JP4996568B2 - IMAGING DEVICE AND IMAGING DEVICE CONTROL METHOD - Google Patents

Description

  The present invention relates to an imaging apparatus and an imaging apparatus control method, and more particularly, to an imaging apparatus having an autofocus function and an imaging apparatus control method.

  2. Description of the Related Art Conventionally, an imaging apparatus using an imaging element such as a CCD or a CMOS image sensor and having an autofocus (AF) function is known. In such an imaging apparatus, a signal indicating contrast is extracted by an HPF (high-pass filter) from the electrical signal based on the subject image formed on the imaging element and amplified. Then, the waveform of the amplified contrast signal is analyzed, and autofocus is executed by focusing on the subject based on the analysis result. In the following, focusing on the subject is appropriately referred to as focusing.

  In other words, an imaging device equipped with an autofocus function takes advantage of the fact that when the focus is not on the subject, the waveform of the contrast signal is smooth, and when the focus is on the subject, it is steep. Perform a focusing operation. More specifically, the focus lens is moved in the optical axis direction, and the lens position where the waveform of the contrast signal obtained from the subject image output from the image sensor is steepest in accordance with lens driving is searched. This series of operations for moving the focus lens to search for the in-focus position is called autofocus scan.

  In addition, autofocus is generally performed using a central portion or a plurality of areas of a light receiving surface of an image sensor as a distance measuring area. A conventional imaging apparatus having an autofocus function detects the distance to a distance measurement area, for example, using the entire face of a subject as a person as a distance measurement area. Based on the detected distance, the focal position, the lens focal length, and the aperture value are adjusted so that the distance to the subject is within the depth of field (see, for example, Patent Document 1).

  Here, the depth of field is a range in the depth (distance) direction where the subject is clearly captured, that is, a focusing range, and changes depending on the distance from the imaging device to the subject, the lens focal length, and the aperture value. When the distance from the imaging device to the subject is long, the lens focal length is short, and the aperture value is large, the distance from the imaging device to the subject is within the depth of field. In this case, the imaging apparatus can clearly capture the subject without performing autofocus.

  Further, Patent Document 2 describes an imaging apparatus having a distance detection device that detects the distance from the imaging apparatus to the subject based on the size of the area occupied by the subject image on the photographing screen on which the photographed subject image is displayed. Has been. Further, Patent Document 3 proposes a technique for detecting a face from an imaging signal, narrowing a scan area from the face detection result, subject distance, and depth of field information, and reducing the time required for autofocus scanning. .

Japanese Patent No. 3164692 JP 2003-75717 A JP 2006-018246 A

  However, the above-described conventional imaging device has a problem in that it cannot perform autofocus with high accuracy in a state where the depth of field is deep and the face detectable range is wide. In addition, the conventional imaging apparatus has a problem in that it is not possible to sufficiently reduce the autofocus scan time that is consumed when performing autofocus.

  For example, in Patent Document 3 described above, an autofocus scan range is set according to the depth of field. For this reason, when the depth of field is deep, the range of the autofocus scan is widened, and the autofocus scan takes a long time.

  Therefore, an object of the present invention is to provide an imaging apparatus and an imaging apparatus control method that can reduce the time required for autofocus scanning.

The present invention, in order to solve the problems described above, an imaging device that outputs an imaging signal in accordance with light incident through the imaging optical system with the full Okasurenzu and the aperture, the imaging output from the imaging device A face detection means for detecting a face from the signal, a subject distance estimation means for estimating an estimated subject distance to the face detected by the face detection means, a focal length of the imaging optical system, and a value of the diaphragm A depth-of-field calculating unit that calculates a depth of field based on the control unit, and a control unit that performs autofocus control based on the imaging signal output at a predetermined cycle from the imaging element while scanning the focus lens. has the door, the subject distance estimation unit before the imaging is instructed to estimate the estimated object distance to the face, the control unit, before the imaging is instructed, the Around the current position of Okasurenzu obtains a first range indicating a range of depth of field in which the calculated in depth of field calculation unit based on the first diaphragm value set in advance, the imaging after There is instructed, said diaphragm, said first be driven to a second aperture in the opening direction than the aperture value, centered on the current position of the focus lens based on said second aperture When a second range indicating a range of depth of field calculated by the depth of field calculating unit is obtained, and when the face detecting unit detects a face from an imaging signal obtained by the second aperture value, When the second range is determined as the scan range of the focus lens in the autofocus control, and the face detection unit cannot detect a face from the imaging signal obtained with the second aperture value, Of the first range, different from the second range An imaging apparatus characterized by determining the extent that the scan range of the focus lens in the autofocus control.

Further, the present invention is a control method of the imaging device, the face detection unit, output from the imaging device that outputs an imaging signal in accordance with light incident through the imaging optical system including a focus lens and a diaphragm A face detection step for detecting a face from the imaging signal; a subject distance estimation unit; a subject distance estimation step for estimating an estimated subject distance to the face detected in the face detection step; and a depth of field calculation unit. A depth-of-field calculating step for calculating a depth of field based on a focal length of the imaging optical system and a value of the aperture; and a control unit that determines in advance from the imaging element while scanning the focus lens. and a control step of performing autofocus control based on the imaging signal outputted by the obtained period, the subject distance estimation step, before the imaging is instructed, Estimates the estimated object distance to Kikao, the control step, before the imaging is indicated, around the current position of the focus lens, the object on the basis of the first aperture value set in advance obtains a first range indicating a range of depth of field is calculated by the depth of field calculation step, after the imaging is instructed, said diaphragm, said first second open direction than aperture A second range that is driven to the aperture value and that indicates the range of the depth of field calculated by the depth of field calculation step based on the second aperture value centered on the current position of the focus lens. Then, when a face is detected by the face detection step from the imaging signal obtained with the second aperture value, the second range is determined as a scan range of the focus lens in the autofocus control, and the second range is determined . Aperture When the face is not detected by the face detection step from the imaging signal obtained in step 1, the focus lens is scanned by the autofocus control in a range different from the second range in the first range. An image pickup apparatus control method is characterized in that the range is determined .

  Since the present invention has the above-described configuration, the time required for autofocus scanning can be shortened.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an exemplary configuration of an imaging apparatus 100 applicable to the embodiment of the present invention. An imaging apparatus 100 illustrated in FIG. 1 performs imaging by attaching a lens unit 300 to the imaging apparatus 100 that is a main body.

  Light from the subject is incident on the imaging device 100 from the lens unit 300 constituting the imaging optical system, and is applied to the imaging device 101 via the mirror 114 and the shutter 115. The image sensor 101 is composed of, for example, a CCD or CMOS image sensor. The image sensor 101 converts the irradiated light into an electrical signal, performs predetermined processing such as gain adjustment and noise removal, and outputs the result as an analog image signal. The A / D converter 116 converts the analog imaging signal output from the imaging element 101 into a digital signal, and generates image data. The image storage buffer 101a temporarily stores the image data output from the A / D converter 116.

  Note that a live view can be realized by sequentially displaying image data based on an imaging signal output from the imaging element 101 at a predetermined cycle on a display device provided in the imaging device 100.

  A face information detection circuit 102 serving as a face detection unit acquires image data from the image accumulation buffer 101a, and detects face information (eye position information, face coordinates, etc.) of the subject from the acquired image data. The face size determination unit 103 determines the size of the detected face based on the information on the face of the subject detected by the face information detection circuit 102. The determined face size is output as face size information.

  The camera control unit 110 includes, for example, a microprocessor, a RAM, and a ROM. The microprocessor operates using the RAM as a work memory according to programs and data stored in advance in the ROM, and controls the overall operation of the imaging apparatus 100. To do.

  A camera control unit 110 as a control unit executes autofocus based on an AF evaluation value supplied from a camera signal processing circuit 107 described later. At the same time, the camera control unit 110 communicates with the lens unit 300 via an interface 119 described later, and acquires the lens focal length and the aperture value. A subject distance estimation unit 104 serving as a subject distance estimation unit is based on the face size determined by the face size determination unit 103 and the lens focal length acquired by the camera control unit 110, and the subject distance from the image sensor 101 to the subject. Is estimated.

  The camera control unit 110 serving as a depth of field calculating unit further determines the depth of field based on the estimated subject distance estimated by the subject distance estimation unit 104, the lens focal length and the aperture value acquired from the lens unit 300. Is calculated.

  Furthermore, the camera control unit 110 includes an AF (autofocus) control unit 111 that controls autofocus based on the calculated depth of field. The AF control unit 111 may be a program that operates on a microprocessor included in the camera control unit 110, or may be configured as dedicated hardware separately.

  The AF control unit 111 performs autofocus control based on subject distance information output from a subject distance estimation unit 104, which will be described later, with an operation on the AF button 131 as a trigger, for example. For example, when the AF button 131 is operated, the AF control unit 111 communicates with a lens unit 300 to be described later via the interface 119 and issues a command to drive the focus lens to the lens system control unit 307. .

  Note that the shutter button 130 and the AF button 131 can be configured to be operated in conjunction with each other. For example, it is conceivable to configure a button in which the AF button 131 is operated in the half-pressed state and the shutter button 130 is operated in the fully-pressed state.

  The camera control unit 110 instructs the shutter control unit 117 to control the operation of the shutter 115 in response to an operation on the shutter button 130. The shutter control unit 117 controls the operation of the shutter 115 according to this command. The shutter 115 is controlled by the shutter controller 117 in cooperation with a diaphragm controller 304 in the lens unit 300 described later.

  In addition, the camera control unit 110 also includes an exposure (AE) control unit (not shown) and the like, and performs exposure control in addition to autofocus control to perform shooting control of the entire imaging apparatus 100. Note that the exposure control by the exposure control unit is not related to the gist of the present invention, and the description thereof will be omitted.

  The camera signal processing circuit 107 performs predetermined signal processing such as γ correction and white balance adjustment on the image data output from the A / D converter 116. In addition, the camera signal processing circuit 107 performs high-pass filter processing on the image data output from the A / D converter 116 and also performs processing for extracting a contrast signal. Then, the extracted contrast signal is analyzed, and an AF evaluation value, which is an evaluation value when performing autofocus control, is generated. The generated AF evaluation value is supplied to the camera control unit 110 and is used for focusing determination during autofocus control.

  Furthermore, the camera signal processing circuit 107 can also perform compression coding processing of image data. The compressed or uncompressed image data output from the camera signal processing circuit 107 can be recorded on the recording medium 109 by the recording circuit 108. The recording medium 109 is composed of, for example, a non-volatile memory, and can be attached to and detached from the imaging apparatus 100. The image data output from the camera signal processing circuit 107 is displayed on the display device 113 using an LCD or the like as a display device by the display circuit 112.

  On the other hand, in the lens unit 300, light from the subject is incident on the photographing lens 301 including the zoom lens and the focus lens in the lens unit 300. The incident light forms an optical image on the image sensor 101 guided through the diaphragm 302, the lens mounts 303 and 106, the mirror 114, and the shutter 115.

  The distance measurement control unit 305 controls the focusing, that is, the focusing operation of the photographing lens 301 based on the control signal from the camera control unit 110. A zoom control unit 306 controls zooming of the photographing lens 301. A diaphragm control unit 304 controls the diaphragm 302 based on a control signal from the camera control unit 110 and photometric information.

  A lens system control unit 307 (described as a lens control unit in FIG. 1) controls the entire lens unit 300. The lens system control unit 307 includes a memory that temporarily stores operation constants, variables, programs, and the like. Further, the lens system control unit 307 stores identification information such as a unique number of the lens unit 300, management information, function information such as an open aperture value, a minimum aperture value, and a focal length, and current and past setting values. It also has a memory.

  The interface 308 is an interface for performing data communication with the imaging apparatus 100. The interface 308 is electrically connected to the interface 119 on the imaging apparatus 100 side by connectors 309 and 118.

<About face detection and face size discrimination>
Next, face detection and face size discrimination applicable to this embodiment will be described. The face information detection circuit 102 performs pattern recognition processing, which will be described later with reference to FIG. 5, and detects face information from the image data. As other methods for detecting the face image data, a method using learning by a neural network or the like, and a method for extracting a characteristic part of a physical shape from an image region are known. Also known is a method of statistically analyzing image features such as the detected skin color and eye shape. Furthermore, methods that have been studied for practical use include a method that uses wavelet transform and image feature amounts.

  Here, pattern recognition is a process of matching (matching) an extracted pattern with one of predetermined concepts (classes). Template matching is a method of comparing an image and a template while moving a template meaning a pattern on the image. These methods can be used, for example, for detecting the position of a target object, tracking a moving object, and aligning images with different shooting times, and in particular, extracting physical shapes such as eyes and nose from an image region. This is a useful method for detecting face information.

  The face size determination unit 103 counts the number of pixels in the face area from the face information detected by the face information detection circuit 102, and determines the face size based on the number of pixels. The face area can be represented by, for example, coordinate information indicating an area detected as a face.

  Not limited to this, the face size determination unit 103 may determine the face size based on the eye position information among the face information detected by the face information detection circuit 102. For example, it is possible to calculate the eye interval on the image data based on the eye position information, make a table using the statistical relationship between the eye interval and the face size obtained in advance, and determine the face size. Conceivable. FIG. 2 shows an example of a statistical relationship between the face size indicated by the number of pixels on the image and the eye spacing. Thus, statistically, the face size can be uniquely associated with the eye interval on the image.

  Further, the face size may be determined by counting the number of pixels in the face area from the predetermined position of the detected face, for example, the coordinate values of the four corners.

  The subject distance estimation unit 104 estimates the subject distance from the imaging device 100 to the subject based on the face size determined by the face size determination unit 103. More specifically, the subject distance estimation unit 104 is based on the face size determined by the face size determination unit 103, and is created in advance from the relationship between the face size and the subject distance, and a conversion table for a lens with a predetermined focal length. The subject distance is estimated with reference to FIG.

  FIG. 3A shows an example of the relationship between the face size represented by the number of pixels on the image and the subject distance. As an example, a table based on the relationship shown in FIG. 3A is created for a wide-angle lens with a lens focal length of 38 mm, and the subject distance is estimated. When the lens focal length is different from 38 mm, the conversion table is referred to using a value obtained by multiplying the determined face size by (38 mm / actual lens focal length (mm)).

  Not limited to this, as illustrated in FIG. 3B, the relationship between the ratio of the detected face area to the image and the subject distance may be used as a table instead of the face size.

  Note that the subject distance varies depending on the size of the image sensor itself and the use area. Therefore, a conversion table for calculating the estimated subject distance may be regenerated according to the mode, or a plurality of conversion tables may be stored in advance. May be.

<About face detection>
Pattern recognition processing by the face information detection circuit 102 will be described with reference to the flowchart of FIG. 4 and FIG. In FIG. 4, the image data 503 acquired from the image storage buffer 101a is preprocessed (step S401), and the pattern of the characteristic part is extracted from the preprocessed image data 503 (step S402). Then, the extracted pattern of the characteristic part is made to correspond to the template 501 based on the standard pattern of the face, and template matching is performed. A recognition pattern is acquired by this template matching (step S403), the acquired recognition pattern is output to the face size determination unit 103 (step S404), and the pattern recognition process is terminated.

  An example of template matching in step S403 will be described more specifically with reference to FIG. First, the center point 502 of the template 501 is placed at a certain coordinate point (i, j) of the acquired image data 503. Then, while scanning the center point 502 in the image data 503, the similarity of the overlapping portion between the template 501 and the image data 503 is calculated, and the position where the similarity is maximized is determined. By matching a pattern extracted from the face image data 503 with a template 501 including shapes such as eyes and ears, coordinate information (face coordinates) indicating eye position information and a face area can be acquired. .

<Imaging Processing According to the Present Embodiment>

  The processing according to this embodiment will be schematically described with reference to FIG. In the first example shown in FIG. 6A, the final focal position is defined as position (B), and the position indicated in the current lens distance information is defined as position (C). In FIG. 6A and FIG. 6B described later, the vertical axis indicates the AF evaluation value, and the horizontal axis indicates the focus lens position. Note that the focus lens position is indicated by a distance focused at the focus lens position in the lens unit 300. The position where the AF evaluation value takes the maximum value is the in-focus position.

  In FIG. 6A, first, face detection is performed in a state where the focus lens is at the position (C), and when it is determined that a face is detected, the depth of field for face detection is calculated from the current aperture value. . In the example of FIG. 6A, the depth of field indicated by the range (a) is in the range of 2 m to 8 m. Next, lens aperture driving is performed to set the aperture value of the next candidate, for example, the full aperture value, and face detection is performed after the aperture driving is completed. Here, since the diaphragm 302 is driven in the open direction compared to the time of the first face detection, the depth of field is shallower, for example, 4 m to 6 m (range (c)). The aperture value of the next candidate is not limited to the full aperture value, and other aperture values can be applied as long as the current aperture value is in the open direction.

  In the example of FIG. 6A, since the final focal position is in the range (c) of the depth of field of 4 m to 6 m, it is determined that the face has been detected. Therefore, the scan range by autofocus is limited to a range (c) of a distance of 4 m to 6 m corresponding to the subject depth. Therefore, it is only necessary to perform the autofocus control within the range 4c to 6m (c). The scan range is reduced from the original scan range of 2m to 8m of 6m range (a) to the new scan range of 4m to 6m of 2m range (c), so that autofocus control can be performed at higher speed. .

  In the second example shown in FIG. 6B, the final focal position is position (C), and the position indicated by the current lens distance information is position (B). That is, the current lens position is on the near end side with respect to the final focal position. First, face detection is performed with the lens in the position (B), and if it is determined that a face has been detected, the depth of field for face detection is calculated from the current aperture value. In the example of Fig.6 (a), it is set as the range (a) whose depth of field is 2m-8m. Next, lens aperture driving is performed to set the aperture value of the next candidate, for example, the full aperture value, and face detection is performed after the aperture driving is completed.

  Here, since the diaphragm 302 is driven in the open direction compared to the time of the first face detection, the depth of field is shallower, for example, 4 m to 6 m (range (c)). Since the final focal position is not within the range (c) of the depth of field of 4 m to 6 m, it is determined in the example of FIG. 6B that no face is detected. In the range (c) of the depth of field 4m to 6m, no face was detected, so either the range (b) of the depth of field 2m to 4m or the range (d) of the depth of field 6m to 8m. A face should be detected in the range of. Here, it can be considered that the estimated subject distance estimated from the face size acquired by the face detection at the lens position (B) corresponds to the final focus position. If the accuracy of the estimated subject distance estimated from the face size is within ± 1 m, for example, the accuracy of being in either the range (b) or the range (d) increases, and the direction for performing the autofocus control is determined. Can do.

  Auto-focusing is performed at a higher speed by reducing the original scanning range from 2m to 8m, 6m range (c) to 2m to 4m or 6m to 8m range (b) or (d). It becomes possible to control. The autofocus scan range is also reduced to about 1/3 from the auto scan range of 6 m based on the original aperture value to 2 m of the new scan range, so that autofocus can be performed at higher speed.

  Next, an example method for realizing the processing described with reference to FIGS. 6A and 6B will be described with reference to the flowcharts of FIGS. Each determination and control in the flowcharts of FIGS. 7 and 8 is performed by the camera control unit 110 and / or the AF control unit 111 according to a predetermined program.

  FIG. 7 is a flowchart showing an example of processing in live view according to the present embodiment. That is, prior to the processing of the flowchart of FIG. 7, it is assumed that the imaging apparatus 100 is operating in the live view mode, the mirror 114 is in the flipped state, and the shutter 115 is in the open state. Image data based on the imaging signal output from the imaging element 101 at a predetermined interval is sequentially displayed on the display device 113 via the display circuit 112, and a live view operation is performed.

  First, in step S6101, the camera control unit 110 calculates the aperture value (first aperture value) controlled by the depth of field adjustment and the AE control unit (not shown). The aperture value does not slow down the frame rate of the live view so that it does not hinder the display of the live view, and the face information detection circuit can perform face detection over a wide range while suppressing the amount of noise. Selected. Based on the calculated aperture value, the aperture controller 304 is controlled to drive the aperture 302.

  In accordance with the light emitted through the lens unit 300, image data based on the imaging signal output from the imaging element 101 is stored in the image accumulation buffer 101a. The face information detection circuit 102 acquires image data from the image accumulation buffer 101a (step S6102). In next step S6103, the face information detection circuit 102 determines whether or not a face is detected from the acquired image data.

  If it is determined that a face is not detected, the process proceeds to step S6111, where normal autofocus control, for example, autofocus control according to the prior art is awaiting to start.

  On the other hand, if it is determined in step S6103 that a face has been detected, the process proceeds to step S6104, and the AF control unit 111 acquires the focal length information of the lens unit 300. Then, in the next step S6105, the current lens distance position information is acquired. For example, the camera control unit 110 communicates with the lens system control unit 307 of the lens unit 300 via the interface 119 and the like, and the focal length information and the lens distance position information are acquired. The acquired focal length information and lens distance position information are passed to the AF control unit 111. The lens distance position information is information indicating a focusing distance corresponding to the current position of the focus lens.

The process moves to step S6106, and the face size is calculated based on the face information detected by the face size determination unit 103 in step S6103. In the next step S6107, the subject distance estimation unit 104 estimates the distance to the subject based on the face size acquired in step S6106 and the focal length information acquired in step S6104. On the other hand , the depth of field is calculated in step S6108 based on the focal length information and the aperture information. Here, for example, it is assumed that the range (a) illustrated in FIG. 6A or FIG. 6B, that is , 6 m having a distance of 2 m to 8 m is calculated as the depth of field.

Then, based on the current lens distance position information acquired in step S6105 and the calculated depth of field, the range in which autofocus scanning is performed is limited in the next step S6109, and the present invention is implemented in step S6110. A start waiting state of autofocus control (referred to as face AF control) according to the form is set. Details of limiting the autofocus scan range in step S6109 will be described later.

  FIG. 8 is a flowchart illustrating an example of processing when, for example, an imaging operation is performed on the imaging apparatus 100 during the live view operation according to the flowchart of FIG. 7 described above. That is, FIG. 8 shows an example of processing at the time of imaging operation performed after step S6110 in the flowchart of FIG. When the AF button 131 or the shutter button 130 is operated, the face AF control is started. First, in step S6201, the camera control unit 110 communicates with the lens unit 300 to acquire the current aperture value. In the next step S6202, the acquired current aperture value is the same as the next candidate aperture value. Is determined. If it is determined that both are the same, the process proceeds to step S6203, and AF control is performed in the scan range based on the current aperture value (first candidate aperture value). After the AF control in step S6203, the process proceeds to step S6216, and an in-focus determination is made.

  On the other hand, if it is determined in step S6202 that the current aperture value is different from the next candidate aperture value, the process proceeds to step S6204. In step S6204, the next candidate aperture value is calculated, and the aperture control unit 304 is controlled by the camera control unit 110 according to the calculated next candidate aperture value (second candidate aperture value), and the aperture 302 is driven. The next candidate aperture value is, for example, a value that drives the aperture 302 by a predetermined amount in the opening direction with respect to the current aperture value (second aperture value).

  For the next candidate aperture value, in order to limit the scan range by autofocus and shorten the scan time, aperture value candidates are tabulated in advance for each lens, focal length, and subject distance and stored in the ROM. deep. In addition to this, in order to improve versatility, the next candidate aperture value may be calculated from depth-of-field information that can be acquired from the lens unit 300.

  When the diaphragm 302 is driven in step S6204, the process proceeds to step S6219, and the face information detection circuit 102 acquires the image data stored in the image accumulation buffer 101a. In step S6205, it is determined whether a face is detected from the acquired image data. If it is determined that a face has been detected, the process proceeds to step S6206.

  In step S6206, the AF control unit 111 calculates the depth of field based on the focal length information and the current aperture information. Here, it is assumed that the range (c) illustrated in FIG. 6A or 6B, that is, the distance of 4 m to 6 m is calculated as the depth of field. In the next step S6207, the autofocus scan range is limited according to the calculated depth of field, and autofocus control is performed in the scan range based on the second candidate aperture value (step S6207). S6208). Then, the process proceeds to step S6216, and an in-focus determination is made.

  Face detection using the second candidate aperture value is a state in which the aperture is opened more than the aperture value at the time of face detection performed before the first AF button 131 or shutter button 130 is operated in step S6102 of FIG. Thus, the process is performed based on the image data captured by the image sensor 101. Therefore, the depth of field becomes shallow and the range in which the face can be detected becomes narrow, and it is only necessary to perform autofocus control within this narrowed range. That is, it is possible to narrow the autofocus scan range.

  On the other hand, if it is determined in step S6205 that a face has not been detected, the process proceeds to step S6209. In step S6209, the depth of field is calculated based on the focal length information (see step S6105) when the face is detected in step S6103 of FIG. 7 and the current aperture information. Here, it is assumed that the range (c) illustrated in FIG. 6A or 6B, that is, the distance of 4 m to 6 m is calculated as the depth of field.

  In the next step S6210, the scan range by autofocus is limited according to the calculated depth of field. Then, the camera control unit 110 compares the scan range limited in step S6210 with the scan range limited in step S6109 in FIG. 7, and stores the difference. In the example of FIG. 6A or 6B described above, this difference becomes a range (b) of a distance 2 m to 4 m and a range (d) of a distance 6 m to 8 m.

  The process moves to step S6211, and the estimated subject distance estimated based on the face size information in step S6107 in FIG. 7 is compared with the lens distance information acquired in step S6105 in FIG. As a result of the comparison, if it is determined that the estimated subject distance estimated based on the face size information is closer than the distance indicated by the lens distance information, the process proceeds to step S6212.

  In step S6212, the autofocus scan range is limited to the range on the close end side. Then, in the next step S6213, the difference from the scan range based on the aperture value of the second candidate, that is, the range indicated by the difference at the closest end among the differences stored in step S6210 is set as the scan range. Auto focus control is performed. In the example of FIG. 6A or 6B described above, the range (b) having a distance of 2 m to 4 m is set as the scan range. Then, the process proceeds to step S6216, and focus determination is performed.

  On the other hand, if it is determined in step S6211 that the estimated subject distance estimated based on the face size information is farther than the distance indicated by the lens distance information, the process proceeds to step S6214, and the autofocus scan range is infinite. Limited to end side. In the next step S6215, the difference from the scan range based on the aperture value of the second candidate, that is, the range indicated by the difference on the infinite end side among the differences stored in step S6210 is set as the scan range. Focus control is performed. In the example of FIG. 6A or 6B described above, a range (d) having a distance of 6 m to 8 m is set as a scan range. Then, the process proceeds to step S6216, and focus determination is performed.

  In step S6216, based on the processing result described above, autofocus control is executed by any of the methods of step S6203, step S6208, step S6213, and step S6215, and the focus determination is performed. If it is determined that the in-focus state has been achieved, the process proceeds to step S6217, and for example, shooting is performed according to the operation on the shutter button 130. At the time of shooting, for example, the aperture value may be changed to a value set by the user for the imaging device 100. On the other hand, if it is determined that the in-focus state has not been achieved, the process proceeds to step S6218, the image is not taken, and the start of autofocus control is awaited.

  In consideration of a lens having a deep depth of field or a lens that is slow to drive, scanning is performed by performing aperture value change, face detection, and depth of field calculation a plurality of times in steps S6202 to S6207. The range may be further narrowed. In this case, the diaphragm 302 is driven in the opening direction by a predetermined amount with respect to the previous diaphragm value.

<Limitation of autofocus scan range>
Next, a method for limiting the autofocus range in step S6109 will be described with reference to FIG. FIG. 9 shows an example of the AF evaluation value with respect to the focus lens position according to the depth of field. In FIG. 9, the vertical axis indicates the AF evaluation value, the horizontal axis indicates the focus lens position, the curve A indicates an example where the depth of field is deep, and the curve B indicates an example where the depth of field is shallow. . A position C indicates a focal point.

  As shown by the curve A, when the depth of field is deep, the change range of the autofocus evaluation value is small, and the range in which the face can be detected becomes wide. Therefore, in order to find the focal point, it is necessary to detect the AF evaluation value from a wide autofocus range.

  On the other hand, as shown by the curve B, when the depth of field is shallow, the range of change in the autofocus evaluation value with respect to the movement of the focus lens becomes large, so the range in which the face can be detected becomes narrow. Therefore, the in-focus point can be found by detecting the AF evaluation value from the autofocus range that is narrower than that when the depth of field is deep.

  As described above, for example, the autofocus scan range is set to a predetermined multiple of the depth of field, and the area around the estimated subject distance is set as the autofocus range. As a result, when the depth of field is deep, the autofocus scan range can be wide, and when the depth of field is shallow, the autofocus scan range can be narrow.

  In this way, by using the face information obtained by changing the depth of field, the autofocus scan is performed by setting a narrow autofocus scan range. As a result, the autofocus can be performed with high accuracy and the time required for the autofocus can be shortened. Furthermore, the autofocus scan range is set so as to include the estimated subject distance estimated by the subject distance estimation unit 104, and the autofocus range is set so as to focus scanning around the estimated subject distance. To do. Thereby, efficient autofocus control can be realized.

  Here, as shown in FIGS. 10 (a) and 10 (b), the depth of field is a focal length, a lens focal length, an allowable confusion circle, and an aperture value corresponding to the estimated estimated object distance. The range from the near point to the far point determined based on the following formulas (1) and (2) is used.

Near point (depth toward you) = (hyperfocal distance (Hd) × focusing distance) / (hyperfocal distance (Hd) + focusing distance) (1)
Far point (depth toward the back side) = (hyperfocal distance (Hd) × focusing distance) / (hyperfocal distance (Hd) −focusing distance) (2)

  For example, as shown in FIG. 10B, when the hyperfocal point becomes the in-focus point, the subject is almost clear in the range from the midpoint (Hd / 2) between the imaging position (0) and the hyperfocal point to infinity. It will be reflected. The hyperfocal length increases as the lens focal length increases and the aperture value decreases. The midpoint (Hd / 2) between the imaging position (0) and the hyperfocal point is also the shortest distance point that enters the depth of field when the hyperfocal point is the focal point, that is, the near point.

The hyperfocal distance is determined based on the following equation (3).
Hyperfocal length = (lens focal length) 2 / (permissible circle of confusion × aperture value) (3)
Here, the permissible circle of confusion means “blur tolerance” that is a lower limit value that can be recognized with the naked eye at a normal observation distance.

  In the present embodiment, the depth of field calculated for limiting the autofocus range and setting the movement range of the focus lens is the focal length corresponding to the estimated subject distance estimated by the subject distance estimation unit 104. And calculated based on lens focal length information and aperture information. This is not limited to this example. For example, when the image pickup apparatus 100 is shipped from the factory, the subject distance (focusing distance) corresponding to the position of the focus lens may be measured and stored in the memory. . In this case, in step S6108 of FIG. 7, the depth of field is based on the focal length read from the memory corresponding to the focus lens position when the face was photographed in step S6102, and the lens focal length information and aperture information. Can be calculated.

1 is a block diagram illustrating a configuration of an example of an imaging apparatus applicable to an embodiment of the present invention. It is a figure which shows an example of the statistical relationship between the face size shown by the pixel count on an image, and the space | interval of eyes. It is a figure which shows the example of the relationship between face size and object distance. It is a flowchart which shows an example pattern recognition process by a face information detection circuit. It is a figure for demonstrating an example pattern recognition process by a face information detection circuit. It is a figure for demonstrating roughly the process by embodiment of this invention. It is a flowchart which shows a process of an example at the time of the live view by embodiment of this invention. 6 is a flowchart illustrating an example of processing when an imaging operation is performed on an imaging apparatus during a live view operation according to an embodiment of the present invention. It is a figure for demonstrating the method to limit an auto-focus range. It is a figure for demonstrating the depth of field.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image pick-up device 101 Image pick-up element 101a Image storage buffer 102 Face information detection circuit 103 Face size discrimination | determination part 104 Subject distance estimation part 107 Camera signal processing circuit 110 Camera control part 111 AF control part 114 Mirror 115 Shutter 116 A / D converter 119 Interface 130 shutter button 131 AF button 300 lens unit 301 photographing lens 302 aperture 304 aperture control unit 307 lens system control unit

Claims (5)

An imaging device that outputs an imaging signal in accordance with light incident through the imaging optical system with the full Okasurenzu and stop,
Face detection means for detecting a face from the imaging signal output from the imaging device;
Subject distance estimation means for estimating an estimated subject distance to the face detected by the face detection means;
A depth-of-field calculating means for calculating a depth of field based on a focal length of the imaging optical system and a value of the diaphragm;
Control means for performing autofocus control based on the image pickup signal output at a predetermined cycle from the image pickup device while scanning the focus lens;
The subject distance estimating means estimates an estimated subject distance to the face before imaging is instructed,
The control means includes
Before the imaging is instructed, a range of the depth of field calculated by the depth of field calculation means based on a preset first aperture value centered on the current position of the focus lens is set. Find the first range to show,
After the imaging is instructed, said diaphragm, said also driven in a second aperture in the opening direction than the first aperture value, centered on the current position of the focus lens, the second diaphragm value A second range indicating a range of the depth of field calculated by the depth of field calculation means based on
When the face detection unit detects a face from the imaging signal obtained with the second aperture value, the second range is determined as a scan range of the focus lens in the autofocus control ,
When the face detection unit cannot detect a face from the imaging signal obtained with the second aperture value, a range different from the second range in the first range is determined by the autofocus control. An imaging apparatus comprising: determining a scan range of the focus lens . Wherein,
If from said image signal obtained in the previous SL second aperture face detecting means does not detect the face, compared with the focal length corresponding to the current position and the previous Ki推 constant object distance of the focus lens And
If the estimated subject distance is farther than the focal distance, of the first range, to determine the scope of the infinite side than the second range to scan range of the focus lens in the autofocus control ,
If the estimated subject distance is shorter than the in-focus distance, a range closer to the second range than the second range in the first range is determined as a scan range of the focus lens in the autofocus control. The imaging apparatus according to claim 1. The control means includes
After the imaging is instructed, it performs face detection by the face detection unit from the image signal obtained by a predetermined amount driven in an opening direction of the throttle from the first aperture, when a face is detected Further , a process of detecting the face by the face detection means from the image pickup signal obtained by driving the diaphragm in the open direction by a predetermined amount is repeatedly performed, and the aperture value in the open direction in which the face is detected is set to the first value . The imaging apparatus according to claim 1 or 2 , wherein the aperture value is 2 . The subject distance estimating means includes
The imaging apparatus according to any one of claims 1 to 3, wherein the estimated subject distance is estimated based on a size of an image of the face detected by the face detection unit based on the imaging signal. . A method for controlling an imaging device,
A face detection step in which a face detection unit detects a face from the imaging signal output from an imaging element that outputs an imaging signal according to light incident through an imaging optical system including a focus lens and an aperture; and
A subject distance estimation means for estimating an estimated subject distance to the face detected in the face detection step;
A depth of field calculating means for calculating a depth of field based on a focal length of the imaging optical system and a value of the aperture; and
A control step for performing autofocus control based on the imaging signal output at a predetermined cycle from the imaging element while scanning the focus lens;
The subject distance estimation step estimates an estimated subject distance to the face before imaging is instructed,
The control step includes
Before the imaging is instructed, a range of the depth of field calculated by the depth of field calculation step based on a preset first aperture value centered on the current position of the focus lens is set. Find the first range to show,
After the imaging is instructed, said diaphragm, said also driven in a second aperture in the opening direction than the first aperture value, centered on the current position of the focus lens, the second diaphragm value A second range indicating a range of depth of field calculated by the depth of field calculation step based on,
When a face is detected by the face detection step from the imaging signal obtained with the second aperture value, the second range is determined as a scan range of the focus lens in the autofocus control ,
When a face cannot be detected by the face detection step from the imaging signal obtained with the second aperture value, a range different from the second range in the first range is determined by the autofocus control. A control method for an imaging apparatus , wherein the scan range of the focus lens is determined .

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