JP2010060932A - Automatic focusing device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out auto-focus processing to automatically focus by using a brightness signal obtained from an imaging element. <P>SOLUTION: This method performs accumulation addition of focal evaluation values obtained by AF scanning when there is no change in photographing conditions between the AF scanning made right before and the current AF scanning, and initializes the accumulated focal evaluation values when detecting a change. Then it carries out focusing by using the accumulated focal evaluation values. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an automatic focusing apparatus and an automatic focusing method for automatically focusing on a subject.

  2. Description of the Related Art Conventionally, in an electronic still camera or the like, a focusing operation using a luminance signal obtained from an image sensor such as a CCD is one of autofocus methods for automatically focusing on a subject by moving a focus lens position. There is. In this autofocus method, an evaluation value (hereinafter referred to as a focus evaluation value) is obtained by integrating high-frequency components of a signal in a distance measurement area set in a shooting screen. Then, based on the obtained focus evaluation value, the focus lens is moved within a predetermined range to detect the focus lens position with the highest contrast (hereinafter referred to as AF scan), and the focal point is generally obtained. .

  In this autofocus method, when the illuminance of the subject is low or the contrast of the subject is low and the high-frequency component of the luminance signal is small, the focus evaluation value decreases and the ratio of the noise component contained in the luminance signal increases, resulting in a good match. It becomes difficult to obtain the focus accuracy.

  In Patent Document 1, when it is determined that focusing cannot be performed by the focusing determination by the first AF scan, the second AF scanning is performed, and the focus evaluation values obtained by the two AF scannings are added. Thus, a technique for improving focusing accuracy and focusing accuracy is described.

JP 2000-258681 A

  However, in the method described in Patent Document 1, since the focus evaluation value is added even when the shooting scene changes between the first AF scan and the second AF scan, the added focus There was a problem that the evaluation value would be an incorrect value.

  Further, in the method of Patent Document 1, even if the shooting scene has not changed, the second AF scan is performed only when it is determined that focusing is impossible in the first AF scan. For this reason, there has been a problem that correction cannot be made when a false focus evaluation value peak is detected due to the influence of noise or the like and it is determined that focusing is possible.

  Accordingly, an object of the present invention is to provide an automatic focusing device and an automatic focusing method capable of performing an autofocus operation for automatically focusing using a luminance signal obtained from an image sensor with higher accuracy. There is.

In order to solve the above-described problem, the present invention is configured to acquire a focus evaluation value based on an imaging signal obtained by photoelectrically converting light incident on an imaging device via an imaging optical system including a focus lens. An automatic focusing device that obtains a focus position of a focus lens using a focus evaluation value acquired at each focus lens position while moving the lens, and focus evaluation of each movement position while moving the focus lens within a predetermined range Focus evaluation value acquisition means for acquiring values, accumulation means for cumulatively adding the focus evaluation values acquired by the focus evaluation value acquisition means for each movement position, and focus evaluation value acquisition means for acquiring focus evaluation values. It is detected whether or not the shooting condition during the acquisition operation has changed from the shooting condition during the second acquisition operation in which the focus evaluation value is acquired by the focus evaluation value acquisition unit one time before the acquisition. A change detection unit, a focusing unit that obtains a focus position of the focus lens using the focus evaluation value accumulated by the accumulation unit, and a focus evaluation value acquisition unit that controls the focus evaluation value according to a user instruction. The automatic focusing device is characterized by having control means for performing acquisition and initializing the accumulated focus evaluation value when a change is detected by the change detecting means.

  In addition, the present invention is configured to acquire a focus evaluation value based on an imaging signal obtained by photoelectrically converting light incident on an imaging device via an imaging optical system including a focus lens, and moving each focus lens while moving the focus lens. An automatic focusing method for obtaining a focus lens focus position using a focus evaluation value acquired at a lens position, wherein a focus evaluation value is acquired at each moving position while the focus lens is moved within a predetermined range. Shooting in the acquisition step, the accumulation step of accumulating the focus evaluation value acquired in the focus evaluation value acquisition step for each moving position, and the first acquisition operation for acquiring the focus evaluation value in the focus evaluation value acquisition step A variable for detecting whether or not the condition has changed from the imaging condition in the second acquisition operation in which the focus evaluation value is acquired in the focus evaluation value acquisition step one time before the acquisition. The focus evaluation value obtained by the detection step, the focus evaluation value cumulatively added in the accumulation step, and the focus evaluation value acquisition step according to a user instruction by controlling the focus evaluation value acquisition step by controlling the focus evaluation value acquisition step. And a control step of initializing the cumulatively added focus evaluation value when a change is detected in the change detection step.

  Since the present embodiment has the above-described configuration, it is possible to perform an autofocus operation for automatically focusing using a luminance signal obtained from the image sensor with higher accuracy.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an exemplary configuration of an electronic still camera 100 to which the present invention can be applied. The system control unit 115 includes, for example, a CPU, a RAM, and a ROM, and controls the overall operation of the electronic still camera 100 using the RAM as a work memory in accordance with a program stored in advance in the ROM.

  An imaging optical system is configured by a photographing lens 101 including a zoom mechanism, an aperture and shutter 102 for controlling the amount of light, and a focus lens 104 for focusing on the imaging element 108. The image sensor 108 is composed of, for example, a CCD or a CMOS imager, converts incident light into electric charge by photoelectric conversion, and outputs it as an image signal.

  The image pickup signal output from the image pickup device 108 is supplied with noise to the A / D conversion unit 109 after the noise is removed by a CDS circuit by a signal processing unit (not shown) and the gain is controlled by a non-linear amplification circuit. The A / D conversion unit 109 converts the supplied imaging signal into a digital signal and outputs it. The output of the A / D conversion unit 109 is supplied to the image processing unit 110, subjected to predetermined image processing such as gamma correction and contour correction, and output as image data. The image processing unit 110 performs white balance processing of image data based on the control of the WB processing unit 111.

  The image data output from the image processing unit 110 is supplied to the format conversion unit 112 and also supplied to the face detection module 123 and the moving object detection unit 124, which will be described in detail later. The format conversion unit 112 converts the supplied image data into a format suitable for recording on a recording medium in an image recording unit 114 (to be described later) and for supplying to the operation display unit 117. The image data whose format has been converted by the format converter 112 is temporarily stored in the DRAM 113 which can be read and written at high speed.

  The image recording unit 114 includes, for example, an interface for a removable nonvolatile memory, and records image data stored in the DRAM 113 in the attached nonvolatile memory. Further, the image recording unit 114 may record image data on a storage medium built in the electronic still camera 100.

  The image data stored in the DRAM 113 is supplied to the operation display unit 117 via the VRAM 116 that is a memory for image display. The operation display unit 117 includes a display device made of, for example, an LCD and a driving circuit thereof, and displays the supplied image data on the display device. The operation display unit 117 further performs display for assisting operation of the electronic still camera 100 and display indicating the camera state. In addition, the operation display unit 117 displays a shooting screen and a distance measurement area during imaging.

  The operation unit 118 is provided with a plurality of operation elements that accept user operations, outputs a control signal corresponding to the operation on the operation elements, and supplies the control signal to the system control unit 115. Based on this control signal, the system control unit 115 controls each unit of the electronic still camera 100 so as to perform an operation according to a user operation. The operation unit 118 includes, for example, a menu switch for performing various settings such as a shooting function of the electronic still camera 100 and settings for image playback, a zoom lever for instructing a zoom operation of the optical system, and an operation mode switching between a shooting mode and a playback mode. A switch or the like is provided.

  The shooting mode SW 119 switches shooting modes such as ON and OFF of the face detection mode. The main SW 120 switches the power on / off of the system of the electronic still camera 100.

  The switch SW121 instructs a shooting standby operation such as an autofocus (AF) operation or an automatic exposure (AE) operation. The switch SW122 instructs photographing after an operation on the switch SW121. For example, a shutter button is formed by the switches SW121 and 122, the switch SW121 is operated when the shutter button is half-pressed, and the switch SW122 is operated when the shutter button is pressed.

  The AF processing unit 105 includes a drive unit that drives the focus lens 104 in the optical axis direction, and moves the focus lens 104 back and forth in the optical axis direction based on the control of the system control unit 115. The AE processing unit 103 has a driving unit that drives the aperture and the shutter 102, and controls the aperture opening and the shutter speed according to the control of the system control unit 115 based on the image data supplied from the image processing unit 110. To do. The EF processing unit 107 controls the light emission of the strobe 106 in accordance with the control of the system control unit 115.

  The face detection module 123 performs face detection by analyzing the image data supplied from the image processing unit 110, and performs system control on face information (position, size, reliability, etc.) indicating one or more detected faces. To the unit 115.

  A known face detection technique can be used for face detection in the present embodiment. As a known face detection technique, a method based on learning using a neural network or the like, template matching is used to search a part having a characteristic shape of eyes, nose, mouth, etc. from an image, and if the degree of similarity is high, it is regarded as a face There are methods. In addition, many other methods have been proposed, such as a method that detects image feature amounts such as skin color and eye shape and uses statistical analysis. In general, a plurality of these methods are combined to improve the accuracy of face detection. Specific examples include a face detection method using wavelet transform and image feature amount described in JP-A-2002-251380.

  The moving object detection unit 124 analyzes the image data supplied from the image processing unit 110, and detects whether or not a subject or background in the screen based on the image data is moving. As an example, the moving object detection unit 124 holds at least one piece of image data supplied from the image processing unit 110. Then, the stored image data and the image data newly supplied from the image processing unit 110 are compared to obtain difference information, and moving object information (motion amount, position, and so on) such as a subject and a background is obtained from the obtained difference information. Range). The detected moving body information is supplied to the system control unit 115.

  The angular velocity sensor unit 125 detects the movement of the electronic still camera 100 itself on which the angular velocity sensor unit 125 is mounted. The detected camera motion information is supplied to the system control unit 115.

<Embodiment>
Next, the automatic focusing process according to the embodiment of the present invention will be described in detail with reference to FIGS. FIG. 2 is an exemplary flowchart showing an overall flow of the automatic focusing process according to the embodiment of the present invention. Each process in the flowchart of FIG. 2 is executed by the system control unit 115 according to a program.

  In the embodiment of the present invention, the focus evaluation value acquired by the AF scan is cumulatively added if there is no change in the shooting condition between the previous AF scan and the current AF scan, and the change is detected. , The accumulated focus evaluation value is initialized. Then, focusing processing is performed using the focus evaluation value that has been cumulatively added. For example, the change of the photographing condition is detected by the system control unit 115 as a change detecting unit.

  In FIG. 2, for example, when the main SW 120 is turned on, the state of the switch SW 121 is checked in step S201. If it is determined that the switch SW121 is not in the ON state, the process returns to step S201. On the other hand, if it is determined that the switch SW121 is in the ON state, the system control unit 115 serving as a control unit holds information indicating the current time in a register or the like, and the process proceeds to step S202.

  In FIG. 2, the switch SW121 is referred to as a first SW, and the switch SW122 is referred to as a second SW. The same applies to other flowcharts.

  In step S202, an AF scan is performed, and a focus evaluation value at each focus lens position is acquired. The acquired focus evaluation value at each focus lens position is temporarily stored in, for example, a RAM included in the system control unit 115. As an example, the system control unit 115 as a focus evaluation value acquisition unit controls the AF processing unit 105 to move the focus lens 104 by a predetermined step at predetermined intervals along the optical axis direction. At this time, the image data supplied from the image processing unit 110 is analyzed for each step based on the imaging signal output from the imaging element 108, and a focus evaluation value for each step, that is, each focus lens position is obtained. That is, a focus evaluation value is obtained for each movement position of the focus lens 104. The focus evaluation value is obtained, for example, by integrating the high-frequency component of the luminance signal in the distance measurement area set in the shooting screen, as already described as the prior art.

  When the focus evaluation value for each focus lens position is acquired in step S202, the process proceeds to step S203. In step S203, the first AF setting when the switch SW121 is turned on in the immediately preceding step S201 and the second AF setting when the switch SW121 is turned on in the previous step S201 with respect to the immediately preceding step S201 are performed. Compare with AF setting. As a result of the comparison, if it is determined that the second AF setting is different from the first AF setting and the first AF setting is changed with respect to the second AF setting, the process proceeds to step S209.

  In step S209, a system control unit 115 serving as a control unit is initialized to 0, which will be described later. Here, by resetting the cumulative evaluation value, it is possible to control so as not to add the previous focus evaluation values. When the cumulative evaluation value is reset, the process proceeds to step S210.

  On the other hand, if it is determined in step S203 that the second AF setting matches the first AF setting and the first AF setting is not changed with respect to the second AF setting, the process proceeds to step S204. It is transferred to. Here, the AF setting is a shooting setting that is assumed to be changed according to a user instruction when changing a shooting scene or a shooting angle of view. Settings of the electronic still camera 100 that can be applied as AF settings include zoom position, shooting distance range settings such as normal settings and macro settings, and distance measurement area settings such as one-point distance measurement and multi-point distance measurement. The AF setting is set by the system control unit 115 according to a user operation on the operation unit 118, for example, and is stored in a RAM or a non-volatile memory (not shown).

  Hereinafter, “the switch SW121 is turned on in the immediately preceding step S201” will be described as “the current switch SW121 is turned on” as appropriate. Similarly, “the switch SW121 was turned on in the previous step S201 with respect to the immediately previous step S201” is described as “the previous switch SW121 was turned on” as appropriate.

  In step S204, the time interval from the previous switch SW121 being turned on to the current switch SW121 being turned on is acquired, and it is determined whether or not the acquired time interval is equal to or greater than a predetermined time. As a result of the determination, if it is determined that the predetermined time or more has elapsed, it is assumed that there has been a change in the shooting conditions, and the process proceeds to step S209. On the other hand, if it is determined that the predetermined time or more has not elapsed, the process proceeds to step S205.

  In step S205, a scene determination process is performed to determine whether the shooting scene has changed between the previous switch SW121 being turned on and the current switch SW121 being turned on, and the process proceeds to step S206. Details of the scene determination process in step S205 will be described later.

  In step S206, based on the scene determination result in step S205, it is determined whether or not the shooting scene has changed between the previous switch SW121 being turned on and the current switch SW121 being turned on. If it is determined that it has changed, it is determined that the shooting conditions have changed, and the process proceeds to step S209. On the other hand, if it is determined that there is no change, the process proceeds to step S207.

  In step S207, the shape based on the focus evaluation value acquired in step S202 (second acquisition operation) when the previous switch SW121 was turned on, and the shape acquired in step S202 when the switch SW121 was turned on this time (first acquisition). Compare the shape with the focus evaluation value. More specifically, for example, with the focus evaluation value on the vertical axis and the focus lens position on the horizontal axis, the shape formed by the focus evaluation value when the corresponding focus evaluation values are arranged for each focus lens position (the focus evaluation value shape and Compare). Then, it is determined whether or not the focus evaluation value shape based on the focus evaluation value acquired when the previous switch SW121 was turned on is different from the focus evaluation value shape based on the focus evaluation value acquired when the current switch SW121 was turned on. Perform evaluation value shape determination. Details of the focus evaluation value shape determination method in step S207 will be described later.

  In the next step S208, based on the result of the evaluation value shape determination in step S207, the focus evaluation value shape acquired when the previous switch SW121 is turned on is different from the focus evaluation value shape obtained when the current switch SW121 is turned on. Determine whether or not. If it is determined that the shapes are different, it is determined that the shooting conditions have changed, and the process proceeds to step S209. On the other hand, if it is determined that the shapes are not different, the process proceeds to step S210.

  In step S210, the system control unit 115 as an accumulation unit adds the focus evaluation value acquired when the switch SW121 is turned on to the accumulated evaluation value to obtain a new accumulated evaluation value. Cumulative evaluation value When it is initialized to 0 by the reset process in step S209 described above, the focus evaluation value is added to the initialized value to obtain a new cumulative evaluation value. The cumulative evaluation value is initialized to 0 when the switch SW121 is turned on immediately after the main SW 120 is turned on. Further, it may be initialized to 0 when a photographing operation is performed in step S217 described later.

  In the next step S211, focusing determination described later is performed using the accumulated evaluation value, and in the next step S212, it is determined whether or not focusing is possible based on the determination result in step S211. If it is determined that focusing is possible, the process proceeds to step S213.

  In step S213, the system control unit 115 as a focusing unit controls the AF processing unit 105 so that the focus lens 104 is moved to the focus lens position where the cumulative evaluation value takes the peak value. The AF processing unit 105 drives the focus lens 104 according to the control of the system control unit 115, and moves the focus lens 104 to the focus lens position. When the focus lens 104 is moved, the process proceeds to step S215.

  On the other hand, if it is determined in step S212 that focusing is not possible based on the determination result in step S211, the process proceeds to step S214. In step S214, the system control unit 115 controls the AF processing unit 105 so as to move the focus lens 104 to a fixed point. In step S214, the fixed point is set in advance to a distance where a subject is likely to exist, for example. As an example, it is conceivable to set a fixed point for each shooting mode provided according to the shooting distance, such as a short-distance shooting mode, a medium-distance shooting mode, and a long-distance shooting mode. When the focus lens 104 is moved, the process proceeds to step S215.

  In step S215, the state of the switch SW122 is checked. If it is determined that the state of the switch SW122 is ON, the process proceeds to step S217, and the photographing operation is started. Details of the photographing operation in step S217 will be described later. On the other hand, if it is determined that the state of the switch SW122 is not ON, the process proceeds to step S216, and the state of the switch SW121 is examined. If the state of switch SW121 is ON, the process returns to step S215. On the other hand, if the state of the switch SW121 is not ON, the process returns to step S201.

  Next, an example of the scene determination process in step S205 described above will be described using the flowchart of FIG. First, in step S301, the luminance component of the image data based on the imaging signal is compared when the previous switch SW121 is turned on and when the current switch SW121 is turned on. For example, the system control unit 115 holds the image data fetched from the image processing unit 110 in a RAM or the like, and calculates the luminance component between the fetched image data and the image data held when the switch SW121 was turned on last time. Compare.

  If it is determined that the luminance component has changed by a predetermined value or more as a result of the comparison of the luminance components, the process proceeds to step S306, and the determination result indicates that the shooting scene has changed, and the processing is as shown in FIG. It returns to step S206 of the flowchart. On the other hand, if it is determined that the luminance component has not changed by a predetermined value or more, the process proceeds to step S302.

  In step S302, the amount of motion of the image since the previous switch SW121 was turned on is checked to determine whether the amount of motion is greater than or equal to a predetermined amount. Here, the amount of motion is, for example, the moving object detection unit 124 as image motion amount detection means, and the image data captured from the image processing unit 110 is held in a memory or the like. At the same time, the acquired image data is compared with the image data held in the memory when the switch SW121 was previously turned on, and a difference is obtained. Then, the obtained difference amount is set as a motion amount. The image area to be compared may be the entire screen, or may be limited to an area that seems to be a subject (such as an area based on the position or size detected by the face detection module 123).

  If it is determined in step S302 that the amount of motion is greater than or equal to the predetermined amount, the process proceeds to step S306. On the other hand, if it is determined that the amount of movement is equal to or less than the predetermined amount, the process proceeds to step S303.

  In step S303, based on the detection result of the angular velocity sensor unit 125 as the apparatus motion amount detection means, the camera motion amount from when the previous switch SW121 was turned on is checked to determine whether the camera motion amount is greater than or equal to a predetermined amount. The If it is determined that the camera motion amount is greater than or equal to the predetermined amount, the process proceeds to step S306. On the other hand, if it is determined that the camera motion amount is not equal to or greater than the predetermined amount, the process proceeds to step S304.

  In step S304, it is checked whether or not the face detected by the face detection module 123 as the face detection means has changed since the previous switch SW121 was turned on. For example, a face is detected when the previous switch SW121 is turned on, and when the face is not detected when the current switch SW121 is turned on, or vice versa, it is determined that the detected face has changed. Also, it is determined that there has been a change in the detected face even when the face size detected when the switch SW121 is turned on the previous time and the face size detected when the switch SW121 is turned on this time have changed by a predetermined amount or more. Is done. When the size of the face changes more than a predetermined amount, it is determined that the distance to the main subject has changed.

  If it is determined in step S304 that there has been a change in face detection, the process proceeds to step S306. On the other hand, if it is determined that the face detection has not changed, the process proceeds to step S305. In step S305, the determination result indicates that the scene has not changed, and the process proceeds to step S206 in the flowchart of FIG.

  Next, an example of the focus determination process in step S211 of FIG. 2 described above will be described with reference to the flowcharts of FIGS.

  Here, the focus evaluation value is a mountain shape as illustrated in FIG. 7 when the horizontal axis represents the focus lens position and the vertical axis represents the focus evaluation value, except for special cases such as perspective competition. become. Therefore, whether or not the shape of the focus evaluation value is mountain-shaped is determined by the difference between the maximum value and the minimum value of the focus evaluation value, the length of the inclined portion with an inclination equal to or greater than the predetermined value SlopeThr, and the inclination. It is possible to perform in-focus determination by determining from the gradient of the existing portion. In the following, it is assumed that the determination result in the focus determination is output as “◯” or “×” as follows.

○: The focus of the subject can be adjusted from the peak position of the focus evaluation value.
X: Focus adjustment of the subject based on the peak position of the focus evaluation value is impossible.

  The case where the focus adjustment of the subject based on the peak position of the focus evaluation value of “×” is impossible means, for example, the case where the contrast of the subject image is insufficient or the focus distance where the AF scan is performed This is a case where the subject is located at a distance outside the range.

  Here, as shown in FIG. 7, the boundary points in the range where the slope is recognized to continue from the top of the mountain (point A) are point D and point E, and the distance from point D to point E is the width of the mountain. Let L be. The sum (SL1 + SL2) of the difference SL1 between the focus evaluation values at points A and D and the difference SL2 between the focus evaluation values at points A and E is defined as a value SL.

  FIG. 4 is a flowchart of an example showing the overall flow of the focus determination process in step S211. First, in step S401, the maximum value max and the minimum value min of the focus evaluation value and the focus lens position (hereinafter, the scan point io) that gives the maximum value max are obtained. Next, in step S402, a variable L representing the peak width of the focus evaluation value and a variable SL representing the mountain gradient are each initialized to zero.

  Note that the focus lens position, that is, the scan point, is set to 0 at a far end of a predetermined range where AF scanning is performed, N (> 0) at a close end, and one at a predetermined interval from the far end to the close end. It is assumed to be indicated by an increasing value i. Hereinafter, the scan point at the position corresponding to the value i is appropriately described as the scan point i. For example, the focus lens position that gives the maximum value described above corresponds to the value io.

  In the next step S403, it is checked whether or not the scan point io giving the maximum value is the position of the far end in the predetermined range where the AF scan is performed. If it is determined that it is not the far end position, the process proceeds to step S404. Investigate monotonic decrease toward infinity. On the other hand, if it is determined that the position is the far end position, the process proceeds to step S405.

  An example of the process for checking the monotonic decrease toward the infinity in step S404 will be described with reference to the flowchart of FIG. First, in step S501, a value i as a counter variable is initialized to a value io indicating a scan point io.

  In the next step S502, the focus evaluation value d [i-1] at the scan point i-1 that is infinity from the scan point i by one scan point from the focus evaluation value d [i] at the scan point i. The value obtained by subtracting is compared with a predetermined value SlopeThr. As a result, if d [i] −d [i−1] <SlopeThr, it is determined that no monotonic decrease in the infinity direction has occurred, and a process of checking the monotonic decrease in the infinity direction is performed. The process ends, and the process proceeds to step S405 in the flowchart of FIG.

  On the other hand, if d [i] −d [i−1] ≧ SlopeThr in step S502, it is determined that a monotonic decrease in the infinity direction has occurred, and the process proceeds to step S503. In step S503, a variable L that represents the length (mountain width) of the portion where the focus evaluation value is inclined with a slope equal to or greater than a certain value and a variable SL that represents the amount of decrease in the monotonically decreasing section are expressed by the following equations ( Update according to 1) and equation (2).

L = L + 1 (1)
SL = SL + (d [i] -d [i-1]) (2)

  In the next step S504, a value obtained by subtracting 1 from the value i is set as a new value i, and the point to be detected is moved to the infinity side by one scan point. In step S505, it is checked whether or not the scan point i has reached the far end position in the predetermined range where the AF scan has been performed. When it is determined that the value i is 0, that is, the start point for detecting the monotonic decrease has reached the far end position in the predetermined range where the AF scan has been performed (step S505), the process of checking the monotonic decrease toward the infinity direction is performed. finish.

  In step S404, the monotonous decrease from the scan point io in the infinity direction is checked as described above. When the process of step S404 ends, the process proceeds to step S405.

  Returning to FIG. 4, in step S405, it is checked whether or not the scan point io giving the maximum value is the closest end position in the predetermined range where the AF scan is performed. The process proceeds to step S406, and the monotonic decrease toward the closest end is checked. On the other hand, if it is determined that the position is the closest end position, the process proceeds to step S407.

  An example of the process for checking the monotonic decrease toward the closest end in step S406 will be described with reference to the flowchart of FIG. First, in step S601, a value i as a counter variable is initialized to a value io indicating a scan point io.

  In the next step S602, the focus evaluation value d [i + 1] at the scan point i + 1 that is closer to the nearest end from the scan point i by one scan point is subtracted from the focus evaluation value d [i] at the scan point i. The value is compared with a predetermined value SlopeThr. As a result, if d [i] −d [i + 1] <SlopeThr, it is determined that there is no monotonic decrease in the closest end direction, and a process of checking the monotonic decrease in the close end direction is performed. The process ends, and the process proceeds to step S407 in FIG.

  On the other hand, if d [i] −d [i + 1] ≧ SlopeThr in step S602, it is determined that a monotonic decrease in the closest end direction has occurred, and the process proceeds to step S603. In step S603, a variable L that represents the length (mountain width) of the portion where the focus evaluation value is inclined with a slope equal to or greater than a certain value and a variable SL that represents the amount of decrease in the monotonically decreasing section are expressed by the following equations ( Update according to 3) and equation (4).

L = L + 1 (3)
SL = SL + (d [i] -d [i + 1]) (4)

  In the next step S604, a value obtained by adding 1 to the value i is set as a new value i, and the point to be detected is moved to the closest end by one scan point. In step S605, it is checked whether or not the scan point i has reached the closest end position in a predetermined range where the AF scan has been performed. When it is determined that the value i is N, that is, the start point for detecting the monotonic decrease has reached the closest end position in the predetermined range where the AF scan has been performed (step S605), a process for checking the monotonic decrease toward the close end Exit.

  In step S406, the monotonic decrease from the scan point io toward the closest end is checked as described above. When the process in step S406 ends, the process proceeds to step S407.

  Returning to FIG. 4, in step S407 and subsequent steps, it is determined whether or not the obtained focus evaluation value has a mountain shape based on the processing results in steps S403 to S406, and based on the peak position of the focus evaluation value. It is determined whether or not the subject can be focused.

  In step S407, from the focus evaluation value d [n] at the nearest end scan point n in the predetermined range in which the AF scan is performed, the scan point n-1 is closer to infinity by one scan point than the scan point n. The focus evaluation value d [n-1] is reduced. Then, it is determined whether or not the subtraction result is equal to or greater than the predetermined value SlopeThr, and the scan point io that gives the maximum focus evaluation value is the closest end in the predetermined range where the scan is performed.

  If it is determined that these conditions are satisfied, it is determined that focus adjustment of the subject based on the peak position of the focus evaluation value is impossible, and the process proceeds to step S411. In this case, it is considered that the in-focus position may be close to the predetermined range where the AF scan is performed.

  On the other hand, if it is determined that the subtraction result is not equal to or greater than the predetermined value SlopeThr or that the scan point io is not the closest end in the predetermined range where the scan is performed, the process proceeds to step S408.

  In step S408, the focus at the scan point 1 that is one scan point closer to the near end than the scan point 0 from the focus evaluation value d [0] at the far end scan point 0 in the predetermined range in which the AF scan was performed. The evaluation value d [1] is reduced. Then, it is determined whether or not the subtraction result is equal to or greater than the predetermined value SlopeThr and the scan point io that gives the maximum focus evaluation value is the far end in the predetermined range where the scan is performed.

  If it is determined that these conditions are satisfied, it is determined that focus adjustment of the subject based on the peak position of the focus evaluation value is impossible, and the process proceeds to step S411. In this case, it is considered that the in-focus position may be on the infinity side from the predetermined range where the AF scan is performed.

  On the other hand, if it is determined that the subtraction result is not equal to or greater than the predetermined value SlopeThr or that the scan point io is not on the far end side in the predetermined range where the scan is performed, the process proceeds to step S409.

  In step S409, the following determination is made. That is, the length L of the inclined portion having an inclination equal to or greater than a certain value is not less than the predetermined value Lo, the average value SL / L of the inclination of the inclined portion is not less than the predetermined value SLo / Lo, and the focus It is determined whether or not the difference between the maximum value max and the minimum value min of the evaluation value is greater than or equal to a predetermined value.

  If it is determined that these conditions are satisfied, the focus of the subject can be adjusted from the peak position of the focus evaluation value, and the process proceeds to step S410. That is, in this case, it can be determined that the obtained focus evaluation value is mountain-shaped within a predetermined range in which AF scanning is performed.

  On the other hand, the length L is not equal to or greater than the predetermined value Lo, the average value SL / L of the inclination is not equal to or greater than the predetermined value SLo / Lo, or the difference between the maximum value max and the minimum value min of the focus evaluation value is the predetermined value. Otherwise, the next judgment is made. That is, in this case, the focus adjustment of the subject based on the peak position of the focus evaluation value is impossible. In this case, the process proceeds to step S411. That is, in this case, it can be determined that there is a possibility that the obtained focus evaluation value is not mountain-shaped within a predetermined range where AF scanning is performed.

  Next, an example of focus evaluation value shape determination processing in step S207 in the flowchart of FIG. 2 described above will be described with reference to the flowchart of FIG. Prior to the processing of FIG. 8, the processing of steps S401 to S406 in the flowchart of FIG. Thereby, the maximum value max and the minimum value min of the focus evaluation value and the focus lens position that gives the maximum value max are obtained, and the variable L that represents the width of the peak of the focus evaluation value is obtained.

  In addition, when the switch SW121 is turned on this time, the focus evaluation value is the maximum value of the focus evaluation value and the focus evaluation value at the boundary on the near side and the far end side of the range where the inclination is recognized to be continued from the position of the maximum value of the focus evaluation value. A difference SL1 and a difference SL2 are obtained respectively. These can be obtained based on the processing described in FIG. 5 or FIG.

  Note that these values when the previous switch SW121 is turned on are already obtained at the time of the previous processing, and can be used for the current processing by holding these values.

  In FIG. 8, in step S801, the length width L of the portion where the focus evaluation value is inclined with an inclination of a certain value or more when the switch SW121 is turned on last time, and the width L when the current switch SW121 is turned on. Find the difference between And it is judged whether this difference is more than predetermined value. If it is determined that the value is equal to or greater than the predetermined value, the process proceeds to step S806. On the other hand, if it is determined that the difference in width L is not greater than or equal to the predetermined value, the process proceeds to step S802.

  In step S802, the difference between the average value SL / L of the inclined portion when the previous switch SW121 was turned on and the average value SL / L when the current switch SW121 was turned on is obtained. And it is judged whether this difference is more than predetermined value. If it is determined that the value is equal to or greater than the predetermined value, the process proceeds to step S806. On the other hand, if it is determined that the difference between the average values SL / L is not greater than or equal to the predetermined value, the process proceeds to step S803.

  In step S803, the difference between the difference max-min between the maximum value max and the minimum value min of the focus evaluation value when the switch SW121 was previously turned on and the difference max-min when the switch SW121 was turned on this time is obtained. And it is judged whether this difference is more than predetermined value. If it is determined that the value is equal to or greater than the predetermined value, the process proceeds to step S806. On the other hand, if it is determined that the difference max-min is not greater than or equal to the predetermined value, the process proceeds to step S804.

  In step S804, it is determined whether or not the difference between the ratio SL1 / SL2 of the difference SL1 and the difference SL2 when the previous switch SW121 is ON and the ratio SL1 / SL2 when the current switch SW121 is ON is greater than or equal to a predetermined value. Is done. If it is determined that the difference is greater than or equal to the predetermined value, the process proceeds to step S806. On the other hand, if it is determined that the difference is not greater than or equal to the predetermined value, the process proceeds to step S805.

  In step S805, it is determined that the shape of the focus evaluation value is the same when the current switch SW121 is turned on and when the previous switch SW121 is turned on. On the other hand, in step S806, it is determined that the shape of the focus evaluation value differs between when the current switch SW121 is turned on and when the previous switch SW121 is turned on.

  When the determination in step S805 or step S806 is made, the process proceeds to step S208 in FIG.

  The focus evaluation value shape determination is not limited to the method performed according to the flowchart of FIG. For example, when the switch SW121 of the previous time and this time is ON, the difference absolute value of the focus evaluation value is obtained at each focus lens position, and this is added through each focus lens position to obtain the sum of absolute differences of the focus evaluation values. It may be determined that the sum of absolute differences is equal to or greater than a predetermined value and the focus evaluation value shapes are different.

  Next, the photographing operation in step S217 in the flowchart of FIG. 2 will be described more specifically with reference to the flowchart of FIG. First, in step S901, a flag BfFlg indicating whether or not the storage capacity of the DRAM 113 is full is set to a value “FALSE” indicating that it is not full.

  In the next step S902, the system control unit 115 performs photometry based on the image data supplied from the image processing unit 110, and measures the subject brightness. In the next step S903, the system control unit 115 controls the AE processing unit 103 in accordance with the subject brightness measured in step S902 to drive the shutter and the diaphragm, thereby performing exposure to the image sensor 108. The light imaged on the surface of the image sensor 108 is photoelectrically converted into an analog signal, which is supplied to the A / D converter 109 after pre-processing such as output noise removal and nonlinear processing of the image sensor 108 to be converted into a digital signal. Conversion is performed (step S904).

  The output of the A / D conversion unit 109 is subjected to white balance adjustment by the image processing unit 110 by the WB processing unit 111 to obtain appropriate output image data (step S905). The image data output from the image processing unit 110 is converted into a predetermined format such as a JPEG format by the format conversion unit 112 (step S906) and temporarily stored in the DRAM 113. In the next step S907, it is checked whether or not the storage capacity of the DRAM 113 is full.

  If it is determined that the DRAM 113 is full, the process proceeds to step S908, and the above-described flag BfFlg is set to a value “TRUE” indicating that the storage capacity of the DRAM 113 is full. In the next step S909, the image data temporarily stored in the DRAM 113 is stored in an external memory such as a built-in memory (not shown) of the electronic still camera 100 or a memory card mounted with the electronic still camera 100 in the image recording unit 114. Transfer to a storage medium and store.

  On the other hand, if it is determined in step S907 that the storage capacity of the DRAM 113 is not full, a series of shooting operations is terminated. In this case, the image data stored in the DRAM 113 is stored in a predetermined recording medium by the image recording unit 114 when the storage capacity of the DRAM 113 becomes full due to the subsequent shooting or according to a user operation on the operation unit 118. To be recorded.

  As described above, according to the embodiment of the present invention, each time an AF scan is performed, it is determined whether or not the focus evaluation value from the previous AF scan is to be added, and only when it is determined that the addition should be performed. The focus evaluation value is added. Therefore, since the focus control can be performed using the accumulated evaluation value obtained by accumulating appropriate focus evaluation values, the accuracy of the focus control is improved. In addition, since the focus evaluation values obtained by many AF scans can be cumulatively added, the S / N ratio is improved, and this can also improve the focusing accuracy on the main subject.

It is a block diagram which shows the structure of an example of the electronic still camera which can apply this invention. It is a flowchart of an example which shows the whole flow of the automatic focusing process by embodiment of this invention. It is a flowchart of an example which shows a scene determination process. It is an example flowchart which shows the whole flow of a focusing determination process. It is a flowchart which shows an example of a process which investigates the monotonous decrease | decrease to an infinite direction. It is a flowchart which shows an example of a process which investigates the monotone decrease to a near end direction. It is a figure which shows the shape of an example of a focus evaluation value. It is a flowchart which shows a process of an example of focus evaluation value shape determination. It is a flowchart which shows the process of an example of imaging operation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Electronic still camera 104 Focus lens 105 AF process part 108 Image pick-up element 109 A / D conversion part 110 Image processing part 113 DRAM
115 System control unit 121 Switch SW
122 Switch SW
123 face detection module 124 moving object detection unit 125 angular velocity sensor unit

Claims (12)

A focus evaluation value is obtained based on an imaging signal obtained by photoelectrically converting light incident on the image sensor via an imaging optical system including a focus lens, and the focus position of the focus lens is obtained using the focus evaluation value. An automatic focusing device for
Focus evaluation value acquisition means for acquiring the focus evaluation value for each moving position while moving the focus lens within a predetermined range;
Accumulating means for accumulating the focus evaluation value acquired by the focus evaluation value acquiring means for each moving position;
Focusing means for obtaining a focus position of the focus lens using the focus evaluation value cumulatively added by the accumulating means;
In the first acquisition operation in which the focus evaluation value acquisition unit acquires the focus evaluation value, the focus evaluation value is acquired by the focus evaluation value acquisition unit one time before the acquisition. Change detecting means for detecting whether or not the photographing condition during the second acquisition operation has changed;
When the change detecting unit detects that the photographing condition has changed, the accumulating unit is controlled to initialize the cumulatively added focus evaluation value, and then acquired in the first acquisition operation. An automatic focusing apparatus comprising: a control unit that cumulatively adds focus evaluation values. The change detecting means includes
When it is determined that the shooting scene in the first acquisition operation has changed with respect to the shooting scene in the second acquisition operation, it is detected that the shooting condition has changed. The automatic focusing device according to claim 1. The change detecting means includes
The change in the shooting scene is detected based on a luminance component in the first acquisition operation and a luminance component in the second acquisition operation of the imaging signal. Automatic focusing device. An image motion amount detecting means for detecting a motion amount of the image based on the image signal based on the image signal;
The change detecting means includes
The change in the photographic scene is detected based on the amount of motion detected by the image motion amount detection unit from the second acquisition operation to the first acquisition operation. 3. The automatic focusing device according to 3. It further has a device movement amount detection means for detecting the movement amount of the imaging device on which the automatic focusing device is mounted,
The change detecting means includes
5. The automatic focusing device according to claim 2, wherein a change in the shooting scene is detected based on the amount of motion detected by the device motion amount detection unit. 6. Further comprising face detection means for performing face detection on an image based on the imaging signal;
The change detecting means includes
A change in the photographing scene is detected based on the result of the face detection during the first acquisition operation by the face detection unit and the result of the face detection during the second acquisition operation. The automatic focusing device according to any one of claims 2 to 5. The change detection unit is configured to change a shooting setting according to a user instruction during shooting between the time when the second acquisition operation is performed and the time when the first acquisition operation is performed. The automatic focusing device according to claim 1, wherein it is detected that the photographing condition has changed. The change detecting means includes
The imaging condition is considered to have changed if a time interval from the execution of the second acquisition operation to the execution of the first acquisition operation is a predetermined time or more. 8. The automatic focusing device according to any one of 7 above. The change detecting means includes
When it is determined that the shape based on the focus evaluation value acquired in the first acquisition operation has changed with respect to the shape based on the focus evaluation value acquired in the second acquisition operation, the imaging condition The automatic focusing device according to claim 1, wherein it is detected that the change has occurred. The control means includes
10. The focus evaluation value acquisition unit is controlled to cause the focus evaluation value to be acquired in accordance with a user instruction to an imaging apparatus on which the automatic focusing device is mounted. The automatic focusing device according to any one of claims. A focus evaluation value is obtained based on an imaging signal obtained by photoelectrically converting light incident on the image sensor via an imaging optical system including a focus lens, and the focus position of the focus lens is obtained using the focus evaluation value. An automatic focusing method for
A focus evaluation value acquisition step of acquiring the focus evaluation value for each moving position while moving the focus lens within a predetermined range;
A cumulative step of cumulatively adding the focus evaluation value acquired in the focus evaluation value acquisition step for each moving position;
A focusing step for obtaining a focus position of the focus lens using the focus evaluation value accumulated and added in the accumulation step;
In the first acquisition operation for acquiring the focus evaluation value in the focus evaluation value acquisition step, the focus evaluation value is acquired in the focus evaluation value acquisition step one time before the acquisition. A change detection step for detecting whether or not the shooting condition during the second acquisition operation has changed;
If it is detected in the change detection step that the photographing condition has changed, the accumulation step is controlled to initialize the cumulatively added focus evaluation value, and then acquired in the first acquisition operation. And a control step for accumulating and adding focus evaluation values.   An imaging apparatus comprising the automatic focusing device according to any one of claims 1 to 10.

Images