JP2015040991A - Image-capturing device, image-capturing system, method for controlling image-capturing device, program, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image-capturing device capable of executing AF control based on a contrast method suitable for tracking a moving body.SOLUTION: The image-capturing device has an image-capturing element for photoelectrically converting an optical image, focal point detection means for performing contrast AF on the basis of a signal from the image-capturing element, and control means for performing focusing control on the basis of a contrast evaluation value calculated by the focal point detection means. The control means selects, in accordance with the moving speed of a subject, a first control mode for performing focusing control while driving a focus lens or a second control mode for performing focusing control without driving the focus lens.

Description

  The present invention relates to an imaging apparatus that performs AF control using a contrast method.

  In recent years, a subject image formed by a photographing optical system is photoelectrically converted into an electrical signal using an image sensor such as a CCD or CMOS, and the image signal obtained thereby is recorded on a recording medium or the like. Digital cameras (imaging devices) are widely used. In such a digital camera, so-called contrast AF control is performed in which the focus state of a subject image is detected based on a difference (contrast) in the amount of high-frequency components included in an image signal acquired by an image sensor.

  In AF control using the contrast method, so-called hill-climbing contrast AF is used. In this AF control, in order to detect the peak of the contrast at the in-focus position, the imaging optical system is driven little by little, the image pickup signals at a plurality of locations are captured, the contrast at each position is compared, and based on the detected peak information The photographic optical system is driven to the in-focus position. Patent Document 1 discloses an imaging apparatus that captures a moving object using AF control using a contrast method.

JP 2010-107711 A

  However, in the configuration of Patent Document 1, when the moving object is caused to follow, the focusing surface of the focus lens repeats the operation of overtaking and returning the subject. For this reason, on the monitor, the through image of the subject is displayed as if the focal plane is shaken back and forth, so that the appearance of the screen deteriorates. In addition, since the focus lens is driven in reverse, the stop accuracy is reduced due to backlash. In addition, since it takes time to reversely drive the focus lens, it is difficult to focus on a subject moving at high speed or close to the focus lens because it is difficult for the focus surface of the focus lens to overtake the subject. Further, since the change in the contrast evaluation value due to the drive of the focus lens and the change in the contrast evaluation value due to the movement of the subject are combined, an error occurs in peak detection as the movement speed of the subject increases.

  Therefore, the present invention provides an imaging apparatus, an imaging system, an imaging apparatus control method, a program, and a storage medium that can execute contrast AF control suitable for moving object tracking.

  An imaging apparatus according to one aspect of the present invention includes an imaging element that photoelectrically converts an optical image, a focus detection unit that performs contrast AF based on a signal from the imaging element, and a contrast evaluation value calculated by the focus detection unit Control means for performing focus control based on the first control mode for performing the focus control while driving the focus lens according to the moving speed of the subject, or the focus lens. A second control mode for performing the focusing control without driving is selected.

  An imaging system according to another aspect of the present invention includes a lens device including a photographing optical system and the imaging device.

  According to another aspect of the present invention, there is provided a control method for an image pickup apparatus that performs contrast AF based on a signal from an image pickup device. The first method performs focus control while driving a focus lens. Whether to change the first control mode to the second control mode in which the focus control is performed without driving the focus lens according to the step of setting the control mode and the moving speed of the subject. Determining, and performing the focusing control in the second control mode.

  A program according to another aspect of the present invention is configured to cause a computer to execute a method for controlling the imaging apparatus.

  A storage medium according to another aspect of the present invention stores the program.

  Other objects and features of the present invention are illustrated in the following examples.

  According to the present invention, it is possible to provide an imaging apparatus, an imaging system, an imaging apparatus control method, a program, and a storage medium that can execute contrast AF control suitable for moving object tracking.

It is a block diagram which shows the structure of the imaging system in a present Example. It is a flowchart which shows the autofocus control (AF control) in a present Example. It is a flowchart which shows the operation | movement of ambush contrast AF in a present Example. It is a figure which shows the locus | trajectory of a focus lens and a to-be-photographed object locus | trajectory in a present Example. 3 is a flowchart showing a part of autofocus (AF) operation in the present embodiment. It is a flowchart which shows the imaging | photography operation | movement in a present Example.

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

  First, the configuration of the imaging system in the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of the imaging system 10. In FIG. 1, reference numeral 100 denotes a lens device (interchangeable lens) configured to include a lens unit (imaging optical system). Reference numeral 101 denotes a zoom lens (first lens group) disposed at the tip of the lens apparatus 100, and is held so as to be able to advance and retract in the direction of the optical axis OA (optical axis direction). Reference numeral 102 denotes an aperture. The diaphragm 102 adjusts the amount of light during photographing by adjusting the aperture diameter. Reference numeral 103 denotes a second lens group. Reference numeral 104 denotes a focus lens (third lens group). The focus lens 104 adjusts the focus from infinity to the closest end by moving back and forth in the optical axis direction.

  Reference numeral 111 denotes a zoom actuator. The zoom actuator 111 performs zoom driving by driving the zoom lens 101 so as to advance and retreat in the optical axis direction. Reference numeral 112 denotes a diaphragm actuator. The aperture actuator 112 controls the aperture diameter of the aperture 102 to adjust the amount of photographing light. Reference numeral 113 denotes a focus actuator. The focus actuator 113 performs focus adjustment by driving the focus lens 104 back and forth in the optical axis direction.

  Reference numeral 114 denotes a zoom control circuit. The zoom control circuit 114 detects the position of the zoom lens 101 and drives the zoom lens 101 via the zoom actuator 111. Reference numeral 115 denotes an aperture control circuit. The diaphragm control circuit 115 detects the diaphragm position of the diaphragm 102 and drives the diaphragm 102 via the diaphragm actuator 112 to control the opening of the diaphragm 102. Reference numeral 116 denotes a focus control circuit. The focus control circuit 116 detects the position of the focus lens 104 and drives the focus lens 104 via the focus actuator 113. The focus control circuit 116 performs focus adjustment by driving the focus lens 104 forward and backward in the optical axis direction based on the focus detection result.

  Reference numeral 117 denotes a lens MPU that performs all calculations and controls of the lens apparatus 100. The lens MPU 117 controls the zoom control circuit 114, the aperture control circuit 115, and the focus control circuit 116. Also, in response to a request from the camera MPU 125, the camera MPU 125 is notified of lens information such as lens position information and lens ID. In this embodiment, the lens device 100 is detachably attached to the imaging device 120 (imaging device body). That is, the lens device 100 is connected to the imaging device 120 via the mount 130 indicated by the dotted line at the center in FIG. In the imaging system 10 of the present embodiment, the lens apparatus 100 is an interchangeable lens that can be attached to and detached from the imaging apparatus 120, but is not limited thereto. The present embodiment can also be applied to an imaging system in which the lens device 100 and the imaging device 120 are integrally configured.

  Reference numeral 121 denotes an optical low-pass filter, which is an optical element that reduces false colors and moire in a captured image. Reference numeral 122 denotes an image sensor composed of a CMOS sensor and its peripheral circuits. The image sensor 122 photoelectrically converts an optical image (subject image). Reference numeral 123 denotes an image sensor control circuit. The imaging element control circuit 123 controls the imaging operation of the imaging element 122, A / D converts the acquired image signal, and transmits it to the camera MPU 125 and the focus detection unit 124. Reference numeral 126 denotes a display such as an LCD. The display 126 displays information related to the shooting mode of the imaging device 120, a through image of the subject image at the time of shooting preparation, a confirmation image after shooting, a focus state display image at the time of focus detection, and the like. Reference numeral 127 denotes an operation switch (operation SW). The operation switch 127 includes a power switch, an AF start switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like. Reference numeral 128 denotes a detachable memory (flash memory) that records a captured image.

  Reference numeral 124 denotes a focus detection unit (focus detection means). The focus detection unit 124 performs focus detection (contrast AF) by a contrast method based on a signal from the image sensor 122, that is, based on a contrast component of image information obtained by the image sensor control circuit 123. Reference numeral 125 denotes a camera MPU (control means) that performs all operations and controls of the imaging apparatus 120. The camera MPU 125 controls the image sensor control circuit 123, the focus detection unit 124, the display 126, the operation switch 127, and the memory 128. The camera MPU 125 is electrically connected to the lens MPU 117 via the signal line of the mount 130. The camera MPU 125 can output to the lens MPU 117 an acquisition request for unique information for each interchangeable lens such as the lens position and lens ID, and a drive request for the zoom lens 101, the focus lens 104, and the aperture 102. . The camera MPU 125 incorporates a ROM that stores a program for controlling the operation of the imaging apparatus 120 and a RAM for storing variables, and a focus detection method described later is executed according to the program stored in the ROM.

  A signal (pixel signal) output from the image sensor 122 is input to the focus detection unit 124 via the image sensor control circuit 123. The focus detection unit 124 performs a frequency analysis of a specific region of the image data and calculates a contrast evaluation value. The camera MPU 125 performs focusing control based on the contrast evaluation value calculated by the focus detection unit 124. In contrast AF, the movement (drive) of the focus lens 104 and the calculation of the contrast evaluation value are repeated, and the position of the focus lens 104 at which the contrast evaluation value is maximized is set as the in-focus position.

  Next, with reference to FIG. 2, a focus detection method (an imaging device control method) in the present embodiment will be described. FIG. 2 is a flowchart showing the focus detection method in this embodiment. Each step in FIG. 2 is mainly executed based on a command from the camera MPU 125.

  First, in step S101, when the user operates the operation switch 127 to instruct AF start, the camera MPU 125 starts AF control. In step S102, the camera MPU 125 drives the imaging element control circuit 123 and drives the focus lens 104 via the lens MPU 117, the focus control circuit 116, and the focus actuator 113. That is, the camera MPU 125 executes hill-climbing contrast AF (first control mode) based on the contrast evaluation value acquired from the focus detection unit 124. At this time, the camera MPU 125 uses the RAM (storage means) built in the camera MPU 125 as the in-focus history based on the time t when the contrast evaluation value is maximized and the position p of the focus lens 104 detected by the focus control circuit 116. To remember.

  Subsequently, in step S103, the camera MPU 125 performs an ambush AF condition determination. In the ambush AF condition determination, for example, the camera MPU 125 determines whether or not the moving speed of the subject (subject image) obtained by the hill-climbing contrast AF executed in step S102 is equal to or higher than a predetermined value. If the moving speed of the subject is equal to or higher than the predetermined value, the process proceeds to step S104. On the other hand, if the moving speed of the subject is less than the predetermined value, the process returns to step S102. The camera MPU 125 again performs hill-climbing contrast AF. Further, when the number of combinations (t, p) of the time t and the position p obtained during the hill-climbing contrast AF executed in step S102 is equal to or less than a predetermined value, the moving speed of the subject (subject image) is calculated. Since it cannot be performed, the process returns to step S102. In the determination in step S103, whether or not the shooting mode set by the user operating the operation switch 127 is a specific mode (for example, a sports shooting mode) may be added to the determination condition.

  In step S104, the camera MPU 125 executes the ambush contrast AF (second control mode). Details of the ambush contrast AF will be described later. When the ambush contrast AF is completed, the process proceeds to step S105, and the camera MPU 125 determines the AF end. In step S105, when the user instructs to end AF by operating the operation switch 127 or the like, the process proceeds to step S106, and the AF control is ended. On the other hand, if the end of AF is not instructed, the process returns to step S102, and the camera MPU 125 executes hill-climbing contrast AF.

  As described above, in this embodiment, the camera MPU 125 performs the focus control without driving the focus lens 104 or the first control mode in which the focus control is performed while driving the focus lens 104 according to the moving speed of the subject. The second control mode to be performed is selected. More preferably, the camera MPU 125 changes the first control mode to the second control mode (ambush contrast AF) when the moving speed of the subject exceeds a predetermined speed in the first control mode (mountain climbing contrast AF). change.

  Next, the operation of the ambush contrast AF in this embodiment (step S104 in FIG. 2) will be described with reference to FIGS. FIG. 3 is a flowchart showing the operation of the ambush contrast AF. FIG. 4 is a diagram illustrating a focus lens locus and a subject locus.

  First, in step S201 in FIG. 3, the camera MPU 125 performs a moving object prediction calculation and determines the moving speed of the focus lens 104. The moving object prediction is performed, for example, as follows using the focusing history stored in the RAM of the camera MPU 125. That is, the camera MPU 125 obtains a quadratic function approximation curve based on the combinations (t11, p11), (t12, p12), and (t13, p13) of the time (focusing time) and position shown in FIG. The subject in-focus position pp21 at t21 is predicted. Here, the prediction of the in-focus position of the subject is obtained from a three-point quadratic function approximation curve, but the present invention is not limited to this, and other calculation methods may be used.

  The focus lens position (position p21) is obtained using, for example, the following expression (1).

p21 = pp21 + α (1)
In Expression (1), α is a value to be added so that the focus position by the focus lens 104 can pass the subject focus position at time t21. The value is, for example, a number proportional to the predicted speed v21 at time t21.

  Further, based on the focus lens position p20 (not shown) at the current time t20, the time t20, the time t21, and the focus lens position p21 at the time t21, the focus lens moving speed v is expressed by the following equation (2). To be determined.

v = (p21-p20) / (t21-t20)
Here, linear movement of the focus lens 104 is considered, but other movement methods may be applied.

  Subsequently, in step S202, the camera MPU 125 instructs the lens MPU 117 to perform the forward drive of the focus lens 104. In step S <b> 203, the camera MPU 125 determines whether or not a predetermined time has elapsed after starting the forward driving of the focus lens 104. If the predetermined time has not elapsed, the process proceeds to step S204. On the other hand, if the predetermined time has elapsed, the ambush contrast AF is terminated because the subject is lost.

  In step S <b> 204, the camera MPU 125 determines whether or not the contrast evaluation value calculated after starting the forward driving of the focus lens 104 exceeds the maximum value. If the camera MPU 125 determines that the focus surface driven by the focus lens has passed the subject image position (subject focus position) and the contrast evaluation value has exceeded the maximum value (peak), the process proceeds to step S205. On the other hand, if the contrast evaluation value does not exceed the peak, the process returns to step S202. With such control, when the subject moves differently from the prediction during the forward driving of the focus lens 104, or when the subject moves out of the AF area (focus detection area), the ambush contrast AF is terminated and the mountain climbs again. AF can be redone.

  In step S205, the camera MPU 125 stops the forward drive of the focus lens 104 and waits for the subject to pass through the focusing surface. Subsequently, in step S <b> 206, the camera MPU 125 determines whether or not a predetermined time has elapsed after stopping the forward drive of the focus lens 104. If the predetermined time has not elapsed, the process proceeds to step S207. On the other hand, if the predetermined time has elapsed, the ambush contrast AF is terminated. By such control, when the subject moves differently from the prediction while the focus lens 104 is stopped, or when the subject moves out of the AF area, the ambush contrast AF can be terminated and the hill-climbing AF can be performed again. .

  In step S207, the camera MPU 125 determines whether or not the contrast evaluation value calculated after stopping the forward drive of the focus lens 104 exceeds a maximum value (peak). If it is determined that the contrast evaluation value has exceeded the peak due to the subject passing through the in-focus plane, the process returns to step S201 to repeat the ambush contrast AF operation. At this time, the camera MPU 125 stores the time t at which the contrast evaluation value reaches the maximum value (peak) and the position p of the focus lens 104 in the RAM built in the camera MPU 125 as a focusing history. On the other hand, if it is not determined that the contrast evaluation value has exceeded the peak, the process returns to step S206.

  In this embodiment, the focus lens 104 is driven while determining whether or not the contrast evaluation value exceeds the maximum value in steps S203 and S204, but these steps may be omitted. At this time, after moving to the drive position of the focus lens 104 determined in step S201, the drive of the focus lens 104 is stopped, and waiting for the subject to pass through the in-focus plane. FIG. 5 is a flowchart showing the ambush contrast AF operation (step S104a) in this case. Steps S201a, S202a, and S205a to S207a in FIG. 5 are the same as steps S201, S202, and S205 to S207 in FIG. According to the control shown in FIG. 5, it is not necessary to calculate the contrast evaluation value while performing the forward drive of the focus lens 104. For this reason, it is possible to increase the drive speed of the focus lens 104 and to follow the subject faster.

  As described above, the RAM (storage unit) of the camera MPU 125 sequentially stores the in-focus position and the in-focus position calculation time obtained in the first control mode. The camera MPU 125 calculates the moving speed of the subject based on the in-focus position and the calculation time stored in the RAM. More preferably, the camera MPU 125 predicts the focus position of the subject based on the focus position and the calculation time stored in the RAM.

  Preferably, the camera MPU 125 drives the focus lens 104 forward in the moving direction of the subject in the second control mode. Then, the camera MPU 125 determines whether or not the contrast evaluation value exceeds the peak before the predetermined time elapses. If the camera MPU 125 cannot detect the peak of the contrast evaluation value before the predetermined time elapses, the camera MPU 125 changes the second control mode to the first control mode.

  Next, with reference to FIG. 6, an operation when the user operates the operation switch 127 and gives an instruction for shooting will be described. FIG. 6 is a flowchart showing the photographing operation in the present embodiment. Each step in FIG. 6 is executed based on a command from the camera MPU 125.

  First, in step S301, the camera MPU 125 performs a moving object prediction calculation to determine the moving speed and moving position of the focus lens 104. The moving object prediction calculation is performed using a method similar to the method described in step S201. Here, as the time corresponding to the time t21, a value considering the shooting preparation time is employed.

  Subsequently, in step S302, the camera MPU 125 drives the focus lens 104 forward. In step S303, the camera MPU 125 stops driving the focus lens 104 and waits for the subject to pass through the in-focus plane. Subsequently, in step S304, the camera MPU 125 determines whether or not a predetermined time has elapsed since the forward drive of the focus lens 104 was stopped. If the predetermined time has not elapsed, the process proceeds to step S305. On the other hand, if the predetermined time has elapsed, the process proceeds to step S306 to start shooting.

  In step S305, the camera MPU 125 determines whether or not the contrast evaluation value calculated after stopping the forward drive of the focus lens 104 exceeds a maximum value (peak). If it is determined that the contrast evaluation value has exceeded the maximum value (peak) due to the subject passing through the in-focus plane, the process proceeds to step S306 and imaging is started. On the other hand, if it is determined that the contrast evaluation value does not exceed the peak, the process returns to step S304.

  According to the present embodiment, the driving direction of the focus lens is one direction, and when the through image of the subject is displayed on the monitor, the focusing surface moves in one direction, so that the appearance of the screen is improved. In addition, since the operation to reversely drive the focus lens is not performed, backlash does not occur and the lens stopping accuracy is improved. In addition, since the operation of reversing the focus lens is not performed, there is a margin in control time, and it is possible to improve the tracking performance for a subject moving at high speed or close. In addition, since the change of the contrast evaluation value is observed by stopping the focus lens, the peak of the contrast evaluation value can be detected with high accuracy.

[Other Embodiments]
The present invention is also realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and the computer (or CPU, MPU, etc.) of the system or apparatus reads the program. To be executed. In this case, a computer-executable program describing the procedure of the imaging apparatus control method and a storage medium storing the program constitute the present invention.

  According to each embodiment, it is possible to provide an imaging apparatus, an imaging system, an imaging apparatus control method, a program, and a storage medium that can execute contrast AF control suitable for moving object tracking.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

120 Imaging Device 122 Imaging Device 124 Focus Detection Unit 125 Camera MPU

Claims (12)

An image sensor that photoelectrically converts an optical image;
Focus detection means for performing contrast AF based on a signal from the image sensor;
Control means for performing focusing control based on the contrast evaluation value calculated by the focus detection means,
The control means is a first control mode for performing the focus control while driving a focus lens according to a moving speed of the subject, or a second control mode for performing the focus control without driving the focus lens. An imaging device characterized by selecting.   The control means changes the first control mode to the second control mode when the moving speed of the subject becomes a predetermined speed or more in the first control mode. The imaging apparatus according to 1. A storage means for sequentially storing the in-focus position obtained in the first control mode and the calculation time of the in-focus position;
The imaging apparatus according to claim 1, wherein the control unit calculates a moving speed of the subject based on the in-focus position and the calculation time stored in the storage unit.   The imaging apparatus according to claim 3, wherein the control unit predicts a focus position of the subject based on the focus position and the calculation time stored in the storage unit. The control means in the second control mode,
Perform forward drive of the focus lens in the moving direction of the subject,
5. The imaging apparatus according to claim 1, wherein it is determined whether or not the contrast evaluation value exceeds a peak before a predetermined time elapses.   6. The control unit according to claim 5, wherein when the peak of the contrast evaluation value cannot be detected before the predetermined time elapses, the control unit changes the second control mode to the first control mode. Imaging device.   The imaging apparatus according to claim 1, wherein the first control mode is a mode in which hill-climbing contrast AF is performed. A lens device equipped with a photographing optical system;
An imaging system comprising: the imaging device according to claim 1. A method for controlling an imaging apparatus that performs contrast AF based on a signal from an imaging element,
Setting a first control mode for performing focus control while driving the focus lens;
Determining whether to change the first control mode to a second control mode in which the focus control is performed without driving the focus lens according to the moving speed of the subject;
And a step of performing the focusing control in the second control mode.   The imaging according to claim 9, wherein when the moving speed of the subject becomes equal to or higher than a predetermined speed in the first control mode, the first control mode is changed to the second control mode. Control method of the device.   A program configured to cause a computer to execute the control method of the imaging apparatus according to claim 9 or 10.   A storage medium storing the program according to claim 11.