JP5384173B2 - Auto focus system - Google Patents

Description

  The present invention relates to an autofocus system, and in particular, an autofocus having an AF frame autotracking function for automatically tracking an AF frame (AF area) indicating a range of a subject to be focused by autofocus (AF) to a predetermined subject. About the system.

  Conventionally, in an autofocus (AF) system that automatically adjusts the focus of a camera, the camera must be instructed where to focus. At this time, in a general camera or the like, the position to be focused is fixed at the center of the shooting range, and for example, the person in the center of the shooting range is focused.

  However, when shooting a moving subject, it is inconvenient if the focus position is fixed in this way. Therefore, for example, when shooting a scene where the subject moves rapidly, such as sports, with a TV camera or the like, an AF area automatic tracking system in which the autofocus area (AF area) follows the subject movement for the purpose of focusing on the subject. Is known (see, for example, Patent Document 1).

  Also, an image representing a person's face is detected from the captured image, and the face that is the subject is automatically focused, or the face area representing the face in the detected image is enlarged. A digital camera that automatically changes the zoom magnification is known (see, for example, Patent Document 2).

JP 2006-267221 A JP 2004-320286 A

  However, in a scene where the ratio of the face area of the subject to the entire screen is small, if the size of the area surrounded by the AF frame is matched with the face area of the subject, the change in the AF evaluation value becomes small and the focus accuracy is lowered.

  Also, in a scene where the ratio of the subject's face area to the entire screen is large, if the size of the area surrounded by the AF frame is adjusted to the subject's face area, the amount of data during autofocus will increase and the processing time will not be in time. End up.

  On the other hand, for face detection, it is desirable to reliably detect and track the face area of the subject regardless of the ratio of the face area of the subject to the entire screen.

  The present invention has been made in view of such circumstances, and prevents the reduction in focus accuracy while detecting and tracking the face area of the subject regardless of the size of the face area of the subject with respect to the entire screen. An object of the present invention is to provide an autofocus system capable of keeping the processing time of focus within an appropriate time.

In order to achieve the above object, an autofocus system according to the present invention includes a face area detecting means for detecting a face area of a subject, and a size of the face area detected by the face area detecting means within a predetermined range. A face area determining means for determining whether or not the face area size is not within the predetermined range by the face area determining means. AF frame setting means for setting the size of the area surrounded by the AF frame to be different from the size of the area surrounded by the tracking frame indicating the face area to be tracked . AF frame setting means for setting the size to fall within the predetermined range; and the size of the area surrounded by the tracking frame is the size of the face area detected by the face area detection means. Tracking frame setting means for setting the size of the face area to be matched with each other, and the AF frame setting means is surrounded by the AF frame when the size of the face area is smaller than a lower limit value of the predetermined range. When the size of the face area is larger than the upper limit value of the predetermined range, the size of the area surrounded by the AF frame is set to the upper limit value. It is characterized by being set to match the value .

  According to the present invention, regardless of the size of the face area of the subject with respect to the entire screen, the face area of the subject is detected and tracked, and the focus accuracy is prevented from being lowered. Can fit in.

  According to this aspect, it is possible to reliably detect and track the face area of the subject regardless of the size of the face area of the subject with respect to the entire screen.

  According to this aspect, it is possible to reliably prevent a reduction in focus accuracy and to keep the autofocus processing time within an appropriate time.

  According to this aspect, it is possible to more reliably prevent a decrease in focus accuracy.

  According to this aspect, the autofocus processing time can be kept within an appropriate time more reliably.

  As one aspect of the present invention, the AF frame setting unit is an area surrounded by the AF frame when the face area determination unit determines that the size of the face area is within the predetermined range. Is set so as to coincide with the size of the face area detected by the face area detecting means.

  According to the present invention, regardless of the size of the face area of the subject with respect to the entire screen, the face area of the subject is detected and tracked, and the focus accuracy is prevented from being lowered. Can fit in.

It is the block diagram which showed the whole structure of AF frame automatic tracking system applied to a television camera system. It is explanatory drawing of AF frame (AF area). It is the flowchart which showed the processing procedure of AF frame automatic tracking in an image processing unit. It is a figure which shows the magnitude relationship of a tracking frame and AF frame.

  Hereinafter, an AF frame automatic tracking 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 AF frame automatic tracking system according to the present invention. The AF frame automatic tracking system 1 shown in FIG. 1 includes a television camera 10, an image processing unit 18 and an AF frame operation unit 20 that constitute an AF frame automatic tracking device.

  The television camera 10 includes a camera body 14 composed of an HD camera compatible with a high-definition television [HD (High Definition) TV] system, and a lens device 12 having a photographing lens (optical system) attached to a lens mount of the camera body 14. It consists of.

  The camera body 14 is equipped with an image sensor (for example, a CCD), a required signal processing circuit, and the like. The 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 and output as an HDTV video signal (HDTV signal) from the video signal output terminal of the camera body 14 to the outside.

  In addition, a viewfinder 16 is installed in the camera main body 14, and a captured image of the television camera 10 is displayed on the viewfinder 16. The viewfinder 16 displays various types of information other than the captured video. For example, an image showing the currently set AF frame and tracking frame range (position, size, shape). (Frame image) is displayed superimposed on the captured video. The AF frame indicates a range (outline) of a subject to be focused by autofocus (AF). The tracking frame indicates the range (outline) of the face area of the subject to be tracked for face detection.

  The lens device 12 includes a photographing lens (zoom lens) attached to the lens mount of the camera body 14 so that the subject 30 is imaged on the imaging surface of the imaging element of the camera body 14 by the photographing lens. It has become.

  Although not shown, the photographic 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 elements. The mechanism is electrically driven. For example, the focus lens group and the zoom lens group move in the optical axis direction, the focus (subject distance) adjustment is performed by moving the focus lens group, and the focal length (zoom magnification) is adjusted by moving the zoom lens group. Adjustments are made.

  In the AF-related system, it is sufficient that at least the focus lens group can be driven electrically, and other movable parts may be driven only manually.

  The lens device 12 includes an AF unit 40 and a lens CPU (not shown). The lens CPU controls the entire lens device 12. The AF unit 40 is a processing unit for acquiring information necessary for performing focus control (automatic focus adjustment) by AF, and is configured from an AF processing unit, an AF imaging circuit, and the like (not shown). Has been.

  The AF imaging circuit is disposed in the lens device 12 to acquire an AF processing video signal, and an output signal from an imaging device such as a CCD (referred to as an AF imaging device) or an AF imaging device is output in a predetermined format. A processing circuit for outputting as a signal is provided. The video signal output from the AF imaging circuit is a luminance signal.

  On the imaging surface of the AF imaging element, subject light branched from subject light incident on the imaging element of the camera body 14 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 body 14. The subject image captured by the AF image sensor matches the subject image captured by the image sensor of the camera body 14. It should be noted that the shooting ranges of the two do not need to be completely the same. For example, the shooting range of the AF imaging element may be a larger range including the shooting range of the imaging element of the camera body 14.

  The AF processing unit acquires a video signal from the AF imaging circuit, and based on the video signal, calculates a focus evaluation value indicating the level of contrast of the subject image within an AF area (AF frame) that is an AF target range. calculate. For example, a high frequency component signal is extracted from a video signal obtained from an AF image sensor by a high-pass filter, and then a range corresponding to an AF area set as described later in the high frequency component signal. Are integrated for each screen (one frame). The integrated value obtained for each screen in this manner indicates the level of contrast of the subject image in the AF area, and the integrated value is given to the lens CPU as a focus evaluation value.

  The lens CPU obtains AF frame information (AF frame information) indicating the range (contour) of the AF area from the image processing unit 18 as will be described later, and the range within the AF frame specified by the AF frame information is obtained. The AF area is designated as the AF area. Then, the focus evaluation value obtained from the image (video signal) in the AF area is acquired from the AF processing unit.

  In this way, every time a video signal for one screen is acquired from the AF imaging circuit (each time the focus evaluation value is obtained by the AF processing unit), the focus evaluation value is acquired from the AF processing unit, and the acquired focus is obtained. The focus lens group is controlled so that the evaluation value is maximum (maximum), that is, the contrast of the subject image in the AF frame is maximum.

  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.

  Note that the above-described AF processing unit obtains a video signal from the AF image sensor mounted on the lens device 12 in order to calculate the focus evaluation value, but the video imaged by the image sensor of the camera body 14 The video signal may be obtained from the camera body 14. Also, any AF means for automatically focusing on the subject within the AF frame may be used.

  Here, as shown in FIG. 2, the AF area 200 is set as a rectangular area with respect to the imaging area 202 (or imaging range) of the imaging element in the camera body 14, and a frame 204 indicating its outline is an AF frame. In this case, a subject photographed in the range of the AF area 200 (within the AF frame 204) of the image sensor is a target to be focused by AF.

  In the present specification, the range of the AF frame 204 (AF area 200) with respect to the imaging area 202 is determined by three factors including the position, size, and shape (aspect ratio) of the AF frame 204. It is assumed that the range of the AF frame is changed when at least one of the three elements of position, size, and shape is changed.

  The lens device 12 is connected to the camera body 14 via a cable or directly, and various kinds of information are transmitted through serial communication interfaces (SCI) 12a and 14a provided in the lens device 12 and the camera body 14, respectively. You can communicate. As a result, information on the AF frame currently set in the AF unit 40 is also transmitted to the camera body 14, and the position of the AF frame currently set in the captured image displayed on the viewfinder 16 by processing in the camera body 14. The image of the AF frame corresponding to the size and shape is superimposed and displayed.

  The image processing unit 18 is a component of the AF frame control device. For example, the image processing unit 18 is housed in a housing and is installed on the lens barrel side portion of the taking lens of the lens device 12 or the outer wall surface of the housing of the camera body 14. The position where the image processing unit 18 is installed in the lens device 12 or the camera body 14 is not limited to this, and may be installed in any other position. It may be arranged.

  The image processing unit 18 includes an SCI 18a, and the SCI 18a is connected to the lens device 12, and can exchange various signals with the lens CPU through the SCI 12a. Thereby, AF frame information for designating the range of the AF frame set by the AF frame setting unit 59 is given from the image processing unit 18 to the lens CPU of the lens device 12, and the AF unit 40 based on the AF frame information. The range of the AF frame is set.

  The image processing unit 18 is provided with a video input connector for capturing a video signal, and a video output connector of the camera body 14 is connected to the video input connector via a down converter 42 with a cable. As a result, the HDTV signal output from the video output connector of the camera body 14 is converted (down-converted) into a standard television [NTSC (National Television System Committee)] video signal (SDTV signal) by the down converter 42. Are input to the image processing unit 18.

  Although details will be described later, when executing the AF frame automatic tracking process, the image processing unit 18 sequentially captures one frame of the captured image from the video signal input from the camera body 14 and selects a predetermined image from the captured image. A process for detecting the subject to be tracked is performed. Then, an AF frame range and a tracking frame range for detecting the face of the subject are determined so that the subject can be focused by AF, and the determined AF frame range and tracking frame range are determined by the lens apparatus. To 12 lens CPUs. The configuration and processing contents of the image processing unit 18 will be described later.

  The AF frame operation unit 20 is a component of the AF frame control device, and is provided as an apparatus integrated with the image processing unit 18. A part or all of the AF frame operation unit 20 may be configured as a separate device from the image processing unit 18 and connected to the image processing unit 18 with a cable or the like. In the present embodiment, a size operation member 60 (for example, a knob) for changing the size of the AF frame by manual operation, and a shape operation member 62 (for example, a knob) for changing the shape of the AF frame by manual operation. , A tracking start switch 64 for instructing start of AF frame automatic tracking, and a tracking stop switch 66 for instructing stop of AF frame automatic tracking are provided. The setting states of these operating members 60, 62, 64, 66 are It is read by the CPU 50 in the image processing unit 18.

  In the present embodiment, a position operation member (for example, a joystick or a trackball) is provided as an operation member of the AF frame operation unit 20 to move the position of the AF frame up and down and left and right by a user's manual operation. Absent. This corresponds to a case where a space cannot be secured. If there is a space for providing a position operation member, a position operation member may be provided so that the position of the AF frame can be changed manually. However, this is not always necessary in the present invention.

  Next, the configuration and processing contents of the image processing unit 18 will be described.

  The image processing unit 18 includes an SCI 18a, a CPU 50 that supervises the processing in the image processing unit 18, a decoder (A / D converter) 52, a face area detecting unit 54, a face area determining unit 56, a tracking frame setting unit 58, and an AF frame setting. Part 59 and the like.

  The SCI 18a is an interface circuit for performing serial communication with the SCI 12a of the lens apparatus 12 as described above, and transmits the AF frame information and the like to the lens apparatus 12.

  The decoder 52 is a circuit for converting the video signal (SDTV signal) of the video captured by the television camera 10 input from the down converter 42 to the image processing unit 18 into data that can be digitally processed by the image processing unit 18. A / D conversion processing for converting an analog SDTV signal into a video signal of digital data is performed.

  The face area detection unit 54 is a face area detection unit that captures image data from the decoder 52, detects the face area of the subject, and sets a face detection frame.

  The face area determination unit 56 determines whether or not the size of the face area (area surrounded by the face detection frame) of the subject detected by the face area detection unit 54 is within a predetermined range. Means.

  The tracking frame setting unit 58 is tracking frame setting means for setting a tracking frame indicating the range (outline) of the face area of the subject to be tracked.

  The AF frame setting unit 59 is an AF frame setting unit that sets an AF frame indicating a range (outline) of a subject to be focused by autofocus (AF) according to the determination result in the face area determination unit 56.

  The image processing unit 18 also includes a memory that can be written and read by the CPU 50, and is appropriately used for storing processing data.

  Next, the AF frame automatic tracking process by the image processing unit 18 configured as described above will be described. FIG. 3 is a flowchart showing a processing procedure of AF frame automatic tracking in the image processing unit. When the AF frame automatic tracking is not being executed, the AF frame setting unit 59 first performs an AF frame setting process for setting the range of the AF frame (step S2). In this AF frame setting process, the position (center position) of the AF frame is set to be the center position of the shooting range (imaging area), and the size and shape of the AF frame are set to the size operation member 60 of the AF frame operation unit. And the setting of the shape operation member 62 for changing the shape of the AF frame by manual operation. Then, AF frame information indicating the range (position, size, shape) of the AF frame set in this way is transmitted to the lens CPU of the lens apparatus 12 through the SCI 18a. Thereby, the range of the AF frame set in the AF unit 40 of the lens apparatus 12 becomes the range designated by the AF frame information.

  When the start of AF frame automatic tracking is instructed, processing for executing AF frame automatic tracking is started (step S4).

  Subsequently, the face area detection unit 54 captures image data of a captured image for one frame from the decoder 52 (step S6). Then, a well-known face detection process for detecting the face (face image) of an arbitrary person included in the captured image is performed (step S8). Note that the face detection process may be performed only on the periphery of the AF frame including the range of the AF frame.

  Here, the operation of the operator (cameraman) until the transition to the execution of the AF automatic tracking as described above will be described. When the AF automatic tracking is not executed, the AF frame is photographed by the AF frame setting process in step S2. It is fixed in the center of the image (shooting angle of view). First, the operator sets the shooting angle of view of the television camera by pan / tilt operation or the like so that the subject to be tracked is included within the range of the AF frame. When the subject to be tracked is included in the AF frame range, the automatic start switch is pressed. As a result, AF frame automatic tracking is started with the subject set within the AF frame as the subject to be tracked.

  In addition, if the operator operates the shooting angle of view so that the subject to be tracked is within the range of the AF frame without being aware of whether or not the subject to be tracked is a face, the subject If it is a face, AF frame automatic tracking by face detection processing is automatically selected and executed. If it is not a face, AF frame automatic tracking by pattern matching processing is automatically performed. It is automatically selected and executed.

  Returning to FIG. 3, the AF frame setting unit 59 first changes (updates) the AF frame range so that the position, size, and shape are suitable for the face detected within the AF frame range. (Step S10). For example, the range recognized as the face when the face is detected by the face detection process in step S8 is changed to the range of the AF frame.

  Next, when the range of the AF frame is updated, the face area detection unit 54 takes in image data of a captured image for one frame from the decoder 52 (step S12). Then, as in step S8, face detection processing is performed to detect the face of an arbitrary person included in the captured image (step S14).

  It is determined whether or not a face has been detected by the face detection process in step S14 (step S16). If it is determined NO in step S16, the process returns to capturing image data in step S12.

  On the other hand, if YES is determined in step S16, the face area determination unit 56 determines whether the size of the face detection frame indicating the face area detected by the face area detection unit 54 is smaller than WAKU_MIN. (Step S18). Here, WAKU_MIN is a value determined as the minimum width of the AF frame set on the screen. For example, it is a value that defines the minimum number of pixels in the horizontal or vertical direction of the screen or an arbitrary direction for the AF frame set on the screen. In the example shown in FIG. 3B, when the total number of pixels in the horizontal direction of the screen is 640 pixels, WAKU_MIN = 64 pixels.

  If NO is determined in step S18, the face area determination unit 56 further determines whether or not the size of the face detection frame indicating the face area detected by the face area detection unit 54 is larger than WAKU_MAX. (Step S20). Here, WAKU_MAX is a value determined as the maximum width of the AF frame set on the screen. For example, it is a value that defines the maximum number of pixels in the horizontal or vertical direction of the screen or an arbitrary direction for the AF frame set on the screen. In the example shown in FIG. 3B, when the total number of pixels in the horizontal direction of the screen is 640 pixels, WAKU_MAX = 320 pixels.

  If NO is determined in step S20, the tracking frame setting unit 58 sets the size of the area surrounded by the tracking frame to the same size as the area surrounded by the face detection frame (step S22). . Then, the AF frame setting unit 59 sets the size of the area surrounded by the AF frame to the same size as the area surrounded by the face detection frame (step S24). As described above, when the process proceeds to step S24, as shown in FIG. 4B, the size of the area surrounded by the tracking frame and the size of the area surrounded by the AF frame are both set as shown in FIG. The same size is set, and the size is set to be the same as the size of the area surrounded by the face detection frame.

  On the other hand, if YES is determined in step S18, the tracking frame setting unit 58 sets the size of the area surrounded by the tracking frame to the same size as the area surrounded by the face detection frame (step S26). ). However, the width of the area surrounded by the AF frame in the AF frame setting unit 59 is set to WAKU_MIN (step S28). As described above, when the process proceeds to step S28, the size of the region surrounded by the AF frame is different from the size of the region surrounded by the tracking frame. Specifically, as shown in FIG. 4A, the width of the AF frame in the horizontal direction of the screen is set to WAKU_MIN, and the AF frame is set to be larger than the tracking frame.

  As a result, as shown in FIG. 4A, in a scene where the ratio of the face area of the subject to the entire screen is small, the AF frame does not become too small, and a necessary change amount in the AF evaluation value can be recognized. The effect of maintaining the focus accuracy can be obtained. On the other hand, even if the ratio of the face area of the subject to the entire screen becomes small, the tracking frame faithfully captures the range in which the face is detected, and thus the face of the subject can be tracked.

  Following such step S28, the process returns to capturing of the image data in step S12.

  If YES is determined in step S20, the tracking frame setting unit 58 sets the size of the area surrounded by the tracking frame to the same size as the area surrounded by the face detection frame (step S30). ). However, the AF frame setting unit 59 sets the width of the size of the area surrounded by the AF frame to WAKU_MAX (step S32). As described above, when the process proceeds to step S32, the size of the area surrounded by the AF frame is different from the size of the area surrounded by the tracking frame. Specifically, as shown in FIG. 4C, the width of the AF frame is set to WAKU_MAX, and the AF frame is set to be smaller than the tracking frame.

  As a result, in a scene where the ratio of the face area of the subject to the entire screen is large as shown in FIG. 4C, the AF frame does not become too large and the amount of data does not increase, so the AF processing time does not increase. An effect is obtained. On the other hand, even if the ratio of the face area of the subject to the entire screen is large, the tracking frame covers the range in which the face is detected, so that the tracking of the face of the subject can be performed reliably.

  When the operator instructs to stop the AF frame automatic tracking, that is, when the tracking stop switch is turned on, the AF frame automatic tracking process is stopped, and the process returns to step S6. That is, the AF frame is returned to the center of the imaging range and fixed, and AF frame automatic tracking is not executed.

  As described above, in the present invention, by changing the sizes of the AF frame and the tracking frame according to the shooting scene, AF can be performed with high accuracy and speed while tracking the subject.

  Specifically, a face area detection unit 54 that detects the face area of the subject, and a face area determination that determines whether the size of the face area detected by the face area detection unit 54 is within a predetermined range. When the size of the face area is determined not to be within the predetermined range by the unit 56 and the face area determination unit 56, the size of the area surrounded by the AF frame is set to the size of the area surrounded by the tracking frame. The AF frame setting unit 59 is set so as to be different from the above, so that the face area of the subject is detected and tracked regardless of the size of the face area of the subject with respect to the entire screen, and a reduction in focus accuracy is prevented. The autofocus processing time can be kept within an appropriate time.

  The autofocus system of the present invention has been described in detail above, but the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the scope of the present invention. Of course.

DESCRIPTION OF SYMBOLS 1 ... Autofocus system, 10 ... Television camera, 12 ... Lens apparatus, 14 ... Camera body, 16 ... Viewfinder, 18 ... Image processing unit, 20 ... AF frame operation part, 40 ... AF unit, 50 ... CPU, 52 ... Decoder 54... Face area detection unit 56. Face area determination unit 58. Tracking frame setting unit 59. AF frame setting unit 60. Size operation member 62. Tracking stop switch

Claims (2)

Face area detecting means for detecting the face area of the subject;
Face area determination means for determining whether or not the size of the face area detected by the face area detection means is within a predetermined range;
When the face area determining means determines that the size of the face area is not within the predetermined range, the size of the area surrounded by the AF frame indicating the area to be focused by autofocus is tracked. AF frame setting means for setting to be different from the size of the area surrounded by the tracking frame indicating the face area to be set , so that the size of the area surrounded by the AF frame falls within the predetermined range AF frame setting means to perform,
Tracking frame setting means for setting the size of the area surrounded by the tracking frame to match the size of the face area detected by the face area detection means,
When the size of the face area is smaller than the lower limit value of the predetermined range, the AF frame setting means sets the size of the area surrounded by the AF frame to match the lower limit value, When the size of the face area is larger than the upper limit value of the predetermined range, the size of the area surrounded by the AF frame is set to match the upper limit value;
Auto-focus system according to claim. The AF frame setting means determines the size of the area surrounded by the AF frame when the face area determination means determines that the size of the face area is within the predetermined range. Setting to match the size of the face area detected by the detecting means;
The autofocus system according to claim 1 .

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