JP2007206433A - Focusing apparatus, imaging apparatus, and control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide focusing technology for improving following property to a moving object by scanning during continuous photographing, and also, performing scanning-setting for improving the following property. <P>SOLUTION: The center position in a moving extent in the case of moving the focus lens during the continuous photographing is calculated on the basis of the stored position of the focus lens at the past photographing, and a focal state is obtained by shifting the moving range of the focus lens in accordance with the calculated center position, and the focus lens is moved from the focal state to a position focused on the object. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a focus adjustment technique.

  In an electronic camera, focus adjustment is performed with the lens position where the high-frequency component of the luminance signal of the subject image formed on the image sensor is maximized as the focus position where the desired subject image is in focus. A high-frequency component of the luminance signal of the subject image means that the contrast of the subject image is high, indicating that the subject is in focus compared to the case where it is low (hereinafter, the focus evaluation value is used as an index indicating the in-focus state). And). This is a so-called contrast detection type focus adjustment technique (for example, “NHK Technology Research Report (Showa 40, Vol. 17, No. 1, No. 86, pages 21 to 37)”). In such a contrast detection method, there is a case where a scanning operation, which is an operation of acquiring a focus state in the range by moving the focus lens in a predetermined range, may be performed. Then, the focus lens is moved to a position where the subject is in focus.

  Since such an operation is performed, in so-called continuous shooting with a short shooting interval, the time for performing the scanning operation is limited, and it becomes difficult to capture the in-focus position. In addition, the load on the system increases due to various image processing such as development and conversion of images that are successively captured in continuous shooting. For these reasons, during continuous shooting, the focus is often locked at the focus lens position of the first imaging.

  On the other hand, in general, continuous shooting often captures a moving subject. This is a serious problem considering that it is technically possible to increase the number of shootings in continuous shooting. That is, in the focus lock as described above, as the number of times of shooting increases, an out-of-focus image that is not focused on the moving subject is shot.

To deal with this problem, for example, Patent Document 1 describes that the scanning range is changed based on the movement direction of the in-focus position until the time of continuous photographing.
JP 2002-122773 A

  Japanese Patent Application Laid-Open No. H10-228561 discloses that the distribution width of the scanning range is made different. However, when the amount of movement of the subject is large, the in-focus position is out of the scan range.

  Accordingly, an object of the present invention is to provide a focus adjustment technique that improves the followability to a moving subject while securing time for acquiring a focus state.

  In order to achieve the above-described object, the technical idea related to the focus adjustment disclosed in the present application is that the focus lens driving means for driving the focus lens and the focus lens are moved in a predetermined range, and the predetermined range is adjusted. Control means for determining the focus state based on an output signal from the image pickup means obtained along with the movement of the focus lens and controlling the drive means so that the subject image is in focus, and obtained by the control means Storage means for storing the focus position of the focus lens, and the control means calculates a reference position of a moving range when the focus lens is moved based on the position of the focus lens stored in the storage means Then, the movement range of the focus lens is shifted in the subject movement direction in accordance with the calculated reference position.

  Further, another technical idea is that an output from a driving unit that drives a focus lens and an imaging unit obtained by moving the focus lens in a predetermined range and moving the focus lens in the predetermined range. A control unit that determines the focus state based on the signal and controls the driving unit so that the subject image is in focus; and an instruction unit that instructs to perform imaging a plurality of times. In this case, the control means determines the focus state by moving the focus lens within the predetermined range at a predetermined speed before each imaging a plurality of times, and determines the focus state before moving at the predetermined speed. The focus lens is moved to a position for determining the focus state at a speed faster than the predetermined speed.

  According to the technical idea related to the focus adjustment of the present invention, it is possible to dramatically improve the followability to a moving subject while shortening the time required for the focus adjustment operation.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a main part of an electronic camera to which an embodiment of the present invention is applied.

  Reference numeral 101 denotes a photographing lens including a zoom mechanism, reference numeral 102 denotes an aperture and shutter for controlling the amount of light, reference numeral 103 denotes an AE processing unit, and reference numeral 104 denotes a focus lens as a focus adjustment optical system for focusing on an image sensor described later. Reference numeral 105 denotes an AF processing unit. The AF processing unit 105 will be described in the description of FIG. Reference numeral 106 denotes a strobe, 107 denotes an EF processing unit, and 108 denotes an image sensor as light receiving means or photoelectric conversion means for converting reflected light from a subject into an electric signal.

  Reference numeral 109 denotes a CDS circuit that removes output noise of the image sensor 108 and an A / D conversion unit including a non-linear amplification circuit performed before A / D conversion, 110 an image processing unit, and 111 a WB processing unit. 112 is a format conversion unit, 113 is a high-speed built-in memory (for example, random access memory, hereinafter also referred to as DRAM), 114 is an image recording unit comprising a recording medium such as a memory card and its interface, 115 is a shooting sequence, etc. A system control unit 116 for controlling the system is an image display memory (hereinafter also referred to as VRAM). In addition to image display, 117 is an operation display unit that displays a shooting screen and a distance-measuring area at the time of shooting, and 118 is an operation unit for operating the camera from the outside. . Reference numeral 119 denotes a shooting mode switch for setting shooting modes such as a program, landscape, person, and sports, and 120 denotes a drive mode switch for setting drive modes such as single shooting, continuous shooting (continuous shooting), and self-timer shooting. Here, the continuous shooting mode is a mode in which image recording is repeated while a photographing switch SW2, which will be described later, is pressed.

  Reference numeral 121 denotes an AF mode switch that selects a continuous AF mode that continues to focus on the subject without pressing SW1, which will be described later, and a single AF mode that focuses after the scanning operation and then maintains the focus lens position. is there. 122 is a main switch for powering on the system, 123 is a switch for performing a shooting standby operation such as AF and AE (hereinafter referred to as SW1), and 124 is a shooting switch for performing shooting after the operation of SW1 (hereinafter referred to as SW1). (Denoted as SW2).

  The DRAM 113 is used as a high-speed buffer as temporary image storage means, or a working memory for image compression / decompression. The operation unit 118 includes, for example, the following. There are a menu switch for performing various settings such as a shooting function of the image pickup apparatus and a setting at the time of image reproduction, a zoom lever for instructing a zoom operation of the shooting lens, an operation mode switching switch between a shooting mode and a playback mode, and the like.

  Hereinafter, the operation flow of the electronic camera described above will be described in detail with reference to FIG. The following operation flow is an operation based on a control process performed by the system control 115 unless otherwise specified.

  First, the state of the main switch 122 is detected in step S201, and if it is ON, the process proceeds to step S202. Here, the function of the main switch 122 is to turn on the system. In step S202, the remaining capacity of the image recording unit 114 is checked. If the remaining capacity is 0, the process proceeds to step S203, and if not, the process proceeds to step S204. In step S203, a warning is given that the remaining capacity of the image recording unit 114 is 0, and the process returns to step S201. The warning may be displayed on the operation display unit 117, a warning sound may be emitted from a voice output unit (not shown), or both may be performed.

  In step S204, it is detected whether the AF mode is the continuous AF mode or the single AF mode. If it is the continuous AF mode, the process proceeds to step S205, and if it is the single AF mode, the process proceeds to step S206. In step S205, continuous AF is performed according to the flowchart of FIG.

  In step S206, the state of the switch SW1 is checked. If it is ON, the process proceeds to step S208, and if not, the process proceeds to step S207. Here, the function of SW1 is to perform a shooting standby operation such as AF or AE. In step S207, the state of the main switch 122 is checked. If it is ON, the process proceeds to step S204, and if not, the process proceeds to step S201. In step S208, the AE processing unit 103 performs AE processing from the output of the image processing unit 110.

  In step S209, an AF operation is performed according to the flowchart of FIG. In step S210, the state of SW2 is checked. If ON, the process proceeds to step S212, and if not, the process proceeds to step S211. Here, the function of SW2 is to perform photographing after operation of SW1. In step S211, the state of SW1 is checked. If it is not ON, the process returns to step S204. If it is ON, the process returns to step S210, and the focus is locked until SW2 is turned ON or SW1 is turned OFF. In step S212, the photographing operation is performed according to the flowchart of FIG. In step S213, the remaining capacity of the image recording unit 114 is checked. If the remaining capacity is 0, the process proceeds to step S203, and if not, the process proceeds to step S214.

  In step S214, it is detected whether the continuous shooting mode is set by the drive mode switch 120 or whether the continuous shooting mode is set to the default shooting mode by the shooting mode switch 119. If it is the continuous shooting mode, the process proceeds to step S216; otherwise, the process proceeds to step S215. In step S215, the captured image is displayed on the display unit 117 while SW2 is ON. If SW2 is OFF, the process proceeds to step S211. In step S216, if SW2 is not ON, the process proceeds to step S211. If SW2 is ON, the process returns to step S209 for continuous shooting, and the process proceeds to an AF operation in the continuous shooting mode according to the flowchart of FIG.

  Hereinafter, the continuous AF subroutine of S205 in the flowchart of FIG. 2 will be described with reference to the flowchart of FIG. 3 is a flowchart of a subroutine of continuous AF (step S205) in the flowchart of FIG. 2, and the AF processing unit 105 and the like perform processing based on the control processing of the system control unit 115.

  First, in step S301, a focus evaluation value is acquired as a result of processing in the AF processing unit 105. In step S302, the system control unit 115 checks whether the peak detection flag is TRUE. If it is TRUE, the system control unit 115 proceeds to step S317, and if not TRUE, the system control unit 115 proceeds to step S303. In step S303, the current position of the focus lens 104 is acquired. In step S304, 1 is added to the acquisition counter for counting acquisition of the focus evaluation value and acquisition of the current position of the focus lens 104. This acquisition counter is set to 0 in advance in an initialization operation (not shown). In step S305, it is checked 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 S307, and if the value of the acquisition counter is not 1, the process proceeds to step S306.

  In step S306, it is checked whether “current focus evaluation value” is larger than “previous focus evaluation value”. If “current focus evaluation value” is larger than “previous focus evaluation value”, the process proceeds to step S307; otherwise, the process proceeds to step S313. In step S307, the current focus evaluation value is stored as a maximum focus evaluation value in a calculation memory (not shown) built in the system control unit 115. In step S308, the current position of the focus lens 104 is stored in a calculation memory (not shown) built in the system control unit 115 as the peak position of the focus evaluation value. In step S309, the current focus evaluation value is stored as a previous focus evaluation value in a calculation memory (not shown) built in the system control unit 115. In step S310, it is checked whether or not the current position of the focus lens 104 is at the end of the distance measurement scan range. If the current position of the focus lens 104 is at the end of the scan range, the process proceeds to step S311; otherwise, the process proceeds to step S312. In step S311, the moving direction of the focus lens 104 is reversed. In step S312, a signal is output to move the focus lens 104 by a predetermined amount.

  In step S313, it is checked whether or not “maximum focus evaluation value−current focus evaluation value” is greater than a predetermined amount. If “the maximum value of the focus evaluation value−the current focus evaluation value” is larger than the predetermined amount, the process proceeds to step S314; otherwise, the process proceeds to step S309. Here, if “the maximum value of the focus evaluation value−the current focus evaluation value” is larger than the predetermined amount, that is, if the predetermined value is decreased from the maximum value, the peak position corresponding to the maximum value is regarded as the in-focus position. In step S314, the focus lens 104 is moved to the peak position corresponding to the maximum focus evaluation value stored in step S308. In step S315, the peak detection flag is set to TRUE. In step S316, the acquisition counter is set to zero.

  In step S317, the system control unit 115 checks whether or not the current focus evaluation value has changed by a predetermined ratio or more with respect to the maximum focus evaluation value. If there is a large change of a predetermined ratio or more, the process proceeds to step S319, and if it is a small change, the process proceeds to step S318. In step S318, the position of the focus lens 104 is held as it is. In step S319, the peak detection flag is set to FALSE to reset the focus lens position at which the focus evaluation value is maximized, and the maximum value and peak position of the focus evaluation value are reset.

  As described above, the focus lens is driven so as to be always in focus in the continuous AF operation.

  Hereinafter, the subroutine of the AF operation in step S209 in the flowchart of FIG. 2 will be described with reference to the flowchart of FIG. 4 and FIG. FIG. 4 is a flowchart of the AF operation (step S209) subroutine in the flowchart of FIG. 2 and is based on the control processing of the system control unit 115. FIG. 5 is a diagram for explaining a scan range setting method, in which the horizontal axis indicates the number of times of photographing and the vertical axis indicates the position of the focus lens.

  First, in step S401, it is checked whether the continuous shooting mode is set by the drive mode switch 120 or whether the continuous shooting mode is set to the default shooting mode by the shooting mode switch 119. If it is the continuous shooting mode, the process proceeds to step S412; otherwise, the process proceeds to step S402.

  In step S402, the AF mode switch 121 checks whether the AF mode setting is the continuous AF mode or the single AF mode. If it is the continuous AF mode, the process proceeds to step S403, and if it is not the continuous AF mode, the process proceeds to step S405. In step S403, it is checked whether or not the peak detection flag in the flowchart of FIG. 3 is TRUE. If it is TRUE, the process proceeds to step S404, and if it is not TRUE, the process proceeds to step S405.

  In step S404, a scan range having a predetermined narrow scan width centered on the current focus lens position is set mainly for the purpose of improving the focusing accuracy. This is because the focus lens is positioned in the vicinity of the in-focus position where the focus evaluation value shows the maximum value by the continuous AF operation.

  Here, the setting of the scan range in S404 is set so as to satisfy the number of scan data necessary for focus determination according to the flowchart of FIG. 7 described later and at the same time, the scan time is not unnecessarily increased. Further, the speed of the focus lens during scanning may be changed for each scan. For example, the speed of the focus lens may be increased during the scanning operation on the near side. This takes into account that the image plane speed is higher on the close side.

  On the other hand, in step S405, the entire scannable range corresponding to the set mode is set as the scan range.

  In step S406, a scan operation of the scan range set in step S404 or step S405 is performed according to the flowchart of FIG. In step S407, in-focus determination is performed from the in-focus state acquired in step S406 according to the flowchart of FIG.

  In step S408, if the result of focus determination in step S407 is “◯”, the process proceeds to step S409, and if “x”, the process proceeds to step S410. In step S410, it is checked whether or not the entire scanable range in the set mode has been scanned. If the entire area scan has been completed, the process proceeds to step S411. If the entire area scan has not been completed, the process returns to step S405. In step S409, the focus lens 104 is moved to the peak position calculated in the scan operation in step S406 or step S418 described later. In step S411, the focus lens 104 is moved to a preset position called a fixed point.

  The AF operation so far corresponds to the AF operation at the time of imaging other than the continuous shooting mode, and the setting of the scan range is changed depending on the set AF mode (continuous AF mode, single AF mode). On the other hand, the AF operation when the continuous shooting mode is set will be described next.

  In step S <b> 412, the system control unit 115 checks whether it is the first continuous shooting. If it is the first continuous shooting, the process proceeds to step S403. If it is not the first continuous shooting, the process proceeds to step S413. In the first continuous shooting, the operation is the same as that of continuous AF. This expects that a narrower scan range is set in step S404 than in the case via S405, and the release time lag is shortened.

  In step S413, the system control unit 115 checks whether or not it is the second continuous shooting. If it is the second continuous shooting, the process proceeds to step S414, and if it is not the second continuous shooting, the process proceeds to step S415. In step S414, the position (peak position FP1) of the focus lens 104 at the time of the first continuous imaging is set as the center ObjP2 as the reference position of the scan range. The scan range is set with priority given not to extend the time between images during continuous shooting. This is because the AF operation can be completed between shootings in consideration of processing performed during continuous shooting, for example, the readout time of the image signal from the image sensor and the check time for the next shooting operation. Set the scan range.

In step S415, the system control unit 115 checks whether or not it is the third continuous shooting. If it is the third continuous shooting, the process proceeds to step S416, and if it is not the third continuous shooting, the process proceeds to step S417. In step S416, there is information on the two in-focus positions (peak positions FP1, FP2) of the first and second continuous shooting as the in-focus position history information. Assuming that the time between continuous shooting is constant, subject distance prediction (prediction of peak position at the time of the third imaging) is performed by primary approximation, and the center position ObjP3 is obtained as a reference position of the scan range from Equation (1). Ask.
ObjP3 = FP2 + (FP2-FP1) × FpAdj3 (1)
The parameter FpAdj (n) is a parameter for setting the weighting of the result of the object distance prediction and the immediately previous in-focus position, and takes a value of 0 to 1. In the drawing showing the focus lens position in FIG. 5, FpAdj (n) is 1. A scan range is set based on the center position ObjP3 calculated in this way, and the subject image is shifted from the previous scan range in the moving direction.

In step S417, there is information on at least three in-focus positions as the in-focus position history information. Therefore, if the time between continuous shootings is constant, subject distance prediction (prediction of peak position at the time of current imaging) is performed by quadratic approximation, and the center position ObjP4 is expressed as an equation ( 2) Find from. A scan range is set based on the center position ObjP4 calculated in this manner, and the subject image is shifted from the previous scan range in the moving direction.
ObjP4 = (FP1-3FP2 + 3FP3) × FpAdj4 + FP3 (1-FpAdj4)
= (FP1-3FP2 + 2FP3) × FpAdj4 + FP3 (2)
Similarly, in the fifth and subsequent continuous shooting, subject distance prediction (prediction of peak position at the time of current imaging) is performed by secondary approximation, and the center position ObjP (n) is used as the reference position of the scan range. Obtained from equation (3). A scan range is set based on the center position ObjP (n) calculated in this way, and the subject image is shifted from the previous scan range in the moving direction.
ObjP (n) = (FP (n−1) −3FP (n−2) + 2FP (n)) × FpAdj (n) + FP (n−1) (3)
In step S418, scanning is performed according to the flowchart of FIG. 6 described later, and in step S409, the focus lens 104 is moved to the peak position (may be the peak position in the previous shooting).

  It should be noted that the focus determination as in step S407 is not performed after the second continuous shooting. This is because even when the focus determination result according to the flowchart of FIG. 7 to be described later is “×”, the peak position at the time of the previous shooting is taken rather than shooting by driving the focus lens 104 to the fixed point. This is because it is considered that there is a high possibility of blurring when shooting with the camera.

  In the description of the above embodiment, in the case of the first shooting (S412), the mode is shifted to the same mode as the continuous AF mode. In this regard, by performing the following in the continuous shooting mode, the center position for the first shooting can be calculated. That is, when the continuous shooting mode is set, setting is made in advance so as to shift to the continuous AF mode in S204 of FIG. In this way, the center position can be calculated and predicted from the first time during continuous shooting from the information on the focal point before SW1.

  Hereinafter, the subroutine of the scanning operation (steps S406 and S418) in the flowchart of FIG. 4 will be described with reference to the flowchart of FIG. FIG. 6 is a flowchart of the subroutine of the scanning operation (steps S406 and S418) in the flowchart of FIG. 4 and is based on the control processing of the system control unit 115.

  First, in step S601, the focus lens 104 is moved to a scan start position at a speed faster than the speed during the scan operation.

  In this embodiment, the scan start position is set at one end of the set scan range. Although there may be a case where it is not one end as in the present embodiment, there is a case where time is required for the scanning operation. In step S602, the focus evaluation value of the area corresponding to the AF frame set in the imaging area and the position of the focus lens 104 are stored in a calculation memory (not shown) built in the system control unit 115. In step S603, it is checked whether or not the lens position is at the scan end position. If it is the end position, the process proceeds to step S605; otherwise, the process proceeds to step S604. The scan end position is set at the other end of the set scan range. In step S604, the focus lens 104 is driven and moved in a predetermined direction by a predetermined amount. In step S605, the peak position of the focus lens corresponding to the position where the focus evaluation value is maximized is calculated from the focus evaluation value stored in step S602 and its lens position.

  FIG. 12 is a diagram showing the movement of the focus lens in the time of continuous shooting by time transition. That is, at the time of the first shooting, the system control unit 115 controls the focus lens to move from the current position a1 to the scan start position a2 at a speed higher than the speed during the scanning operation. Thereafter, the scanning operation is performed from the scanning start position a2. As a result, the focus lens stops at the peak position FP1, and at the time of the second shooting, the FP1 moves as the current focus lens position b1 to the scan start position b2 at a speed faster than the speed during the scanning operation. The unit 115 controls. Further, the peak position FP2 at the time of the second photographing is set as the current position C1 of the focus lens, and is moved to the scan start position C2 calculated as described above at high speed.

  Similarly, in d1 to d2, the focus lens is moved faster than the subsequent scanning operation. By doing so, it is possible to secure a sufficient scan range and perform focus adjustment with high follow-up even when the subject distance moves greatly.

  The in-focus determination subroutine (step S407) in the flowchart of FIG. 4 will be described below with reference to FIGS.

  FIG. 10 shows a mountain-shaped in-focus state where the horizontal axis represents the focus lens position and the vertical axis represents the focus evaluation value. Whether or not the focus evaluation value appears in such a mountain shape 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 greater than a certain value (SlopeThr), and the inclination. Judging from the slope of the part. Thereby, in-focus determination is performed. The determination result in the focus determination is output as “◯” or “×” as shown below.

  “◯” indicates that the focus of the subject can be adjusted from the peak position of the focus evaluation value. “X” indicates that the contrast of the subject is insufficient or the subject is located at a distance outside the scanned distance range.

  Here, as shown in FIG. 10, points that are recognized to be inclined from the top of the mountain (point A) are point D and point E, and the width of point D and point E is the width of mountain L and point A. The sum SL1 + SL2 of the focus evaluation value difference SL1 at point D and the focus evaluation value difference SL2 between point A and point E is SL.

  FIG. 7 is a flowchart of the focus determination (step S407) subroutine in the flowchart of FIG. 4 and is based on the control processing of the system control unit 115.

  First, in step S701, the maximum and minimum focus evaluation values and the scan point io that gives the maximum value are obtained. In step S702, a variable L representing the peak width of the focus evaluation value and a variable SL representing the mountain gradient are both initialized to zero. In step S703, it is checked whether or not the scan point io giving the maximum value is the far end position in the predetermined range where the scan was performed. If not, the process proceeds to step S704 and the monotonic decrease in the infinity direction is checked. . If it is the far end position, this process is skipped and the process proceeds to step S705.

  Here, the processing for checking the monotonic decrease in the infinity direction in step S704 will be described. The flowchart is shown in FIG.

First, in step S801, a counter variable i is initialized to io. In step S802, the difference between the focus evaluation value d [i] at the scan point i and the focus evaluation value d [i-1] at the scan point i-1 that is one scan point away from i at a predetermined distance is predetermined. Compare with the value SlopeThr. If d [i] −d [i−1]> = SlopeThr, it is determined that a monotonic decrease in the infinity direction has occurred, and the process proceeds to step S803. Then, 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 updated according to the following equations.
L = L + 1,
SL = SL + (d [i] -d [i-1])
On the other hand, if d [i] −d [i−1]> = SlopeThr, it is determined that no monotonic decrease in the infinity direction has occurred, and the process for checking the monotonic decrease in the infinity direction is terminated. The process proceeds to step S705.

  When the process of checking the monotonic decrease in the infinity direction is continued, the process proceeds to step S804, and i = i−1 is set, and the point to be detected is moved to the one scan point infinity side. In step S805, it is checked whether or not the counter i has reached the value (= 0) of the far end position in the predetermined range in which scanning has been performed. If the value of the counter i is 0, that is, if the starting point for detecting the monotonic decrease has reached the far side end position in the predetermined range where the scan has been performed, the processing for checking the monotonic decrease in the infinity direction is terminated, and step S705 is completed. Proceed to

  As described above, the monotonic decrease from i = io to infinity is checked.

  In step S705, 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 scan is performed. If not, the process proceeds to step S706 and monotonously decreases in the near end direction. Investigate. If it is the close end position, this process is skipped and the process proceeds to step S707.

  Here, the processing for checking the monotonic decrease toward the closest end in step S706 will be described. The flowchart is shown in FIG.

First, in step S901, the counter variable i is initialized to io. In step S902, the difference between the focus evaluation value d [i] at the scan point i and the focus evaluation value d [i + 1] at the scan point i + 1 from the nearest end by one scan point from i is defined as a predetermined value SlopeThr. Compare. If d [i] -d [i + 1]> = SlopeThr, it is determined that a monotonic decrease in the closest end direction has occurred, and the process proceeds to step S903. Then, 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 updated according to the following equations.
L = L + 1,
SL = SL + (d [i] -d [i + 1])
On the other hand, if d [i] −d [i + 1]> = SlopeThr, it is determined that no monotonic decrease in the closest end direction has occurred, and the processing for checking the monotonic decrease in the close end direction is terminated. The process proceeds to step S707.

  When the process of checking the monotonic decrease in the near end direction is continued, the process proceeds to step S904, i = i + 1 is set, and the point to be detected is moved to the one scan point closest end side. In step S905, it is checked whether or not the counter i has reached the value (= N) of the closest end position in a predetermined range in which scanning has been performed. If the value of the counter i is N, that is, the start point for detecting the monotonic decrease has reached the closest end position in the predetermined range in which scanning has been performed, the processing for checking the monotonic decrease in the near end direction is terminated, and step The process proceeds to S707.

  As described above, the monotonic decrease from i = io toward the near end is checked.

  When the process of checking the monotonic decrease in the infinity direction and the near-end direction is completed, whether the obtained focus evaluation value is mountain-like or not is compared with each threshold value, Make a judgment of ○ ×.

  In step S707, the scan point io giving the maximum focus evaluation value is the closest end in the predetermined range where the scan was performed, and the focus evaluation value d [n] at the closest end scan point n is calculated from n. If the difference in the focus evaluation value d [n-1] at the scan point n-1 from infinity for one scan point is equal to or greater than the predetermined value SlopeThr, the process proceeds to step S711. Otherwise, the process proceeds to step S708. In step S708, the scan point io giving the maximum focus evaluation value is the far end in the predetermined range where the scan was performed, and the focus evaluation value d [0] at the far end scan point 0 is 0. If the difference in the focus evaluation value d [1] at the scan point 1 from the closest end for one scan point is greater than or equal to the predetermined value SlopeThr, the process proceeds to step S711. Otherwise, the process proceeds to step S709.

  In step S709, the length L of the portion inclined with a gradient equal to or greater than a certain value is equal to or greater than a predetermined value Lo, and the average value SL / L of the gradient of the inclined portion is equal to or greater than the predetermined value SLo / Lo. If the difference between the maximum and minimum focus evaluation values is greater than or equal to a predetermined value, the process proceeds to step S710. Otherwise, the process proceeds to step S711. In step S710, the obtained focus evaluation value has a mountain shape, and the determination result is “◯” because the focus of the subject can be adjusted. In step S711, since the obtained focus evaluation value is not mountain-shaped and the focus of the subject cannot be adjusted, the determination result is “x”.

  As described above, the focus determination in step S407 in the flowchart of FIG. 4 is performed.

  Hereinafter, the subroutine of the imaging operation in step S212 in the flowchart of FIG. 2 will be described with reference to the flowchart of FIG. FIG. 11 is a flowchart of the subroutine of the photographing operation (step S212) in the flowchart of FIG. 2, and is based on the control process of the system control unit 115.

  First, in step S1101, the subject brightness is measured. In step S1102, the image sensor 108 is exposed according to the subject brightness measured in step S1101. The image formed on the image sensor surface is photoelectrically converted into an analog signal, which is sent to the A / D converter 109 in step S1103, and after preprocessing such as output noise removal and nonlinear processing of the image sensor 108. Converted to a digital signal. In step S1104, the output signal from the A / D conversion unit 109 is white balance adjusted by the image processing unit 110 by the WB processing unit 111 to obtain an appropriate output image signal. In step S 1105, the output image signal is converted into an image format such as a JPEG format by the format converter 112 and temporarily stored in the DRAM 113. In step S1106, the data in the DRAM 113 is transferred and stored in the image recording unit 114 to an external storage medium such as a memory in the camera or a memory card attached to the camera.

  The setting of the narrow scan width described above is not limited to the uniform scan width setting. For example, if the scan center position based on subject prediction is far from the previous shooting position, the subject movement amount is considered to be large, so the scan width is set wide within the range where the AF operation ends within the continuous shooting shooting interval. It is also effective. In addition, the above-described scan range width setting is not limited as long as focusing can be prioritized and the continuous shooting interval time may be extended.

  In the above description, the center position ObjP (n) of the scan range is calculated. However, it may be a reference position that defines the scan range, not necessarily the center position of the scan range. For example, a position shifted by a predetermined position from the center position of the scan range to the tele side may be used. A reference position suitable for calculation can be obtained.

  In the above description, the method for determining the scan range may be determined from the time of the scan operation and the speed of the focus lens during the scan.

  As described above, according to the focus adjustment technique described in the present embodiment, the subject movement prediction is performed based on the history of the focus position so far. At this time, by calculating the center position of the scan range, it is possible to provide a focus adjustment technique with improved followability to a moving subject.

It is a block diagram which shows the structure of the electronic camera in an Example. It is a flowchart figure showing operation | movement of the electronic camera in an Example. FIG. 3 is a flowchart of a subroutine of continuous AF (S205) in FIG. FIG. 3 is a flowchart of a subroutine of AF operation (S209) in FIG. It is explanatory drawing of the scanning range setting method in FIG. FIG. 5 is a flowchart of a scan (S406, S418) subroutine in FIG. FIG. 5 is a flowchart of a subroutine for focus determination (S407) in FIG. It is explanatory drawing of the operation | movement which calculates | requires the monotonous decrease | decrease in an infinite direction. It is explanatory drawing of the operation | movement which calculates | requires the monotone decrease of a near end direction. It is a figure for demonstrating the concept of determination of a focus evaluation value. FIG. 5 is a flowchart of a shooting operation subroutine in FIG. 4. It is a transition diagram of focus lens movement in the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Shooting lens 102 Aperture and shutter 103 AE processing unit 104 Focus lens 105 AF processing unit 106 Strobe 107 EF processing unit 108 Image sensor 109 A / D conversion unit 110 Image processing unit 111 WB processing unit 112 Format conversion unit 113 DRAM
114 Image recording unit 115 System control unit 116 VRAM
117 Operation display section 118 Operation section 119 Shooting mode switch 120 Drive mode switch 121 AF mode switch 122 Main switch 123 Shooting standby switch 124 Shooting switch

Claims (9)

Focus lens driving means for driving the focus lens;
The focus lens is moved in a predetermined range, a focus state is determined based on an output signal from the imaging means obtained along with the movement of the focus lens in the predetermined range, and the subject image is in a focused state. Control means for controlling the drive means to be
Storage means for storing the focus position of the focus lens obtained by the control means,
The control means calculates a reference position of a moving range when the focus lens is moved based on the position of the focus lens stored in the storage means, and the focus lens of the focus lens is calculated according to the calculated reference position. A focus adjusting apparatus characterized by shifting a moving range in a subject moving direction.   2. The control unit according to claim 1, wherein when the movement range of the focus lens is shifted in a subject movement direction, the control unit moves a range wider than the movement range based on the calculation of the reference position to determine a focus state. Focusing device.   The control means stores the position of the focus lens in a focused state, and calculates the reference position based on the stored position of the focus lens. The focus adjustment device described in 1.   The focus adjustment apparatus according to claim 1, wherein the control unit calculates the reference position during continuous shooting. Driving means for driving the focus lens;
The focus lens is moved in a predetermined range, a focus state is determined based on an output signal from the imaging means obtained along with the movement of the focus lens in the predetermined range, and the subject image is in a focused state. Control means for controlling the drive means to be
An instruction means for instructing to perform imaging a plurality of times,
When there is an instruction from the instruction means, the control means judges the focus state by moving the focus lens within the predetermined range at a predetermined speed before each of the plurality of imaging operations, and determines the focus state. A focus adjustment apparatus, wherein the focus lens is moved at a speed faster than the predetermined speed to a position where the focus state is determined before the movement at.   5. The focus adjustment apparatus according to claim 4, wherein the focus lens is moved before the movement at each predetermined speed so that the movement range at the predetermined speed is shifted as the subject moves.   An imaging apparatus comprising: the focus adjustment apparatus according to claim 1; and an imaging element. A focus lens driving means for driving the focus lens, and a focus state based on an output signal from the imaging means obtained by moving the focus lens in a predetermined range and moving the focus lens in the predetermined range Control of the focus adjustment apparatus including control means for controlling the drive means so that the subject image is in focus, and storage means for storing the focus position of the focus lens obtained by the control means. A method,
Based on the position of the focus lens stored in the storage means, the reference position of the movement range when moving the focus lens is calculated, and the subject is moved in the movement range of the focus lens according to the calculated reference position. A control method characterized by controlling to shift in a direction. A focus unit is determined based on an output signal from a driving unit that drives the focus lens and an image signal obtained by moving the focus lens within a predetermined range and moving the focus lens within the predetermined range. And a control method for the focus adjustment apparatus, comprising: a control unit that controls the driving unit so that a subject image is in focus; and an instruction unit that instructs to perform imaging a plurality of times.
When there is an instruction from the instruction means, the focus lens within a predetermined range is moved at a predetermined speed before each imaging for a plurality of times to determine the focus state, and before the movement at the predetermined speed. And moving the focus lens to a position for determining the focus state at a speed faster than the predetermined speed.

Images