JP2011039335A - Focusing device and imaging apparatus including the same - Google Patents

Abstract

To provide a focus adjustment device capable of selecting a focus adjustment activation form corresponding to a change in a subject when a focus evaluation value changes by a predetermined value or more.
An image pickup means for picking up an image formed by an optical system and outputting an image pickup signal; and a focus for detecting a focus evaluation value based on the image pickup signal in association with a focus adjustment position of the optical system. Detection means 21, target detection means 21 for detecting an image of a specific target in the image by the optical system, and a change amount of the focus evaluation value when the optical system is at a specific focus adjustment position is a first predetermined value. The focus adjustment of the optical system is started, and based on whether or not the amount of change in the position of the image of the specific object in the image plane of the optical system exceeds a second predetermined value. And a control means 21 for varying the focus adjustment activation mode of the optical system.
[Selection] Figure 1

Description

  The present invention relates to a focus adjustment apparatus and an imaging apparatus including the same.

  2. Description of the Related Art Conventionally, in an imaging apparatus such as a digital camera, a technique for performing focus adjustment of an optical system using a focus evaluation value based on a high-frequency component of an image captured by an image sensor is known. In such an imaging apparatus, when focus adjustment is performed on a subject during moving image shooting, it is determined that the state of the subject has changed when the focus evaluation value changes by a predetermined amount, and the focus adjustment operation is performed. A technique for restarting is disclosed (see Patent Document 1).

JP 2003-121721 A

  However, such as when the subject moves in a direction perpendicular to the optical axis and a part of the subject moves out of the focus detection area for performing focus detection, or when the subject turns sideways from the front-facing state, etc. The focus evaluation value may change even though the subject distance does not change. On the other hand, in the above prior art, when the focus evaluation value changes by a predetermined amount, the focus adjustment operation is restarted even if the subject distance does not change. However, there is a problem that power is wasted due to unnecessary image adjustment or unnecessary focus adjustment operation.

  The problem to be solved by the present invention is to provide a focus adjustment device capable of selecting a focus adjustment activation form corresponding to a change in a subject when a focus evaluation value changes by a predetermined value or more.

  The present invention solves the above problems by the following means. In addition, although the code | symbol corresponding to drawing which shows embodiment of this invention is attached | subjected and demonstrated, this code | symbol is only for making an understanding of this invention easy, and is not the meaning which limits this invention.

  [1] A focus adjustment apparatus according to the present invention includes an image pickup means (22) for picking up an image formed by an optical system and outputting an image pickup signal, and a focus evaluation value based on the image pickup signal, Focus detection means (21) for detecting in association with a focus adjustment position, target detection means (21) for detecting an image of a specific object in the image by the optical system, and when the optical system is at a specific focus adjustment position When the amount of change in the focus evaluation value exceeds a first predetermined value, the focus adjustment of the optical system is started, and the amount of change in the position of the specific target image in the image plane of the optical system Control means (21) for varying the focus adjustment activation form of the optical system based on whether or not the second predetermined value is exceeded.

  [2] In the invention related to the focus adjustment device, the control means (21) may determine the specific focus adjustment when the change amount of the position of the image of the specific target is less than the second predetermined value. The optical system is focused in the vicinity of the position.

  [3] In the invention relating to the focus adjusting apparatus, the control means (21) may further include the optical system when the amount of change in the position of the image of the specific target is greater than or equal to the second predetermined value. The focus adjustment activation form of the optical system is made different based on the size of the image of the specific object in the image.

  [4] In the invention related to the focus adjustment device, the control means (21) may be arranged near the specific focus adjustment position when the size of the image of the specific target is a third predetermined value or more. The optical system is focused.

  [5] In the invention related to the focus adjustment device, the control means (21) sets an adjustment range when adjusting the focus of the optical system in the vicinity of the specific focus adjustment position to a depth of focus of an image by the optical system. It is characterized by determining based on.

  [6] In the invention related to the focus adjustment device, the control means (21) prohibits activation of focus adjustment of the optical system when a composition change occurs.

  [7] An imaging apparatus according to the present invention includes the focus adjustment apparatus according to the above invention.

  [8] In the invention related to the imaging apparatus, the control means (21) may cause the amount of change in the focus evaluation value when the optical system is at a specific focus adjustment position during the continuous shooting to be the first predetermined value. When it exceeds, the focus adjustment of the optical system is started.

  ADVANTAGE OF THE INVENTION According to this invention, when a focus evaluation value changes more than predetermined value, the focus adjustment apparatus which can select the focus adjustment starting form according to the to-be-photographed object's change can be provided.

FIG. 1 is a block diagram showing a digital camera 1 according to this embodiment. FIG. 2 is a flowchart showing an operation example of the camera 1 of the present embodiment. FIG. 3 is a flowchart showing another operation example of the camera 1 of the present embodiment.

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

  FIG. 1 is a main part configuration diagram showing a digital camera 1 according to an embodiment of the present invention. A digital camera 1 according to the present embodiment (hereinafter simply referred to as a camera 1) includes a camera body 2 and a lens barrel 3, and the camera body 2 and the lens barrel 3 are detachably coupled by a mount unit 4. Yes.

  The lens barrel 3 is an interchangeable lens that can be attached to and detached from the camera body 2. As shown in FIG. 1, the lens barrel 3 includes a photographic optical system including lenses 31, 32, 33 and a diaphragm 34.

  The lens 32 is a focus lens, and can adjust the focal length of the photographing optical system by moving in the direction of the optical axis L1. The focus lens 32 is provided so as to be movable along the optical axis L1 of the lens barrel 3, and its position is adjusted by the focus lens drive motor 36 while its position is detected by the encoder 35.

  The specific configuration of the moving mechanism along the optical axis L1 of the focus lens 32 is not particularly limited. For example, a rotating cylinder is rotatably inserted into a fixed cylinder fixed to the lens barrel 3, a helicoid groove (spiral groove) is formed on the inner peripheral surface of the rotating cylinder, and the focus lens 32 is fixed. The end of the lens frame is fitted into the helicoid groove. Then, by rotating the rotating cylinder by the focus lens drive motor 36, the focus lens 32 fixed to the lens frame moves straight along the optical axis L1.

  As described above, the focus lens 32 fixed to the lens frame by rotating the rotary cylinder with respect to the lens barrel 3 moves straight in the direction of the optical axis L1, but the focus lens drive motor 36 as the drive source is the lens. The lens barrel 3 is provided. The focus lens drive motor 36 and the rotary cylinder are connected by a transmission composed of a plurality of gears, for example, and when the drive shaft of the focus lens drive motor 36 is driven to rotate in any one direction, it is transmitted to the rotary cylinder at a predetermined gear ratio. Then, when the rotating cylinder rotates in any one direction, the focus lens 32 fixed to the lens frame moves linearly in any direction of the optical axis L1. When the drive shaft of the focus lens drive motor 36 is rotated in the reverse direction, the plurality of gears constituting the transmission also rotate in the reverse direction, and the focus lens 32 moves straight in the reverse direction of the optical axis L1. .

  The position of the focus lens 32 is detected by the encoder 35. As described above, the position of the focus lens 32 in the optical axis L1 direction correlates with the rotation angle of the rotating cylinder, and can be obtained by detecting the relative rotation angle of the rotating cylinder with respect to the lens barrel 3, for example.

  As the encoder 35 of this embodiment, an encoder that detects the rotation of a rotating disk coupled to the rotational drive of the rotating cylinder with an optical sensor such as a photo interrupter and outputs a pulse signal corresponding to the number of rotations, or a fixed cylinder And the contact point of the brush on the surface of the flexible printed wiring board provided on either one of the rotating cylinders, and the brush contact provided on the other, the amount of movement of the rotating cylinder (in either the rotational direction or the optical axis direction) A device that detects a change in the contact position according to the detection circuit using a detection circuit can be used.

  The focus lens 32 can move in the direction of the optical axis L1 from the closest end to the infinite end by the rotation of the rotating cylinder described above. Incidentally, the current position information of the focus lens 32 detected by the encoder 35 is sent to the camera control unit 21 to be described later via the lens control unit 37, and the focus lens drive motor 36 calculates the focus calculated based on this information. The driving position of the lens 32 is driven by a command signal sent from the camera control unit 21 via the lens control unit 37.

  The diaphragm 34 is configured such that the aperture diameter around the optical axis L1 can be adjusted in order to limit the amount of light flux that passes through the photographing optical system and reaches the image sensor 22 and to adjust the blur amount. The adjustment of the aperture diameter by the diaphragm 34 is performed, for example, by sending an appropriate aperture diameter calculated in the automatic exposure mode from the camera control unit 21 via the lens control unit 37. Further, the set aperture diameter is input from the camera control unit 21 to the lens control unit 37 by a manual operation by the operation unit 27 provided in the camera body 2. The aperture diameter of the aperture 34 is detected by an aperture sensor (not shown), and the lens controller 37 recognizes the current aperture diameter.

  On the other hand, the camera body 2 is provided with an imaging element 22 that receives the light beam from the photographing optical system on the optical axis L1 and on the planned focal plane of the photographing optical system. The image sensor 22 is composed of a device such as a two-dimensional CCD image sensor, a MOS sensor, or a CID, and converts the received optical signal into an analog image signal. The analog image signal generated by the image sensor 22 is transmitted to an AFE (Analog front end) circuit 28.

  An AFE (Analog front end) circuit 28 receives the analog image signal output from the image sensor 22 and performs gain adjustment by amplifying the analog image signal in accordance with the ISO sensitivity. The AFE circuit 28 also includes an A / D converter. The A / D converter converts the analog image signal after gain adjustment into a digital image signal and transmits the digital image signal to the camera control unit 21.

  The camera body 2 is provided with an observation optical system for observing an image picked up by the image pickup device 22. The observation optical system of the present embodiment includes an electronic view finder (EVF) 25 composed of a liquid crystal display element, a liquid crystal driving circuit 24 for driving the electronic view finder (EVF), and an eyepiece lens 26. The liquid crystal drive circuit 24 reads captured image information captured by the image sensor 22 and sent to the camera control unit 21, and drives the electronic viewfinder 25 based on the read image information. As a result, the user can observe the current captured image through the eyepiece lens 26. In place of or in addition to the observation optical system using the optical axis L2, a liquid crystal display can be provided on the back surface of the camera body 2, and a captured image can be displayed on the liquid crystal display.

  A camera control unit 21 is provided in the camera body 2. The camera control unit 21 includes peripheral components such as a microprocessor and a memory, and includes an AF calculation unit, a characteristic subject calculation unit, and a calculation unit for performing calculations for controlling each unit constituting the camera 1. Yes.

  The AF calculation unit of the camera control unit 21 calculates a focus evaluation value used when performing focus adjustment of the photographing optical system by the focus lens 32 based on the photographed image information sent from the AFE circuit 28 to the camera control unit 21. calculate. In addition, when a subject recognition mode in which specific subject recognition is performed by a specific subject calculation unit described later is selected, the AF calculation unit extracts a predetermined high-frequency component from the spatial frequency of the image data in the specific subject area. The absolute values of the extracted high frequency components are integrated. On the other hand, in a normal shooting mode in which specific subject recognition is not performed, a predetermined high-frequency component is extracted from the spatial frequency of image data in a preset focus detection area and extracted, as is conventionally known. Accumulate absolute values of high frequency components. For example, in the case of multi-area autofocus, a plurality of focus detection areas having a predetermined size are arranged at predetermined positions on the screen. This integrated value is the focus evaluation value, and the focus evaluation value represents the contrast of the image in the focus detection area or the specific subject area set as the focus detection area.

  Then, the camera control unit 21 drives the focus lens drive motor 36 by controlling the focus lens drive motor 36 via the lens control unit 37 based on the focus evaluation value calculated by the AF calculation unit, As a result, the focus lens 32 is moved to a lens position where the focus evaluation value reaches a peak.

  The specific subject calculation unit of the camera control unit 21 detects the specific subject region in the image by comparing the template image data (reference image data) with the captured image. Such a specific subject detection function by the specific subject calculation unit includes, for example, face recognition for recognizing a human face area. A plurality of template image data is stored in advance in a memory provided in the camera control unit 21, and the photographer can select desired template image data from among them. Alternatively, the photographer may designate a specific subject area from the photographed images and store it as a template image.

  In addition, the specific subject calculation unit of the camera control unit 21 searches an image data area that matches the template image data by using a pattern matching method from images repeatedly shot. When the specific subject is recognized in the image, the coordinates indicating the position and size of the recognized specific subject area are output, and the camera control unit 21 receives the coordinates of the specific subject area from the specific subject calculation unit. Then, based on the information, an operation for adjusting the focus on the specific subject, an operation for tracking the specific subject, and the like are performed.

  The operation unit 27 is a shutter release button or an input switch for the user to set various operation modes of the camera 1, and switches between a still image shooting mode / moving image shooting mode, an auto focus mode / manual focus mode, In the autofocus mode, the one-shot mode / continuous mode can be switched and the subject recognition mode for recognizing a specific subject can be selected. Various modes set by the operation unit 27 are sent to the camera control unit 21, and the operation of the entire camera 1 is controlled by the camera control unit 21.

  Next, the operation of this embodiment will be described. FIG. 2 is a flowchart showing an operation example of the camera 1 of the present embodiment.

  In the following, an example will be described in which the shooting mode is set to the moving image shooting mode and the subject recognition mode for recognizing a specific subject is selected from the autofocus modes. In the following operation example, a case where a face area (face area) is detected by face recognition for recognizing a person's face area when a specific subject is recognized will be described as an example.

  Further, the process described below is performed every time the focus evaluation value is calculated by the AF calculation unit of the camera control unit 21 in a state where the focus lens 32 is stopped (a state in which the focus adjustment operation is not performed). To be executed.

  First, in step S1, it is determined whether or not the focus evaluation value calculated by the AF calculation unit of the camera control unit 21 has changed compared to the previous processing. Specifically, the focus evaluation value calculated at the time of the current process is compared with the focus evaluation value calculated at the time of the previous process, and the focus evaluation is based on whether or not these differences are equal to or greater than a predetermined value. A determination is made as to whether the value has changed. Here, in this operation example, since the subject recognition mode is set and the face recognition for recognizing the face area of the person is performed when the specific subject is recognized, it is calculated by the AF calculation unit. The focus evaluation value relates to an image in the face area where the face area is detected. If the focus evaluation value has changed by a predetermined value or more, the process proceeds to step S2, and if the focus evaluation value has not changed by a predetermined value or more (if the amount of change is less than the predetermined value or has changed completely). If not, the process ends without performing steps S2 to S9, which will be described later, and waits until the AF calculation unit calculates the focus evaluation value again.

  In step S2, the specific subject calculation unit of the camera control unit 21 performs specific subject recognition by face recognition by pattern matching using a template, and whether or not the position of the recognized face area in the shooting screen has moved. Is determined. Specifically, the camera control unit 21 reads the history information of the face area position within a predetermined period (for example, about several frames) before the previous process stored in the memory provided in the camera control unit 21. The amount of movement of the face area position within the predetermined period is calculated. If the face area position has moved by a predetermined amount or more in the predetermined period, it is determined that the face area position has moved, and the process proceeds to step S3. On the other hand, if the face area position has not moved by a predetermined amount or more in the predetermined period (if the moving amount is less than the predetermined amount or has not moved at all), the process proceeds to step S4.

  When determining whether or not the face area position has moved by a predetermined amount or more, for example, when the face area has moved by a length equal to or greater than the vertical or horizontal length of the face area within a predetermined period. In other words, it can be determined that the face area position has moved by a predetermined amount or more when the face area position has moved to such an extent that it does not overlap the original face area position within a predetermined period.

  In step S3, the size of the recognized face area is calculated based on the result of the specific subject recognition by the face recognition performed in step S2, and whether or not the size of the face area in the shooting screen is equal to or larger than a predetermined value. Is determined. When determining whether or not the size of the face area is equal to or larger than a predetermined value, for example, when the size of the face area is 1/20 or more of the shooting magnification, or the reference number of imaging pixels When it occupies 5% or more, it can be determined that the size of the face area is greater than or equal to a predetermined value.

  If it is determined in step S3 that the size of the face area is equal to or larger than the predetermined value, the process proceeds to step S4, and a proximity search that performs focus adjustment in a relatively narrow range is executed. On the other hand, when it is determined that the size of the face area is not equal to or larger than the predetermined value (when the size of the face area is less than the predetermined value), the process proceeds to step S6, and a restart search for performing focus adjustment in a wide range is executed. .

  Here, when it is determined in step S3 that the size of the face area is equal to or larger than the predetermined value, the specific subject is the main subject in the screen, and the focus evaluation value is obtained even with a small change in the orientation and position of the face. It is considered that there is a high possibility that the amount of change in the distance (photographing distance) between the camera 1 and the specific subject is small while the face area position is likely to change. Therefore, in this embodiment, when it is determined that the size of the face area is equal to or larger than the predetermined value, the process proceeds to step S4 described later, and a proximity search that performs focus adjustment in a relatively narrow range is executed.

  On the other hand, if it is determined in step S2 that the position of the face area is moving, and it is determined in step S3 that the size of the face area is less than a predetermined value, the interval between the camera 1 and the specific subject is determined. The distance (shooting distance) is relatively large and the specific subject is likely to move in the optical axis direction, and therefore the distance between the camera 1 and the specific subject may have changed. It is considered high. Therefore, in the present embodiment, if it is determined in step S2 that the face area position is moving, and if it is determined in step S3 that the size of the face area is less than a predetermined value, steps described later are performed. Proceeding to S6, a restart search for performing focus adjustment over a wide range is executed.

  If it is determined in step S2 that the amount of movement of the face area position is less than the predetermined amount, and even if the amount of movement of the face area position is greater than or equal to the predetermined amount, the size of the face area on the shooting screen is a predetermined value. If it is determined that the above is true, the process proceeds to step S4 and a neighborhood search is performed. The proximity search is a search for detecting the peak of the focus evaluation value by calculating the focus evaluation value by the AF calculation unit while moving the focus lens 32 in the vicinity of the lens position of the current focus lens 32. is there. The search range in the vicinity search is not particularly limited as long as it is in the vicinity of the current lens position of the focus lens 32. For example, a range within 2 to 3 times the depth of focus of the image by the optical system is particularly preferable. From the viewpoint of the quality of a captured image to be obtained, it is preferable to be within the range of the focal depth of the image by the optical system. Alternatively, the search range in the neighborhood search can be a range in which the moving amount of the image plane is ± 100 μm.

  Next, in step S5, it is determined whether or not the peak of the focus evaluation value has been detected as a result of the proximity search in step S4. When the peak of the focus evaluation value is obtained, the process proceeds to step S8, and the position of the focus lens 32 is set to the position where the focus evaluation value reaches the peak, and it is determined that the focus is achieved. On the other hand, when the focus evaluation value peak is not detected, the process proceeds to step S6.

  If it is determined in step S3 that the size of the face area in the shooting screen is less than the predetermined value, or if no focus evaluation value peak is detected in step S5, the process proceeds to step S6. A startup search is performed. The restart search is a search for calculating the focus evaluation value by the AF calculation unit and detecting the peak of the focus evaluation value while moving the focus lens 32 in a wider range than the vicinity search described above. Specifically, in the restart search, the focus evaluation value is calculated by the AF calculation unit while moving the focus lens 32 in the direction in which the focus evaluation value increases, and the peak of the focus evaluation value is detected. Alternatively, the search operation is executed until the focus lens 32 moves to the infinite end position or the closest end position within the driveable range.

  Next, in step S7, it is determined whether or not a peak of the focus evaluation value has been detected as a result of the restart search in step S6. When the peak of the focus evaluation value is obtained, the process proceeds to step S8, and the position of the focus lens 32 is set to the position where the focus evaluation value reaches the peak, and it is determined that the focus is achieved. On the other hand, if the focus evaluation value peak is not detected, the process proceeds to step S9.

  In step S9, since the peak of the focus evaluation value is not detected as a result of the restart search in step S7, in-focus processing is performed. As an example of the in-focus process, there is a process of moving the focus lens 32 to a predetermined lens position, for example, the closest end.

  The camera 1 of this embodiment operates as described above. In the above, the shooting mode is set to the moving image shooting mode, and as a result, a scene in which auto focus is always performed is illustrated. However, in addition to the moving image shooting mode, the continuous mode (half of the release button) is used. A mode for repeatedly performing the focus adjustment operation regardless of the pressing operation is selected, and the same can be applied to the case where live view display is performed using an image captured by the image sensor 22.

  In this embodiment, when a specific subject is recognized by face recognition for recognizing a human face area, and the focus evaluation value of an image corresponding to the specific subject changes, the size of the face area in the shooting screen is calculated. If the size of the face area is equal to or larger than the predetermined value, a neighborhood search that performs a search in the vicinity of the lens position of the current focus lens 32 is executed instead of a restart search that performs focus adjustment over a wide range. is there. Therefore, it is possible to effectively prevent an unnecessary focus adjustment operation, thereby saving power. Further, by preventing an unnecessary focus adjustment operation, it is possible to improve responsiveness, and it is also possible to effectively prevent a blurred image from being shot during moving image shooting.

  The embodiment described above is described for facilitating the understanding of the invention, and is not described for limiting the invention. Therefore, each element disclosed in the above embodiment includes all design changes and equivalents belonging to the technical scope of the above invention.

  For example, in the above-described embodiment, a case where a face area (face area) is detected by face recognition for recognizing a person's face area when a specific subject is recognized has been described as an example. However, a specific subject is recognized. The method for this is not particularly limited to the method by face recognition, and various methods can be used.

  Also, as shown in FIG. 3, when it is determined in step S1 that the focus evaluation value has changed, it is determined whether or not the composition has been changed (step S1 ′ in FIG. 3), and the composition is changed. Only when the operation is not performed, the above-described operations of steps S2 to S9 may be performed. FIG. 3 is a flowchart showing another operation example of the camera 1 of the present embodiment. In this case, the composition can be changed by, for example, using an angular velocity sensor (not shown) provided in the camera body 2 to detect whether or not the panning operation of the camera 1 has been performed by the angular velocity sensor. A determination can be made as to whether or not this has been done.

DESCRIPTION OF SYMBOLS 1 ... Digital camera 2 ... Camera body 21 ... Camera control part 22 ... Imaging device 3 ... Lens barrel 32 ... Focus lens 36 ... Focus lens drive motor 37 ... Lens control part

Claims (8)

An image pickup means for picking up an image formed by the optical system and outputting an image pickup signal;
Focus detection means for detecting a focus evaluation value based on the imaging signal in association with a focus adjustment position of the optical system;
Object detection means for detecting an image of a specific object in the image by the optical system;
When the amount of change in the focus evaluation value when the optical system is at a specific focus adjustment position exceeds a first predetermined value, the focus adjustment of the optical system is started, and in the image plane of the optical system Control means for varying a focus adjustment activation form of the optical system based on whether or not a change amount of the position of the image of the specific object exceeds a second predetermined value. apparatus. The focus adjustment apparatus according to claim 1,
The control means adjusts the optical system in the vicinity of the specific focus adjustment position when the amount of change in the position of the image of the specific target is less than the second predetermined value. Focus adjustment device. The focusing apparatus according to claim 1 or 2,
When the amount of change in the position of the image of the specific target is equal to or greater than the second predetermined value, the control unit is further based on the size of the image of the specific target in the image of the optical system, A focus adjustment device characterized in that a focus adjustment activation form of the optical system is made different. The focus adjustment apparatus according to claim 3.
The control means adjusts the focus of the optical system in the vicinity of the specific focus adjustment position when the size of the image of the specific target is a third predetermined value or more. . In the focus adjustment apparatus according to any one of claims 2 to 4,
The focus adjustment apparatus, wherein the control means determines an adjustment range when the optical system is focused in the vicinity of the specific focus adjustment position based on a focal depth of an image by the optical system. In the focus adjustment apparatus according to any one of claims 1 to 5,
The focus adjustment apparatus is characterized in that the control means prohibits activation of focus adjustment of the optical system when a composition change occurs.   An imaging apparatus comprising the focus adjustment apparatus according to claim 1. The imaging apparatus according to claim 7,
The control means activates focus adjustment of the optical system when a change amount of a focus evaluation value when the optical system is at a specific focus adjustment position exceeds the first predetermined value during continuous shooting. An imaging apparatus characterized by that.

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