast value corresponds to the optimum lens position BF. When the lens 150 is moved to the optimum lens position BF, the image of the document 600 is brought into focus on the imaging surface of the area sensor 110.

  Next, a contrast detection pattern used for calculating a contrast value in AF control will be described. FIG. 12A is an example of a first pattern image that is a contrast detection pattern having a low spatial frequency. FIG. 12B is an example of a second pattern image that is a contrast detection pattern having a high spatial frequency. The contrast detection pattern includes a pattern in which the density changes to a one-dimensional rectangular wave shape as shown in FIG. The spatial frequency of the contrast detection pattern used as the AF reference pattern 131 needs to be determined according to the reading resolution of the area sensor 110 so that the contrast value can be appropriately acquired.

  If the spatial frequency of the contrast detection pattern is too high for the reading resolution of the area sensor 110, the density change of the contrast detection pattern cannot be reproduced in the scan image. Therefore, the spatial frequency of the contrast detection pattern needs to be equal to or lower than the spatial frequency that can be reproduced in the scan image.

  For example, it is assumed that the MTF characteristics of the imaging optical system of the area sensor 110 and the document table 130 are always 1 regardless of the frequency, that is, the document table 130 ideally forms an image on the area sensor 110. In this case, if the reading resolution of the area sensor 110 is 200 dpi, the density change of the contrast detection pattern can be reproduced in the scan image if the spatial frequency of the contrast detection pattern is reduced to 100 dpi or less by half according to the sampling theorem. Actually, blurring according to the MTF characteristic occurs, so the spatial frequency of the contrast detection pattern needs to be set low according to the MTF characteristic.

  FIG. 13 is a flowchart illustrating an example of general AF control. FIG. 13A shows AF control for calculating a low resolution mode contrast value. In the AF control in the low resolution mode, an image having a low spatial frequency pattern as shown in FIG. FIG. 13B shows AF control for calculating a contrast value in the high resolution mode. In the AF control in the high resolution mode, an image having a high spatial frequency pattern as shown in FIG. As the contrast detection pattern, as shown in FIG. 12, a pattern whose density changes into a rectangular wave shape can be used. In the case of a pattern in which the density changes in such a one-dimensional direction, noise can be removed by performing an averaging process in a direction orthogonal to the density change direction (a direction in which the density does not change).

  As already described, in the AF control, it is desirable to use a scan image in the low resolution mode as in the AF control of FIG. Therefore, as shown in FIG. 13A, a low spatial frequency pattern image is acquired (S1301), the contrast value of the acquired image is calculated (S1302), and the optimum lens position BF is calculated based on the contrast value ( S1303).

  Also, in the AF control using the high spatial frequency pattern image, as shown in FIG. 13B, the live view operation of the area sensor 110 is stopped and the high resolution mode is set (S1300). Subsequently, a high spatial frequency pattern image is acquired (S1301a), the contrast value of the acquired image is calculated (S1302), and the optimum lens position BF is calculated based on the contrast value (S1303). Thereafter, the area sensor 110 is reset to the low resolution mode, and the live view operation is started (S1304).

  Here, when the operation mode of the area sensor 110 is the low resolution mode, the high spatial frequency pattern exemplified in FIG. 12B cannot be reproduced in the image, and the lens position at which the focus is best (the lens position at which the contrast value is maximized). Cannot be detected. Therefore, in the AF control, the low spatial frequency pattern shown in FIG.

  On the other hand, the defocus characteristic of the lens 150 described with reference to FIG. 11 varies depending on the spatial frequency of the scanned image. When the contrast value is calculated for the low spatial frequency component as shown in FIG. 12A and when the contrast value is calculated for the high spatial frequency component as shown in FIG. As shown in FIG. 4, the lens position for the best focus is different.

  FIG. 14 is a diagram illustrating the defocus characteristics of the lens 150 depending on the operation mode of the area sensor 110. The horizontal axis in FIG. 14 indicates the lens position of the lens 150 in the optical axis direction. The vertical axis represents the contrast value calculated from the subject image acquired by the area sensor 110. As shown in FIG. 14, when a high spatial frequency characteristic 91, which is a defocus characteristic at a high spatial frequency, is compared with a low spatial frequency characteristic 92, which is a defocus characteristic at a low spatial frequency, lenses corresponding to respective peak positions. It can be seen that the positions are different positions. Here, a lens position at which the high spatial frequency characteristic 91 has a peak is defined as a high spatial frequency best focus BFH, and a lens position at which the low spatial frequency characteristic 92 has a peak is defined as a low spatial frequency best focus BFL.

  As is clear from FIG. 14, the high spatial frequency best focus BFH and the low spatial frequency best focus BFL are different, so even if AF control is performed using a low spatial frequency pattern in the low resolution mode, the best focus for the high spatial frequency component is achieved. It will not be. When the document scanner 101 scans a book or text document in the high resolution mode, it is high spatial frequency components such as the outline of the text that influence the resolution of the scanned image. Therefore, even if an image is acquired in a state where the high spatial frequency component is out of the best focus, the resolution is lowered, and the scan image quality is deteriorated. That is, even when the original 600 as assumed by the document scanner 101 is scanned in the low resolution mode, it is difficult to perform appropriate AF control for the high spatial frequency component that is originally desired.

  If the AF control is performed in the high resolution mode as in the AF control shown in FIG. 13B, an appropriate AF adjustment result can be obtained for the high spatial frequency component. However, it cannot be compatible with the live view operation in which the low resolution mode is essential. Therefore, AF control is performed after the live view operation is stopped. In this case, since the live view is temporarily stopped while the user is preparing for scanning such as alignment of the original 600, convenience for the user is reduced. Alternatively, a control flow may be considered in which AF control is not performed in the standby state, but AF control is performed after a scan start instruction is issued. However, even if there is no decrease in convenience due to the stop of the live view, the time from the scan start instruction to the start of the scan becomes longer, so the productivity decreases.

  As described above, in the conventional AF control, it is necessary to perform the AF control in the low resolution mode in the same way as the live view in order to perform the AF control without causing the user's convenience and productivity to be lowered. However, even if the document scanner 101 performs AF control in the low resolution mode, the quality of the read image is low, and high spatial frequency components cannot be read. Therefore, as described below, the document scanner 101 according to the present embodiment stores in advance the difference between the high spatial frequency best focus BFH and the low spatial frequency best focus BFL described with reference to FIG. deep. Thereby, after calculating the low spatial frequency best focus BFL, the optimum lens position based on the low spatial frequency best focus BFL can be adjusted by the offset value 93. That is, the offset value 93 is an adjustment value for adjusting the optimum lens position BF.

<Hardware configuration of image forming apparatus>
Based on the above description, the configuration and characteristics of the document scanner 101 according to the present invention will be described. Next, the hardware configuration of the document scanner 101 will be described. As shown in FIG. 3, the document scanner 101 includes an area sensor 110, a control device 111, a control I / F 113, an image I / F 114, a temperature sensor 115, a timer 116, a motor 117, and a lens 150. , And illumination 120. The details of the area sensor 110, the illumination 120, and the lens 150 have already been described.

  The control device 111 controls the operation of various devices such as the motor 117 and the illumination 120 using information from the operation device 201 included in the operation panel 200 and information acquired from the temperature sensor 115 and the timer 116. Do. The control device 111 performs image processing on the image signal input from the area sensor 110 and generates image data.

  The storage device 112 stores various data such as image data acquired via the area sensor 110, a contrast value calculated from the image data, and an offset value 93 calculated from the contrast value. The storage device 112 also stores an imaging program to be described later and also functions as a work area for executing the imaging program. The storage device 112 includes a volatile storage device and a nonvolatile storage device.

  The control I / F 113 is an interface for exchanging control instructions with the image reading apparatus main body 300. The image I / F 114 is an interface for exchanging image data with the image reading apparatus main body 300.

  The temperature sensor 115 measures the temperature in the operating environment of the document scanner 101 and notifies the control device 111 of temperature information. The temperature information is identification data associated when the offset value 93 generated in the control device 111 is stored in the storage device 112.

  The timer 116 notifies the control device 111 of time data for determining timing for executing AF control described later.

  The area sensor 110 can be operated by appropriately switching between the two operation modes. The operation modes included in the area sensor 110 are a high resolution mode and a low resolution mode. The high resolution mode is an operation mode for outputting image data corresponding to the entire effective pixel area of the area sensor 110 with respect to a subject image formed on the imaging surface via the lens 150. The low resolution mode is an operation mode in which image data is output at high speed by thinning out the outputs of some pixels in the effective pixel region of the area sensor 110. Switching between these operation modes is under the control of the control device 111. The high resolution mode is also called a still image mode, and the low resolution mode is also called a moving image mode.

  The lens 150 is configured such that the lens position is moved by driving the motor 117. The control device 111 performs drive control of the motor 117. The motor 117 and the control device 111 constitute lens driving means. The lens 150 acquires a subject image at a predetermined timing while moving the lens position by position control of the driving unit. The lens position adjustment timing and the lens position adjustment method depend on time information input from the timer 116, temperature information input from the temperature sensor 115, a user or administrator instruction input from the operation panel 200, and the like. It is determined.

<Functional configuration of imaging device>
Next, functional blocks of the document scanner 101 will be described with reference to FIG. Each function illustrated in FIG. 4 is realized by the hardware included in the document scanner 101 described with reference to FIG. 3 and the scan program 10 stored in the storage device 112. As shown in FIG. 4, the scan program 10 is configured so that the operation of each function is controlled around the control unit 11.

  The scan program 10 includes a control unit 11, an image processing unit 21, an illumination unit 31, an imaging unit 41, a lens driving unit 51, an operation unit 61, a live view display unit 71, an image storage unit 81, It has.

  The control unit 11 includes a scan control unit 17, a lens position correction unit 18, an optimum lens position calculation unit 13, a time measurement unit 16, a temperature measurement unit 15, a lens offset control unit 14, and a lens offset table holding unit. 12. The control unit 11 controls the operation and processing of each functional block realized by the scan program 10.

  Based on the scan start command from the operation unit 61, the scan control unit 17 notifies the lighting unit 31 of a lighting instruction. The illumination unit 31 turns on the illumination 120 based on the lighting instruction from the scan control unit 17. Further, the scan control unit 17 notifies the imaging unit 41 of a high-resolution imaging instruction based on a scan start command from the operation unit 61. Further, the scan control unit 17 notifies the lens position correction unit 18 of an instruction to move the position of the lens 150 simultaneously with an instruction to the imaging unit 41. The lens position correction unit 18 instructs the lens driving unit 51 to drive the lens. The lens position of the lens 150 is moved by a lens driving instruction to the lens driving unit 51.

  The lens position correction unit 18 performs display control using the live view function and AF control. The lens position correction unit 18 notifies the imaging unit 41 of a low-resolution imaging instruction based on a scan start command from the operation unit 61. Further, the lens position correcting unit 18 notifies the instruction to the imaging unit 41 based on the temperature information from the temperature measuring unit 15 and the time information from the time measuring unit 16. The lens position correction unit 18 receives an optimum lens position instruction from the optimum lens position calculation unit 13 and determines an offset position of the lens 150 based on a lens offset addition instruction from the lens offset control unit 14. In order to move the lens 150 to the determined offset position, the lens position correction unit 18 instructs the lens driving unit 51 to drive the lens.

  The time measurement unit 16 executes processing for notifying the control unit 11 of the time measured by the timer 116 as time data.

  The temperature measurement unit 15 executes processing for notifying the control unit 11 of the temperature measured by the temperature sensor 115 as temperature data.

  The optimum lens position calculation unit 13 calculates the optimum lens position of the lens 150 based on the contrast value from the contrast detection unit 24, which is an evaluation value calculation unit, and the calculated optimum lens position is optimal for the lens position correction unit 18. Notify as a lens position instruction.

  The lens offset control unit 14 obtains a corresponding offset value from the offset value table stored in the lens offset table holding unit 12 based on the time data and temperature data notified by the time measurement unit 16 and the temperature measurement unit 15. Execute the reading process.

  The lens offset table holding unit 12 stores an offset value table to be described later. The offset value table may be stored in a non-volatile memory included in the storage device 112 so that the offset value table is retained even when the power of the document scanner 101 is turned off.

  The image processing unit 21 includes an autofocus image processing unit 22, a scan image processing unit 23, and a contrast detection unit 24.

  The autofocus image processing unit 22 executes processing to be used for autofocus processing based on the image acquired by the imaging unit 41. If the live view function is in operation, the live view image is transferred to the live view display unit 71.

  The scan image processing unit 23 executes processing so that it can be used for scan processing based on the image acquired by the imaging unit 41. If the operation mode of the imaging unit 41 is the high resolution mode, the image from the imaging unit 41 is transferred to the image storage unit 81.

  In the contrast detection unit 24, the autofocus image processing unit 22 in the image processing unit 21 processes the image from the imaging unit 41, and calculates a contrast value for the processed image.

  The illumination unit 31 turns on or off the illumination 120 based on a turn-on instruction or a turn-off instruction from the scan control unit 17.

  The imaging unit 41 changes the operation mode of the area sensor 110 based on the high resolution shooting instruction from the scan control unit 17 and the low resolution shooting instruction from the lens position correction unit 18 and converts the subject image into an image signal. Then, the image processing unit 21 is notified.

  The lens driving unit 51 moves the lens position of the lens 150 based on the lens driving instruction from the lens position correcting unit 18.

  The operation unit 61 detects a scan start operation on the document scanner 101 and notifies the scan control unit 17 and the lens position correction unit 18.

  The live view display unit 71 displays a live view image when the imaging unit 41 is operated in the low resolution mode.

  The image storage unit 81 stores an image to be read when the imaging unit 41 is operated in the high resolution mode.

  Note that the scan control unit 17 and the lens position correction unit 18 correspond to a switching control unit that switches the operation mode of the area sensor 110 in the present embodiment.

<Operation Flow of Image Reading Device>
Next, an imaging method according to the present invention will be described. The imaging method according to the present invention is realized by executing the imaging program according to the present invention. Therefore, in the following, an embodiment of the imaging method according to the present invention will be described by describing the flow of processing of the scan program 10 which is an embodiment of the imaging program according to the present invention.

  In the following, the steps of each process are expressed as S501, S502,. The scan program 10 executed in the document scanner 101 is classified into two processing blocks, “standby processing” and “scanning processing”. First, standby processing will be described.

  When the operation of the document scanner 101 is started, the area sensor 110 is set to the low resolution mode (S501). Subsequently, the imaging unit 41 captures the subject image obtained by imaging the reading target into the image processing unit 21, and notifies the live view display unit 71 of the image data via the autofocus image processing unit 22. Accordingly, live view display processing for displaying an image of the subject in real time is executed (S502).

  The live view display process is a preview function that acquires an image before scanning the original 600 in real time and displays a moving image, and the user confirms the appearance of the original 600 and aligns the original 600 in advance. This process is executed for the purpose. Therefore, the live view display process contributes to improvement of user convenience. Since the image acquisition and display must be performed at high speed in the live view display process, the image is acquired in the low resolution mode (moving image mode) without using the information of all the pixels of the area sensor 110 when acquiring the image. The

  Subsequently, a scan start determination process is executed (S503). When the operation of the operation panel 200 is detected in the operation unit 61, the operation unit 61 notifies the scan control unit 17 of the start of scanning, and shifts to processing at the time of scanning (S503: YES). Further, if the operation of the operation panel 200 is not detected within a certain time during the elapsed time counted by the time measuring unit 16, the AF execution determination process is executed without shifting to the scanning process (S503: NO). (S504).

  In the AF execution determination process (S504), the execution timing is determined based on a certain time interval in the elapsed time counted by the time measurement unit 16. In the AF execution determination process (S504), if it is not determined that it is the execution timing (S504: NO), the process proceeds to the scan start determination process without performing the AF process.

  If it is the execution timing of the AF process, the process proceeds to the AF adjustment process (S504: Yes, S505). Details of the AF adjustment processing will be described later. After the AF adjustment process is completed, the process proceeds to a scan start determination process.

  As with live view, AF processing is faster in low-resolution mode (moving image mode) than in high-resolution mode (still image mode). There is an advantage that no switching is required. Therefore, it is desirable to execute the AF process in the low resolution mode (moving image mode).

  Next, scanning processing will be described. First, the live view is stopped (S506). This is pre-processing for switching the operation mode of the area sensor 110 to the high resolution mode.

  Subsequently, a high resolution mode setting process for switching the operation mode of the area sensor 110 from the low resolution mode to the high resolution mode is executed (S507). This is because the resolution of the original 600 image is increased to improve the discrimination.

  Subsequently, the illumination 120 is turned on (S508). This is because the quality of the image of the original 600 is improved by illuminating the original 600 in order to remove the external influence.

  Subsequently, a document scanning process for capturing an image of the document 600 placed on the document table 130 is executed (S509). By the document scanning process, the area sensor 110 acquires the image of the document table 130 together with the image of the document 600 placed on the document table 130. Since the AF reference pattern 131 is displayed on the document table 130, the AF reference pattern 131 is also acquired together with the image of the document 600. Therefore, processing for deleting the AF reference pattern 131 from the acquired image is also executed.

  After the above document scanning process is completed, the illumination 120 is turned off (S510). This is to consume wasteful power consumption.

<Details of AF adjustment processing>
Next, details of the AF adjustment process (S505) will be described. As already described, the operation mode of the area sensor 110 when the AF adjustment process (S505) is executed is the low resolution mode. Therefore, the AF reference pattern 131 is also a contrast detection pattern for low spatial frequency (see FIG. 12A). In the AF adjustment processing (S505), the AF control using the AF reference pattern 131, which is a low spatial frequency contrast detection pattern, is performed so that the lens 150 is positioned in an optimum focus state with respect to the document 600 including the high spatial frequency. This process automatically adjusts from the result.

  In other words, the image acquired by the imaging unit 41 is processed by the autofocus image processing unit 22, and the contrast value in the processed image is calculated by the contrast detection unit 24. Based on the calculated contrast detection unit 24, the optimum lens position calculation unit 13 identifies the lens position that is the in-focus position. This contributes to improving the image quality of an image obtained by capturing the original 600 to be read.

  Since the focus state may change with time due to factors such as temperature change, it is desirable to execute AF control at a certain frequency so as to suppress the change with time. For example, when the detection is performed by detecting the temperature, the method is performed at a constant temperature interval, and when the detection is performed over time, the method is performed at a constant time interval or a time interval in which the interval gradually increases.

<AF adjustment processing flow>
FIG. 6 is a flowchart for explaining a detailed process flow in the AF adjustment process (S505). First, the area sensor 110 acquires an image of the AF reference pattern 131 (S601). Subsequently, the contrast value of the acquired AF reference pattern 131 is calculated (S602). Here, images are acquired at a plurality of locations (for example, 5 locations) while moving the position of the lens 150, and a contrast value at each lens location is calculated.

  Subsequently, the optimum lens position is calculated (S603). Here, an approximate curve indicating the relationship between the lens position and the contrast value is calculated using a least square method or the like, and the lens position at which the contrast value is maximum in the approximate curve is calculated. This optimum lens position is the low spatial frequency best focus BFL that provides the best focus for the low spatial frequency component.

  Subsequently, an offset value 93 is added to the calculated optimum lens position (S604). Finally, the offset value 93 is added to correct the lens position as the optimum lens position.

  Since the offset value 93 depends on the optical characteristics of the lens 150, a predetermined fixed value may be used as the offset. Further, since there are individual differences in the optical characteristics of the lens 150, the offset may be measured and held in advance in order to eliminate the influence of the individual differences. The measurement of the offset value 93 will be described later.

  In addition, since the optical characteristics of the lens 150 change over time due to the influence of temperature or the like, a plurality of offset values 93 are prepared in order to suppress the influence of the change over time, and one of the values is set to a predetermined condition (elapsed time, You may select and use according to temperature etc.

  By adding the offset value 93 to the optimal lens position calculated by acquiring the image of the low spatial frequency pattern in this way, the lens position that is the best focus for the high spatial frequency component can be obtained, and appropriate AF Can be realized.

  Since the acquired image has a low spatial frequency pattern, it may be in the low resolution mode, and the AF control can be executed while the live view is being executed. Thus, by performing optimal lens position calculation and lens position correction in the low resolution mode in parallel with the live view, appropriate AF control can be performed without incurring user convenience and productivity reduction.

<Offset measurement processing flow>
Here, the measurement process of the offset value 93 stored in the lens offset table holding unit 12 will be described. As shown in FIG. 9, a plurality of offset values 93 are stored in a table structure associated with an identifier such as a measurement condition. In the AF adjustment flow already described, for example, as shown in FIG. 9A, the lens offset table holding unit 12 can specify the offset value 93 in association with the temperature information acquired by the temperature measuring unit 15. Remember. This temperature information may be a temperature change amount from a predetermined reference temperature, or may indicate a specific temperature. In addition, as shown in FIG. 9B, the lens offset table holding unit 12 may store the offset information 93 so that the offset value 93 can be specified in association with the time information acquired by the time measuring unit 16. This time information may be an elapsed time from a predetermined reference time, or may indicate a specific time.

  FIG. 7 is a flowchart showing the flow of the offset measurement process. First, the area sensor 110 is set to a high resolution mode (still image mode) which is the second operation mode (S701).

  Subsequently, a high spatial frequency pattern contrast detection pattern is photographed to obtain a second pattern image (S702). Here, as the high spatial frequency pattern, for example, a pattern that changes in density to a rectangular wave shape at a high spatial frequency as illustrated in FIG. 12B may be used.

  Next, a second evaluation value that is a contrast value of the acquired second pattern image is calculated (S703). Here, the acquisition of the second pattern image (S702) and the calculation of the second evaluation value (S703) are executed at predetermined timing intervals while moving the lens 150. These processes are executed over the entire movable range of the lens 150. Next, a high spatial frequency best focus BFH, which is the lens position corresponding to the peak of the contrast value of the high spatial frequency component calculated while moving the lens 150 and is the second optimal lens position, is calculated (S704).

  Next, the operation mode of the area sensor 110 is switched, and the area sensor 110 is set to the low resolution mode which is the first operation mode (S705). Subsequently, a low spatial frequency pattern contrast detection pattern is photographed to obtain a first pattern image (S706). Here, as the low spatial frequency pattern, for example, a pattern whose density changes to a rectangular wave shape at a low spatial frequency as shown in FIG.

  Next, a first evaluation value that is a contrast value of the acquired first pattern image is calculated (S707). Here, the acquisition of the first pattern image (S706) and the calculation of the first evaluation value (S707) are executed at predetermined timing intervals while moving the lens 150. These processes are executed over the entire movable range of the lens 150. Next, the low spatial frequency best focus BFL which is the lens position corresponding to the peak of the contrast value of the low spatial frequency component calculated while moving the lens 150 and is the first optimal lens position is calculated (S708).

  Next, a difference between the low spatial frequency best focus BFL and the high spatial frequency best focus BFH is calculated, and the calculated offset value 93 is associated with the temperature information when the processing is executed, and the lens offset table is stored. Store in the unit 12 (S709). The offset value 93 calculated and stored as described above can be used in the offset adjustment process already described.

  Note that the order of calculating the optimum lens position in the high resolution mode and the calculation of the optimum lens position in the low resolution mode may be reversed. First, the optimum lens position in the low resolution mode is calculated first, and then the optimum lens position in the high resolution mode is calculated. The lens position may be calculated.

  The timing for executing the offset measurement processing described above may be executed at the time of manufacturing before the use of the document scanner 101 is started. In addition, when the accumulated time measured by the time measuring unit 16 exceeds a predetermined threshold, the temperature variation measured by the temperature measuring unit 15 may exceed the predetermined threshold. In this case, it may be displayed on the display unit provided in the operation panel 200 that the threshold value has been exceeded.

<Error avoidance processing flow>
Next, error detection processing when AF fails in the AF adjustment processing according to the present embodiment described with reference to FIG. 6 will be described with reference to the flowchart of FIG.

  In the AF adjustment process, an image of the AF reference pattern 131 is acquired as a contrast detection pattern, and a contrast value is calculated. However, the AF reference pattern 131 is provided on the document table 130. Therefore, it can be assumed that the AF reference pattern 131 is hidden by a user's hand or a document. Also, it is assumed that sudden external light is applied to the AF reference pattern 131 and the AF reference pattern 131 cannot be identified.

  Even if this image is acquired when part or all of the AF reference pattern 131 is hidden, or when the AF reference pattern 131 becomes indistinguishable by strong light, the contrast value cannot be obtained correctly. As described above, when the AF adjustment process is executed in a situation where the contrast value cannot be acquired correctly, the optimal lens position is erroneously detected, and the lens 150 is moved to an abnormal position to output an abnormal image whose resolution is greatly reduced. There is a possibility that.

  In the error avoidance process according to this embodiment, before executing the AF adjustment process (S505), the control unit 11 sends the current lens position information to the storage unit (storage device 112) immediately before the lens position. It is stored as a certain “previous lens position” (S801). A storage unit configured by the control unit 11 and the storage device 112 corresponds to an error determination unit.

  Subsequently, the area sensor 110 acquires an image of the AF reference pattern 131 (S802). Subsequently, the contrast value of the acquired AF reference pattern 131 is calculated (S803). For example, images are acquired at a plurality of locations (for example, 5 locations) while moving the position of the lens 150, and the contrast value at each lens location is calculated.

  Subsequently, the optimum lens position is calculated (S804). For example, an approximate curve indicating the relationship between the lens position and the contrast value is calculated using the least square method or the like, and the lens position at which the contrast value is maximum in the approximate curve is calculated. Subsequently, an offset value 93 is added to the calculated optimum lens position (S805).

  Next, a lens position determination process for determining whether or not the optimum lens position adjusted by adding the offset value 93 corresponds to an abnormal value is executed (S806). In the lens position determination process, the previous lens position, which is the immediately preceding lens position, is compared with the adjusted lens position, and it is determined whether the difference is equal to or less than a predetermined threshold value. If the difference is equal to or smaller than the threshold value, the lens position after adjustment is a normal value because it is within the allowable range. In this case, the process ends (S806: Yes).

  If the difference in the lens position determination process is larger than the threshold value, the allowable range is exceeded (S1306: No), the lens position after adjustment is discarded, and the lens position change to change the previous lens position to the lens position after adjustment. Processing is executed (S807).

  As a specific method for determining the abnormality, the difference between the current lens position (AF adjustment result) and the held “previous lens position” is checked. If the difference is less than a predetermined allowable value, it is normal and the allowable value is exceeded. There is a way to judge that there is an abnormality. As the allowable value, a value obtained by adding a margin to an assumed change amount of the lens position including a temperature change and various variations is set in advance. However, the present invention is not limited to this, and various forms such as, for example, recognizing and determining the shape of the contrast detection pattern, or providing an abnormality detection pattern for determining whether or not the contrast detection pattern is covered, etc. May be used.

  Subsequently, an error notification process is performed to notify the user that the lens position has been returned to the previous lens position (S808). In the error notification process, the error content may be displayed on the display unit included in the operation panel 200, or may be displayed to the extent that an error has occurred. For example, a message that prompts the AF reference pattern 131 not to be covered with the hand or the document 600 so that the AF reference pattern 131 can be correctly captured may be displayed.

  When it is determined in the lens position determination process (S806) that the allowable range is exceeded (S806: No), the area sensor 110 performs the AF adjustment process again, and the area sensor 110 captures the image of the AF reference pattern 131. You may return to the process (S802) to acquire.

  As described above, according to the document scanner 101 in the present embodiment, even when the area sensor 110 is operated in the low resolution mode and AF control is executed, the optimum lens position corresponding to the high spatial frequency included in the document 600 is determined. Can be calculated.

  If scanning is performed by moving the lens 150 to the calculated optimum lens position, it is possible to execute from live view to scanning operation in the low resolution mode. That is, according to the document scanner 101, it is possible to execute from live view processing to scanning processing without switching the operation mode of the area sensor 110. This can improve user convenience and productivity when scanning books and the like.

DESCRIPTION OF SYMBOLS 10 Scan program 11 Control part 12 Lens offset table holding part 13 Optimal lens position calculation part 14 Lens offset control part 15 Temperature measurement part 16 Time measurement part 17 Scan control part 18 Lens position correction part 21 Image processing part 22 Autofocus image processing part 23 Scan image processing unit 24 Contrast detection unit 31 Illumination unit 41 Imaging unit 51 Lens drive unit 61 Operation unit 71 Live view display unit 81 Image storage unit 91 High spatial frequency characteristic 92 Low spatial frequency characteristic 93 Offset value 101 Document scanner 102 Scanner 110 Area sensor 111 Control device 112 Storage device 113 Control I / F
114 Image I / F
DESCRIPTION OF SYMBOLS 115 Temperature sensor 116 Timer 117 Motor 120 Illumination 130 Document stand 131 AF reference pattern 132 Document arrangement area 140 Support part 150 Lens 200 Operation panel 201 Operation device 600 Document

JP 2013-029656 A

Claims (10)

An imaging unit that acquires both an image of a subject arranged in an effective image area and an image of a specific pattern via an imaging lens;
An evaluation value calculation unit for calculating a focus evaluation value based on the image of the specific pattern in the effective image region;
An optimum lens position calculation unit for calculating an optimum lens position corresponding to a focus state based on the focus evaluation value;
A storage unit that stores in advance an adjustment value for adjusting the optimum lens position;
A switching control unit that controls switching of an operation mode of the imaging unit;
The optimal lens position for the image of the specific pattern acquired by operating the imaging unit in the first operation mode is acquired based on the adjustment value when the imaging unit is operated in the second operation mode. A lens position correction unit that corrects the lens position to focus on the subject image;
An imaging apparatus comprising: The first operation mode in the switching control unit is a low resolution mode,
The second operation mode in the switching control unit is a high resolution mode,
The specific pattern has a predetermined low spatial frequency component that is reproducible in the low resolution mode.
The imaging apparatus according to claim 1. The imaging unit acquires a first pattern image having a low spatial frequency component in the first operation mode and a second pattern image having a high spatial frequency component in the second operation mode,
The evaluation value calculating unit calculates a first evaluation value based on a low spatial frequency component included in the first pattern image and a second evaluation value based on a high spatial frequency component included in the second pattern image;
The optimum lens position calculating unit calculates a first optimum lens position based on the first evaluation value and a second optimum lens position based on the second evaluation value;
The lens position correction unit calculates the adjustment value based on a difference between the first optimum lens position and the second optimum lens position;
The imaging apparatus according to claim 2. The storage unit is configured by a nonvolatile memory.
The imaging apparatus according to any one of claims 1 to 3, wherein The storage unit stores a plurality of adjustment values associated with a predetermined condition in a state where the adjustment values can be distinguished from each other.
The imaging apparatus according to any one of claims 1 to 4, wherein the imaging apparatus is characterized in that With a time measurement unit,
The condition is an elapsed time from a predetermined reference time.
The imaging apparatus according to claim 5. It has a temperature measurement unit,
The condition is a temperature change amount from a predetermined reference temperature.
The imaging apparatus according to claim 5. An error determination unit for determining whether or not the optimal lens position calculated by the optimal lens position calculation unit is normal;
The storage unit stores the immediately preceding position of the imaging lens immediately before the optimal lens position calculating unit calculates the optimal lens position;
When it is determined that the error determination unit is abnormal, the optimal lens position calculation unit sets the immediately preceding position stored in the storage unit as the optimal lens position.
The image pickup apparatus according to claim 1, wherein the image pickup apparatus is an image pickup apparatus. An imaging unit including an original platen for setting an effective image area, an imaging element for acquiring an image of a subject and a specific pattern image arranged in the effective image area, and generating image data; and an imaging lens; Executed in an imaging apparatus including a storage unit that stores in advance an adjustment value for adjusting an optimum lens position that is an in-focus position with respect to the image, and a switching control unit that controls switching of an operation mode of the imaging unit. An imaging method,
An imaging step of acquiring both the image of the subject and the image of the specific pattern arranged in the effective image area via the imaging lens;
An evaluation value calculating step for calculating a focus evaluation value based on the image of the specific pattern in the effective image region;
An optimum lens position calculating step for calculating an optimum lens position corresponding to a focus state based on the focus evaluation value;
The optimal lens position for the image of the specific pattern acquired by operating the imaging unit in the first operation mode is acquired based on the adjustment value when the imaging unit is operated in the second operation mode. A lens position correction step for correcting the lens position to focus on the subject image;
An imaging method characterized by comprising: An imaging program executed in an imaging apparatus including an imaging lens and an imaging element,
An imaging unit that acquires both an image of a subject arranged in an effective image region and an image of a specific pattern via the imaging lens;
An evaluation value calculation unit for calculating a focus evaluation value based on the image of the specific pattern in the effective image region;
An optimum lens position calculation unit for calculating an optimum lens position corresponding to a focus state based on the focus evaluation value;
A storage unit that stores in advance an adjustment value for adjusting the optimum lens position;
A switching control unit that controls switching of an operation mode of the imaging unit;
The optimal lens position for the image of the specific pattern acquired by operating the imaging unit in the first operation mode is acquired based on the adjustment value when the imaging unit is operated in the second operation mode. A lens position correction unit that corrects the lens position to focus on the subject image;
An imaging program comprising: