JP5868163B2 - IMAGING DEVICE, IMAGING DEVICE CONTROL METHOD, PROGRAM - Google Patents

Description

  The present invention relates to an imaging device, an imaging device control method, and a program. Specifically, the present invention relates to an imaging apparatus such as an electronic still camera or a video camera, a control method for the imaging apparatus, and a program for controlling the imaging apparatus.

Conventionally, in electronic still cameras and video cameras, as a focusing method that moves the focus lens position and focuses on the subject, autofocus is performed automatically using an image signal obtained from an image sensor such as a CCD. The (AF) method is used. In this AF method, there is a technique of speeding up by determining the subject peak position from the shape of the focus evaluation value and changing the focus speed at a position away from the subject peak position during the AF scan operation.
For example, a ratio between the change amount of the focus evaluation value and the change amount of the lens position within a predetermined time is calculated as an evaluation value change rate, and the lens position is changed depending on whether the evaluation value change rate is in an increasing state or a decreasing state. Some change speed. (See Patent Document 1)
Also, the peak position is predicted from three points where the focus evaluation value is increasing, and the variation in the prediction result is driven within a predetermined range. When the increase becomes near 0 before that, the focus is stopped, and the predicted peak position is far away. In some cases, the object is moved at a high speed and then re-predicted at a low speed. (See Patent Document 2)

Japanese Patent Laid-Open No. 7-7650 JP-A-8-29667

When an AF scan method that acquires a focus evaluation value while driving the focus lens is applied, there is a time lag between the determination of being near the subject peak position and the speed control. In addition, when the camera settings such as the contrast, frequency, aperture, and exposure of the subject are different, the shape of the focus evaluation value is different. As a result, when determining the subject peak position based on the shape of the focus evaluation value, depending on the subject, it is not in time to decelerate to a predetermined speed that is a sampling interval that can secure AF accuracy up to the vicinity of the subject peak position. There is a problem of end.
However, Patent Literature 1 and Patent Literature 2 do not consider the time lag from the determination of the shape of the focus evaluation value to the speed control. Also, the method of determining the peak shape of the focus evaluation value is not changed according to the setting of the subject or camera. For this reason, depending on the setting of the subject and the camera, the speed control may not be in time for the subject peak position, resulting in poor focus accuracy.

In order to solve the above-described problems, the present invention provides an imaging unit that sequentially generates an imaging signal by photoelectrically converting light from a subject while the focus lens is moving, and a contrast of the subject from the imaging signal corresponding to a predetermined area. an imaging apparatus comprising: a generating means for generating a focus evaluation value, and a control unit for controlling the driving of the focus lens based on the focus evaluation value indicating the control unit, said at set scan range When a scan operation for driving the focus lens in one direction is performed and the focus lens is driven at a first speed during the scan operation, the gradient of the focus evaluation value with respect to the position of the focus lens is a first If equal to or greater than a threshold value, the change of the driving speed of the focus lens to the first speed smaller than the second speed, the first threshold value, before Contrast value of the subject, the frequency of the subject, the size of the predetermined area, aperture state, characterized in that it is set based on at least one of the driving speed of the current of the focus lens.

The present invention is a method for controlling an imaging apparatus, the step of photoelectrically converting light from a subject while a focus lens is moving to sequentially generate an imaging signal, and the imaging signal corresponding to a predetermined region from the imaging signal. Generating a focus evaluation value indicating contrast, controlling a drive of the focus lens based on the focus evaluation value , and performing a scan operation of driving the focus lens in one direction within a set scan range If, during that drives the focus lens at a first speed during said scanning operation, if the slope of the focus evaluation value with respect to the position of the focus lens is equal to or greater than a first threshold value, the focus lens the driving speed and a step of changing said first velocity less than the second speed, the first threshold value, the object to be Contrast value of the body, the frequency of the subject, the size of the predetermined area, aperture state, characterized in that it is set based on at least one of the driving speed of the current of the focus lens.

The present invention is a program to be executed by a computer of an imaging apparatus, the step of photoelectrically converting light from a subject during the movement of a focus lens to sequentially generate an imaging signal, and the imaging signal corresponding to a predetermined area Generating a focus evaluation value indicating the contrast of the object from the image, controlling the driving of the focus lens based on the focus evaluation value , and scanning operation for driving the focus lens in one direction within a set scan range And when the focus lens is driven at the first speed during the scanning operation and the gradient of the focus evaluation value with respect to the position of the focus lens is equal to or higher than a first threshold , and a step of changing the driving speed of the focus lens in the first speed is less than the second speed The first threshold value is set based on at least one of the contrast value of the subject, the frequency of the subject, the size of the predetermined region, the aperture state, and the current driving speed of the focus lens. And

  By changing how the focus lens is decelerated in the vicinity of the focus position in accordance with the setting of the subject and camera, AF can be performed with high accuracy and high speed regardless of the setting of the subject and camera.

FIG. 1 is a block diagram illustrating a configuration of an imaging apparatus to which an embodiment of the present invention is applied. FIG. 2 is a flowchart for explaining the operation of the imaging apparatus to which the embodiment of the present invention is applied. FIG. 3 is a flowchart for explaining the AF operation in FIG. 2 to which the embodiment of the present invention is applied. FIG. 4 is a flowchart for explaining the initial focus drive in FIG. 3 to which the embodiment of the present invention is applied. FIG. 5 is a flowchart for explaining the peak detection check in FIG. 4 to which the embodiment of the present invention is applied. FIG. 6 is a flowchart for explaining setting of the focus speed in FIG. 3 to which the embodiment of the present invention is applied. FIG. 7 is a flowchart for explaining focus evaluation value gradient detection in FIGS. 3 and 5 to which the embodiment of the present invention is applied. FIG. 8 is a flowchart for explaining the calculation of the focus evaluation value gradient threshold SlopeThr in FIGS. 3, 4 and 5 to which the embodiment of the present invention is applied.

Embodiments of the present invention will be described below with reference to FIGS.
First, an overall configuration of an imaging apparatus to which an embodiment of the present invention is applied will be described with reference to FIG. An imaging apparatus to which an embodiment of the present invention is applied is an electronic camera 1. FIG. 1 is a block diagram showing the configuration of an electronic camera 1 to which an embodiment of the present invention is applied. The photographing lens 101 is one or more lens groups including a zoom mechanism. The aperture and shutter 102 controls the amount of light. The AE processing unit 103 performs AE processing. The focus lens 104 focuses light from the subject on an image sensor 107 described later. The motor 105 is a drive source for driving the focus lens 104. The AF processing unit 106 performs AF processing. As the image sensor 107, light receiving means or photoelectric conversion means for converting light from a subject into an electrical signal is applied. The A / D converter 108 includes a CDS circuit that removes output noise of the image sensor 107 and a non-linear amplifier circuit that is performed before A / D conversion. The image processing unit 109 performs image processing. The format conversion unit 110 converts an output image into a predetermined standard format. DRAM 111 is a high-speed built-in memory such as a random access memory. The DRAM 111 is used as a high-speed buffer as temporary image storage means or a working memory for image compression / decompression. The image recording unit 112 includes a recording medium such as a memory card and its interface. The system control unit 113 controls the system such as a shooting sequence. The system control unit 113 includes a memory 131 that stores a computer program (software), and a CPU 132 that reads and executes the computer program stored in the memory 131. The VRAM 114 is an image display memory. The image display unit 115 performs image display, operation assistance display, and camera state display. Further, the image display unit 115 displays a shooting screen and a distance measurement area during shooting. The operation unit 116 is used for operating the electronic camera 1 from the outside. The operation unit 116 includes, for example, a menu switch for performing various settings such as a shooting function of the electronic camera 1 and a setting at the time of image reproduction, a zoom lever for instructing a zoom operation of the photographing lens, an operation mode switching switch between a shooting mode and a playback mode, including. The shooting mode switch 117 is a switch used to select a shooting mode such as a macro mode, a distant view mode, or a sports mode. The shooting mode switch 117 can change the distance measuring distance range, the AF operation, and the like according to the shooting mode selected by the user. The main switch 118 is a switch for turning on the system. A switch 119 (hereinafter also referred to as SW1) is a switch for performing a shooting standby operation such as AF or AE. The switch 120 (hereinafter sometimes referred to as SW2) is a photographing switch that performs photographing after the operation of SW1. The acceleration sensor unit 121 detects the movement of the electronic camera 1 due to camera shake or panning. The moving object detection unit 122 detects a moving object from the luminance information in the screen.

  Hereinafter, the operation of the electronic camera 1 to which the embodiment of the present invention is applied will be described in detail with reference to FIGS. The following processing is stored in the memory 131 of the system control unit 113 as a computer program (software), and is executed by the CPU 132 of the system control unit 113 reading and executing it.

First, the overall operation of the electronic camera 1 will be described with reference to FIG. FIG. 2 is a flowchart for explaining the operation of the electronic camera 1.
First, in step S <b> 201, the AE processing unit 103 executes AE processing using the output of the image processing unit 109. Then, the process proceeds to S202.
In S202, the system control unit 113 checks whether the state of the switch 119 (SW1) is “ON”. If it is ON (if “Yes”), the process proceeds to S203; otherwise (if “No”), the process proceeds to S201.
In S203, the system control unit 113 performs an AF operation described later. Then, the process proceeds to S204. Note that the exposure conditions (shutter speed, aperture, sensitivity) during the AF operation are determined in the immediately preceding AE process of S201.
In S204, the system control unit 113 checks whether the state of the switch 119 (SW1) is ON. If it is ON (if “Yes”), the process proceeds to S205; otherwise (if “No”), the process proceeds to S201.
In S205, the system control unit 113 checks whether the state of the switch 120 (SW2) is ON. If it is ON (if “Yes”), the process proceeds to S206; otherwise (if “No”), the process proceeds to S204.
In S206, the system control unit 113 performs a shooting operation. Then, the process proceeds to S201.

Next, the AF operation in S203 of the electronic camera 1 will be described with reference to FIG. FIG. 3 is a flowchart for explaining the AF operation in S203 in FIG.
In S301, the system control unit 113 sets a distance measurement area to a predetermined area in the screen. Then, the process proceeds to S302.
In S <b> 302, the system control unit 113 sets a scan range corresponding to the shooting mode and the focal length. Then, the process proceeds to S303.
In S303, the system control unit 113 performs initial focus driving. In this initial focus drive, the system control unit 113 drives the focus lens 104 via the AF processing unit 106 and moves the focus lens 104 to a predetermined AF scan start position. Details of the initial focus drive will be described later. Then, the process proceeds to S304.
In S304, the system control unit 113 sets the focus speed. The focus speed refers to the drive speed of the focus lens. A method for setting the focus speed will be described later. Then, the process proceeds to S305.
In S305, the system control unit 113 starts focus driving in a predetermined direction at the focus speed set in S304. The system control unit 113 sets the “predetermined direction” to a direction opposite to the driving direction of the focus lens 104 in the initial focus driving of S303. Then, the process proceeds to S306.
In S306, the system control unit 113 acquires the focus evaluation value in the distance measurement area set in S301. Then, the process proceeds to S307.
In step S307, the system control unit 113 acquires the current position of the focus lens 104. Then, the process proceeds to S308.
In S308, the system control unit 113 detects the gradient of the focus evaluation value based on the change in the focus lens position and the focus evaluation value. A specific detection method will be described later. Then, it progresses to S309.
In step S309, the system control unit 113 calculates the gradient evaluation value slope threshold SlopeThr. The focus evaluation value gradient threshold SlopeThr is a threshold used as an index for determining whether or not the focus lens 104 is in the vicinity of the focus position. A method for calculating the focus evaluation value gradient threshold SlopeThr will be described later. Thereafter, the process proceeds to S310.
In S310, the system control unit 113 determines whether the gradient of the focus evaluation value detected in S308 is equal to or greater than the value of the gradient threshold SlopeThr of the focus evaluation value calculated in S309, and whether the focus speed is set to “high speed”. Investigate. The focus speed checked in this step is set in S304 or S311 described later. If the detected gradient is equal to or greater than the calculated SlopeThr and the focus speed is set to a high speed (if “Yes”), the process proceeds to 311, otherwise (if “No”) 313. Proceed to
In S311, the system control unit 113 sets the focus speed to a low speed. Then, the process proceeds to S312. That is, when the system control unit 113 can determine that the current position of the focus lens 104 is in the vicinity of the focus position, the system control unit 113 sets the focus speed to a low speed. Thereafter, the process proceeds to S312.
In step S312, the system control unit 113 drives the focus lens 104 at the focus speed set in step S311 (= focus drive). As described above, according to the processes of S310 to S311 to S312, when the focus drive is started at a high speed when the AF scan starts, the focus lens can be decelerated when the vicinity of the focus position can be determined. Then, the process proceeds to S313.
In step S313, the system control unit 113 checks whether the current position of the focus lens 104 acquired in step S307 is within the scan range set in step S302. If the current position of the focus lens 104 is within the scan range (if “Yes”), the process proceeds to S306; otherwise (if “No”), the process proceeds to S314.
A series of processing of S306 to S313 is performed in a time corresponding to one frame of the current frame rate. Further, the system control unit 113 associates the focus evaluation value acquired in S306 with the lens position acquired in S307, and uses it in calculating the peak position of the focus evaluation value in S315 described later. The system control unit 113 drives the focus lens 104 via the AF processing unit 106 while acquiring the focus evaluation value. That is, the focus lens position corresponding to the focus evaluation value has a certain width. Therefore, the system control unit 113 calculates the position of the focus lens 104 at the center timing of the exposure time, and associates the calculated position of the focus lens 104 with the focus evaluation value.
In step S <b> 314, the system control unit 113 stops driving the focus lens 104 via the AF processing unit 106. Then, the process proceeds to S315.
In S315, the system control unit 113 calculates the peak position of the focus evaluation value using the focus evaluation value acquired in S306 and the position of the focus lens 104 associated therewith (acquired in S307). Then, the process proceeds to S316.
In S316, the system control unit 113 performs in-focus determination. Then, the process proceeds to S317.
In S317, the system control unit 113 drives the focus lens 104 to the peak position of the focus evaluation value obtained in S315 via the AF processing unit. Then, the AF operation ends.

Next, with reference to FIG. 4, the initial focus drive in S303 of FIG. 3 will be described. FIG. 4 is a flowchart for explaining the initial focus driving process in S303 of FIG.
First, in S401, the system control unit 113 sets the focus speed to a low speed. Here, for the “low speed” in the initial focus driving, for example, a minimum speed at which a gradient of a focus evaluation value described later can be determined is applied. Then, the process proceeds to S402.
In S402, the system control unit 113 starts focus driving in a predetermined direction via the AF processing unit 106 at the focus speed set in S401. As the “predetermined direction”, for example, a direction considered to have a high probability of existence of a subject, a direction toward either the far end or the near end with respect to the current focus lens position can be applied. Then, the process proceeds to S403.
In step S403, the system control unit 113 acquires a focus evaluation value in the distance measurement area set in step S301. Then, the process proceeds to S404.
In step S <b> 404, the system control unit 113 acquires the current position of the focus lens 104. Then, the process proceeds to S405.
In S405, the system control unit 113 performs a peak detection check. In the peak detection check, the system control unit 113 checks whether or not the peak of the focus evaluation value has been detected, and if not detected, whether the focus evaluation value has increased, decreased, or has not changed. To do. That is, the system control unit 113 checks a change in the focus evaluation value. Details of the peak detection check will be described later. Then, the process proceeds to S406.
In S406, the system control unit 113 checks whether the peak detection result checked in S405 is OK. If the peak detection result is OK, that is, if a peak is detected (if “Yes”), the process proceeds to S409; otherwise (if “No”), the process proceeds to S407.
In step S407, the system control unit 113 checks whether the peak detection result checked in step S405 is a decrease and whether the number of decreases is greater than a decrease count threshold. If the peak detection result is a decrease and the number of reductions is greater than the reduction number threshold (if “Yes”), the process proceeds to S409; otherwise (if “No”), the process proceeds to S408.
In step S408, the system control unit 113 checks whether the current position of the focus lens 104 has reached the end in the traveling direction. If reached (if “Yes”), the process proceeds to S409; otherwise (if “No”), the process proceeds to S403.
In step S409, the system control unit 113 calculates a focus evaluation value gradient threshold SlopeThr. The gradient evaluation value slope threshold SlopeThr serves as an index for determining whether or not the focus lens 104 is in the vicinity of the focus position. A method for calculating the gradient evaluation value slope threshold SlopeThr will be described later. Thereafter, the process proceeds to step S410.
In S410, the system control unit 113 checks whether or not the gradient of the focus evaluation value is equal to or greater than the gradient threshold SlopeThr of the focus evaluation value calculated in S409. This focus evaluation value is detected in gradient detection of the focus evaluation value in S502 described later. If the gradient of the focus evaluation value is equal to or greater than the gradient threshold value SlopeThr of the focus evaluation value (if “Yes”), the process proceeds to S411, otherwise (if “No”), the process proceeds to S412.
In step S411, the system control unit 113 sets the result of the FASTAF determination to “NG”. Then, the process proceeds to S413.
In step S <b> 412, the system control unit 113 sets the result of the FASTAF determination to “OK”. Then, the process proceeds to S413.
The result of FASTAF determination is one of the indexes for determining whether or not to start focus driving at high speed in S305, which is the AF scan operation start timing. The FASTAF determination is performed based on the gradient threshold value SlopeThr of the focus evaluation value, as shown in S411 and S412. Thus, when the focus lens 104 is not in the vicinity of the focus position, the result of the FASTAF determination is “OK”, and when the focus lens 104 is in the vicinity of the focus position, it is “NG”. The result of the FASTAF determination is used for setting the focus speed in S304 described later.
In step S <b> 413, the system control unit 113 stops the focus lens 104 via the AF processing unit 106. Then, the process proceeds to S304.

Next, the peak detection check process of S405 in FIG. 4 will be described with reference to FIG. FIG. 5 is a flowchart for explaining the peak detection check process of S405 in FIG.
First, in step S <b> 501, the system control unit 113 obtains the maximum and minimum focus evaluation values acquired in step S <b> 403 so far and stores them in the memory 131. Then, the process proceeds to S502.
In S502, the system control unit 113 calculates a gradient threshold value SlopeThr of the focus evaluation value (a calculation method will be described later). Thereafter, the process proceeds to step S503.
In step S <b> 503, the system control unit 113 detects a gradient of the focus evaluation value (a detection method will be described later). Thereafter, the process proceeds to S504.
In S504, the system control unit 113 checks whether or not the focus evaluation value acquired this time has increased by a predetermined amount or more with respect to the focus evaluation value acquired last time. If it has increased by a predetermined amount or more (if “Yes”), the process proceeds to S505; otherwise (if “No”), the process proceeds to S514.
In step S505, the system control unit 113 clears the decrease count (sets it to 0). Then, the process proceeds to S506.
In step S506, the system control unit 113 increments the number of increases (= the number of times that the focus evaluation value acquired this time has been determined to be greater than the focus evaluation value acquired last time). Then, the process proceeds to S507.
In step S507, the system control unit 113 checks whether the number of increases is greater than the acceleration / deceleration determination threshold value. The acceleration / deceleration determination threshold value is a threshold value that serves as an index when determining whether or not to set the focus speed to “high speed”. In the peak detection check, since it is desired to determine the direction of the subject focus position at the earliest possible stage, the acceleration / deceleration determination threshold value is a threshold value determined by, for example, the minimum number of times (for example, twice) at which the direction of the subject focus position can be determined. . If the number of increases is greater than the acceleration / deceleration determination threshold (if “Yes”), the process proceeds to S508; otherwise (if “No”), the process proceeds to S511.
In S508, the system control unit 113 checks whether or not the gradient of the focus evaluation value is equal to or greater than the gradient threshold SlopeThr of the focus evaluation value calculated in S502. If the gradient of the focus evaluation value is equal to or greater than the gradient threshold SlopeThr of the focus evaluation value (if “Yes”), the process proceeds to S509; otherwise (if “No”), the process proceeds to S510.
In step S509, the system control unit 113 sets the focus speed to “low speed”. Then, the process proceeds to S512.
In S510, the system control unit 113 sets the focus speed to “high speed”. Then, the process proceeds to S512.
In step S511, the system control unit 113 sets the result of the FASTAF determination to “OK”. Then, the process proceeds to S513.
In S512, the system control unit 113 sets the result of FASTAF determination to “NG”. Then, the process proceeds to S513.
In S513, the system control unit 113 sets the peak detection result to “increase”. Then, the process proceeds to S525.
In S514, the system control unit 113 checks whether or not the current focus evaluation value is smaller than a predetermined value with respect to the previous focus evaluation value. If it is less than the predetermined value (if “Yes”), the process proceeds to S515; otherwise (if “No”), the process proceeds to S521.
In S515, the system control unit 113 examines the following four items (1) to (4). (1) Whether the number of increases is 1 or more. (2) Whether the current focus evaluation value has decreased by a predetermined rate or more than the maximum focus evaluation value stored in S501. (3) Whether the difference between the maximum value and the minimum value stored in S501 is greater than or equal to a predetermined amount. (4) Is the peak position the end of the focus evaluation value data acquired so far? If all of (1) to (4) are satisfied (if “Yes”), the process proceeds to S520; otherwise (if “No”), the process proceeds to S516.
In S516, the system control unit 113 clears the increase count to zero. Then, the process proceeds to S517.
In S517, the system control unit 113 increments the decrease count. Then, the process proceeds to S518.
In step S518, the system control unit 113 sets FASTAF determination to OK. Then, the process proceeds to S519.
In S519, the system control unit 113 sets the peak detection result to “decrease”. Then, the process proceeds to S525.
In S520, the system control unit 113 sets the peak detection result to “OK”. In other words, the system control unit 113 determines that the peak of the focus evaluation value has been detected when it determines “Yes” in S515. Then, the process proceeds to S525.
In step S521, the system control unit 113 checks whether the number of times that the focus evaluation value has not changed is greater than the acceleration / deceleration determination threshold value. If there are many (if “Yes”), the process proceeds to S522; otherwise (if “No”), the process proceeds to S523.
In S522, the system control unit 113 sets the focus speed to “high speed”. Then, the process proceeds to S523.
In step S523, the system control unit 113 sets the FASTAF determination to “OK”. Then, the process proceeds to S524.
In S524, the system control unit 113 sets the peak detection result to “no change”. Then, the process proceeds to S525.
In S525, the system control unit 113 drives the focus lens 104 via the AF processing unit 106 at the set focus speed. Then, the process proceeds to S406.

  According to such processing, the system control unit 113 determines the focus position based on the manner of change in the focus evaluation value until the focus lens 104 is driven to the AF scan start position (that is, the shape of the focus evaluation value). Whether it is in the vicinity can be determined. Further, the system control unit 113 drives the focus lens 104 at a high speed when it is away from the focus position during focus driving, and drives the focus lens 104 at a low speed near the focus position. Thereby, the focus drive time can be shortened.

Next, the focus speed setting process of S304 in FIG. 3 will be described with reference to FIG. FIG. 6 is a flowchart for explaining the setting of the focus speed in S304 in FIG.
First, in step S601, the system control unit 113 checks whether the FASTAF determination is “OK”. If it is “OK” (if “Yes”), the process proceeds to S602; otherwise (if “No”), the process proceeds to S608.
In step S <b> 602, the system control unit 113 checks whether the amount of movement of the electronic camera 1 detected by the acceleration sensor unit 121 is equal to or less than a predetermined amount. If it is not more than the predetermined amount (if “Yes”), the process proceeds to S603, otherwise (if “No”), the process proceeds to S608. Thereby, in the focus evaluation value gradient detection in S308 and S502, which will be described later, it is possible to reduce the influence of erroneous detection caused by fluctuations in the focus evaluation value due to camera shake.
In step S <b> 603, the system control unit 113 checks whether the change in the angle of view detected by the moving object detection unit 122 is smaller than a predetermined value. If it is smaller than the predetermined amount (if “Yes”), the process proceeds to S604; otherwise (if “No”), the process proceeds to S608.
In S604, it is checked whether or not the brightness of the distance measurement area is within a predetermined range. If it is within the predetermined range (if “Yes”), the process proceeds to S605. If it is not within the predetermined range (if “No”), the process proceeds to S608.
In step S605, the system control unit 113 checks whether the focal length is longer than a predetermined value in the current camera setting. If it is longer than the predetermined (if “Yes”), the process proceeds to S606; otherwise (if “No”), the process proceeds to S608.
In step S606, the system control unit 113 checks whether the distance measurement distance range is longer than a predetermined value in the current camera setting. If the distance measurement distance range is longer than the predetermined range (if “Yes”), the process proceeds to S607; otherwise (if “No”), the process proceeds to S608.
In step S <b> 607, the system control unit 113 sets the focus speed to “high speed”. Then, the process proceeds to S305.
In step S608, the system control unit 113 sets the focus speed to “low speed”. Then, the process proceeds to S305.

Next, the focus detection value gradient detection process in S308 and S502 will be described with reference to FIG. FIG. 7 is a flowchart showing the contents of focus evaluation value gradient detection processing in S308 of FIG. 3 and S502 of FIG.
First, in S701, the system control unit 113 sets the current lens position acquired in S307 or S404 to “Pos1”. Then, the process proceeds to S702.
In S702, the system control unit 113 sets “T1” as the current focus evaluation value acquired in S306 or S403. Then, the process proceeds to S703.
In S703, the system control unit 113 sets “Pos2” as the previous lens position acquired in S307 or S404. Then, the process proceeds to S704.
In S704, the system control unit 113 sets “T2” as the previous focus evaluation value acquired in S306 or S403. Then, the process proceeds to S705.
In step S705, the system control unit 113 calculates the gradient of the focus evaluation value. The gradient of the focus evaluation value is
(Gradient of focus evaluation value) = (T1−T2) / (Pos1−Pos2)
Is calculated by Then, the process proceeds to S309 or S503.

Next, calculation of the gradient evaluation value slope threshold SlopeThr in S309 of FIG. 3, S409 of FIG. 4, and S503 of FIG. 5 will be described with reference to FIG. FIG. 8 is a flowchart showing processing for calculating the gradient evaluation value slope threshold SlopeThr in S309 of FIG. 3, S409 of FIG. 4, and S503 of FIG.
First, in step S801, the system control unit 113 checks the current aperture and the state of the shutter 102, and acquires the current aperture value. Then, the process proceeds to S802.
In step S802, the system control unit 113 acquires the size of the distance measurement area set in step S301. Then, the process proceeds to S803.
In step S803, the system control unit 113 acquires the contrast value in the distance measurement area set in step S301. Then, the process proceeds to S804. The “contrast value in the distance measurement area” is the difference between the maximum value and the minimum value of the luminance values in the distance measurement area set in S301. Thereby, even if the subject is not in focus, the contrast of the subject in the distance measurement area can be grasped to some extent.
In step S804, the system control unit 113 acquires the frequency within the distance measurement area set in step S301. Then, the process proceeds to S805. Various known methods can be applied to obtain the frequency within the distance measurement area. Therefore, detailed description is omitted.
In step S <b> 805, the system control unit 113 acquires the current focus speed of the focus lens 104. Then, the process proceeds to S806.
In S806, a reference value SlopeThr0 is determined. The reference value SlopeThr0 is a value that serves as a reference for the focus evaluation value gradient threshold SlopeThr when calculating the focus evaluation value gradient threshold SlopeThr in S807 described later. The reference value SlopeThr0 is determined in the setting of the reference subject and the electronic camera 1. Further, how to determine the reference value SlopeThr0 may be changed depending on the application. For example, in the initial focus drive in S303 of FIG. 3, the focus speed may be reduced at a position that exceeds the peak of the focus evaluation value of the subject so that the peak of the focus evaluation value of the subject can be detected during the AF scan operation performed later. . On the other hand, during the AF scan operation, the focus lens speed must be reduced before the peak position of the focus evaluation value of the subject is exceeded in order to ensure the necessary AF accuracy. Therefore, SlopeThr0 is changed in S409 or S502 during initial focus driving before AF scan and in S309 during AF scan operation. Specifically, the reference value SlopeThr0 in the initial focus drive is set to be larger than the reference value SlopeThr0 in the AF scan operation. Therefore, the value of the gradient threshold value SlopeThr of the focus evaluation value in the initial focus drive is larger than the value of the gradient threshold value SlopeThr of the focus evaluation value in the AF scan operation. According to such a configuration, in the initial focus drive, the focus lens 104 can be quickly moved to a predetermined scan start position. In the AF scan operation, AF accuracy can be increased. Then, the process proceeds to S807.
In step S <b> 807, the system control unit 113 calculates a focus evaluation value gradient threshold SlopeThr. The focus evaluation value gradient threshold SlopeThr is calculated by, for example, the following equation.

SlopeThr = SlopeThr0 × MMP × WinSize × Freq × (1 / Speed) × (1 / FNum)

FNum: coefficient determined by the aperture value MMP: coefficient determined by the contrast in the distance measurement area Freq: coefficient determined by the frequency in the distance measurement area WinSize: coefficient determined by the size of the distance measurement area Speed: coefficient determined by the focus speed

Hereinafter, the method of determining the above-described SlopeThr0 and each coefficient will be described. First, the F value (FNum0), the subject contrast value (MMP0), the subject frequency (Freq0), the distance measurement area size (WinSize0), and the focus speed (Speed0), which are the references, are temporarily determined. From the focus evaluation value peak shape under the condition, the slope of the focus evaluation value peak at the timing when the focus speed is desired to be decelerated is set to SlopeThr0. FNum is a coefficient determined by the aperture value. When the aperture value changes, the depth of focus changes and the gradient of the focus evaluation value peak changes. Therefore, FNum is used as a coefficient for changing SlopeThr according to the aperture value. As the aperture value increases, the depth of focus becomes deeper and the gradient becomes smaller.

FNum = current F value / FNum0

Calculate and decide on. MMP is a coefficient determined by the contrast in the distance measurement area. Since the gradient of the focus evaluation value peak increases as the contrast value increases, the MMP is, for example,

MMP = current subject contrast value / MMP0

Calculate and decide on. Freq is a coefficient determined by the frequency in the ranging area. Since the gradient of the focus evaluation value peak increases as the frequency of the subject increases, Freq is, for example,

Freq = Current subject frequency / Freq0

Calculate and decide on. WinSize is a coefficient determined by the size of the distance measurement area. As the size of the distance measurement area increases, the signal amount increases and the gradient of the focus evaluation value peak also increases.

WinSize = current WiSize / WinSize0

Calculate and decide on. Speed is a coefficient determined by the focus speed. Since the gradient of the focus evaluation value peak increases as the speed increases, the speed is, for example,

Speed = Current focus speed / Speed0

Calculate and decide on.
In this calculation formula, the gradient threshold value SlopeThr of the focus evaluation value is calculated using all of the coefficients as the reference value SlopeThr0. However, the calculation formula may be calculated using at least one of the coefficients. . According to such a calculation method, the gradient threshold value SlpeThr of the focus evaluation value is determined based on at least one of the contrast value of the subject, the frequency of the subject, the size of the ranging area, the aperture state, and the focus speed.
Thereby, even when the shape of the focus evaluation value differs depending on the setting of the subject and the camera, it is possible to appropriately determine the subject peak position. Then, the process proceeds to any of S310, S409, and S503.

  In this embodiment, the focus lens speed is adjusted at a low speed or a high speed binary value by determining whether the gradient of the focus evaluation value is larger than a predetermined threshold value. May be finely varied.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. A part of the above-described embodiments may be appropriately combined. Also, when a software program that realizes the functions of the above-described embodiments is supplied from a recording medium directly to a system or apparatus having a computer that can execute the program using wired / wireless communication, and the program is executed Are also included in the present invention. Accordingly, the program code itself supplied and installed in the computer in order to implement the functional processing of the present invention by the computer also realizes the present invention. That is, the computer program itself for realizing the functional processing of the present invention is also included in the present invention. In this case, the program may be in any form as long as it has a program function, such as an object code, a program executed by an interpreter, or script data supplied to the OS. As a recording medium for supplying the program, for example, a magnetic recording medium such as a hard disk or a magnetic tape, an optical / magneto-optical storage medium, or a nonvolatile semiconductor memory may be used. As a program supply method, a computer program that forms the present invention is stored in a server on a computer network, and a connected client computer downloads and programs the computer program.

  101: Shooting lens, 102: Aperture and shutter, 103: AE processing unit, 104: Focus lens, 105: Motor, 106: AF processing unit, 107: Image sensor, 108: A / D conversion unit, 109: Image processing unit 110: Format conversion unit, 111: DRAM, 112: Image recording unit, 113: System control unit, 114: VRAM, 115: Image display unit, 116: Operation unit, 117: Shooting mode switch, 118: Main switch, 119 : Shooting standby switch, 120: shooting switch, 121: acceleration sensor unit, 122: moving object detection unit

Claims (13)

An imaging unit that sequentially generates an imaging signal by photoelectrically converting light from the subject while the focus lens is moving, and a generation unit that generates a focus evaluation value indicating the contrast of the subject from the imaging signal corresponding to a predetermined area. An imaging device comprising: a control unit that controls driving of the focus lens based on the focus evaluation value ;
The control unit performs a scan operation for driving the focus lens in one direction within a set scan range, and when driving the focus lens at a first speed during the scan operation , If the slope of the focus evaluation value with respect to the position is equal to or greater than the first threshold value, to change the driving speed of the focus lens to said first speed is less than the second speed,
The first threshold value is set based on at least one of the contrast value of the subject, the frequency of the subject, the size of the predetermined region, the aperture state, and the current driving speed of the focus lens. An imaging device. The control unit performs an initial operation for driving the focus lens in a direction opposite to the scan operation before the scan operation, and performs the scan operation based on the focus evaluation value acquired in the initial operation. The imaging apparatus according to claim 1 , wherein a driving speed of the focus lens when starting is set. The controller performs an initial operation of driving the focus lens in a direction opposite to the scan operation before the scan operation, and a gradient of the focus evaluation value acquired at the end of the initial operation with respect to the position of the focus lens is equal to or greater than the second threshold value, the imaging apparatus according to the driving speed of the focus lens at the time of starting the scanning operation to claim 1 or 2, characterized in that set in the second speed. When the gradient of the focus evaluation value acquired at the end of the initial operation with respect to the position of the focus lens is smaller than the second threshold and when a predetermined imaging condition is satisfied, the control unit is configured to start the scan operation. The imaging apparatus according to claim 3 , wherein a driving speed of the focus lens is set to the first speed. The imaging apparatus according to claim 3 or 4 , wherein the second threshold value is larger than the first threshold value. The first threshold value when the contrast value of the subject is a first value is larger than the first threshold value when the contrast value of the subject is a second value lower than the first value. the imaging apparatus according to any one of claims 1 to 5, characterized in that set. The first threshold value when the frequency of the subject is a third value is set to be larger than the first threshold value when the frequency of the subject is a fourth value lower than the third value. the imaging apparatus according to any one of claims 1 to 6, wherein Rukoto. The first threshold value when the size of the predetermined area is a fifth value is compared with the first threshold value when the size of the predetermined area is a sixth value smaller than the fifth value. that Te is set larger imaging apparatus according to any one of claims 1 to 7, characterized in. The first threshold value when the aperture state is the first state is set smaller than the first threshold value when the aperture state is the second state on the open side with respect to the first state. the imaging apparatus according to any one of claims 1 to 8, characterized in Rukoto. The first threshold value when the current driving speed of the focus lens is the first speed is the first threshold value when the current driving speed of the focus lens is a second speed smaller than the first speed. the imaging apparatus according to any one of claims 1 to 9, characterized in that it is set smaller than the threshold value. The contrast value of the subject, the imaging apparatus according to any one of claims 1 to 10, wherein the is a value based on the difference between the maximum value and the minimum value of the luminance values in a predetermined region. A method for controlling an imaging apparatus,
During the movement of the focus lens, photoelectrically converting light from the subject to sequentially generate imaging signals;
Generating a focus evaluation value indicating contrast of a subject from the imaging signal corresponding to a predetermined area;
Controlling the driving of the focus lens based on the focus evaluation value ;
Performing a scanning operation for driving the focus lens in one direction within a set scanning range ;
When the focus lens is driven at the first speed during the scan operation, and the gradient of the focus evaluation value with respect to the position of the focus lens is equal to or higher than the first threshold , the drive speed of the focus lens Changing to a second speed less than the first speed ,
The first threshold value is set based on at least one of the contrast value of the subject, the frequency of the subject, the size of the predetermined region, the aperture state, and the current driving speed of the focus lens. A method for controlling the imaging apparatus. A program to be executed by a computer of an imaging apparatus,
During the movement of the focus lens, photoelectrically converting light from the subject to sequentially generate imaging signals;
Generating a focus evaluation value indicating contrast of a subject from the imaging signal corresponding to a predetermined area;
Controlling the driving of the focus lens based on the focus evaluation value ;
Performing a scanning operation for driving the focus lens in one direction within a set scanning range ;
When the focus lens is driven at the first speed during the scan operation, and the gradient of the focus evaluation value with respect to the position of the focus lens is equal to or higher than the first threshold , the drive speed of the focus lens Changing to a second speed less than the first speed ,
The first threshold value is set based on at least one of the contrast value of the subject, the frequency of the subject, the size of the predetermined region, the aperture state, and the current driving speed of the focus lens. Program.

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