JP2007279333A - Device and method for deciding focusing position - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily bring a remote subject into focus in a device and a method for deciding a focusing position used for a digital camera or the like equipped with an automatic focusing function. <P>SOLUTION: A subject image formed through an imaging optical system is converted into image data, and a predetermined object is detected from the image data. Whether the detected predetermined object is included in the center area of an image shown by the image data is discriminated, and the object nearest to the center of the image is extracted out of the objects discriminated to be included in the center area. A focusing position for the extracted object is decided, and the imaging optical system is moved to the focusing position. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an in-focus position determining apparatus and method for a digital camera or the like having an automatic focusing function.

  2. Description of the Related Art Conventionally, in an imaging apparatus such as a digital camera or a digital video camera, an autofocus (hereinafter referred to as “AF”) mechanism that automatically focuses a photographic lens on a predetermined subject has been widely used. This type of AF mechanism measures the distance to the subject by irradiating the subject with infrared rays from the imaging device, detecting the angle of the infrared rays reflected by the subject and returning to the imaging device, and the measurement distance position In this method, the position of the photographing lens is set so as to focus on an object (active method), or the image signal output by the imaging means of the photographing device is processed as described in Patent Document 1. Thus, there is known a method (passive method) in which the in-focus state is detected and the photographing lens is set at a position where the best in-focus state is obtained.

As the above-described passive AF mechanism, a contrast detection method in which the in-focus state is determined from the contrast of an image is widely known. This AF mechanism of the contrast detection method moves the photographic lens within the operating range for focusing (for example, from the closest side to the infinity side) by step driving, acquires image data from the imaging means for each movement, The imaging lens is set at a position corresponding to the maximum value of the focus evaluation value (contrast value) of the acquired image data.
Hei 11-146405

  In the case of the above-described contrast detection method, there is also known a method for determining a focus position using a detection result of a person's face or eyes from image data in addition to the maximum value of the focus evaluation value. In this case, in many cases, the imaging lens is moved from the closest side to the infinity side, and the focus evaluation value is calculated and the face is detected for each movement. If a face is detected at a position closest to the peak value of the detected focus evaluation value and corresponding to the peak value, that position is set as the focus position. In other words, the person in front is focused on. However, there is a person in the foreground, but it is inconvenient when it is desired to photograph a person in the distance as a subject.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an in-focus position determining apparatus and method that can easily focus on a far object.

  In order to solve the above-described problems, an in-focus position determination apparatus according to the present invention moves an imaging optical system that forms a subject image on a predetermined imaging plane, and moves the imaging optical system along the optical axis direction. Drive means; conversion means for converting the imaged subject image into image data; and object detection means for detecting a predetermined object from the image data, the detection being performed by the object detection means. In the in-focus position determining apparatus that determines an in-focus position with respect to the predetermined object, and the driving unit moves the imaging optical system to the in-focus position, the detected predetermined object is indicated by the image data Discriminating means for discriminating whether or not the image is included in the central area of the image, and extracting means for extracting an object closest to the center of the image among the objects determined to be included in the central area And by the extraction means Is characterized, further comprising determination means for determining an in-focus position, the relative said object extracted Te.

Further, a focus evaluation value calculation unit that calculates a focus evaluation value based on the image data, a maximum value detection unit that detects a maximum value exceeding a predetermined threshold from the calculated focus evaluation value,
The determining means determines the in-focus position based on the position of the maximum value corresponding to the object extracted by the extraction means among the detected maximum values. Also good.

  Further, the in-focus position determining apparatus according to the present invention includes an imaging optical system that forms an image of a subject on a predetermined imaging plane, a driving unit that moves the imaging optical system along an optical axis direction, and the imaging Conversion means for converting the subject image into image data, and object detection means for detecting a predetermined object from the image data, and a combination of the predetermined object detected by the object detection means. In a focus position determination apparatus that determines a focus position, and the driving unit moves the imaging optical system to the focus position, the detected predetermined object is included in a central region of an image indicated by the image data. A determination unit that determines whether or not the image pickup optical system is located when the determination unit determines that the predetermined object detected by the determination unit is included in a central region of the image. And a determination means The driving means moves the imaging optical system from the infinity side to the close side, and after the determination of the in-focus position by the determination means, the driving optical system moves the imaging optical system. It is characterized by stopping.

Further, a focus evaluation value calculation unit that calculates a focus evaluation value based on the image data, a maximum value detection unit that detects a maximum value exceeding a predetermined threshold from the calculated focus evaluation value,
And the determination means detects the predetermined object in the vicinity of the position corresponding to the detected maximum value, and the predetermined object is in the central region of the image data. The in-focus position may be determined in accordance with the position of the imaging optical system when the determination unit determines that it is included.

  In the above description, the movement of the imaging optical system is stopped by the driving unit after the focus position is determined. For example, as a specific method, the focus evaluation value is detected after the maximum value of the focus evaluation value is detected. In addition to the method of determining the in-focus position by lowering the focus, the method of determining the in-focus position by lowering the focus evaluation value below a certain threshold, the amount of movement of the imaging optical system, and the change of the focus evaluation value And determining the in-focus position by a combination of the determination results of the determining means for determining whether or not the detected predetermined object is included in the center area of the image indicated by the image data, and after determining the in-focus position, The movement of the imaging optical system may be stopped at the time, or the calculation of the focus evaluation value may be stopped. Further, focusing before actual focusing depends on the amount of movement of the imaging optical system, the change in the focus evaluation value, and whether the detected predetermined object is included in the center area of the image indicated by the image data. The determination of the position may be predicted, and the movement of the imaging optical system may be stopped or the calculation of the focus evaluation value may be stopped. Furthermore, it may be after the in-focus position has been determined. In addition to determining the in-focus position, the movement of the imaging optical system is stopped or the calculation of the in-focus evaluation value is stopped when other conditions are satisfied. It may be.

  The object may be a person's face or eyes.

  Further, the in-focus position determination method according to the present invention moves an imaging optical system that forms a subject image on a predetermined imaging plane along the optical axis direction, and converts the formed subject image into image data. In the in-focus position determination method of detecting a predetermined object from the image data, determining a focus position with respect to the detected predetermined object, and moving the imaging optical system to the focus position. It is determined whether or not the detected predetermined object is included in a central area of an image indicated by the image data, and among the objects determined to be included in the central area, the image is the most An object close to the center of the object is extracted, a focus position with respect to the extracted object is determined, and the imaging optical system is moved to the focus position.

  Further, the in-focus position determination method according to the present invention moves an imaging optical system that forms a subject image on a predetermined imaging plane along the optical axis direction, and converts the formed subject image into image data. In the in-focus position determination method of detecting a predetermined object from the image data, determining a focus position with respect to the detected predetermined object, and moving the imaging optical system to the focus position. The imaging optical system is moved from the infinity side toward the close side, and it is determined whether or not the detected predetermined object is included in a central region of an image indicated by the image data, and the detected The position of the imaging optical system when it is determined that the predetermined object is included in the center area of the image is set as the in-focus position, and after the in-focus position is determined, the movement of the imaging optical system is performed. It is characterized by stopping.

  By detecting a predetermined object from the image data converted based on the subject image and determining the in-focus position for the object closest to the center of the image among the objects in the center area of the image, It is possible to easily focus on the object at the center of the image. For example, if the subject is far away but there are many people in front of it, the AF mechanism that determines the in-focus position to focus on the face of the person on the near side is the mainstream. When the subject is far away as in the invention, the photographer sets the angle of view etc. so that the subject is at the center of the image, so that it is easy for a subject far away even if there is a person on the near side. You can focus on.

  Further, when the imaging optical system is moved from the infinity side to the close side, image data is acquired for each movement, a predetermined object is detected from the image data, and the object is in the central region of the image By taking the position of the imaging optical system at that time as the in-focus position and stopping the subsequent movement of the imaging optical system, it is possible to easily focus on a distant subject and to determine the in-focus position. Time can be shortened.

  Embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, a digital camera will be described as an example of an electronic apparatus provided with the in-focus position determination device according to the present invention. However, the scope of the present invention is not limited to this, for example, a digital video camera, The present invention is also applicable to other electronic devices having an electronic imaging function such as a camera-equipped mobile phone and a camera-equipped PDA.

[First Embodiment]
1 and 2 show an example of a digital camera, and are external views as seen from the back side and the front side, respectively. As shown in FIG. 1, an operation mode switch 11, a menu / OK button 12, a zoom / up / down lever 13, a left / right button 14, a back are provided on the back of the main body 10 of the digital camera 1 as an interface for operation by a photographer. A (return) button 15 and a display switching button 16 are provided, and a finder 17 for photographing and a monitor 18 for photographing and reproduction are further provided. A shutter button 19 is provided on the upper surface of the main body 10.

  The operation mode switch 11 is a slide switch for switching operation modes of a still image shooting mode, a moving image shooting mode, and a playback mode. Each time the menu / OK button 12 is pressed, the monitor 18 displays various menus for setting the shooting mode, flash emission mode, number of recording pixels, sensitivity, and the like, or based on the menu displayed on the monitor 18. It is a button for determining selection / setting.

  The zoom / up / down lever 13 is tilted up and down to adjust the telephoto / wide angle during shooting, and the cursor in the menu screen displayed on the monitor 18 is moved up and down during various settings. The left / right button 14 is a button for moving and displaying the cursor in the menu screen displayed on the monitor 18 at various settings.

  The Back button 15 is a button for stopping various setting operations when pressed and displaying the previous screen on the monitor 18. The display switching button 16 is a button for switching ON / OFF of the display of the monitor 18, various guide displays, ON / OFF of character display, and the like when pressed. The viewfinder 17 is used for a user to look into the subject for composition and focus when photographing a subject. The subject image seen from the finder 17 is projected through the finder window 23 on the front surface of the main body 10.

  The contents set by the operation of each button and lever described above can be confirmed by the display on the monitor 18, the position of the lamp in the finder 17, the position of the slide lever, and the like. The monitor 18 displays a through image for confirming the subject when photographing. As a result, the monitor 18 functions as an electronic viewfinder, displays still images and moving images after shooting, and displays various setting menus.

  Further, as shown in FIG. 2, a photographing lens (imaging optical system) 20, a lens cover 21, a power switch 22, a finder window 23, a flash light 24, and a self-timer lamp 25 are provided on the front surface of the main body 10. Is provided with a media slot 26.

  The photographic lens 20 is for forming a subject image on a predetermined image plane (CCD or the like inside the main body 10), and includes a focus lens, a zoom lens, and the like. The lens cover 21 covers the surface of the photographic lens 20 when the power of the digital camera 1 is turned off or in the playback mode, and protects the photographic lens 20 from dirt and dust. The power switch 22 is a switch for switching on / off the power of the digital camera 1. The flashlight 24 is used to instantaneously irradiate the subject with light necessary for photographing while the shutter button 19 is pressed and the shutter inside the main body 10 is opened. The self-timer lamp 25 is for informing the subject of the opening / closing timing of the shutter when shooting with the self-timer. The media slot 26 is a filling port for filling an external recording medium 70 such as a memory card. When the external recording medium 70 is filled, data reading / writing is performed.

  FIG. 3 is a block diagram showing a functional configuration of the digital camera 1. As an operation system of the digital camera 1, the operation mode switch 11, the menu / OK button 12, the zoom / up / down lever 13, the left / right button 14, the back (return) button 15, the display switching button 16, the shutter button 19, and the power switch 22. In addition, an operation system control unit 74 that is an interface for transmitting operation contents of these switches, buttons, and levers to the CPU 75 is provided.

  Further, a focus lens 20a and a zoom lens 20b are provided as components of the photographing lens 20. Each of these lenses is step-driven by a focus lens driving unit (driving unit) 51 and a zoom lens driving unit 52 including a motor and a motor driver, and is configured to be movable in the optical axis direction. The focus lens driving unit 51 step-drives the focus lens 20 a based on the focus driving amount data output from the AF processing unit 62. The zoom lens driving unit 52 controls step driving of the zoom lens 20 b based on the operation amount data of the zoom / up / down lever 13.

  The diaphragm 54 is driven by a diaphragm driving unit 55 including a motor and a motor driver. The aperture drive unit 55 adjusts the aperture diameter of the aperture 54 based on aperture value data output from the AE (automatic exposure) / AWB (auto white balance) processing unit 63.

  The shutter 56 is a mechanical shutter and is driven by a shutter drive unit 57 including a motor and a motor driver. The shutter drive unit 57 controls the opening / closing of the shutter 56 in accordance with the pressing signal of the shutter button 19 and the shutter speed data output from the AE / AWB processing unit 63.

  Behind the optical system is a CCD (conversion means) 58 that is a photographing element. The CCD 58 has a photocathode in which a large number of light receiving elements are arranged two-dimensionally, and subject light that has passed through the optical system is imaged on the photocathode and subjected to photoelectric conversion. In front of the photocathode, a microlens array (not shown) for condensing light on each pixel and a color filter array (not shown) in which RGB filters are regularly arranged are arranged. Yes. The CCD 58 outputs the charges accumulated for each pixel as serial analog image data line by line in synchronization with the vertical transfer clock signal and horizontal transfer clock signal supplied from the CCD control unit 59. The charge accumulation time (that is, exposure time) in each pixel is determined by an electronic shutter drive signal given from the CCD controller 59.

  Analog image data output from the CCD 58 is input to the analog signal processing unit 60. The analog signal processing unit 60 includes a correlated double sampling circuit (CDS) that removes noise from the analog image signal, an auto gain controller (AGC) that adjusts the gain of the analog image signal, and converts the analog image data into digital image data. It comprises an A / D converter (ADC) for conversion. The digital image data is CCD-RAW data having RGB density values for each pixel.

  The timing generator 72 generates a timing signal. The timing signal is input to the shutter drive unit 57, the CCD control unit 59, and the analog signal processing unit 60, and the operation of the shutter button 19 and the opening / closing of the shutter 56 are performed. The charge capturing of the CCD 58 and the processing of the analog signal processing 60 are synchronized. The flash controller 73 controls the light emission operation of the flashlight 24.

  The image input controller 61 writes the CCD-RAW data input from the analog signal processing unit 60 in the frame memory 68. The frame memory 68 is a working memory used when various digital image processing (signal processing) to be described later is performed on the image data. For example, an SDRAM that transfers data in synchronization with a bus clock signal having a fixed period. (Synchronous Dynamic Random Access Memory).

  The display control unit 71 is for displaying the image data stored in the frame memory 68 on the monitor 18 as a through image. For example, the display control unit 71 combines a luminance (Y) signal and a color (C) signal into one signal. Is converted to a composite signal and output to the monitor 18. Through images are acquired at predetermined intervals and displayed on the monitor 18 while the shooting mode is selected. The display control unit 71 displays on the monitor 18 an image based on the image data stored in the frame memory 68 and the image data stored in the external recording medium 70 and read out by the media control unit 69. Let

  The AF processing unit (determining unit, focusing evaluation value calculating unit, maximum value detecting unit) 62 and AE / AWB processing unit 63 determine shooting conditions based on the pre-image. The pre-image is an image based on the image data stored in the frame memory 68 as a result of the CPU 75 having detected a half-press signal generated when the shutter button 19 is half-pressed and causing the CCD 58 to perform pre-photographing. .

  The AF processing unit 62 detects the focal position based on the pre-image and outputs focus drive amount data. In the present embodiment, as a method for detecting the focus position, a passive method for detecting the focus position is used by utilizing the feature that the focus evaluation value of the image is high in a focused state.

  The AE / AWB processing unit 63 measures subject luminance based on the pre-image, determines an aperture value, shutter speed, etc., outputs aperture value data and shutter speed data (AE), and white balance at the time of shooting. Is adjusted (AWB).

  The image processing unit 64 performs image quality correction processing such as gamma correction, sharpness correction, and contrast correction on the image data of the main image, and converts the CCD-RAW data into Y data which is a luminance signal and Cb which is a blue color difference signal. YC processing is performed for conversion into YC data comprising data and Cr data which is a red color difference signal. The main image is an image stored in the frame memory 68 via the analog signal processing unit 60 and the image input controller 61 when analog image data is fetched from the CCD 58 by being executed when the shutter button 19 is fully pressed. It is an image based on the data. The upper limit of the number of pixels of the main image is determined by the number of pixels of the CCD 58. For example, the number of recorded pixels can be changed by an image quality setting (setting such as fine and normal) that can be set by the user. On the other hand, the number of pixels of the through image or the pre-image may be smaller than that of the main image.

  The face detection unit (object detection means) 65 is for detecting a person's face and eyes from the image data stored in the frame memory 68. In the present embodiment, the following description will be made assuming that a face is detected. However, a human eye may be detected. Moreover, you may make it detect an animal's face, eyes, etc.

  The compression / decompression processing unit 67 performs compression processing on the image data that has been subjected to processing such as image quality correction by the image processing unit 64 in a compression format such as JPEG, and generates an image file. Additional information is added to the image file based on various data formats. The compression / decompression processing unit 67 reads a compressed image file from the external recording medium 70 in the reproduction mode, and performs decompression processing. The decompressed image data is output to the display control unit 71, and the display control unit 71 displays an image based on the image data on the monitor 18.

  The media control unit 69 corresponds to the media slot 26 in FIG. 2, and reads an image file or the like stored in the external recording medium 70 or writes an image file.

  A CPU (discriminating means, extracting means) 75 controls each part of the main body of the digital camera 1 in accordance with operations of various buttons, levers, switches, and signals from the respective functional blocks. The data bus 76 is connected to the image input controller 61, various processing units 62 to 67, the frame memory 68, various control units 69 and 71, and the CPU 75, and transmission and reception of various signals and data via the data bus 76. Is done.

  Next, a simple series of flows of the digital camera 1 will be described with reference to the flowchart of FIG. First, the CPU 75 determines whether the operation mode is the shooting mode or the reproduction mode according to the setting of the operation mode switch 11 (step S1). In the reproduction mode (step S1; reproduction), reproduction processing is performed (step S11). This reproduction process is a process for the media control unit 69 to read an image file stored in the external recording medium 70 and display an image based on the image data included in the image file on the monitor 18. When the reproduction process is completed, the CPU 75 determines whether or not the power switch 22 of the digital camera 1 is turned off (step S10). If the power is turned off (step S10; YES), the power of the digital camera 1 is turned on. Turn off and end processing.

  On the other hand, when it is determined in step S1 that the operation mode is the shooting mode (step S1; shooting), the CPU 75 performs display control of the through image (step S2). The through image display is a process of displaying the above pre-image on the monitor 18. Next, the CPU 75 determines whether or not the shutter button 19 has been half-pressed (step S3). When half-pressed is not performed (step S3; NO), the CPU 75 repeats the process of step S2. When half-pressed (step S3; YES), the AE / AWB processing unit 63 determines the exposure (step S4).

  Subsequently, an in-focus position determination process is performed (step S5). This in-focus position determination process will be described in detail later. When the in-focus position determination process is performed, it is determined whether or not the half-press of the shutter button 19 has been released (step S6). When the half-press is released (step S6; YES), the CPU 75 shifts the process to step S2. If the half-press is not released (step S6; NO), the CPU 75 determines whether or not the shutter button 19 is fully pressed (step S7). If it is not fully pressed (step S7; NO), the process proceeds to step S6. If it is fully pressed (step S7; YES), the CPU 75 performs a photographing process (step S8). The photographing process refers to a process from analog image data based on the subject image formed on the photoelectric surface of the CCD 58 to A / D conversion and various signal processings performed by the image processing unit 64. In addition, as the image capturing process, the image data that has been subjected to the signal processing may be compressed by the compression / decompression processing unit 67 to generate an image file.

  When the photographing process is completed, the CPU 75 performs a process of displaying the photographed image on the monitor 18, and records the photographed image on the external recording medium 70 (step S9). Then, the CPU 75 determines whether or not an off operation has been performed by the power switch 22 (step S10). If the off operation has been performed (step S10; YES), the power of the digital camera 1 is turned off, and the process ends. If an off operation has not been performed (step S10; NO), the process proceeds to step S1.

  FIG. 5 is a flowchart showing the flow of the in-focus position determination process, and FIG. 6 is a flowchart showing the flow of the rough search process. Before describing each process, the face detection and in-focus position determination method in the present embodiment will be described in detail with reference to FIG. FIG. 7 is an example of a through image displayed on the monitor 18 when photographing a subject (child 91a) at a distance in an athletic meet such as a school. As shown in FIG. 7, when the person 91d is in front of the child 91a to be photographed, the general AF mechanism focuses on the face detected on the close side, so the in-focus position is, for example, the person 91d. It was set to either.

  Therefore, the user adjusts the angle of view and the like so that the photographed subject (child 91a) is positioned at the center in the frame 900 displayed in the monitor 18. When the shutter button 19 is half-pressed, the focus lens 20a is moved, and face detection is performed every time the movement is performed. When a face is detected, the position and focus of the face are detected only when the face is in the frame 900. The position of the lens 20a is stored. In the case of FIG. 7, since the faces of the children 91b and 91c are in the frame 900 in addition to the child 91a, the positions of the three faces and the position of the focus lens 20a when the faces are detected are stored. The Here, the stored face position is a position on the XY plane of the image (for example, an XY coordinate value). Furthermore, the face closest to the center of the frame 900 is extracted from the detected faces. In the case of FIG. 7, the face closest to the center of the frame 900 is the child 91a. Therefore, the child 91a is recognized as a subject and the focus position of the face is set. That is, it is determined whether or not the detected face is in the center area of the image, and the face closest to the center of the image is extracted from the faces in the center area of the image, and the face is focused. In this way, even when there is a subject to be photographed in the distance, the subject can be easily focused on by aligning the subject with the center of the frame 900.

  Next, the in-focus position determination method in FIG. 5 will be described. First, the CPU 75 executes a rough search process (step S21). FIG. 6 is a flowchart showing the flow of rough search processing. The CPU 75 outputs an instruction signal to the focus lens driving unit 51 in order to move the focus lens 20a to the initial position (step S31). The subject image formed by the CCD 58 is converted into image data and output (step S32), and the face detection unit 65 detects a human face from the output image data (step S33). When a face is detected and the face is in the center area of the image indicated by the image data (step S34; YES), the CPU 75 stores the detected position of the face and the current position of the focus lens 20a (step S35). . Here, the center area of the image may be a preset area such as the frame 900, or may allow the user to arbitrarily set the position and size of the frame 900, for example. . Further, for example, when a face is not detected from the frame 900, the position or size of the frame 900 is changed according to the detection result by moving the position of the frame 900 or increasing the area of the area. The face detection within the frame 900 may be performed again.

  Then, the CPU 75 determines whether or not the focus lens 20a is at the last position (step S36). If it is not the last position (step S36; NO), the focus lens 20a is moved to the next position to move the focus lens 20a to the next position. An instruction signal is output to the drive unit 51 (step S39). If it is the last position (step S36; YES) and the face position is stored in step S35 (step S37; YES), the CPU 75 extracts the face closest to the center of the image from the stored faces. (Step S38) The position of the focus lens 20a stored corresponding to the extracted face is set as a temporary in-focus position (Step S39). Then, the rough search process ends. On the other hand, when there is no stored face position (step S37; NO), the CPU 75 ends the rough search process as an AF error.

  Returning to FIG. 5, when the AF error is not determined in the rough search process (step S22; NO), the CPU 75 performs the main search process for a predetermined range including the stored temporary focusing position of the focus lens 20a (step S23). ). The search process is a process of moving the focus lens 20a within a set range, calculating a focus evaluation value for each movement, detecting a local maximum value, and determining a focus position. Then, the CPU 75 moves the focus lens 20a to a position corresponding to the detected maximum value (step S24), and ends the focus position determination process.

  As described above, a face is detected from the image data output from the CCD 58, and the position of the face in the central area of the image and the position of the focus lens 20a when the face is detected are stored, and then the image By extracting the face closest to the center of the image from the faces in the center area, and focusing on that face, even if there is a subject that you want to shoot far away, you can easily focus on that subject it can. That is, in the through image display stage, the subject can be easily focused by adjusting the angle of view and the like so that the subject in the distance is at the center of the monitor 18.

  Note that the in-focus position determination method according to the present embodiment is effective when photographing a subject located far away. However, since there are many cases where it is desired to photograph a subject that is close, the user can set whether the subject is far away or close (normal mode) using the operation system described in FIGS. When the subject is set to be far away, the focus position is determined using the focus position determination method described in the present embodiment, and the subject is set to be close (normal mode). In this case, the focus position may be determined using a known technique so that the closest face is in focus.

[Second Embodiment]
In the first embodiment, the focus lens 20a is moved within the operating range from a predetermined initial position, and the face is detected from the image data for each movement to determine the in-focus position. In the second embodiment, the focus lens 20a is moved from the infinity side to the close side, and the focus position is determined based on the position of the focus lens 20a when the face is detected in the center area of the image. A case where the movement of the focus lens 20a is stopped will be described. The overall view, functional configuration diagram, main process flow, and in-focus position determination process of the digital camera 1 in the second embodiment are the same as those described in the first embodiment. Only the rough search process different from that of the first embodiment will be described.

  FIG. 8 is a flowchart showing a flow of rough search processing in the second embodiment. First, the CPU 75 outputs an instruction signal to the focus lens driving unit 51 in order to move the focus lens 20a to the infinity side (step S41). The subject image formed by the CCD 58 is converted into image data and output (step S42), and the face detection unit 65 detects a human face from the output image data (step S43). When a face is detected and the face is in the center area of the image indicated by the image data (for example, the frame 900 shown in FIG. 7) (step S44; YES), the CPU 75 temporarily sets the current position of the focus lens 20a. The focus position is set (step S45), and the rough search process is terminated. In the in-focus position determination process, the main search process is performed based on the temporary in-focus position.

  On the other hand, when the detected face is not in the center area of the image (step S44; NO), the CPU 75 determines whether or not the focus lens 20a is at the last position (step S46). Step S46; NO), in order to move the focus lens 20a to the next position, an instruction signal is output to the focus lens driving unit 51 (Step S47). If it is the last position (step S48; YES), the CPU 75 sets an AF error (step S48), and ends the rough search process.

  As described above, after the focus lens 20a is moved from the infinity side to the close side and the position of the focus lens 20a when the face is detected in the center area of the image is determined as the temporary in-focus position, the rough search process is performed. By not performing it, it is possible to easily focus on a subject located far away, and it is possible to shorten the time for determining a focus position when photographing a subject far away. In addition, the same effects as those described in the first embodiment can be obtained.

[Third Embodiment]
In the first and second embodiments, the method has been described in which the temporary in-focus position is determined using the face detection result, and the in-focus position is determined by performing the main search based on the temporary in-focus position. In the third embodiment, a method for determining the focus position based on the face detection result and the peak value of the focus evaluation value will be described. The overall view, functional configuration diagram, main process flow and focus position determination process of the digital camera 1 in the third embodiment are the same as those described in the first embodiment. Description will be omitted, and only rough search processing different from that of the first embodiment will be described.

  FIG. 9 is a flowchart showing the flow of rough search processing in the third embodiment. First, the CPU 75 outputs an instruction signal to the focus lens driving unit 51 in order to move the focus lens 20a to the infinity side (step S51). The subject image formed by the CCD 58 is converted into image data and output (step S52), and the face detection unit 65 detects a human face from the output image data (step S53). When a face is detected and the face is in the center area of the image indicated by the image data (for example, the frame 900 shown in FIG. 7) (step S54; YES), the AF processing unit 62 uses the AF area as the center area or the face. And the focus evaluation value is calculated (step S55). Then, the AF processing unit 62 detects a peak value from the calculated focus evaluation value. If a peak value is detected (step S56; YES) and the peak value is equal to or greater than a predetermined threshold value (step S57; YES), the CPU 75 sets the current position of the focus lens 20a as a temporary in-focus position (step S58). ), The rough search process is terminated. In the in-focus position determination process, the main search process is performed based on the temporary in-focus position.

  On the other hand, when the detected face is not in the center area of the image (step S54; NO), the AF processing unit 62 sets the AF area to multipoint AF and calculates a focus evaluation value (step S59), and step S60. Transfer processing to. Furthermore, also when the peak value of the focus evaluation value is not detected (step S56; NO), or when the detected peak value is smaller than a predetermined threshold value (step S57; NO), the process proceeds to step S60. In step S60, the CPU 75 determines whether or not the focus lens 20a is at the last position. If the focus lens 20a is not at the last position (step S60; NO), the focus lens drive unit moves the focus lens 20a to the next position. An instruction signal is output to 51 (step S61), and the process proceeds to step S52. If it is the last position (step S60; YES), the CPU 75 sets the AF error (step S62) and ends the rough search process.

  As described above, the focus position is determined based on the position of the focus lens 20a when the face is detected in the center region of the image and the peak value of the focus evaluation value exceeding the predetermined threshold is detected. Thus, the in-focus position can be determined with higher accuracy. In addition, when the focus lens 20a is moved from the infinity side and the temporary in-focus position is determined, the rough search process is ended, thereby shortening the determination time of the in-focus position when photographing a subject at a distance. it can. In addition, the same effects as those described in the first embodiment can be obtained.

  In the present embodiment, the face is detected in the center area of the image, and the position of the focus lens 20a when the focus evaluation value exceeding a predetermined threshold is detected is set as the temporary focus position. In the following description, the focus lens 20a is not moved. However, the focus lens 20a is moved within the operation range, and the face detection and the focus evaluation value are calculated for each movement. When the position is reached, the peak value corresponding to the face is extracted from the peak values of the focus evaluation value, and the position corresponding to the peak value on the most infinite side among the extracted peak values is the temporary focus position. You may make it. Alternatively, a position corresponding to the peak value having the highest peak among the peak values corresponding to the face on the infinity side from the predetermined position may be set as the temporary in-focus position. Alternatively, the position corresponding to the peak value corresponding to the face closest to the center of the frame 900 among the peak values corresponding to the face may be set as the temporary in-focus position.

Rear view of digital camera Front view of digital camera Functional block diagram of digital camera Flow chart for explaining a series of operations of the digital camera Flow chart for explaining the flow of the in-focus position determination process Flowchart for explaining the flow of rough search processing in the first embodiment Example of monitor screen display Flowchart for explaining the flow of rough search processing in the second embodiment Flowchart for explaining the flow of rough search processing in the third embodiment

Explanation of symbols

1 Digital Camera 11 Operation Mode Switch 12 Menu Button 13 Zoom / Up / Down Lever 14 Left / Right Button 15 BACK (Return) Button 16 Display Switch Button 17 Viewfinder 18 Monitor 19 Shutter Button 20 Imaging Lens 21 Lens Cover 22 Power Switch 23 Viewfinder Window 24 Flashlight 25 Self-timer lamp 26 Media slot

Claims (7)

An imaging optical system that forms an image of a subject on a predetermined imaging plane;
Driving means for moving the imaging optical system along the optical axis direction;
Conversion means for converting the imaged subject image into image data;
Object detection means for detecting a predetermined object from the image data;
An in-focus position determining apparatus for determining an in-focus position with respect to the predetermined object detected by the object detecting means, and for causing the driving means to move the imaging optical system to the in-focus position.
Discrimination means for discriminating whether or not the detected predetermined object is included in a central area of an image indicated by the image data;
An extracting means for extracting an object closest to the center of the image among the objects determined to be included in the central region;
Determining means for determining an in-focus position for the object extracted by the extracting means;
An in-focus position determining device further comprising: A focus evaluation value calculating means for calculating a focus evaluation value based on the image data;
A maximum value detecting means for detecting a maximum value exceeding a predetermined threshold from the calculated focus evaluation value;
Further comprising
The determining means determines the in-focus position based on a position of a maximum value corresponding to the object extracted by the extraction means among the detected maximum values. Item 2. The focusing position determination device according to Item 1. An imaging optical system that forms an image of a subject on a predetermined imaging plane;
Driving means for moving the imaging optical system along the optical axis direction;
Conversion means for converting the imaged subject image into image data;
Object detection means for detecting a predetermined object from the image data;
An in-focus position determining apparatus for determining an in-focus position with respect to the predetermined object detected by the object detecting means, and for causing the driving means to move the imaging optical system to the in-focus position.
Discrimination means for discriminating whether or not the detected predetermined object is included in a central area of an image indicated by the image data;
Determining means for setting the position of the imaging optical system at the time of determination that the predetermined object detected by the determining means is included in a central region of the image as a focus position;
Further comprising
The drive means moves the imaging optical system from the infinity side toward the close side, and stops the movement of the imaging optical system after the focus position is determined by the determination means. An in-focus position determination device. A focus evaluation value calculating means for calculating a focus evaluation value based on the image data;
A maximum value detecting means for detecting a maximum value exceeding a predetermined threshold from the calculated focus evaluation value;
Further comprising
In the vicinity of the position corresponding to the detected maximum value, the determining means detects the predetermined object, and the predetermined object is included in a central region of the image data. The in-focus position determination apparatus according to claim 1, wherein the in-focus position is determined according to a position of the imaging optical system when the determination means determines.   The photographing apparatus according to claim 1, wherein the object is a person's face or eyes. Move the imaging optical system that forms a subject image on a predetermined imaging plane along the optical axis direction,
Converting the imaged subject image into image data;
A predetermined object is detected from the image data;
In the focus position determination method of determining a focus position with respect to the detected predetermined object and moving the imaging optical system to the focus position,
Determining whether the detected predetermined object is included in a central region of an image indicated by the image data;
Of the objects determined to be included in the central region, extract the object closest to the center of the image,
A focusing position determination method, wherein a focusing position with respect to the extracted object is determined, and the imaging optical system is moved to the focusing position. Move the imaging optical system that forms a subject image on a predetermined imaging plane along the optical axis direction,
Converting the imaged subject image into image data;
A predetermined object is detected from the image data;
In the focus position determination method of determining a focus position with respect to the detected predetermined object and moving the imaging optical system to the focus position,
Moving the imaging optical system from the infinity side toward the close side,
Determining whether the detected predetermined object is included in a central region of an image indicated by the image data;
The position of the imaging optical system when it is determined that the detected predetermined object is included in the center region of the image is the in-focus position,
An in-focus position determination method, wherein the movement of the imaging optical system is stopped after the in-focus position is determined.

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