JP2016170319A - Imaging device, control method of the same and program thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic focusing technology that can focus on a subject to be focused at high speed.SOLUTION: An imaging device comprises: specification means that implements a scan operation for specifying a subject area to be focused from a plurality of subject areas prior to reception of a picture-taking preparation instruction; focusing control means that when reception means receives the picture-taking preparation instruction, drives a focus lens so that the subject area to be focused is put into a focusing state on the basis of a scan operation different from the scan operation by the specification means; and display means that displays the subject area put into the focusing state by the focusing control means on a display unit. When the reception means receives the picture-taking preparation instruction in a state where a picture-taking scene does not change after the picture-taking preparation instruction put into the focusing state is displayed on the display unit, the focusing control means is configured to select the subject area different from the subject area displayed on the display unit, and drive the focusing lens so that the selected subject area is put into the focusing state.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an improvement of an automatic focusing technique in an imaging apparatus such as a digital still camera or a digital video camera.

  In digital still cameras, digital video cameras, etc., when performing autofocus (AF), the lens position where the high frequency component of the luminance signal obtained from the image sensor using a CCD (Charge Coupled Device) sensor is maximized is aligned. A method of setting a focal position is used.

  For example, the evaluation value (focus evaluation value) based on the high frequency component of the luminance signal obtained from the image sensor while driving the lens over the entire distance measurement range is stored each time. There is known a scanning method in which the lens position corresponding to the maximum value of is the in-focus position.

  Further, a hill-climbing method (hereinafter referred to as “continuous AF”) is known in which the lens is driven in a direction in which the focus evaluation value increases, and the position where the focus evaluation value is maximized is the focus position.

  Conventionally, there has been a technology that limits the AF distance measurement range in the scanning method performed after the shooting preparation instruction and shortens the time of the AF operation by performing continuous AF before the shooting preparation instruction and maintaining the focused state. It has been proposed (Patent Document 1).

  In addition, a technique has been proposed in which an area selection member capable of selecting a focus detection area is provided to obtain an image focused on a position intended by a photographer (Patent Documents 2 and 3).

Japanese Patent No. 14106485 JP-A-7-199320 JP 2007-286118 A

  In the above-described continuous AF, when an attempt is made to move the lens in the direction in which the focus evaluation value increases, the subject to be focused cannot be focused unless the region to be focused in the screen is known.

  In the above-mentioned Patent Document 1, in continuous AF, the focusing operation is made faster by combining a scanning method in which the lens position corresponding to the maximum focus evaluation value is the in-focus position. However, since the user does not determine the subject (main subject) to be focused in the screen that the user wants to focus on, there is a problem that the subject to be focused cannot be focused depending on the shooting scene. is there.

  In the above Patent Documents 2 and 3, when an area selection member capable of selecting a focus detection area is provided, there is a problem that labor and time for selecting the area of the main subject, and cost for the member are required.

  Therefore, an object of the present invention is to provide an automatic focusing technique that can focus at high speed on a subject to be focused.

  In order to achieve the above object, the present invention provides an imaging apparatus for driving a focus lens to a position where a subject is in focus based on image data output from an imaging means, and accepting an imaging preparation instruction. Means for performing a scanning operation for specifying a subject area to be focused from a plurality of subject areas before the accepting means accepts the photographing preparation instruction, and when the accepting means accepts the photographing preparation instruction, Based on a scanning operation different from the scanning operation by the specifying unit, a focus control unit that drives the focus lens so that the subject area to be focused is in focus, and the focus control unit performs focusing. Display means for displaying the subject area in the state on the display unit, and the focus control means is in a focused state by the display means. When the accepting unit accepts the shooting preparation instruction in a state where the shooting scene does not change after the displayed subject area is displayed on the display unit, the subject area different from the subject area displayed on the display unit is selected. The focus lens is driven so that the selected subject region is in focus.

  According to the present invention, it is possible to provide an automatic focusing technique capable of focusing at high speed on a subject to be focused.

1 is a block diagram illustrating a system configuration of a digital still camera that is an example of an embodiment of an imaging apparatus of the present invention. It is a flowchart figure explaining imaging | photography operation | movement of the digital still camera shown in FIG. It is a flowchart figure explaining the process of the scene stability determination in step S202 of FIG. FIG. 6 is a flowchart for explaining subject detection AF scan in step S208 of FIG. 2; FIG. 5 is a flowchart illustrating a scene change determination process in step S406 of FIG. It is a graph explaining the relationship between the position of the optical axis direction of a focus lens, and a focus evaluation value. It is a flowchart figure explaining the focus determination process in FIG.4 S409. FIG. 5 is a flowchart for explaining subject area specific AF scan processing in step S209 in FIG. 2; It is a figure explaining the example of AF frame setting in FIG. It is a flowchart figure explaining the last reference determination process in step S804 of FIG. FIG. 9 is a flowchart for explaining a previous reference AF scan process in step S806 of FIG. FIG. 12 is a flowchart for explaining main subject area determination in step S1108 of FIG. FIG. 13 is a diagram illustrating an example of main subject area determination in FIG. 12. FIG. 9 is a flowchart for explaining zone AF scan processing in step S809 in FIG. 8; It is a flowchart figure explaining the process of zone update determination in step S1407 of FIG. It is a figure explaining the example of the zone update determination process shown in FIG. It is a flowchart figure explaining the process of uniform surface determination in step S811 of FIG. It is a flowchart figure explaining the process of uniform surface determination in step S1701 and S1705 of FIG. It is a figure explaining the uniform surface determination of FIG. FIG. 9 is a flowchart for explaining focus drive processing in step S813 in FIG. FIG. 3 is a flowchart for explaining continuous AF processing in step S211 of FIG. 2. FIG. 3 is a flowchart for explaining continuous AF processing in step S211 of FIG. 2. It is a flowchart explaining the process of the scene instability judgment in step 212 of FIG. It is a flowchart figure explaining the imaging | photography process in step S215 of FIG. FIG. 24 is a flowchart for explaining main subject region update processing in step S2311 of FIG. FIG. 24 is a flowchart for explaining the main-exposure AF process in step S2302 of FIG. It is a figure which shows the example which increases / decreases the number of frames by AF frame setting. It is a figure which shows the example which increases / decreases the number of frames by AF frame setting. It is a figure which shows the example which increases / decreases the number of frames by AF frame setting. FIG. 26 is a flowchart for explaining a main-exposure AF scan process in step S2411 of FIG. FIG. 24 is a flowchart for explaining the main exposure process in step S2306 of FIG.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a system configuration of a digital still camera which is an example of an embodiment of an imaging apparatus of the present invention.

  In the digital still camera of this embodiment, as shown in FIG. 1, the subject light flux that has passed through the photographing lens 101, the aperture / shutter 102 and the focus lens 104 forms an image on the imaging surface of the image sensor 106 and is photoelectrically converted. The image sensor 106 is composed of a CCD sensor, a CMOS sensor, or the like, and outputs an analog image signal obtained by photoelectric conversion to the A / D converter 107. The A / D conversion unit 107 includes a CDS circuit and a non-linear amplification circuit that removes output noise of the image sensor 106 in addition to converting an analog image signal output from the image sensor 106 into a digital image signal.

  The digital image signal output from the A / D conversion unit 107 is output to the image processing unit 108 and subjected to predetermined image processing. The image data after the image processing is recorded on the image recording unit 111 via the format conversion unit 109 and the DRAM 110 and is displayed on the image display unit 114 via the format conversion unit 109, the DRAM 110 and the VRAM 113.

  The image recording unit 111 includes a recording medium such as a memory card and its interface. The DRAM 110 is used as a high-speed buffer as temporary image storage means, or a working memory for image compression / decompression. In addition to image display, the image display unit 114 displays a shooting screen and a distance measurement area at the time of shooting, in addition to display for assisting operations and display of the camera state.

  The system control unit 112 controls the entire camera such as a shooting sequence. The AE processing unit 103 is connected to the image processing unit 108 and the aperture / shutter 102 and controls the driving of the aperture / shutter 102. The AF processing unit 105 performs focus control by driving the focus lens 104 in the optical axis direction via a motor (not shown).

  The operation unit 115 includes a release button, a power button, a zoom lever, a mode switching dial, and the like operated by the user. The shooting mode switch 116 is a switch for selecting a shooting mode such as a macro mode, a distant view mode, and a sports mode, and changes a distance measuring distance range, an AF operation, and the like according to the shooting mode selected by the user.

  The power switch 117 is a switch for turning on and powering on the system when the power button is operated. A release switch (SW1) 118 is a switch that is turned on by a half-press operation of a release button or the like to give a shooting preparation instruction such as AF or AE. A release switch (SW2) 119 is a switch that is turned on by a full-press operation of a release button or the like to give a shooting instruction.

  The subject detection module 120 detects a subject using the image signal processed by the image processing unit 108, and detects one or more pieces of subject information (if the subject is a face, subject other than the position / size / face) In this case, the position) is sent to the system control unit 112.

  Next, the photographing operation of the digital still camera shown in FIG. 1 will be described with reference to FIGS. Each process in FIG. 2 is executed by the CPU of the system control unit 112 according to a program stored in a storage unit (not shown).

  In FIG. 2, in step S201, the system control unit 112 determines whether or not the release switch (SW1) 118 for instructing shooting preparation is on or off. If it is on, the system control unit 112 proceeds to step S214. The process proceeds to S202.

  In step S202, the system control unit 112 performs scene stability determination, and proceeds to step S203. Details of the scene stability determination process will be described later with reference to FIG.

  In step S203, the system control unit 112 determines whether or not the shooting scene is determined to be stable in step S202. If it is determined that the shooting scene is stable, the system control unit 112 proceeds to step S204, otherwise proceeds to step S205. . Here, the state in which the photographing scene is stable means that the state of the subject to be photographed and the camera are stably maintained and are suitable for photographing.

  In step S205, the system control unit 112 clears the PeakPos update flag and returns to step S201.

  In step S204, the system control unit 112 determines whether the PeakPos update flag in FIG. 23, which will be described later, is TRUE, or whether imaging has been performed in the region selected by the main subject region specific AF scan in FIG. 8, which will be described later. Determine whether.

  If the PeakPos update flag is TRUE, or the image is shot in the area selected by the main subject area specific AF scan, the system control unit 112 proceeds to step S211. If the PeakPos update flag is FALSE or the area selected by the main subject area specific AF scan is not being shot, the system control unit 112 proceeds to step S206.

  In step S206, the system control unit 112 determines whether the subject brightness is equal to or lower than a predetermined value. If the subject brightness is equal to or lower than the predetermined value, the process proceeds to step S210. Otherwise, the process proceeds to step S207.

  In step S210, the system control unit 112 sets an AF frame for low illuminance, and the process proceeds to step S211. The AF frame here is an area for acquiring a focus evaluation value in the screen. The focus evaluation value is a value obtained by converting the analog video signal read from the image sensor 106 into a digital signal by the A / D converter 107 and extracting the high-frequency component of the luminance signal from the output from the output. . The focus evaluation value is stored in the DRAM 110 in association with the position of the focus lens 104 and the AF frame position.

  The acquisition of the focus evaluation value means that the AF processing unit 105 reads out the focus evaluation value stored in the DRAM 110 for determination in AF control. At low illuminance, since the exposure time is extended, AF accuracy in scanning cannot be ensured. For this reason, in the present embodiment, at low illuminance, a scanning operation at the time of subject area specification or subject detection is not performed, and one AF frame of a predetermined size is set near the center of the screen.

  In step S207, the system control unit 112 determines whether or not a subject has been detected by the subject detection module 120. If the subject has been detected, the process proceeds to step S208, and if the subject has not been detected, the process proceeds to S209.

  In step S208, the system control unit 112 performs a subject detection AF scan, which will be described later with reference to FIG. 4, and proceeds to step S211. In step S209, the system control unit 112 performs an AF scan for specifying a subject area, which will be described later with reference to FIG. 8, and proceeds to step S211. In step S211, the system control unit 112 performs continuous AF, which will be described later with reference to FIG. 21, and proceeds to step S212. In step S212, the system control unit 112 performs a scene instability determination described later with reference to FIG. 22, and proceeds to step S213.

  In step S213, the system control unit 112 determines whether or not the shooting scene is determined to be unstable in step S212. If it is determined that the shooting scene is unstable, the process returns to step S201. The process returns to step S211. Here, the shooting scene is unstable means that the state of the subject to be shot and the state of the camera become unstable and are not suitable for shooting.

  In step S214, the system control unit 112 sets the focus degree determination flag to FALSE, and proceeds to step S215. In step S215, the system control unit 112 performs imaging processing described with reference to FIG. 23 described later, and returns to step S201. In parallel with the above-described operation, the brightness of the image displayed on the image display unit 114 is controlled appropriately by controlling the aperture and shutter 102 by the AE processing unit 103 based on the control signal from the system control unit 112 at all times. The AE operation is performed as follows.

  Next, with reference to FIG. 3, the scene stability determination process in step S202 of FIG. 2 will be described.

  In FIG. 3, in step S301, the system control unit 112 determines whether or not the camera operation amount detected by an angular velocity sensor (not shown) is equal to or less than a predetermined amount. If it exceeds, the process proceeds to step S304. Here, whether or not the camera state is stable is determined based on whether or not the camera operation amount is equal to or less than a predetermined amount.

  In step S302, the system control unit 112 determines whether or not the luminance change amount from the previous time is equal to or less than a predetermined amount. If the amount is less than the predetermined amount, the system control unit 112 proceeds to step S303, and if it exceeds the predetermined value, proceeds to step S304. . Here, it is determined that the subject to be photographed has not changed because the luminance change amount is not more than a predetermined value.

  In step S303, the system control unit 112 determines that the shooting scene is in a stable state and ends the process. In step S304, the system control unit 112 determines that the shooting scene is not in a stable state and performs processing. Exit.

  Next, the subject detection AF scan in step S208 of FIG. 2 will be described with reference to FIG.

  In FIG. 4, in step S401, the system control unit 112 performs AF frame setting based on the face information (position / size) detected by the subject detection module 120, and the process proceeds to step S402.

  In step S402, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 to the scan start position, and proceeds to step S403. Here, the scan start position is determined based on the distance of the person estimated from the detected face size, for example.

  In step S403, the system control unit 112 stores the focus evaluation value at the current focus lens position in the DRAM 110, and proceeds to step S404. In step S404, the system control unit 112 acquires the current position of the focus lens 104, stores the acquired position data in the DRAM 110, and proceeds to step S405.

  In step S405, the system control unit 112 determines whether the release switch (SW1) 118 for instructing shooting preparation is on or off. If it is on, the process proceeds to step S214 in FIG. 2, and if it is off, step S406 is performed. Proceed to In step S406, the system control unit 112 performs scene change determination, which will be described later with reference to FIG. 5, and proceeds to step S407. Here, the scene change determination is a process of determining whether or not the scene to be photographed has changed from the state of the camera or the state of the subject.

  In step S407, the system control unit 112 determines whether or not the current position of the focus lens 104 is the same as the scan end position. If both positions are the same, the process proceeds to step S409, and if different, the process proceeds to step S408. move on. Here, the scan end position is determined based on, for example, the distance of the person estimated from the detected face size.

  In step S408, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 by a predetermined amount in the scan end direction, and returns to step S403. In step S409, the system control unit 112 performs in-focus determination described with reference to FIGS. 6 and 7 described later, and proceeds to step S410.

  In step S410, the system control unit 112 determines whether or not the in-focus determination in step S409 is “good”, and if it is “good”, the process proceeds to step S411. Otherwise, the process proceeds to step S414. move on. Here, “◯” is a case where the subject has sufficient contrast and the subject exists within the scanned distance range.

  In step S411, the system control unit 112 calculates an in-focus position where the focus evaluation value acquired in step S403 reaches a peak, and the process proceeds to step S412. In step S412, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 to the in-focus position calculated in step S411, and proceeds to step S413. In step S413, the system control unit 112 sets the peak detection flag to TRUE and ends the AF scan process.

  In step S414, the focus determination in step S409 is not a “good” determination, that is, the subject has insufficient contrast, or the subject exists outside the scanned distance range. Therefore, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 to a position (fixed point) stored in advance in the DRAM 110, and ends the AF scan processing. Here, the fixed point is set to a distance with a high probability of existence of the subject. For example, if a face is detected, the distance of the person estimated from the size of the detected face is used.

  Next, the scene change determination process in step S406 of FIG. 4 will be described with reference to FIG. Note that the scene change determination in step S1106 in FIG. 11, step S1405 in FIG. 14, and step S2107 in FIG. 21, which will be described later, is the same process as in FIG.

  In FIG. 5, in step S501, the system control unit 112 determines whether or not the subject detection state (for example, the face detection state) detected by the subject detection module 120 has changed. If the subject detection state has changed, the system control unit 112 ends the determination process and returns to step S201 in FIG. 2, and if not, proceeds to step S502. Here, the subject detection state is whether or not a subject is detected. That is, if the subject has been detected at the previous scene change determination and no subject has been detected at the current scene change determination, the subject detection state has changed.

  In step S502, the system control unit 112 determines whether or not the amount of camera motion detected by an angular velocity sensor (not shown) is greater than or equal to a predetermined amount. Returning to S201, if the predetermined amount is exceeded, the process proceeds to step S503.

  In step S503, the system control unit 112 determines whether or not continuous AF, which will be described later with reference to FIG. 21, is being performed. If continuous AF is being performed, the process proceeds to step S504, and continuous AF is being performed. Otherwise, the process proceeds to step S505.

  In step SS504, the system control unit 112 determines whether or not the subject luminance difference is equal to or smaller than a predetermined value. If the subject luminance difference is equal to or smaller than the predetermined value, the system control unit 112 ends the determination process. This determination process is terminated, and the process returns to step S201 in FIG. Here, the subject brightness difference is a difference between the subject brightness value acquired at the previous scene change determination and the subject brightness value detected at the current scene change determination. If the difference in the subject luminance values is large, it is determined that the scene has changed.

  In step S505, the system control unit 112 determines whether or not the exposure time is equal to or longer than the predetermined time. If the exposure time is equal to or longer than the predetermined time, the system control unit 112 ends the determination process and returns to step S201 in FIG. If the exposure time is less than the predetermined time, the process proceeds to step S506. The reason why this determination process is terminated when the exposure time is equal to or longer than the predetermined time is that when the exposure time is equal to or longer than the predetermined time, the interval for acquiring the focus evaluation value is extended, so that the AF accuracy cannot be ensured. .

  In step S506, the system control unit 112 determines whether or not the aperture state of the aperture and the shutter 102 has changed. If the aperture state has changed, the system control unit 112 proceeds to step S507, and the aperture state has changed. If not, the determination process ends. In the present embodiment, the case where the aperture control is used has been exemplified. However, when the exposure control is performed using the ND filter instead of the aperture control, it may be determined whether or not the ND filter state has changed. This is because the peak position of the focus evaluation value changes when the state of the aperture or the ND filter changes.

  In step S507, the system control unit 112 determines whether the subject is detected by the subject detection module 120. If the subject has been detected, the system control unit 112 ends the determination process and returns to step S402 in FIG. 4. If the subject has not been detected, the system control unit 112 ends the determination process, and will be described later with reference to FIG. The process proceeds to step S809.

  Next, with reference to FIGS. 6 and 7, the focus determination process in step S409 in FIG. 4 will be described. First, the relationship between the position of the focus lens 104 in the optical axis direction and the focus evaluation value will be described with reference to FIG.

  As shown in FIG. 6, the focus evaluation value has a mountain shape when the horizontal axis represents the focus lens position and the vertical axis represents the focus evaluation value, except in the case of distance competition. Therefore, focusing is performed by judging the mountain shape from the difference between the maximum value and the minimum value of the focus evaluation value, the length of the inclined portion with a slope equal to or greater than a certain value (SlopeThr), and the slope of the inclined portion. Judgment can be made. The determination result in the focus determination is output by the following ○ determination, × determination, or Δ determination.

  ○ Judgment: The subject has sufficient contrast and the subject exists at a distance within the scanned distance range.

  X: The subject contrast is insufficient, or the subject is located at a distance outside the scanned distance range.

  Δ Determination: In the X determination, the subject is located outside the scanned distance range in the closest direction.

  With reference to FIG. 6, the length L of the inclined portion and the gradient SL / L of the inclined portion with an inclination equal to or greater than a certain value for determining the peak shape of the focus evaluation value will be described.

  Points that are recognized to be inclined from the top of the mountain (point A) are defined as points D and E, and the width between points D and E is defined as the width L of the mountain. The range in which the inclination is recognized to be continued is the range in which the scan point having the focus evaluation value decreased from the point A by a predetermined amount (SlopeThr) or more continues. The scan point is a point at which a focus evaluation value is acquired while the focus lens 104 is continuously driven in the optical axis direction and moved from the scan start point to the scan end point.

  The sum SL1 + SL2 of the difference SL1 between the focus evaluation values of the points A and D and the difference SL2 of the focus evaluation values between the points A and E is defined as SL.

  Next, the focus determination process in step S409 in FIG. 4 will be described with reference to FIG. The focus determination process in step S409 in FIG. 4 is the same as the focus determination process in step S1201 in FIG. 12 and step S1501 in FIG.

  In FIG. 7, in step S701, the system control unit 112 obtains the maximum value and the minimum value of the focus evaluation value, and proceeds to step S702. In step S702, the system control unit 112 obtains a scan point that maximizes the focus evaluation value, and proceeds to step S703. In step S703, the system control unit 112 obtains L and SL for determining the mountain shape from the scan point and the focus evaluation value, and proceeds to step S704.

  In step S <b> 704, the system control unit 112 determines whether or not the mountain shape is stopped on the closest side. Here, in the following case, it is determined that the mountain shape has stopped climbing on the near side. That is, the scan point with the maximum focus evaluation value is the near end in the predetermined range where the scan was performed, and the focus evaluation value of the near end scan point and the scan from the near end scan point by one point at infinity This is a case where the difference in the point focus evaluation values is equal to or greater than a predetermined value. If the system control unit 112 determines that the climbing stop is on the near side, the process proceeds to step S709; otherwise, the process proceeds to step S705.

  In step S705, the system control unit 112 determines whether or not the mountain shape stops climbing to the infinity side. Next, it is determined that the climb to the infinity side is stopped. That is, the scan point having the maximum focus evaluation value is at the infinity end of the predetermined range where the scan was performed, and from the focus evaluation value of the infinity end scan point and the infinity end scan point by one point from the nearest end. This is a case where the difference from the focus evaluation value of the scan point is a predetermined value or more. If the system control unit 112 determines that the climb to the infinity side is stopped, the system control unit 112 proceeds to step S708; otherwise, the process proceeds to step S706.

  In step S706, the system control unit 112 determines that the length L of the portion that is inclined with a certain inclination or more is a predetermined value or more, and the average value SL / L of the inclination of the inclined portion is a predetermined value or more. It is determined whether or not the difference between the maximum and minimum focus evaluation values is greater than or equal to a predetermined value. Then, the system control unit 112 determines that the length L is equal to or greater than a predetermined value, the average slope SL / L of the inclined portion is equal to or greater than the predetermined value, and the difference between the maximum value and the minimum value of the focus evaluation value is predetermined If it is equal to or greater than the value, the process proceeds to step S707; otherwise, the process proceeds to step S708.

  In step S707, since the obtained focus evaluation value is a mountain shape and the subject has contrast and the focus can be adjusted, the system control unit 112 sets the focus determination result as “good” and ends this determination processing.

  In step S708, since the obtained focus evaluation value is not a mountain shape, the subject has no contrast, and focus adjustment is impossible, the focus determination result is determined as x determination, and this determination processing is performed. finish.

  In step S709, the system control unit 112 is in a state where the obtained focus evaluation value does not have a mountain shape but continues to climb in the near end direction, and a subject peak exists on the close side. Since there is a possibility, the in-focus determination result is set as Δ determination, and this determination processing ends.

  Next, the subject area specifying AF scan process in step S209 of FIG. 2 will be described with reference to FIG. Here, AF scanning is performed to identify the area of the main subject in the screen.

  In FIG. 8, in step S801, the system control unit 112 determines whether or not electronic zooming is being performed. If electronic zooming is being performed, the process proceeds to step S802. Otherwise, the process proceeds to step S803.

  In step S802, the system control unit 112 performs AF frame setting for electronic zoom, and the process proceeds to step S804. Here, the electronic zoom is to enlarge the center area of the screen and display it on the image display unit 114. Since the center area of the screen is enlarged, the number of pixels of the image displayed on the image display unit 114 is reduced as compared with the case where the electronic zoom is not performed.

  Therefore, when the AF frame is set so that the ratio of the image displayed on the image display unit 114 during the electronic zoom is the same as when the electronic zoom is not performed, the number of pixels in the AF frame is smaller than when the electronic zoom is not performed. As a result, the S / N of the focus evaluation value decreases. For this reason, it is necessary to change the AF frame setting method between electronic zoom and non-electronic zoom. In the present embodiment, at the time of electronic zoom, one AF frame having a predetermined size is set near the center of the screen.

  In step S803, the system control unit 112 sets N × N AF frames in the screen, and the process advances to step S804. For example, when N = 5 and the size of the AF frame is 10% of the screen in both vertical and horizontal lengths, the AF frame setting shown in FIG. 9 is obtained. The size of N or the AF frame may be set in consideration of the existence probability of the main subject in the screen, or the number of AF frames may be different between the horizontal direction and the vertical direction.

  In step S804, the system control unit 112 performs a previous reference determination process described later with reference to FIG. 10, and the process proceeds to step S805. In step S805, the system control unit 112 proceeds to step S806 if it is determined that the shooting scene does not change much from the previous time as a result of the previous reference determination in step S804, and otherwise proceeds to step S809. In step S806, the system control unit 112 performs a previous reference AF scan process described later with reference to FIG. 11, and proceeds to step S807.

  In step S807, the system control unit 112 determines whether or not the main subject area has been specified in the previous reference AF scan in step S806. If the main subject area has been specified, the process proceeds to step S808. The process proceeds to step S809. In step S808, the system control unit 112 sets the peak detection flag to TRUE, and proceeds to step S809. In step S809, the system control unit 112 performs a zone AF scan, which will be described later with reference to FIG. 14, and proceeds to step S810.

    In step S810, the system control unit 112 determines whether or not the main subject area can be specified in the zone AF scan of step S809. If the main subject area can be specified, the process proceeds to step S808. The process proceeds to step S811. In step S811, the system control unit 112 performs uniform surface determination described with reference to FIGS. 17 and 18 described later, and proceeds to step S812.

  In step S812, since the main subject area could not be specified in the zone AF scan of step S809, the system control unit 112 sets an AF frame in a predetermined area set in advance on the screen, and the process proceeds to step S813. Here, the predetermined area is set to an area where the main subject is likely to exist, for example, one frame is set in the central area of the screen. In step S813, the system control unit 112 performs focus driving, which will be described later with reference to FIG. 20, and ends the subject area specifying AF scan process.

  Next, with reference to FIG. 10, the previous reference determination process in step S804 of FIG. 8 will be described. Here, it is determined whether or not the photographic scene has changed much this time with respect to the photographic scene in which the previous AF scan was performed.

  In FIG. 10, in step S1001, the system control unit 112 determines whether or not the main subject area can be specified in the previous AF scan, and if the main subject area can be specified, the process proceeds to step S1002. If not, the process proceeds to step S1006.

  In step S1002, the system control unit 112 determines whether or not the current position of the focus lens 104 is closer to the predetermined position. If it is closer, the process proceeds to step S1003. If not, step S1006 is performed. Proceed to Here, it is determined whether or not it is closer to the predetermined position, but it may be determined whether or not it is at infinity from the predetermined position.

  In step S1003, the system control unit 112 determines whether the time difference from the previous AF scan is within a predetermined time. If the time difference is within the predetermined time, the process proceeds to step S1004. Otherwise, the process proceeds to step S1006. In step S1004, the system control unit 112 determines whether or not the camera direction is the same as that in the previous AF scan, the process proceeds to step S1005 if it is the same, and the process proceeds to step S1006 if it is different. Here, the direction of the camera refers to, for example, the vertical and horizontal positions of the camera, and is detected by an angular velocity sensor.

  In step S1005, the system control unit 112 determines that there is not much difference from the shooting scene in the previous AF scan, and ends this determination process. In step S1006, the system control unit 112 determines that the previous AF scan and the shooting scene have changed significantly, and ends this determination process.

  Next, referring to FIG. 11, the previous reference AF scan process in step S806 in FIG. 8 will be described.

  In FIG. 11, in step S <b> 1101, the system control unit 112 sets the scan range to range 1 around the current position of the focus lens 104, and proceeds to step S <b> 1102. Here, since it is determined that there is not much difference from the previous shooting scene, the first range is a narrow range.

  In step S1102, the system control unit 112 moves the focus lens 104 to the scan start position, and proceeds to step S1103. In step S <b> 1103, the system control unit 112 converts the analog video signal read from the image sensor 106 into a digital signal by the A / D conversion unit 107. Then, the system control unit 112 stores the high frequency component of the luminance signal extracted by the image processing unit 108 based on the output of the A / D conversion unit 107 as a focus evaluation value in the DRAM 110, and proceeds to step S1104.

  In step S1104, the system control unit 112 acquires the current position of the focus lens 104 and stores the acquired position data in the DRAM 110, and the process proceeds to step S1105. The system control unit 112 determines whether the release switch (SW1) 118 that instructs to prepare for shooting is on or off. If the release switch (SW1) 118 is on, the system control unit 112 ends the process and proceeds to step S214 in FIG. The process proceeds to step S1106.

  In step S1106, the system control unit 112 performs the scene change determination process described above, and proceeds to step S1107. In step S1107, the system control unit 112 determines whether or not the current position of the focus lens 104 is equal to the scan end position. If both positions are equal, the process proceeds to step S1108; otherwise, the process proceeds to step S1109. move on. In step S1108, the system control unit 112 performs main subject area determination described with reference to FIGS. 12 and 13 described later, and ends this process. In step S1109, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 by a predetermined amount in the scan end direction, and then returns to step S1103.

  Next, the main subject area determination in step S1108 in FIG. 11 will be described with reference to FIGS. The main subject area determination process described here is the same as the main subject area determination process in step S1411 of FIG.

  Here, it is determined whether or not the main subject area in the screen has been identified. FIG. 13 is a diagram for explaining an example of main subject area determination in FIG. In this example, the AF frame size is 10% of the screen, N = 5, the scan range is 0 to 500, and the predetermined depth range is ± 10. The numerical values for the scan range and the predetermined depth range are numerical values representing the position of the focus lens 104. This corresponds to the number of pulses when a stepping motor is used as a driving motor (not shown) of the focus lens 104, and the larger value is the closest side.

  In FIG. 12, in step S1201, the system control unit 112 performs the above-described focus determination (see FIG. 7) for all the set AF frames, and the process proceeds to step S1202. Here, for example, it is assumed that the focus determination result as shown in FIG.

  In step S1202, the system control unit 112 calculates the peak position of the focus evaluation value in each AF frame (hereinafter referred to as PeakPos), stores it in the DRAM 110, and proceeds to step S1203. Here, for example, in each AF frame, the peak position calculation result as shown in FIG.

  In step S1203, the system control unit 112 determines whether or not the set AF frame is one frame. If the set AF frame is one frame, the system control unit 112 proceeds to step S1214; The process proceeds to S1204. In step S1204, the system control unit 112 sorts PeakPos of each AF frame of the center M × M frame in ascending order and sets the sorted number as S, and proceeds to step S1205.

  In the following description, M = 3, and the center M × M frame corresponds to a total of nine frames including three vertical frames and three horizontal frames surrounded by a thick line in FIG. For example, in the case of FIG. 13B, the sort numbers 410, 400, 400, 400, 100, 100, 100, and 90 are sorted in the closest order, and the sort number S = 8. Note that in the focus determination in step S1201, the peak position cannot be calculated with the AF frame of x determination, and thus is not subject to sorting.

  In step S1205, the system control unit 112 sets a counter P indicating the closest order of peak positions in the M × M frame calculated in step S1202 to 1, and the process proceeds to step S1206. In step S1206, the system control unit 112 sets the P-th PeakPos in the sort order as PeakPosP, and proceeds to step S1207. Here, for example, in FIG. 13B, when P = 1, PeakPosP = 410.

  In step S <b> 1207, the system control unit 112 determines ◯ in the center M × M AF frames, and detects “a lump” of AF frames within a predetermined depth range with respect to PeakPosP. Then, the system control unit 112 stores the number of AF frames constituting the “chunk” and the position of each AF frame in the DRAM 110, and proceeds to step S1208.

  Here, “a lump” is, for example, a state in which AF frames satisfying a condition are adjacent vertically and horizontally. When there are a plurality of “chunks”, one of the “chunks” may be selected based on the number of AF frames constituting the “chunk” and the position of the “chunks”.

  In step S1208, the system control unit 112 makes a ◯ determination so that one or more of the central M × M AF frames are included in the central N × N AF frames, and a predetermined depth range with respect to PeakPosP. Detects “chunks” inside. Then, the system control unit 112 stores the number of AF frames constituting the “chunk” and the position of each AF frame in the DRAM 110, and the process proceeds to step S1209. Here, for example, “chunks” as indicated by hatching in FIG. 13C are detected from the determination results as shown in FIGS. 13A and 13B.

  In step S1209, the system control unit 112 determines whether or not the “chunk” detected in step S1207 or step S1208 is a “chunk” including the center frame. If the system control unit 112 includes a central frame, the system control unit 112 proceeds to step S1215; otherwise, the system control unit 112 proceeds to step S1210.

  In step S <b> 1210, the system control unit 112 determines whether the “chunk” detected in step S <b> 1207 or step S <b> 1208 is a “chunk” that includes a predetermined number of frames or more in the M × M frame. The system control unit 112 proceeds to step S1215 if the detected “chunk” is a “chunk” including a predetermined number of frames or more in the M × M frame, and proceeds to step S1211 otherwise.

  In step S1211, the system control unit 112 determines that the “chunk” detected in step S1207 or step S1208 includes one frame of the central M × M frame and includes a predetermined number or more of the AF frames in the N × N frame. It is determined whether or not. The system control unit 112 proceeds to step S1215 if the detected “chunk” is a “chunk” including one frame out of the central M × M frames and a predetermined number or more of the AF frames in the N × N frame. Otherwise, the process proceeds to step S1212.

  In step S <b> 1212, the system control unit 112 adds 1 to the counter P and proceeds to step S <b> 1213. In step S1213, the system control unit 112 determines whether or not the counter P is greater than the sort number S. If the counter P is greater than the sort number S, the process proceeds to step S1217; otherwise, the process returns to step S1206. . In step S1214, the system control unit 112 determines whether or not the in-focus determination result in step S1201 is “good”. If yes, the process proceeds to step S1215; otherwise, the process proceeds to step S1217.

  In step S1215, the system control unit 112 determines that the main subject area has been identified, and the process proceeds to step S1216. In step S1216, the system control unit 112 determines and selects each AF frame constituting the cluster as a main subject area, and ends the determination process. If one AF frame is set here, that one frame is selected. In step S1217, the system control unit 112 determines that the main subject area has not been specified, and ends the determination process.

  Next, the zone AF scan process in step S809 in FIG. 8 will be described with reference to FIG. Here, the zone refers to each of the ranges when the focusable distance range is divided into a plurality of ranges.

  In FIG. 14, in step S1401, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 to the scan start position, and proceeds to step S1402. Here, the scan start position is, for example, the infinity end position. In step S1402, the system control unit 112 converts the analog video signal read from the image sensor 106 into a digital signal by the A / D conversion unit 107. The system control unit 112 stores the high-frequency component of the luminance signal extracted from the output of the A / D conversion unit 107 by the image processing unit 108 in the DRAM 110 as a focus evaluation value, and the process proceeds to step S1403.

  In step S1403, the system control unit 112 acquires the current position of the focus lens 104, stores the acquired position data in the DRAM 110, and proceeds to step S1404. In step S1404, the system control unit 112 determines whether the state of the release switch (SW1) 118 that instructs to prepare for shooting is on or off. If the switch is on, the process is terminated and the process proceeds to step S214 in FIG. If it is off, the process proceeds to step S1405.

  In step S1405, the system control unit 112 performs the scene change determination (see FIG. 5) described above, and proceeds to step S1406. In step S1406, the system control unit 112 determines whether or not the focus lens 104 is in a preset zone boundary position. If the focus lens 104 is in the zone boundary position, the process proceeds to step S1407; The process proceeds to S1409. In step S1407, the system control unit 112 performs zone update determination described with reference to FIG. 15 described later, and proceeds to step S1408. Here, zone update refers to scanning an adjacent zone after scanning a certain zone.

  In step S1408, the system control unit 112 determines whether or not it is determined to update the zone in step S1407. If it is determined to update the zone, the process proceeds to step S1409; otherwise, the process proceeds to step S1411. . In step S1409, the system control unit 112 determines whether or not the current position of the focus lens 104 is equal to the scan end position. If both positions are equal, the process proceeds to step S1411. Otherwise, the process proceeds to step S1411. move on. In step S1410, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 by a predetermined amount toward the scan end position, and then returns to step S1402. In step S1411, the system control unit 112 performs the above-described main subject area determination (see FIGS. 12 and 13), and ends this process.

  Next, the zone update determination process in step S1407 of FIG. 14 will be described with reference to FIG. Here, it is determined whether or not the main subject is likely to exist ahead in the scanning direction, that is, whether or not to continue AF scanning. FIG. 16 is a diagram for explaining an example of the zone update determination process shown in FIG. In the example shown in FIG. 16, the size of the AF frame is 10% of the screen, N = 5, and M = 3.

  In FIG. 15, in step S1501, the system control unit 112 performs the above-described focus determination (see FIG. 7) for all the set AF frames, and the process proceeds to step S1502. Here, for example, it is assumed that the focus determination result as shown in FIG.

  In step S1502, the system control unit 112 determines whether or not scanning has been performed up to the final zone. If scanning has been performed up to the final zone, the process proceeds to step S1512. Otherwise, the process proceeds to step S1503. In step S1503, the system control unit 112 determines whether or not there is a circle determination frame. If there is a circle determination frame, the process proceeds to step S1504. Otherwise, the process proceeds to step S1511.

  In step S1504, the system control unit 112 determines whether or not the center frame is Δ. If the center frame is Δ, the process proceeds to step S1511. Otherwise, the process proceeds to step S1505. In step S1505, the system control unit 112 determines whether or not there is a “chunk” having a predetermined number or more of Δ judgment frames in the central M × M frame. If there is, the process proceeds to step 1511; otherwise, the process proceeds to step S1506. In FIG. 16, the predetermined number here is set to 2, for example.

  In step S <b> 1506, the system control unit 112 determines whether or not there is a “chunk” of a predetermined number or more of Δ determination frames in the N × N AF frames so as to include one or more of the central M × M frames. judge. Then, the system control unit 112 proceeds to step S1511 when there are “a lump” of Δ determination frames equal to or larger than the predetermined number in the N × N AF frames, and proceeds to step S1507 otherwise. In FIG. 16, it is assumed that the predetermined number here is 4, for example.

  In step S <b> 1507, the system control unit 112 determines whether or not there are “a lump” of a predetermined number or more of “◯” determination frames in the central M × M frame, and “a lump” of “O” determination frames is a predetermined number or more. If so, the process proceeds to step S1512; otherwise, the process proceeds to step S1508. In FIG. 16, the predetermined number here is set to 5, for example. In step S1508, the system control unit 112 determines whether or not the center frame is “x” determination. If the center frame is “x” determination, the process proceeds to step S1511; otherwise, the process proceeds to step S1509.

  In step S <b> 1509, the system control unit 112 determines whether or not there is a “chunk” that is greater than or equal to a predetermined number of Δ determination frames or × determination frames in the central M × M frame. Then, the system control unit 112 proceeds to step S1511 if there is a “chunk” having a predetermined number or more of Δ judgment frames or x judgment frames, and proceeds to step S1510 otherwise. In FIG. 16, the predetermined number here is set to 2, for example.

  In step S1510, the system control unit 112 determines whether or not there is a “chunk” of a predetermined number or more of Δ judgment frames or × judgment frames in all the N × N frames so as to include one or more central M × M frames. Determine whether or not. Then, the system control unit 112 proceeds to step S1511 if there is a “chunk” of Δ determination frames or x determination frames at a predetermined number or more, and otherwise proceeds to step S1512. In FIG. 16, the predetermined number is 4 as an example.

  In step S1511, the system control unit 112 determines that “the zone is to be updated” and ends the determination process. In step S1512, the system control unit 112 determines that “zone update is not performed” and ends the determination process.

  For example, when N = 5 and M = 3, the area shown by hatching in FIG.

  Next, with reference to FIG. 17, the uniform surface determination process in step S811 of FIG. 8 will be described. Here, the “state that is a uniform surface” is a state in which a focus evaluation value peak cannot be sufficiently obtained even when AF is performed because there is no luminance difference in the screen and no contrast. If the subject area specifying AF scan in step S209 in FIG. 2 is repeated every time the photographing scene is stabilized in the “uniform surface state”, the focus change on the screen is repeated unnecessarily, which is troublesome. Therefore, in this uniform surface determination process, when “a state of a uniform surface” is determined, an operation of stopping the focus lens 104 is performed until “a state of a uniform surface” is not determined.

  In FIG. 17, in step S1701, the system control unit 112 performs uniform surface determination described in FIG. 18 to be described later, and proceeds to step S1702. In step S1702, in the uniform surface determination in step S1701, it is determined whether or not the shooting scene is determined to be a uniform surface. If it is determined to be a uniform surface, the process proceeds to step S1703; This determination process is terminated. In step S1703, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 to a predetermined position, and proceeds to step S1704. Here, the predetermined position is, for example, a hyperfocal distance including infinity on the infinity side of the subject depth.

  In step S1704, the system control unit 112 determines whether the state of the release switch (SW1) 118 that instructs to prepare for shooting is on or off. If it is on, the system control unit 112 ends the determination process and proceeds to step S214 in FIG. If YES in step S1705, the flow advances to step S1705. In step S1705, the uniform surface determination described later with reference to FIG. 18 is performed, and the process proceeds to step S1706. In step S1706, in the uniform plane determination in step S1705, it is determined whether or not the shooting scene is determined to be a uniform plane. If it is determined to be a uniform plane, the process returns to step S1704. This determination process ends, and the process returns to step S201 in FIG.

  With the above processing, the focus lens 104 can be stopped until the “uniform surface” is not reached.

  Next, the uniform surface determination processing in steps S1701 and S1705 of FIG. 17 will be described with reference to FIGS. Here, based on the luminance information in the screen and the focus evaluation value, it is determined whether or not the state is a “uniform surface”. FIG. 19 is a diagram illustrating the uniform surface determination of FIG. In FIG. 19A, the X portion indicates a “state that is a uniform surface”, and the Y portion indicates a “state that is not a uniform surface”.

  In FIG. 18, in step S1801, the system control unit 112 determines whether or not the set AF frame is one frame. If it is one frame, the process proceeds to step S1805. If not, the system control unit 112 proceeds to step S1802. move on.

  In step S1802, the system control unit 112 calculates “the difference between the luminance integrated value of the screen center M × M frame and the luminance integrated values of the four corner M × M frames in the entire screen N × N frame”. The process proceeds to step S1802.

  More specifically, for example, assuming that the frame size is 10%, N = 5, and M = 3, when the X portion of the landscape in FIG. The integral value is obtained by integrating the luminance values in the hatched area indicated by A in FIG. Further, the integrated luminance value of each of the four corner M × M frames in the entire screen N × N frame is obtained by integrating the luminance values of the hatched areas shown in B, C, D, and E in FIG. Become. Assuming that the luminance integration value A of the center M × M frame of the screen is B, C, D, and E, the luminance integration values of the four corner M × M frames are AB, AC, AD, and AE. Is the difference between the integrated luminance value of the screen center M × M frame and the integrated luminance values of the four corner M × M frames in the entire screen N × N frame.

  In step S1803, the system control unit 112 calculates the difference between “the luminance integrated value of the screen center M × M frame and the luminance integrated values of the four corner M × M frames in the entire screen N × N frame” calculated in step S1802. ”Is determined whether there is a luminance difference greater than or equal to a predetermined value. The system control unit 112 proceeds to step S1807 if there is a luminance difference greater than or equal to a predetermined value, otherwise proceeds to step S1804. In step S1804, the system control unit 112 calculates (for example, adds) the focus evaluation value of each AF frame of the center M × M frame as a new focus evaluation value, and proceeds to step 1805.

  In step S1805, the system control unit 112 determines whether or not the focus evaluation value is greater than or equal to a predetermined value. If the focus evaluation value is greater than or equal to the predetermined value, the process proceeds to step S1807; otherwise, the process proceeds to step S1806. In step S1806, the system control unit 112 determines that the shooting scene is “a uniform surface” and ends the determination process. In step S <b> 1807, the system control unit 112 determines that the shooting scene is “not a uniform surface” and ends the determination process.

  Accordingly, in the “state that is a uniform surface” as in the X portion of FIG. 19A, it can be determined that it is “uniform surface”, and “one” as in the Y portion of FIG. 19A. In the “non-surface state”, it can be determined that “the surface is not uniform”.

  Next, the focus driving process in step S813 of FIG. 8 will be described with reference to FIG.

  In FIG. 20, in step S2001, the system control unit 112 determines whether or not the main subject area has been specified. If the main subject area has been specified, the process proceeds to step S2002. Otherwise, the process proceeds to step S2003. In step S2002, the system control unit 112 causes the AF processing unit 105 to drive the focus lens 104 to the closest position in the selected AF frame, and ends this processing. In step S2003, the system control unit 112 determines whether or not there is a ◯ determination in the center M × M frame. If there is a ◯ determination, the process proceeds to step S2004, and if not, the process proceeds to step S2005.

  In step S2004, the system control unit 112 causes the AF processing unit 105 to drive the focus lens 104 to the closest position among the ◯ determinations in the center M × M frame, and ends this processing. In step S2005, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 to a position (fixed point) stored in advance in the DRAM 110, and ends this processing. Here, for example, the fixed point is set to a distance having a high probability of existence of the subject.

  Next, the continuous AF processing in step S211 of FIG. 2 will be described with reference to FIG.

  In FIG. 21, in step S2101, the system control unit 112 sets the focus degree determination flag to TRUE, and the process proceeds to step S2102. In step S2102, the system control unit 112 acquires a focus evaluation value for each set AF frame, and the process advances to step S2103.

  In step S2103, the system control unit 112 determines whether or not the set AF frame is one frame. If the set AF frame is one frame, the process proceeds to step S2105; The process proceeds to S2104. In step S2104, the system control unit 112 resets the evaluation value calculated using the focus evaluation value of the AF frame selected as the main subject area as the focus evaluation value used in step S2105 and thereafter, and the process proceeds to step 1205. Thereby, even if the photographing scene changes and the main subject area in the screen changes, the focus evaluation value of the main subject area in the screen can always be calculated.

  In step S2105, the system control unit 112 calculates the degree of focus based on the focus evaluation value, and proceeds to step S2106. In the present embodiment, the degree of focus is determined in three stages of high, medium, and low based on the focus evaluation value. In step S2106, the system control unit 112 determines whether the state of the release switch (SW1) 118 that instructs to prepare for shooting is on or off. If the switch is on, the system control unit 112 ends the determination process and proceeds to step S215 in FIG. If the process proceeds and is off, the process proceeds to step S2107.

  In step S2107, the system control unit 112 performs the scene change determination (see FIG. 5) described above, and proceeds to step S2108. In step S2108, the system control unit 112 determines whether or not the peak detection flag is TRUE. If it is TRUE, the system control unit 112 proceeds to step S2125, and if it is FALSE, the system control unit 112 proceeds to step S2109.

  In step S2109, the system control unit 112 acquires the current position of the focus lens 104, and proceeds to step S2110. In step S2110, the system control unit 112 adds 1 to an acquisition counter for counting acquisition of the focus evaluation value and acquisition of the current position of the focus lens 104, and the process proceeds to step S2111. This acquisition counter is set to 0 in advance in an initialization operation (not shown). In step S2111, the system control unit 112 determines whether or not the value of the acquisition counter is 1. If the value of the acquisition counter is 1, the process proceeds to step S2114. If the value of the acquisition counter is not 1, the system control unit 112 proceeds to step S2112. Proceed to

  In step S2112, the system control unit 112 determines whether or not “current focus evaluation value” is larger than “previous focus evaluation value”. If larger, the process proceeds to step S2113; The process proceeds to S2120. In step S2113, the system control unit 112 adds 1 to the increase counter and proceeds to step S2114. In step S2114, the system control unit 112 stores the current focus evaluation value as the maximum value of the focus evaluation value in a calculation memory (hereinafter referred to as a built-in memory) built in the system control unit 112, and the process proceeds to step S2115.

  In step S2115, the system control unit 112 stores the current position of the focus lens 104 in the built-in memory as the peak position of the focus evaluation value, and proceeds to step S2116. In step S2116, the system control unit 112 stores the current focus evaluation value in the built-in memory as the previous focus evaluation value, and proceeds to step S2117. In step S2117, the system control unit 112 determines whether or not the current position of the focus lens 104 is at the end of the distance measurement range. If it is at the end of the distance measurement range, the system control unit 112 proceeds to step S2118; The process proceeds to step S2119.

  In step S2118, the system control unit 112 reverses the moving direction of the focus lens 104 by the AF processing unit 105, and the process proceeds to step S2119. In step S2119, the AF processing unit 105 moves the focus lens 104 by a predetermined amount, and the process ends.

  In step S2120, the system control unit 112 determines whether or not “the maximum value of the focus evaluation value−the current focus evaluation value” is greater than a predetermined amount, and if greater than the predetermined amount, the system control unit 112 proceeds to step S2121. If so, the process proceeds to step S2116. Here, when “the maximum value of the focus evaluation value−the current focus evaluation value” is larger than the predetermined amount, that is, when the predetermined value is decreased from the maximum value, the maximum value is regarded as a value at the focus peak position.

  In step S2121, the system control unit 112 determines whether or not the increase counter is greater than 0. If the increase counter is greater than 0, the process proceeds to step S2122; otherwise, the process proceeds to step S2116. In step S2122, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 to the peak position where the focus evaluation value stored in step S2115 is the maximum value, and the process proceeds to step S2123. In step S2123, the system control unit 112 sets the peak detection flag to TRUE and proceeds to step S2124. In step S2124, the system control unit 112 sets the acquisition counter to 0, and proceeds to step S2119.

  In step S2125, the system control unit 112 determines whether or not the current focus evaluation value has fluctuated by a predetermined ratio or more with respect to the maximum value of the focus evaluation value. The process proceeds to S2127, and if not, the process proceeds to Step S2126. In step S2126, the AF processing unit 105 stops the focus lens 104 and holds it at the stop position, and the process proceeds to step S2119.

  In step S2127, the system control unit 112 resets the maximum value and peak position of the focus evaluation value by setting the peak detection flag to FALSE to recalculate the focus lens position where the focus evaluation value is maximized, and the process proceeds to step S2128. . In step S2128, the system control unit 112 resets the increase counter and proceeds to step S2119.

  As described above, in continuous AF, the focus lens 104 is driven so that the main subject is always in focus.

  Next, with reference to FIG. 22, the process of determining scene instability in step 212 of FIG. 2 will be described.

  In FIG. 22, in step S2201, the system control unit 112 determines whether or not the camera operation amount detected by the angular velocity sensor is equal to or greater than a predetermined amount. If it is equal to or greater than the predetermined amount, the process proceeds to step S2205. If not, the process proceeds to step S2202. In step S2202, the system control unit 112 determines whether or not the luminance change amount from the previous time is greater than or equal to a predetermined amount. If it is greater than or equal to the predetermined amount, the system control unit 112 proceeds to step S2205, otherwise proceeds to step S2203.

  In step S2203, the system control unit 112 determines whether or not the subject detection state (for example, the face detection state) detected by the subject detection module 120 has changed. If the subject detection state has changed, the process proceeds to step S2205. If not, the process proceeds to step S2204. Here, the subject detection state is, for example, whether or not a face is detected. That is, if the face is detected in the previous scene instability determination and the face is not detected in the current scene instability determination, the face detection state has changed.

  In step S2204, the system control unit 112 determines that the shooting scene has not changed, and ends this process. In step S2205, the system control unit 112 determines that the shooting scene has changed, and ends this process.

  Next, with reference to FIG. 23, the photographing process in step S215 of FIG. 2 will be described.

  In FIG. 23, in step S2301, the system control unit 112 performs AE processing for main exposure by the AE processing unit 103, and the process proceeds to step S2302. In step S2302, the system control unit 112 performs AF for main exposure described later with reference to FIG. 25, and the process proceeds to step 2303.

  In step S2303, the system control unit 112 determines whether the state of the release switch (SW2) 119 instructing the photographing operation is on or off. If it is on, the process proceeds to step S2305. If it is off, the process proceeds to step S2304. move on. In step S2304, the system control unit 112 determines whether the state of the release switch (SW1) 118 for instructing shooting preparation is on or off. If it is on, the process returns to step S2303. If it is off, the process returns to step S2307. move on.

  In step S2305, the system control unit 112 sets the PeakPos update flag to FALSE, and proceeds to step S2306. In step S2306, the system control unit 112 performs main exposure processing described with reference to FIG. 30 described later, and proceeds to step S2313. In step S2313, the system control unit 112 clears the variable Sw1Contour indicating that the release switch (SW1) 118 is turned on, that is, the release button has been pressed halfway, and ends this processing.

  In step S2307, the system control unit 112 increments Sw1Counter and proceeds to step S2308. Note that Sw1Counter is initialized to 0 when the camera is activated. In step S2308, the system control unit 112 determines whether or not the release switch (SW1) 118 has been turned on the number of times exceeding the predetermined threshold value by comparing Sw1Counter with the predetermined threshold value. That is, it is determined whether or not the release button has been pressed halfway a number of times exceeding a predetermined threshold. Then, the system control unit 112 proceeds to step S2309 if the release switch (SW1) 118 has been turned on the number of times exceeding the predetermined threshold, and ends this process otherwise.

  In step S2309, the system control unit 112 obtains the peak position of the main subject area obtained before the release switch (SW1) 118 is turned on and the peak position of the main exposure AF when the release switch (SW1) 118 described later is turned on. The difference between both peak positions is calculated by comparison. If the difference between the two peak positions is equal to or greater than the predetermined value, the system control unit 112 proceeds to step S2310. This processing takes into consideration that the subject has moved when the release switch (SW1) 118 is on.

  In step S2310, the system control unit 112 sets the PeakPos update flag to TRUE, and proceeds to step 2311. In step S2311, the system control unit 112 performs main subject region update described with reference to FIG. 24 described later, and proceeds to step S2312. In step S2312, the system control unit 112 performs the above-described focus drive (see FIG. 20), and ends this process.

  Next, with reference to FIG. 24, the main subject area update process in step S2311 of FIG. 23 will be described.

  In FIG. 24, in step S2701, the system control unit 112 determines whether or not the set AF frame is one frame. If the set AF frame is one frame, the process proceeds to step S2712, and so on. If not, the process proceeds to step S2702. In step S2702, the system control unit 112 increments the counter P indicating the closest order of the peak positions in the M × M frame calculated in step S1202 of FIG. 12, and proceeds to step 2703. In step S2703, the system control unit 112 determines whether or not the counter P is larger than the sort number S. If the counter P is larger than the sort number S, the system control unit 112 proceeds to step S2711. Otherwise, the process proceeds to step S2704. .

  In step S2704, the system control unit 112 sets the P-th PeakPos as PeakPosP in the sort order, and proceeds to step S2705. In step S2705, the system control unit 112 determines ◯ in the center M × M AF frames, and detects a “chunk” of the AF frames within a predetermined depth range with respect to PeakPosP. Then, the system control unit 112 stores the number of AF frames constituting the “chunk” and the position of each AF frame in the DRAM 110, and the process proceeds to step S2706. As described above, when there are a plurality of “chunks”, one of the “chunks” is selected based on the number of AF frames constituting the “chunk” and the position of the “chunks”. May be.

  In step S2706, the system control unit 112 makes a ◯ determination so that one or more of the central M × M AF frames are included in the central N × N AF frames, and within a predetermined depth with respect to PeakPosP. Detects a “chunk”. Then, the system control unit 112 stores the number of AF frames constituting the “chunk” and the position of each AF frame in the DRAM 110, and proceeds to step S2707. In step S2707, the system control unit 112 determines whether the “chunk” detected in step S2705 or step S2706 is a “chunk” including the central frame. If the system control unit 112 includes the central frame, the system control unit 112 proceeds to step S2712. Otherwise, the system control unit 112 proceeds to step S2708.

  In step S2708, the system control unit 112 determines whether or not the “chunk” detected in step S2705 or step S2706 is a “chunk” that includes a predetermined number or more in the M × M frame. The system control unit 112 proceeds to step S2713 if it is a “cluster” including a predetermined number or more in the M × M frame, and proceeds to step S2709 otherwise.

  In step S <b> 2709, the system control unit 112 determines that the “chunk” detected in step S <b> 2705 or step S <b> 2706 is a “chunk” including one frame out of the central M × M frames and a predetermined number or more of AF frames in the N × N frame. It is determined whether or not there is. The system control unit 112 proceeds to step S2713 if it is a “chunk” including one frame of the central M × M frame and including a predetermined number or more of AF frames in the N × N frame, otherwise proceeds to step S2713. The process proceeds to S2710.

  In step S2710, the system control unit 112 adds 1 to the counter P (increment), and proceeds to step S2711. In step S2712, the system control unit 112 determines whether or not the in-focus determination result in step S1201 of FIG. 12 is ◯. If yes, the process proceeds to step S2713. If not, the process proceeds to step S2711. move on. In step S2713, the system control unit 112 determines that the main subject area has been identified, and the process proceeds to step S2714.

  In step S2714, the system control unit 112 determines and selects each AF frame constituting the cluster as a main subject area, and the process proceeds to step S2715. Here, when one AF frame is set, that one frame is selected. In step S2715, the system control unit 112 sets the peak detection flag to TRUE and ends the update process. In step S2711, the system control unit 112 determines that the main subject area has not been specified, and ends the update process.

  Next, with reference to FIG. 25, the main exposure AF process in step S2302 of FIG. 23 will be described.

  In FIG. 25, in step S2401, the system control unit 112 determines whether or not the main subject detection flag is TRUE. If it is TRUE, the system control unit 112 proceeds to step S2402, and if not TRUE, the system control unit 112 proceeds to step S2403. In step S2402, the system control unit 112 sets the AF frame setting for main exposure to, for example, AF frame setting 1 described later, and proceeds to step S2404. On the other hand, in step S2403, the system control unit 112 sets the AF frame setting for main exposure to, for example, AF frame setting 2 described later, and proceeds to step S2410.

  The frame number setting here is different from N × N set in step S803 in FIG. In this embodiment, in order to reduce the calculation amount of the AF evaluation value, the frame setting L × L is set such that N> L. As the frame size, a frame size that satisfies SizeN <SizeL is set in order to improve the S / N ratio.

  The frame setting may be determined based on the detection result of the main subject. If the main subject has been detected, in step S2402, AF frame setting 1 is set such that N> L and SizeN <SizeL in order to reduce the calculation amount of the AF evaluation value and improve the S / N ratio. If the main subject is not detected, a fine subject is photographed in the frame set for main subject detection, and there is a possibility that a phenomenon such as background loss has occurred. Therefore, in order to increase the resolution of main subject detection, AF frame setting 2 may be set in step S2403 such that N <L ′ and SizeN> SizeL ′. 26, 27 and 28 show examples in which the number of frames is increased or decreased with AF frame settings 1 and 2. FIG.

  In step S2404, the system control unit 112 determines whether or not the degree of focus calculated in step S2105 in FIG. 21 is “high”. If the degree of focus is “high”, the process proceeds to step S2405. If the focus level is not “high”, the process proceeds to step S2406.

  In step S2405, the system control unit 112 sets the scan range 1 around the current position of the focus lens 104, and proceeds to step S2411. Here, a narrow scan range is set by determining that the focus lens 104 is positioned in a state where the main subject is substantially in focus by the continuous AF operation, that is, in the vicinity of a focus position where the focus evaluation value shows a peak.

  In step S2406, the system control unit 112 determines whether or not the focus degree calculated in step S2105 in FIG. 21 is “medium”. If the focus degree is “medium”, the process proceeds to step S2407. If the degree of focus is not “medium”, the process proceeds to step S2408.

  In step S2407, the system control unit 112 sets the scan range 2 around the current position of the focus lens 104, and proceeds to step S2411. Here, the focus lens is positioned near the in-focus position by the continuous AF operation. However, it is determined that the in-focus degree is not as high as the “high” state, and the range that is wider than the scan range 1 is the scan range. Set as 2.

  In step S2408, the system control unit 112 determines whether or not the current position of the focus lens 104 is a macro area. If the current position is the macro area, the process proceeds to step S2409, and if not, the process proceeds to step S2410. In step S2409, the system control unit 112 sets a scan range 3 that is a macro area stored in advance, and the process advances to step S2411. In step S2410, the system control unit 112 sets the scan range 4 that is the entire range of distance measurement stored in advance, and proceeds to step S2411.

  In step S2411, the system control unit 112 performs AF for main exposure described later with reference to FIG. 29, and proceeds to step S2412. In step S2412, the system control unit 112 moves the focus lens 104 to the peak position calculated in step S2506 of FIG. 29 described later, and ends this process.

  Next, with reference to FIG. 29, the main-exposure AF scan process in step S2411 in FIG. 25 will be described.

  In FIG. 29, in step S2501, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 to the scan start position, and proceeds to step S2502. Here, the scan start position is the end position of the scan ranges 1 to 4 set in steps S2405, S2407, S2409, and S2410 in FIG. In step S2502, the system control unit 112 converts the analog video signal read from the image sensor 106 into a digital signal by the A / D conversion unit 107. The system control unit 112 stores the high-frequency component of the luminance signal extracted from the output of the A / D conversion unit 107 by the image processing unit 108 as a focus evaluation value in the DRAM 110, and proceeds to step S2503.

  In step S2503, the system control unit 112 acquires the current position of the focus lens 104, stores the acquired position data in the DRAM 110, and proceeds to step S2504. In step S2504, the system control unit 112 determines whether or not the current position of the focus lens 104 is equal to the scan end position. If both positions are equal, the process proceeds to step S2506; otherwise, the process proceeds to step S2505. move on.

  In step S2505, the system control unit 112 causes the AF processing unit 105 to move the focus lens 104 by a predetermined amount toward the scan end position, and then returns to step S2502. In step S2506, the system control unit 112 calculates the peak position of the focus evaluation value based on the focus evaluation value stored in step S2502 and its lens position, and ends this process. Here, when calculating the peak position of the focus evaluation value, when a plurality of AF frames are set, the calculation is performed based on the closest peak position of the main subject area determined by the main subject area determination described in FIG. Alternatively, the peak position may be calculated by another method.

  Next, with reference to FIG. 30, the main exposure processing in step S2306 in FIG. 23 will be described.

  In FIG. 30, in step S2601, the system control unit 112 exposes the image sensor 106, and the process proceeds to step S2602. In step S2602, the system control unit 112 reads the data accumulated in the image sensor 106, and proceeds to step S2603. In step S2603, the system control unit 112 converts the analog signal read from the image sensor 106 by the A / D conversion unit 107 into a digital signal, and the process proceeds to step S2604.

  In step S2604, the system control unit 112 performs various image processing on the digital signal output from the A / D conversion unit 107 by the image processing unit 108, and the process proceeds to step S2605. In step S2605, the system control unit 112 compresses the image processed in step S2604 according to a format such as JPEG, and the process advances to step S2606. In step S2606, the system control unit 112 records the compressed data in the image recording unit 111, and ends the main exposure process.

  As described above, in the present embodiment, it is possible to focus on the subject to be focused at high speed.

  In addition, this invention is not limited to what was illustrated to the said embodiment, In the range which does not deviate from the summary of this invention, it can change suitably.

  The present invention can also be realized by executing the following processing. That is, the present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus execute the program. It can also be realized by a process of reading and executing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

104 Focus lens 105 AF processing unit 106 Image sensor 108 Image processing unit 110 DRAM
111 Image Recording Unit 112 System Control Unit 118 Release Switch (SW1)
119 Release switch (SW2)
120 Subject detection module

Claims (5)

An imaging device that drives a focus lens to a position where a subject is in focus based on image data output from an imaging means,
Receiving means for receiving a shooting preparation instruction;
Specifying means for performing a scanning operation for specifying a subject area to be focused from a plurality of subject areas before the accepting means accepts the shooting preparation instruction;
When the accepting unit accepts the imaging preparation instruction, the focus lens is driven so that the subject area to be focused is brought into focus based on a scan operation different from the scan operation by the specifying unit. Focus control means,
Display means for displaying on the display unit the subject area brought into focus by the focus control means,
The focus control unit displays the subject area in the focused state by the display unit on the display unit, and then displays the display when the receiving unit receives the shooting preparation instruction in a state where the shooting scene does not change. An imaging apparatus, wherein a subject area different from the subject area displayed on the screen is selected, and the focus lens is driven so that the selected subject area is in focus.   The focus control unit displays the subject area in a focused state by the display unit on the display unit, and then when the receiving unit receives a plurality of the shooting preparation instructions in a state where the shooting scene does not change, The imaging apparatus according to claim 1, wherein a subject area different from the subject area displayed on the display unit is selected.   The focusing control means includes a focusing position obtained by a scanning operation by the specifying means before the accepting means accepts the photographing preparation instruction, and an specifying means after the accepting means accepts the photographing preparation instruction. The subject area different from the subject area displayed on the display unit is selected when the difference between the focus position obtained by the scan operation different from the scan operation is a predetermined value or more. The imaging device described in 1. A control method for an imaging apparatus that drives a focus lens to a position where a subject is in focus based on image data output from an imaging means,
A reception step for receiving a shooting preparation instruction;
A specifying step of performing a scanning operation for specifying a subject area to be focused from a plurality of subject areas before receiving the photographing preparation instruction in the receiving step;
When the imaging preparation instruction is received in the receiving step, the focus lens is driven based on a scanning operation different from the scanning operation in the specific step so that the subject area to be focused is in focus. A focusing control step;
A display step of displaying on the display unit the subject area that is in focus in the focus control step, and
The focus control step displays the subject area in the focus state in the display step on the display unit, and then receives the shooting preparation instruction in the reception step in a state where the shooting scene does not change. A method for controlling an imaging apparatus, comprising: selecting a subject area different from the subject area displayed on the screen and driving the focus lens so that the selected subject area is in focus.   A program for causing a computer to execute each step of the method for controlling an imaging apparatus according to claim 4.