JP4568916B2 - Auto focus system - Google Patents

Description

  The present invention relates to an autofocus system, and in particular, an auto that can automatically focus a position (range) targeted for autofocus (AF) within a shooting range of a camera to track a desired target subject. Concerning the focus system.

  In an imaging system that converts an image of a subject into an electrical signal (image signal) by a photographing element (CCD or the like) like a television camera, a contrast method is generally adopted as an autofocus (hereinafter referred to as AF) method. Yes. In the contrast method, the contrast of the subject image is detected from the image signal captured by the image sensor, and the focus of the photographic lens is controlled so that the contrast becomes the highest, thereby automatically focusing on the best focus state (in-focus state). This is a method of matching.

  In AF such as a contrast method, the entire subject within the shooting range of the camera is not targeted for AF, but only the subject within a part of the shooting range is often targeted. In contrast-based AF, an image signal in a range targeted for AF is extracted from image signals captured by the entire imaging area of the image sensor, and focus is performed so that the contrast of the image signal in the extracted range is the highest. By controlling this, the target of AF is limited to only a certain range of subjects. In this specification, the range of the subject to be AF target in the camera shooting range, or the image range of the subject to be AF out of the entire range of the camera shot image (screen) is referred to as an AF area. A frame indicating the outline of the AF area is referred to as an AF frame.

When a single AF area is fixedly set at a predetermined position within the shooting range, a rectangular AF area is normally set at the center of the shooting range. There is also known one that can change the position of (see, for example, Patent Document 1).
JP 2002-365519 A

  By the way, when the AF area can be changed to a desired position and the target subject to be focused is an object that moves within the shooting range, the operator operates an operation device such as a trackball or a joystick. It is necessary to move the position of the AF area in accordance with the movement of the target subject. For this reason, there has been a problem that the operation is troublesome and requires attention.

  Therefore, if the AF area is automatically tracked with respect to the moving subject, it is effective because the operator does not have to operate the position of the AF area. As a method for automatically tracking an AF area to a desired target subject, it is conceivable to apply a technique of moving object recognition by so-called interframe difference extraction. According to this, only the moving object image is extracted by extracting the difference between the captured image of the current frame of the video captured by the camera and the captured image of the previous frame. As a result, the position of the moving object within the imaging range can be detected. If the moving object is the target subject to be tracked, the AF area can be tracked to the target subject by moving the AF area to the position of the moving object.

  Such an inter-frame difference extraction method has an advantage that it is possible to track a target subject that moves at a relatively high speed. However, with the inter-frame difference extraction method alone, images other than the target subject also move within the shooting range when the camera pans / tilts, so that only the target subject cannot be extracted. There is a problem that the subject cannot be tracked.

  The present invention has been made in view of such circumstances, and even when the camera performs a pan / tilt operation, it is possible to automatically track the target subject to be focused automatically using the inter-frame difference extraction method. The object is to provide a focus system.

  In order to achieve the object, the autofocus system according to claim 1 includes at least an image of a stationary object in a range of a captured image of a previous frame captured before a captured image of a current frame by a camera. A reference pattern image capture range setting means for setting a reference pattern image capture range for capturing a reference pattern image, and a reference pattern image set by the reference pattern image capture range setting means among the captured images of the previous frame Reference pattern image capturing means for capturing an image of the capture range as a reference pattern image, target subject position setting means for setting the position of the target subject image to be tracked as a focus target among the captured images of the previous frame, Based on the position set by the target subject position setting means, the captured image of the previous frame is First comparative image capture range setting means for setting a first comparative image capture range for capturing an image including an image of the target subject and an image other than the target subject in the frame; and a captured image of the previous frame Of these, the first comparative image capturing means for capturing an image of the first comparative image capturing range set by the first comparative image capturing range setting means as the first comparative image, and the range of the captured image of the current frame Matching image range detecting means for detecting a range of an image that most closely matches the reference pattern image captured by the reference pattern image capturing means, and the reference pattern image capturing range setting of the captured image range of the current frame Capturing the first comparison image in the direction and size in which the range detected by the matching image range detecting means is displaced with respect to the reference pattern image capturing range set by the means Second comparative image capture range setting means for setting, as a second comparative image capture range, a range obtained by displacing the first comparative image capture range set by the surrounding setting means, and among the captured images of the current frame, Second comparative image capturing means for capturing an image of the second comparative image capturing range set by the second comparative image capturing range setting means as a second comparative image, and captured by the first comparative image capturing means Based on the difference image obtained by extracting the difference between the first comparison image and the second comparison image captured by the second comparison image capturing means, the image of the target subject in the captured image of the current frame is extracted. A target subject position detecting unit for detecting a position, and a target target position from a position set by the target subject position setting unit within a shooting range of the camera; Auto focus means for adjusting the focus of the optical system of the camera so as to focus on the target subject by changing to the position detected by the body position detection means.

  According to the present invention, when the position of the subject to be moved is detected by a so-called inter-frame difference extraction method and the position to be focused by the autofocus means is changed so as to follow the position, at least the stationary object is stationary. The reference pattern image including the object image is taken from the captured image of the previous frame, and the reference pattern image is displaced on the captured image by detecting the range of the image that best matches the reference pattern image in the captured image of the current frame. It is possible to know the direction and size of the image, that is, the direction and size of the displacement of the image of the stationary object on the captured image due to the pan / tilt operation of the camera. On the other hand, a first comparison image capture range is set in the range of the captured image of the previous frame, and an image including an image of the target subject to be focused and other images (images of still objects, etc.) from the range is set. Captured as a first comparison image. Then, in the range of the captured image of the current frame, a range in which the first comparison image capture range is displaced in the direction and size in which the reference pattern image is displaced is defined as a second comparison image capture range, and the image in that range is the second. By capturing as a comparative image, it is possible to capture an image having the same field angle range as the first comparative image capturing range before the pan / tilt operation of the camera. As a result, only the moving object image from which the image of the stationary object is removed can be extracted from the difference image obtained by extracting the difference between the first comparison image and the second comparison image, and the target subject is moving The position of the subject can be detected from the difference image. By changing the target position for focusing by the autofocus unit based on the position, it is possible to automatically track the target subject as the focus target.

  According to a second aspect of the present invention, in the invention of the first aspect, the reference pattern image capture range setting means and the first comparison image capture range setting means are the same means, and the first comparison image Is used as the reference pattern image. As in the present invention, the first comparison image for obtaining the difference image is also used as the reference pattern image, and the first comparison image is used as the displacement direction of the image of the stationary object on the captured image by the pan / tilt operation of the camera. It can also be used as a basic pattern image for detecting the size and as an image for obtaining a difference image.

  According to a third aspect of the present invention, in the invention according to the first or second aspect, the first comparative image capture range setting means sets the position of the first image capture range to the position of the target subject. The position for setting the first comparison image capture range is changed based on the position detected by the target subject position detection means so as to follow. In the present invention, since it is necessary to include the target subject in the first comparison image, the position of the first comparison image capture range is changed according to the position of the target subject.

  The autofocus system according to a fourth aspect is the invention according to the first, second, or third aspect, in which the autofocus means detects a subject within an AF area set within the shooting range of the camera. The first comparison image capture range setting means sets a range larger than the AF area as the first comparison image while setting the focus area and changing the position of the AF area as the focus target position. It is characterized by being set as a capture range. In the present invention, when the subject to be focused by the autofocus means is set as a subject within the range of a predetermined AF area, the first comparison image capture range is set to a range larger than the AF area, thereby making the first comparison The image includes the target subject and the other image (stationary object).

  According to the autofocus system of the present invention, it is possible to appropriately automatically track the target subject to be focused using the inter-frame difference extraction method even when the camera performs a pan / tilt operation.

  Hereinafter, preferred embodiments of an autofocus system according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing the overall configuration of an imaging system to which an autofocus system according to the present invention is applied. The image pickup system shown in FIG. 1 is an image pickup system used for shooting with, for example, a broadcast television camera. In the figure, a camera head 10 with a replaceable lens, and a shooting lens (optical) mounted on a lens mount of the camera head 10 A lens device 12, a frame operation unit 14, a tracking device 16 and the like provided with a system) are shown.

  The camera head 10 is equipped with an image sensor (for example, a CCD), a required signal processing circuit, and the like, and an image formed by the photographing lens of the lens device 12 is photoelectrically converted by the image sensor and then subjected to signal processing. Necessary signal processing is performed by the circuit. A video signal in a predetermined format generated by the signal processing circuit is output from the video signal output terminal of the camera head 10 to an external device. Further, the camera head 10 is provided with a view finder (monitor) 18 for composition confirmation, etc., and a video signal from the camera head 10 is given to the view finder 18 and is photographed by the camera head 10. A real-time image (video) is displayed on the screen of the viewfinder 18. Further, information on an AF area that is a target range of autofocus (AF), for example, an AF frame, is also displayed on the screen of the viewfinder 18.

  The lens device 12 includes a photographing lens (optical system) (not shown) attached to a lens mount of the camera head 10, and an image of a subject is formed on the imaging surface of the imaging element of the camera head 10 by the photographing lens. . The photographing lens is provided with movable parts for adjusting photographing conditions such as a focus lens group, a zoom lens group, and a diaphragm as its constituent parts. These movable parts are electrically driven by a motor (servo mechanism) (not shown). It is designed to be driven. For example, the focus lens group and zoom lens group move in the optical axis direction, and the focus (subject distance) adjustment is performed by moving the focus lens group, and the focal length (zoom magnification) adjustment is performed by moving the zoom lens group. Is done. In the system relating to autofocus as in the present embodiment, it is sufficient that at least the focus lens group can be driven electrically, and other movable parts may be driven only manually. Further, when the predetermined movable part is electrically driven in accordance with the operation of the operator, it is based on a control signal output in accordance with the operation of the operator from an operation unit (not shown) (such as an operation unit of a controller connected to the lens device 12). Thus, the operation of the movable part is controlled, but details are omitted.

  As shown in the figure, the lens device 12 is equipped with a lens CPU 20 that performs overall control of the lens device 12, an AF processing unit 22 that executes autofocus (AF) processing, an AF imaging circuit 24, and the like. Yes. The AF image pickup circuit 24 is disposed in the lens device 12 to acquire a video signal for AF processing, and outputs an image pickup device (CCD or the like) or an output signal of the image pickup device as a video signal of a predetermined format. Etc. The image pickup element of the AF image pickup circuit 24 is referred to as an AF image pickup element. The video signal output from the AF imaging circuit 24 is a luminance signal.

  On the imaging surface of the AF imaging element, subject light branched from the subject light incident on the imaging element of the camera head 10 is imaged by a half mirror or the like disposed on the optical path of the photographing lens. The shooting range and subject distance (distance of the subject in focus) with respect to the imaging area of the AF imaging element are configured to match the shooting range and subject distance with respect to the imaging area of the imaging element of the camera head 10 and are used for AF. The captured image captured by the image sensor matches the captured image captured by the image sensor of the camera head 10. Note that it is not necessary for the shooting ranges of the two to be completely the same. For example, the shooting range of the AF imaging device may be a larger range including the shooting range of the imaging device of the camera head 10. Further, the image signal from the camera head 10 may be supplied to the AF processing unit 22 without providing an AF image sensor.

  The AF processing unit 22 acquires a video signal from the AF imaging circuit 24, and calculates a focus evaluation value indicating the level of contrast of the subject image based on the video signal. For example, after extracting a high-frequency component signal of a video signal obtained from an AF image sensor with a high-pass filter, a signal in a range corresponding to an AF area that is an AF target range among the high-frequency component signal Are accumulated one screen at a time. The integrated value obtained for each screen in this manner indicates the level of contrast of the subject image, and is given to the lens CPU 20 as a focus evaluation value. The AF area range is designated by the lens CPU 20 as will be described later.

  As will be described in detail later, the lens CPU 20 acquires AF frame information (AF frame information) indicating the range (contour) of the AF area from the frame operation unit 14, and the range within the AF frame designated by the AF frame information. Is designated to the AF processing unit 22 as an AF area. Then, the focus evaluation value obtained from the image (video signal) in the AF area is acquired from the AF processing unit 22, and the acquired focus evaluation value is maximum (maximum), that is, the contrast of the subject image in the AF area is maximum. The focus lens group is controlled so that For example, a hill-climbing method is generally known as a control method for a focus lens group based on a focus evaluation value, and the focus evaluation value starts to decrease by moving the focus lens group in a direction in which the focus evaluation value increases. Is detected, the focus lens group is set at that position. Thereby, the subject in the AF frame is automatically focused.

  The frame operation unit 14 includes an operation member for the operator to specify the setting contents of the AF frame such as the position, size, and shape of the AF frame. Note that the AF frame indicates the outline of an AF area that is an AF target range with respect to a shooting range or a shot image (screen) of the imaging element of the camera head 10 as shown in FIG. When the operation member is operated by the operator, the frame operation unit 14 sets and changes setting contents such as the position of the AF frame in accordance with the operation. In the present embodiment, it is assumed that the shape of the AF frame is limited to a rectangle having a constant aspect ratio. In addition, the setting contents such as the position and size of the AF frame by the operation member of the frame operation unit 14 are changed by a change amount corresponding to the operation amount of the subsequent operation member based on the setting contents of the AF frame before the operation. It is only done by making changes to the settings. For example, as for the position of the AF frame, the AF frame is displaced in the vertical and horizontal directions by a direction and a movement amount corresponding to the rotation direction and the rotation amount of the trackball. Also, if the point that determines the position of the AF frame (the center position of the rectangular AF frame in the present embodiment) within the shooting range (screen of the captured image) is referred to as an AF point, the position of the AF frame is the position of the AF point. Is determined by setting

  On the other hand, when the operation member of the frame operation unit 14 is not operated and the operator is not instructed to change the setting contents of the AF frame, the setting contents of the AF frame are set by the AF frame information given from the tracking device 16 described later. Set and change. The frame operation unit 14 transmits AF frame information indicating the setting contents of the AF frame set or changed by the operation of the operator or the AF frame information from the tracking device 16 to the lens CPU 20 in accordance with a request from the lens CPU 20. As a result, the AF target range is set to the AF frame range set and changed in the frame operation unit 14.

  The tracking device 16 automatically changes the position of the AF area (AF frame) in accordance with the movement of the image of the target object while detecting the image of the target object (target subject) specified by the operator on the captured image. (Automatic tracking) device, and when the operator does not change the AF frame, the tracking device 16 automatically tracks the AF frame, and the operator changes the AF frame. Is performed, the operation has priority over the tracking device 16, and the AF frame is changed according to the operation of the operator.

  The frame operation unit 14 also transmits AF frame information indicating the setting contents of the AF frame set and changed as described above to the camera head 10, and places the AF frame at a corresponding position on the screen of the viewfinder 18. Display. As a result, the operator can recognize the position, size, shape, etc. of the AF frame at that time while looking at the viewfinder 18.

  The tracking device 16 includes an image processing unit 26, an image input unit 28, a serial communication interface 30, and the like. The image input unit 28 acquires the video signal (luminance signal) obtained by the AF imaging circuit 24 via the AF processing unit 22 and obtains the image obtained from the video signal in response to a request from the image processing unit 26. The image data of the image is given to the image processing unit 26.

  Based on the image data acquired from the image input unit 28, the details of which will be described later, the image processing unit 26 detects the movement of the image of the object designated by the operator on the captured image (screen) as described later. Then, the position of the AF frame (AF point) for causing the AF frame to follow the movement of the object is obtained. Then, AF frame information indicating the position of the AF frame is transmitted to the frame operation unit 14 via the serial communication interface 30, and the position of the AF frame when automatically tracking the AF frame is designated.

  Next, the tracking process in the image processing unit 26 in the tracking device 16 will be described in detail with reference to the flowchart of FIG. First, the operator operates the operation member of the frame operation unit 14 while viewing the image displayed on the screen of the viewfinder 18 and the AF frame, and the whole or a part of the object to be tracked as the focus target is displayed in the AF frame. To pay. As a result, the object is brought into focus by AF processing in the lens CPU 20.

  Subsequently, the operator presses the determination button of the frame operation unit 14. As a result, a reference pattern image setting instruction (reference pattern image storage instruction) is given from the frame operation unit 14 to the image processing unit 26.

  When an instruction to set a reference pattern image is given, the image processing unit 26 reads AF frame information indicating the setting contents of the AF frame at that time from the frame operation unit 14 via the serial communication interface 30 and also the lens device 12. The captured image (image data) for one screen (one frame) is taken in from the video signal supplied from the AF processing unit 22 to the image input unit 28 (step S10). The captured image captured at this time is referred to as an A image. Further, when the video signal given from the AF processing unit 22 to the image input unit 28 is, for example, an interlaced video signal composed of two fields of video signals for one screen (one frame). The captured image captured as one screen from the input unit 28 may be a captured image obtained from a video signal for one field, or may be a captured image obtained from a video signal for two fields. In this specification, when a captured image for one screen is a captured image obtained from a video signal for one field in the interlace method or a video signal for two fields, or a video signal for one frame in the non-interlace method. Even if it is a case where it is set as the picked-up image obtained by, one screen shall be called one frame.

  Subsequently, the image processing unit 26 extracts, from the A image, an area within the range that is slightly larger than the AF frame specified by the AF frame information from the A image captured in step S10 as a reference pattern frame range. Then, it is set (stored) as a reference pattern image (step S12). The stored reference pattern image is defined as an A ′ image.

  Here, it is assumed that an A image as shown in FIG. 4A is captured by the image processing unit 26, and the target object to be tracked as a focus target is a round object simply indicated by a symbol M. . At this time, if the AF frame is set by the operator to a range including the object M as indicated by reference numeral F1, the reference pattern frame has the same center position as that of the AF frame F1 and a reference sign F2 larger than the AF frame F1. Is set in the range indicated by. Then, the image in the reference pattern frame F2 is stored as a reference pattern image (A ′ image) shown in FIG.

  Note that the reference pattern image is image data used in pattern matching processing, which will be described later, and the reference pattern frame that is the capture range of the reference pattern image may be set by a method different from the present embodiment. Good. For example, the same range as the AF frame may be used as the reference pattern frame, and the operator may set the AF frame so that the reference pattern frame is an appropriate range as the reference pattern image capture range. Alternatively, the reference pattern frame may be displayed on the viewfinder 18 so that the position, size, etc. of the reference pattern frame can be set by the operator's operation separately from the AF frame.

  When the setting of the reference pattern image (A ′ image) in step S12 in FIG. 3 is completed, the image processing unit 26 repeatedly executes the following steps S14 to S26. First, a new captured image for one frame is captured from the image input unit 28 (step S14). Note that the captured image acquired in step S14 is referred to as a B image. Further, the B image is an image captured after one frame (after 1/30 seconds), for example, with respect to the A image.

  Subsequently, the image processing unit 26 matches the stored reference pattern image (A ′ image) in the predetermined pattern detection range set within the screen range of the B image (the highest correlation value). Is detected by a well-known pattern matching process, and an image in the range is extracted from the B image and stored as a B ′ image (step S16).

  Here, it is assumed that the B image as shown in FIG. The B image is panned with respect to the A image shown in FIG. 5A, and a stationary object other than the object M moves leftward in the captured image, and the object M is stationary. The case where it moved to the right with respect to the object is shown. In addition, when the figure (A) and the figure (C) are compared, the image of the object M simply shown changes from a round shape to a triangle, and the pattern of the image of the object M also changes. Is shown. In this B image, the image range that most closely matches the reference pattern image (A ′ image) shown in FIG. 4B is an image range in which the image of a stationary object other than the object M matches in the reference pattern image. The range is detected as a range indicated by a frame F3 in FIG. That is, an image range having the same angle of view as the image range of the reference pattern frame F2 in FIG. 6A before the camera pans is detected as the range of the frame F3. Then, an image within the range of the frame F3 is extracted as a B ′ image as shown in FIG.

  The pattern detection range may be the entire range of the captured image (B image), or may be a slightly larger range than the reference pattern frame in order to reduce the time required for pattern matching processing and the processing load.

  Subsequently, in FIG. 3, the image processing unit 26 extracts a difference image (C image) obtained by extracting a difference between the stored reference pattern image (A ′ image) and the B ′ image stored in step S16. Ask for. That is, the absolute value of the difference between the luminance values of the corresponding pixels of the A ′ image and the B ′ image is obtained, and an image in which the pixel value of each pixel becomes the obtained value is obtained as a difference image (step S18).

  Then, the barycentric position of the image that is effectively extracted as the difference image (C image) is obtained (step S20). For example, for each pixel of the difference image (C image), the pixel value is 1 when the luminance value is greater than a predetermined threshold value (a value that is determined to be effectively extracted), and the pixel value when the luminance value is less than or equal to the threshold value. The difference image is binarized with a value of 0, and the barycentric position of the set of pixels having a pixel value of 1 is obtained (step S20). When the barycentric position in the difference image (C image) is obtained, the barycentric position in the B image can be obtained by setting the barycentric position as the barycentric position in the B ′ image. In step S20, the barycentric position in the B image is obtained.

  Here, when a difference image (C image) between the reference pattern image (A ′ image) shown in FIG. 4B and the B ′ image shown in FIG. 4D is obtained, as shown in FIG. In addition, only the image of the moving object M is extracted after the stationary object image is erased. Then, the position of the center of gravity P shown in FIG. 5E is obtained from the image of the object M in the extracted A ′ image and B ′ image.

  Next, in FIG. 3, the image processing unit 26 determines whether the image of the object M has moved on the captured image based on the position of the center of gravity obtained in step S20 (step S22). For example, in an AF frame and reference pattern frame update process (step S24), which will be described later, the AF frame and the reference pattern frame so that the center positions of the AF frame and the reference pattern frame coincide with the barycentric position in the B image obtained in step S20. If the position of the center of gravity obtained in step S20 does not match the center position of the currently set AF frame and reference pattern frame, the object M is moved. It determines, and it determines with the target object M not moving other than that.

  4E shows a case where the position of the center of gravity P does not coincide with the center position of the reference pattern frame F2 shown in FIG. 4A, and it is determined that the object M has moved.

  If YES is determined in step S22 in FIG. 3, the image processing unit 26 updates the positions of the AF frame and the reference pattern frame so that the center positions of the AF frame and the reference pattern frame coincide with the center of gravity obtained in step S20. (Step S24). Also, AF frame information indicating the position of the updated AF frame is transmitted to the frame operation unit 14. As a result, the setting content of the AF frame, that is, the position of the AF frame is updated, and the AF frame is moved to the position of the image of the object.

  For example, when the position of the center of gravity P in the difference image (C image) in FIG. 4E is obtained, the B image of the frame F3 in FIG. 4C obtained by extracting the position and the B ′ image in FIG. The position of the center of gravity P in the B image in FIG. The positions of the AF frame and the reference pattern frame are changed so that the position of the center of gravity P in the B image becomes the center position as shown in FIG. Note that the position of the object M in the B image and the position of the center of gravity P do not completely match, but the time from capturing the A image to capturing the B image is very short, and the position of the object M in the B image. There is no significant difference in the position of the center of gravity P. Further, in the reference pattern image (A image) set in the initial stage, when the object M is at the center position of the reference pattern image, the length to the position of the center of gravity P with respect to the center position of the difference image (C image). Therefore, the position of the AF frame and the reference pattern frame is set so that the position of the object M becomes the center position by obtaining the position of the object M. Can be changed.

  Next, in FIG. 3, the image processing unit 26 extracts an image of the updated reference pattern frame range from the B image, and updates (stores) the image as a new reference pattern image (A ′ image) (step S26). . If the position of the reference pattern frame F2 is updated as shown in FIG. 4F, an image within the range of the reference pattern frame F2 is extracted from the B image, and the image as shown in FIG. It is updated as a pattern image (A ′ image).

  When the above process ends, the process returns to step S14 in FIG. 3 and is repeatedly executed from the B image capturing process.

  According to the tracking processing described above, even when the entire captured image including the image of the stationary object is displaced on the screen due to the pan / tilt operation of the camera, the direction and size of the displacement match the reference pattern image. The image can be detected by detecting it from within the captured image, and in order to obtain a difference image in consideration of the direction and size of the displacement, the image range to be compared between the two frames is appropriately set and moved. The position of the object M can be detected.

  As described above, in the above embodiment, the reference pattern image for detecting the displacement of the entire captured image between frames and the image (A ′ image) for obtaining a difference image between frames are the same. It is good also as an image obtained from the range set up individually. For example, an image referred to as a reference pattern image (A ′ image) in the above embodiment is set as one image (first comparison image) used only for obtaining a difference image. In the above embodiment, the reference pattern frame and The frame that has been referred to is also referred to as a first comparison image capture frame that indicates a range in which the first comparison image is captured from the A image. And about the process with respect to a 1st comparison image and a 1st comparison image capture frame, and the process using them, except not performing the pattern matching process of step S16 using the 1st comparison image, said execution In this embodiment, the processing is performed in the same manner as the processing for the reference pattern image and the reference pattern frame and the processing using them.

  On the other hand, the reference pattern frame can be set in a desired range separately from the first comparison image capture frame, and the image within the range of the reference pattern frame in the A image is changed between the entire captured images between frames. A reference pattern image for detection is captured. In this case, it is not necessary for the reference pattern image to include an image of an object to be focused, and it is desirable to set the reference pattern frame so as to include only a still object image as much as possible.

  Then, an image range that most closely matches the reference pattern image in the range of the B image is detected, and the direction and size of the image range displaced from the position of the reference pattern image (reference pattern frame) in the A image are obtained. Thereby, it is possible to know the direction and magnitude of the displacement of the entire captured image due to the pan / tilt operation of the camera. Then, a range in which the first comparison image capture frame is displaced by the determined direction and size of the displacement is defined as a second comparison image capture frame, and an image within the second comparison image capture frame among the B images. As the other image (second comparison image) for obtaining a difference image. The second comparative image corresponds to the B ′ image in the above embodiment.

  A difference image (C image) similar to that of the above-described embodiment is obtained by extracting the difference between the first comparison image and the second comparison image obtained in this manner, and the object to be moved by obtaining the position of the center of gravity. The position of the object can be detected.

  In this embodiment, the update of the reference pattern image in step S26 of the above embodiment corresponds to the update of the first comparison image, and the update of the reference pattern image in this embodiment is not necessarily required. However, when the reference pattern image is not updated, it can be applied only when the pan / tilt operation is performed in a range where the reference pattern image exists in the captured image or when the size of the reference pattern image does not change. . In order not to limit the range of the pan / tilt operation that can be applied, the reference pattern image may be updated with an image included in the B image. For example, the image range of the same subject in which the image pattern does not change between the A image and the B image is detected as much as possible on the movement destination side of the pan / tilt operation of the camera, and the image in the image range is updated as the reference pattern image Can be considered. Or you may make it just update the image of the predetermined range of B image as a reference | standard pattern image.

  In the above embodiment, the frame frequency of the video signal acquired by the AF imaging circuit 24 (AF imaging device) of the lens device 12 is the frame frequency of the video signal obtained by the imaging device of the camera head 10. However, by increasing the frame frequency of the video signal in the AF imaging circuit 24, adaptability to an object that moves at high speed or an object that changes rapidly is improved.

  Moreover, in the said embodiment, although the lens apparatus 12, the frame operation part 14, and the tracking apparatus 16 were illustrated as a separate apparatus, any two or all may be an integral apparatus. In the above embodiment, an operation member (for example, a determination switch for determining an object) related to the processing of the tracking device 16 is also provided in the frame operation unit 14, but may be provided in the tracking device 16.

  In the above-described embodiment, the image signal is acquired for the AF by using an image sensor dedicated for AF that is different from the image sensor for the camera head 10, but the image obtained by the image sensor for the camera head 10 for AF is used. A signal may be used. However, if the AF video signal is obtained from the AF-dedicated imaging device as in the above embodiment, the HD signal is obtained when the camera head 10 is compatible with a high-definition (HD) television system. Since it is possible to perform AF without using a lens, it is advantageous for miniaturization and power saving.

FIG. 1 is a block diagram showing the overall configuration of an imaging system to which an autofocus system according to the present invention is applied. FIG. 2 is a diagram showing an AF frame. FIG. 3 is a flowchart showing the procedure of the tracking process in the tracking device. FIG. 4 is an explanatory diagram used for explaining the tracking process in the tracking device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Camera head, 12 ... Lens apparatus, 14 ... Frame operation part, 16 ... Tracking apparatus, 18 ... Viewfinder, 20 ... Lens CPU, 22 ... AF process part, 24 ... Imaging circuit for AF, 26 ... Image process part, 28: Image input unit, 30: Serial communication interface

Claims (4)

A reference pattern image for setting a reference pattern image capture range for capturing a reference pattern image including at least a still object image out of the range of the captured image of the previous frame captured by the camera before the captured image of the current frame Capture range setting means,
A reference pattern image capturing unit that captures an image of the reference pattern image capturing range set by the reference pattern image capturing range setting unit among the captured images of the previous frame, as a reference pattern image;
Target subject position setting means for setting a position of an image of a target subject to be tracked as a focus target among the captured images of the previous frame;
Based on the position set by the target subject position setting means, a first comparative image capture for capturing an image including an image of the target subject and an image other than the target subject in the range of the captured image of the previous frame. First comparative image capture range setting means for setting a range;
First comparative image capture means for capturing an image of the first comparative image capture range set by the first comparative image capture range setting means among the captured images of the previous frame;
A matching image range detecting means for detecting a range of an image that most closely matches the reference pattern image captured by the reference pattern image capturing means in the range of the captured image of the current frame;
Of the range of the captured image of the current frame, the direction and magnitude of displacement of the range detected by the matching image range detection unit with respect to the reference pattern image capture range set by the reference pattern image capture range setting unit Now, a second comparison image capture range setting means for setting a range obtained by displacing the first comparison image capture range set by the first comparison image capture range setting means as a second comparison image capture range;
Second comparative image capture means for capturing an image of the second comparative image capture range set by the second comparative image capture range setting means among the captured images of the current frame;
Based on the difference image obtained by extracting the difference between the first comparison image captured by the first comparison image capture means and the second comparison image captured by the second comparison image capture means. Target subject position detection means for detecting the position of the target subject image in the captured image of the current frame;
The target subject is brought into focus by changing the position to be focused in the shooting range of the camera from the position set by the target subject position setting means to the position detected by the target subject position detection means. Autofocus means for adjusting the focus of the optical system of the camera,
An autofocus system characterized by comprising   2. The autofocus system according to claim 1, wherein the reference pattern image capturing range setting means and the first comparative image capturing range setting means are the same means, and the first comparative image is used as the reference pattern image.   The first comparison image capture range setting unit is configured to perform the first comparison based on the position detected by the target subject position detection unit so that the position of the first image capture range follows the position of the target subject. 3. The autofocus system according to claim 1, wherein a position for setting an image capture range is changed. The auto-focus means changes a subject within an AF area set within a shooting range of the camera as a focus target and changes a position of the AF area as a focus target position.
4. The autofocus system according to claim 1, wherein the first comparative image capture range setting means sets a range larger than the AF area as the first comparative image capture range.

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