JP2012048070A - Imaging device and method for controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control fluctuations in a focusing distance in an object tracking function which recognizes an object and maintains a focusing state by tracking the movement of the object recognized.SOLUTION: The control method of an imaging device has two control modes. In the first control mode, a focusing lens can be operated by focus control means so that an object of a prescribed kind detected by object detecting means is focused on; and in the second control mode, the focusing lens is not operated while zoom control means is not operating a zoom lens, and the focusing lens can be operated so that a focusing distance is kept unchanged while the zoom control means is operating the zoom lens. The focus control means functions in the first control mode when the object of the prescribed kind is detected by the detecting means so that the zoom control means is operating the zoom lens; and when the object of the prescribed kind is present in a predetermined range including the center of the picked-up image, and functions in the second control mode when the object of the prescribed kind is not present in the predetermined range.

Description

  The present invention relates to an imaging apparatus and a control method thereof.

  In recent years, in the field of imaging devices such as video cameras, research and development of a subject tracking function for maintaining a focused state by recognizing a subject and following the movement of the recognized subject has been advanced. Patent Document 1 proposes an imaging apparatus that sets a focus detection area including a recognized face detection area and performs focus detection. Patent Document 2 proposes an imaging apparatus that detects the eyes of a person and performs focus detection based on the eyes.

  In conventional focusing control, focusing is performed on a recognized subject (main subject). However, there are cases where the main subject is not recognized, such as when the main subject no longer exists on the screen (out of frame). Therefore, when the main subject is not recognized, focusing is mainly performed on the center subject on the screen. Also, considering that there is a high possibility that the main subject will be out of the frame during zooming, focusing on the center subject on the screen will be performed regardless of whether the main subject is recognized or not during zooming. Has also been done.

JP 2006-227080 A JP 2001-215403 A

  However, the conventional focusing control has a problem described with reference to FIG. FIG. 2A shows the operation of conventional focus control (face AF) in which the face frame is moved in accordance with the movement of the subject whose face has been recognized. Here, two frames, a face frame and a normal frame, are set as AF frames, and the AF evaluation values in each frame are sampled. When the face is not recognized, the face frame is set at the center of the screen. This is generally determined by the photographer placing the subject in the center of the screen. The normal frame is set to a wide range including the face frame. This is for focusing on any of the subjects present on the imaging screen even when no subject is present in the center of the screen.

  FIG. 2B shows a state when the zoom operation is performed from this state. Since the subject whose face is recognized may be out of frame during the zoom operation, the face AF is interrupted and the AF frame is returned to the normal position in the center of the screen. Accordingly, the zoom operation is performed while focusing on the subject near the center of the screen. FIG. 2C shows AF processing when the zoom operation is finished in a state where the subject whose face has been recognized is out of the frame. Since the subject is out of the frame, the face frame remains at the normal position in the center of the screen. It is set and the in-focus state is maintained.

  On the other hand, when the subject does not frame out during the zoom operation, as shown in FIGS. 2D and 2E, the AF operation becomes unstable. FIG. 2D shows a focused state when the zoom operation is being performed and the subject remains in the imaging screen without being out of frame. In this case, the face AF is interrupted, the face frame moves to the center of the screen, and the focus is shifted to the subject located at the center of the screen (the subject whose face is recognized is out of focus). Next, FIG. 2E shows a focused state when the zoom operation is finished. The face AF is resumed with the face frame aligned with the subject whose face has been recognized again. That is, after the focus is once deviated from the subject whose face is recognized by the zoom operation, the focus on the subject whose face is recognized again is restored by the end of the zoom operation. As described above, since the focus distance frequently varies in a short time, the visibility of the image is impaired.

  This invention is made | formed in view of such a condition, and it aims at providing the technique which suppresses the fluctuation | variation of a focusing distance.

  In order to solve the above-described problem, the first aspect of the present invention provides an imaging unit that generates a captured image by photoelectrically converting incident light from an optical system having a zoom lens and a focus lens, and a predetermined image included in the captured image. A detection unit that detects a type of subject, a focus control unit that drives the focus lens, and a zoom control unit that drives the zoom lens, wherein the focus control unit is a predetermined type detected by the detection unit A first control mode in which the focus lens is driven so as to focus on the subject, or if the zoom control means is not driving the zoom lens, the zoom control means does not drive the focus lens and the zoom control means A second control mode for driving the focus lens so as not to change the in-focus distance when the lens is being driven. The focus control unit is operable, and when the predetermined type of subject is detected by the detection unit and the zoom control unit is driving the zoom lens, the predetermined type of subject is centered on the captured image. If it is within the predetermined range, it operates in the first control mode, and if the predetermined type of subject is not in the predetermined range, it operates in the second control mode, and the focus control means Is operated in the first control mode when the predetermined type of object is detected by the detection unit and the zoom control unit is not driving the zoom lens, and the focus control unit is operated by the detection unit. An imaging apparatus is provided that operates in the second control mode when no subject is detected.

  Other features of the present invention will become more apparent from the accompanying drawings and the following description of the preferred embodiments.

  With the above configuration, according to the present invention, it is possible to suppress fluctuations in the focusing distance.

The block diagram which shows the structure of DVC100 which concerns on 1st Embodiment. The figure explaining the subject of conventional focusing control FIG. 3A is a flowchart showing focus control according to the first embodiment, and FIG. 3B is a flowchart showing details of AF processing in S305 of FIG. FIG. 3A is a diagram showing a cam locus of the focus lens 105 in the MF zoom process in S306 of FIG. 3A, and FIG. 3B is a flowchart showing details of the MF zoom process in S306 of FIG. The figure explaining the operation | movement achieved by the focus control of Fig.3 (a) Flowchart showing focus control according to the second embodiment

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The technical scope of the present invention is determined by the claims, and is not limited by the following individual embodiments. In addition, not all combinations of features described in the embodiments are essential to the present invention.

  Hereinafter, an embodiment in which an imaging apparatus of the present invention is applied to a digital video camera (DVC) will be described. However, the imaging apparatus of the present invention is not limited to DVC, and can be applied to, for example, a digital still camera.

[First Embodiment]
FIG. 1 is a block diagram showing the configuration of the DVC 100 according to the first embodiment. In FIG. 1, 101 is a fixed first group lens, 102 is a zoom lens that moves in the optical axis direction to perform zooming (magnification), and 103 is a stop. Reference numeral 104 denotes a fixed second lens group, and reference numeral 105 denotes a focus compensator lens (hereinafter referred to as “focus lens”) having both a function of correcting the movement of the focal plane accompanying zooming and a focusing function. The fixed first group lens 101, the zoom lens 102, the diaphragm 103, the fixed second group lens 104, and the focus lens 105 constitute an inner focus type optical system (imaging optical system).

  Reference numeral 106 denotes an image sensor as a photoelectric conversion element constituted by a CCD sensor or a CMOS sensor. The image sensor 106 photoelectrically converts incident light from the optical system. Reference numeral 107 denotes a CDS / AGC circuit that samples the output of the image sensor 106 and adjusts the gain. A camera signal processing circuit 108 performs various image processing on the output signal from the CDS / AGC circuit 107 to generate a video signal. Reference numeral 109 denotes a monitor unit configured by an LCD or the like, and displays a video signal from the camera signal processing circuit 108. A recording unit 115 records the video signal from the camera signal processing circuit 108 on a recording medium such as a magnetic tape, an optical disk, or a semiconductor memory.

  Reference numeral 110 denotes a zoom drive source for moving the zoom lens 102, and reference numeral 118 denotes a zoom position detection unit that detects the position of the zoom lens 102. Reference numeral 111 denotes a focus drive source for moving the focus lens 105, and reference numeral 119 denotes a focus position detection unit that detects the position of the focus lens 105. The zoom drive source 110 and the focus drive source 111 are configured by actuators such as a stepping motor, a DC motor, a vibration type motor, and a voice coil motor.

  Reference numeral 112 denotes an AF gate that passes only signals in an area (focus detection area) used for focus detection among image signals of all pixels from the CDS / AGC circuit 107. Reference numeral 113 denotes an AF signal processing circuit, which extracts a high frequency component, a luminance difference component (difference between the maximum value and the minimum value of the luminance level of the signal that has passed through the AF gate 112), and the like from the signal that has passed through the AF gate 112 and performs AF evaluation. Generate a value signal. The AF evaluation value signal is output to the camera / AF microcomputer 114. The AF evaluation value signal represents the sharpness (contrast state) of the captured image generated based on the output signal from the image sensor 106, but the sharpness changes depending on the focus state of the imaging optical system. As a result, the signal indicates the in-focus state of the imaging optical system.

  The camera / AF microcomputer 114 controls the operation of the entire DVC 100. The camera / AF microcomputer 114 (focus control means) performs AF control for controlling (moving) the focus lens 105 by controlling the focus drive source 111 based on the AF evaluation value signal. This AF control is referred to as “TV-AF control”. Further, the camera / AF microcomputer 114 (zoom control means) performs zoom control for moving (driving) the zoom lens 102 by controlling the zoom drive source 110 in accordance with an instruction from the user via the operation key 117.

  The face detection unit 116 performs a known face recognition process on the image signal to detect a face area in the captured image, and transmits the detection result to the camera / AF microcomputer 114. In the present embodiment, the human face is the focusing target, but other types of subjects may be the focusing target. In that case, the face detection unit 116 is configured to detect a predetermined type of subject to be focused.

  Based on the detection result, the camera / AF microcomputer 114 transmits information to the AF gate 112 so as to add a focus detection area (hereinafter referred to as “face frame”) to a position including the face area in the captured image. AF control is performed. Hereinafter, such AF control is referred to as “face AF”. When a plurality of faces are detected, the camera / AF microcomputer 114 (subject selection means) selects one face having a high priority as a main face based on a predetermined condition, and an area corresponding to the main face (for example, A rectangular area circumscribing the main face) is set as the focus detection area. The predetermined condition in this case includes the largest face, the face closest to the center of the angle of view (the center of the captured image), the condition selected by the user with the operation key 117, or a combination of these conditions. Is mentioned. The main face is selected at any time, and when a face with a higher priority than the main face being selected is detected, the selection is changed, and the face area is changed accordingly.

  The face recognition process includes, for example, a method of extracting a skin color area from the gradation color of each pixel represented by image data and detecting the face with a matching degree with a face contour plate prepared in advance. . Also known is a method of performing face recognition by extracting facial feature points such as eyes, nose and mouth using a well-known pattern recognition technique.

  Next, focus control according to the first embodiment will be described with reference to FIG. In the focus control of the present embodiment, focusing is performed only on the subject whose face is recognized. Therefore, when the face detection unit 116 does not detect a face in the captured image, the camera / AF microcomputer 114 controls the focus lens 105 so as not to change the in-focus distance. Such focus control is referred to as “face-only AF”.

  Prior to the description of FIG. 3A, the control mode of the camera / AF microcomputer 114 (focus control means) will be described. The camera / AF microcomputer 114 can operate in a control mode (first control mode) in which the focus lens 105 is driven so as to focus on the face detected by the face detection unit 116. The camera / AF microcomputer 114 can also operate in a control mode (second control mode) for controlling the focus lens 105 so as not to change the in-focus distance. In this control mode, control is slightly different depending on whether or not zooming is in progress (the camera / AF microcomputer 114 is driving the zoom lens 102). That is, when the zoom is not being performed, the camera / AF microcomputer 114 does not drive the focus lens 105. On the other hand, when the zoom is being performed, a process (MF (manual focus) zoom process) for driving the focus lens 105 so as to compensate for the change in the focus distance accompanying the movement of the zoom lens 102 and not to change the focus distance. Do.

  Referring to FIG. 3A again, in S301, the camera / AF microcomputer 114 determines whether or not a face is detected by the face detection unit 116. If not detected, the process proceeds to S308. In step S308, the camera / AF microcomputer 114 determines whether zooming is in progress. The camera / AF microcomputer 114 operates in the second control mode regardless of the determination result. That is, when zooming, the camera / AF microcomputer 114 executes MF zoom processing at S306 and returns the processing to S301, and when not zooming, returns the direct processing to S301. In either case, the in-focus distance does not change.

  If a face is detected in S301, in S302, the camera / AF microcomputer 114 determines whether zooming is in progress. If zooming is in progress, the process proceeds to S303. Otherwise, the process proceeds to S307, and the camera / AF microcomputer 114 operates in the first control mode. That is, in S307, the camera / AF microcomputer 114 sets the face frame to an area corresponding to the face position, and then in S305, the camera / AF microcomputer 114 drives the focus lens 105 so as to focus on the face frame. To do.

  When zooming is not performed in S302, in S303, the camera / AF microcomputer 114 determines whether the face detected in S301 is within a predetermined range including the center of the captured image, thereby determining the position of the face. It is determined whether or not it is near the center. If the face position is near the center, the process proceeds to S304. If the face position is not near the center, the process proceeds to S306 (in this case, the camera / AF microcomputer 114 operates in the second control mode).

  If the face detected in S301 is present near the center of the captured image, the subject / face microcomputer and the user's camera shake are unlikely to deviate from the angle of view, so the camera / AF microcomputer 114 operates in the first control mode. That is, in S304, the camera / AF microcomputer 114 sets the face frame at the center of the captured image. (Or an area corresponding to the position of the face. Since the face exists near the center of the captured image, the “center of the captured image” and the “area corresponding to the position of the face” are not strictly distinguished. However, in practice, focusing on the “detected face” is performed.) Thereafter, in S305, the camera / AF microcomputer 114 drives the focus lens 105 so as to focus on the face frame.

  When a plurality of faces are detected in S301, the camera / AF microcomputer 114 selects one of them as described above, but prohibits changing this selection during zooming. This is to prevent the main face from changing one after another due to a change in the angle of view during zooming.

  Next, the details of the AF process in S305 of FIG. 3A will be described with reference to FIG. In S310, the camera / AF microcomputer 114 acquires the AF evaluation values of the face frame and the normal frame (see FIG. 2) from the AF signal processing circuit 113. In S311, the camera / AF microcomputer 114 adds the AF evaluation values of the face frame and the normal frame acquired in S310. In step S312, the camera / AF microcomputer 114 executes TV-AF processing using the AF evaluation value added in step S311.

  Next, the details of the MF zoom process in S306 of FIG. 3A will be described with reference to FIG. FIG. 4A is a diagram illustrating the cam locus of the focus lens 105 for each distance of the subject to be focused. In the case of the inner focus type focus lens, the focus distance is maintained by moving the focus lens at the subsequent stage of the zoom lens according to the change in the position of the zoom lens. This cam trajectory data is stored in the camera / AF microcomputer 114 and is used for setting the movement target of the focus lens 105 and the zoom lens 102 during zooming.

  FIG. 4B is a flowchart showing the MF zoom process of the camera / AF microcomputer 114. In step S401, the camera / AF microcomputer 114 acquires the zoom / focus position from the zoom position detection unit 118 and the focus position detection unit 119, and sets the current focus position as p (n). In S402, the camera / AF microcomputer 114 acquires cam locus data a (n) and b (n) that are close to the current focus position p (n). In S403, the camera / AF microcomputer 114 acquires cam track data a (n + 1) and b (n + 1) at the zoom position to be reached after 1V period at the same subject distance as the cam track data acquired in S402. Here, the zoom position to be reached after 1V period is a position determined by a designated zoom speed. In addition, although the zoom target position after 1V period is used here, this is set based on the interrupt period of the MF zoom process, and is not limited to this.

In S404, the camera / AF microcomputer 114 uses the acquired data to calculate a focus target position p (n + 1) that should be reached after the 1V period according to the following equation.
p (n + 1) = [p (n) -a (n)] / [b (n) -a (n)] * [b (n + 1) -a (n + 1)] + a (n (1)

  That is, when the focus lens position is p (n), a ratio in which p (n) internally divides the line segment b (n) -a (n) is obtained, and the line segment b (n + 1) -a ( A point dividing n + 1) is interpolated as p (n + 1).

  In S405, the camera / AF microcomputer 114 sends the zoom drive source 110 and the focus drive source 111 so that the zoom lens 102 reaches the target zoom position after the 1V period and the focus lens 105 reaches the calculated target focus position. Output a control signal. Thereby, zoom / focus drive control is performed.

  Next, the operation achieved by the focus control of FIG. 3 will be described with reference to FIG. Since FIG. 5A is the same as that described with reference to FIG. FIG. 5B shows a state when the zoom operation is performed from a state where the subject whose face is recognized is focused. During zooming, AF processing is interrupted and MF zoom processing is being performed. That is, since the focus with respect to the current subject distance (in-focus distance) is maintained, the focused state with respect to the subject whose face has been recognized remains maintained. Even if the subject eventually goes out of the frame, the current focus position is maintained during zooming.

  Next, FIG. 5C shows a state in which the subject is out of frame during zooming and the zoom operation is finished. If the subject is out of the frame and the face is not recognized when the zoom operation is completed, AF processing is not performed, and the focus position is maintained as it was before zooming started. When the subject returns to the angle of view by panning or the like, AF processing (face AF) is resumed. At this time, the focus position is maintained at the original position. Is done.

  On the other hand, FIGS. 5 (e) and 5 (f) show the operation of the AF process when the zoom operation is finished with the subject remaining in the center frame. If a face is detected within the center frame (near the center) during zooming, the face frame is set as the center frame and AF processing is executed.

  As described above, according to the present embodiment, when a face is not detected in the captured image, the in-focus distance is maintained (the focus lens is fixed when the zoom is not performed, and the MF zoom process is performed when the zoom is performed). Is done). Even when a face is detected in the captured image, if the position of the face is not near the center of the captured image but is being zoomed, MF zoom processing is performed to maintain the in-focus distance. Thereby, it becomes possible to suppress the fluctuation | variation of a focusing distance.

[Second Embodiment]
In the first embodiment, when a face is not detected, “face only AF” that is a focus control for maintaining the in-focus distance is performed. In the second embodiment, when a face is detected, priority is given to focusing on the face, but when no face is detected, “face priority AF”, which is focus control for focusing on other subjects, can also be selected. The configuration will be described. Since the basic configuration of the DVC 100 according to the second embodiment is the same as that of the first embodiment, detailed description thereof is omitted (see FIG. 1). However, the user can select “Face Only AF” (first focusing mode) or “Face Priority AF” (second focusing mode) via the operation key 117, and the camera / AF microcomputer 114 can be selected by the user. According to the above, it functions as a focusing mode selection means for selecting any focusing mode.

  The focus control according to the second embodiment will be described below with reference to FIG. In FIG. 6, steps in which the same or similar processing as in FIG.

  In step S <b> 601, the camera / AF microcomputer 114 determines whether “Face Only AF” is selected. If “Face Only AF” is selected, the process proceeds to S301, and the subsequent processes are the same as in the first embodiment. If “Face priority AF” is selected, the process proceeds to S602.

  In step S <b> 602, the camera / AF microcomputer 114 determines whether a face is detected by the face detection unit 116. If it has been detected, the process proceeds to S603; otherwise, the process proceeds to S604.

  In step S603, the camera / AF microcomputer 114 determines whether zooming is in progress. If zooming is in progress, the process proceeds to S604; otherwise, the process proceeds to S605. Note that, during zooming, as in the first embodiment, changing the selection when a plurality of faces is detected is prohibited.

  If a face is detected in S602 and if zooming is in progress in S603, in S604, the camera / AF microcomputer 114 sets the face frame to the center of the captured image. Thereafter, in S305, the camera / AF microcomputer 114 drives the focus lens 105 so as to focus on the face frame (third control mode). In this case, since the face frame is set regardless of the face position, the setting of the face frame in S604 is the same as the setting of the face frame in S304 (although the position of the face frame to be set may be the same as a result). Is a different concept.

  On the other hand, if zooming is not performed in S603, the camera / AF microcomputer 114 sets the face frame to an area corresponding to the face position in S605. Thereafter, in S305, the camera / AF microcomputer 114 drives the focus lens 105 so as to focus on the face frame (first control mode).

  As described above, when “Face priority AF” is selected, AF control is performed so that the subject in the center of the screen is always focused during zooming regardless of whether or not a face is detected. If zooming is not in progress, AF control is performed to focus on the face if a face is detected, and AF control is performed to focus on the subject in the center of the screen if no face is detected.

  As described above, in the second embodiment, not only “Face Only AF” but also “Face Priority AF” can be selected. Therefore, the user can select AF control according to the purpose and application.

[Other Embodiments]
The present invention can also be 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 a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (7)

An imaging means for generating a captured image by photoelectrically converting incident light from an optical system having a zoom lens and a focus lens;
Detecting means for detecting a predetermined type of subject included in the captured image;
Focus control means for driving the focus lens;
Zoom control means for driving the zoom lens;
With
The focus control means is a first control mode in which the focus lens is driven to focus on a predetermined type of object detected by the detection means, or when the zoom control means is not driving the zoom lens. When the zoom control unit is driving the zoom lens without driving the focus lens, the focus lens can be operated in a second control mode for driving the focus lens so as not to change the focus distance;
The focus control means, when the detection means detects the predetermined type of subject and the zoom control means is driving the zoom lens,
When the predetermined type of subject exists within a predetermined range including the center of the captured image, the first type of operation is performed.
When the predetermined type of object does not exist within the predetermined range, the second control mode operates.
The focus control unit operates in the first control mode when the predetermined type of object is detected by the detection unit and the zoom control unit is not driving the zoom lens;
The imaging apparatus characterized in that the focus control means operates in the second control mode when the predetermined type of object is not detected by the detection means. A focus mode selection means for selecting the first focus mode or the second focus mode;
When the first focusing mode is selected,
The focus control means, when the detection means detects the predetermined type of subject and the zoom control means is driving the zoom lens,
When the predetermined type of subject exists within a predetermined range including the center of the captured image, the first type of operation is performed.
When the predetermined type of object does not exist within the predetermined range, the second control mode operates.
The focus control unit operates in the first control mode when the predetermined type of object is detected by the detection unit and the zoom control unit is not driving the zoom lens;
The focus control unit operates in the second control mode when the predetermined type of subject is not detected by the detection unit;
When the second focusing mode is selected,
The focus control unit operates in the first control mode when the predetermined type of object is detected by the detection unit and the zoom control unit is not driving the zoom lens;
The focus control unit is configured to detect the predetermined type of subject by the detection unit and the zoom control unit is driving the zoom lens, and when the predetermined type of subject is not detected by the detection unit, The imaging apparatus according to claim 1, wherein the imaging apparatus operates in a third control mode in which the focus lens is driven so as to focus on a predetermined range. When the focus control unit operates in the first control mode, the focus control unit drives the focus lens so that a high-frequency component in a focus detection region set corresponding to a position of the predetermined type of subject in the captured image is increased. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is an image pickup apparatus. And a subject selection unit that selects one of the plurality of the predetermined types of subjects when the detection unit detects the plurality of the predetermined types of subjects.
When the focus control unit operates in the first control mode, the focus control unit drives the focus lens to focus on the predetermined type of subject selected by the subject selection unit;
The focus control unit controls the subject selection unit so as not to change the selection when the zoom control unit is driving the zoom lens. The imaging device described in 1. The imaging apparatus according to claim 1, wherein the predetermined type of subject is a human face. A method for controlling an imaging apparatus,
An imaging step in which an imaging unit of the imaging apparatus generates a captured image by photoelectrically converting incident light from an optical system having a zoom lens and a focus lens;
A detection step in which the detection unit of the imaging apparatus detects a predetermined type of subject included in the captured image;
A focus control step in which the focus control means of the imaging apparatus drives the focus lens;
A zoom control step in which the zoom control means of the imaging device drives the zoom lens;
With
The focus control means is a first control mode in which the focus lens is driven to focus on a predetermined type of object detected in the detection step, or when the zoom lens is not being driven in the zoom control step. When the zoom lens is being driven in the zoom control step without driving the focus lens, the focus lens can be operated in the second control mode for driving the focus lens so as not to change the focus distance;
In the focus control step, the focus control means detects the predetermined type of object in the detection step and is driving the zoom lens in the zoom control step.
When the predetermined type of subject exists within a predetermined range including the center of the captured image, the first type of operation is performed.
When the predetermined type of object does not exist within the predetermined range, the second control mode operates.
In the focus control step, the focus control means operates in the first control mode when the predetermined type of object is detected in the detection step and the zoom lens is not being driven in the zoom control step.
In the focus control step, the focus control means operates in the second control mode when the predetermined type of subject is not detected in the detection step.   The program for making a computer perform each process of the control method of Claim 6.

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