JP2011191617A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device capable of performing an appropriate automatic focusing operation, even when a human face is not detected when the face detection autofocusing is selected. <P>SOLUTION: The imaging device includes: an optical system 101 which includes a focusing lens 101c movable forwards and backwards and produces an optical image; an imaging element 301 which converts the optical image into an image signal; a focusing means 305b which advances and retreats the focusing lens 101c such that the optical image is focused on the imaging element 301; a face detection means 305c which outputs an evaluation value exhibiting the position of the human face and to what extent whether to look like the human face in the image based on the image signal; a contrast calculation means 305c which divides the image based on the image signal into a plurality of regions and calculates contrasts with respect to respective regions; and a control means 305b which, when the evaluation value is lower than a threshold, controls a focusing means 305b such that the optical image is focused on the position of the region where a peak value of the contrast becomes highest, among partial adjacent regions each including the position where the evaluation value of the imaging element is highest. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an imaging apparatus capable of detecting a person's face and focusing on the detected person's face.

  Recently, a large number of imaging devices that can detect a person's face and focus on the detected person's face have been commercialized. In this field, there are many prior art documents including Patent Document 1 to Patent Document 3.

JP 2010-15023 A JP 2009-147574 A JP 2009-60379 A

  The person's face is detected by software that executes a predetermined algorithm or hardware that is a circuit of the software. The detection of a person's face is performed depending on whether an evaluation value indicating how likely a person's face is is higher or lower than a predetermined threshold. As a result, an evaluation value exists whether or not a person's face is detected.

  If a person's face is detected, the detected person's face is focused. On the other hand, if a human face is not detected, the face detection autofocus is automatically switched to multipoint autofocus or the like. However, the fact that the user has selected the face detection autofocus has a very high probability that the subject includes a human face. Nevertheless, when switching automatically to multi-point autofocus or the like, there is a problem that a subject unintended by the user is focused.

  The present invention solves the above-described problem, and can perform an appropriate autofocus operation even when the user selects face detection autofocus and does not detect a human face. An object is to provide an apparatus.

  In order to solve the above-described problem, an imaging apparatus according to the present invention includes an optical system that includes a focus lens that can advance and retreat in an optical axis direction, and that generates an optical image of a subject, an imaging device that converts the optical image into an image signal, Focusing means for moving the focus lens forward and backward so that the optical image is focused on the imaging device, and an evaluation value indicating the position of the person's face and how likely the person's face is in the image based on the image signal A face detecting unit that performs division of an image based on the image signal into a plurality of regions and calculates a contrast for each region, and the optical image when the evaluation value is higher than a first threshold value. The focusing means is controlled to focus on the position of the person's face of the image sensor, and the optical image is the image of the image sensor when the evaluation value is lower than the first threshold value. Control means for controlling the focusing means so as to focus on the position of the region where the peak value of the contrast is highest among some of the adjacent regions including the position where the evaluation value is highest. It is characterized by that.

  In this configuration, even when the user selects face detection autofocus and does not detect a person's face, some adjacent areas including the position that can be evaluated to be the most likely person's face are included. It is possible to focus on the position of the region where the peak value of contrast is highest among the regions.

  In addition, the imaging apparatus of the present invention includes an optical system that includes a focus lens that can advance and retreat in the optical axis direction, generates an optical image of a subject, an imaging device that converts the optical image into an image signal, and the optical image is the imaging Focusing means for advancing and retracting the focus lens so as to focus on the element; face detecting means for outputting an evaluation value indicating the position of the person's face and how likely the person's face is in the image based on the image signal; A contrast calculation unit that divides an image based on the image signal into a plurality of regions and calculates a contrast for each region; and when the evaluation value is higher than a first threshold value, the optical image of the person of the image sensor The focusing means is controlled to focus on the position of the face, and when the evaluation value is lower than the first threshold, the optical image has the highest evaluation value of the image sensor. Control means for controlling the focusing means so as to focus on the position of the area where the peak value of the contrast after weighting is the highest among the plurality of areas, and the weight of the area including the position is the highest. It is characterized by comprising.

  In this configuration, even when the user selects face detection autofocus and does not detect a person's face, the area including the position that can be evaluated as most likely to be a person's face is weighted most. It is possible to focus on the position of the region where the peak value of the contrast after weighting is highest among the plurality of regions.

  In addition, when the evaluation value is lower than the second threshold, the control unit focuses the optical image on the position of the region where the peak value of the contrast is the highest among the plurality of regions of the imaging element. The focusing means is controlled as described above.

  In this configuration, when the user has selected face detection autofocus, when the face of a person is not detected and the evaluation value is extremely low, automatic switching to multipoint autofocus is performed. Can do.

  The control means may focus the optical image on the position of the central region of the image sensor when the maximum contrast peak value is lower than a third threshold value. The focusing means is controlled.

  In this configuration, when the user selects face detection autofocus, the person's face is not detected, the evaluation value is extremely low, and the contrast peak value is also obtained by multipoint autofocus. Can be automatically switched to single-point autofocus when the position of a region where is significant cannot be identified.

  The image pickup apparatus according to the present invention further includes selection means for selecting a method for determining a position of the image pickup element for focusing the optical image, and the control means has the evaluation value as the first value. When the value is lower than the threshold value, the position of the image sensor for focusing the optical image is determined based on the method selected by the selection unit.

  In this configuration, when the user selects face detection autofocus and does not detect a person's face, the focus position can be determined based on the method selected by the user. .

  As described above, according to the present invention, an appropriate autofocus operation can be performed even when the user selects face detection autofocus and does not detect a human face. There is an effect.

1 is an external view of a digital camera according to an embodiment of the present invention. 1 is a block diagram of a digital camera according to an embodiment of the present invention. The figure explaining arrangement | positioning of AF area | region Flowchart for explaining an autofocus operation of the digital camera according to the embodiment of the present invention. Diagram explaining multi-point autofocus that places importance on the position with the highest evaluation value

(Embodiment)
(1. Appearance)
FIG. 1 is an external view of a digital camera according to an embodiment of the present invention. FIG. 1A is a front view, and FIG. 1B is a rear view.

  An imaging optical system 101 and a flash 102 are arranged in front of the digital camera 100. The imaging optical system 101 forms an image of subject light on an imaging element in the digital camera 100. The flash 102 emits a flash to compensate for the shortage of the photographing light amount when photographing in a dark place. A shutter button 103 is disposed on the upper surface of the digital camera 100. When the shutter button 103 is pressed, image data based on subject light imaged on the image sensor is recorded on a recording medium such as a memory card.

  A liquid crystal monitor 104, a mode dial 105, and various operation buttons 106 are arranged on the back of the digital camera 100. The liquid crystal monitor 104 displays an image based on subject light imaged on the image sensor. Therefore, it is possible to determine the composition for photographing while observing the image displayed on the liquid crystal monitor 104. The liquid crystal monitor 104 can display an image based on the image data recorded on the recording medium.

  By operating the mode dial 105, the operation mode of the digital camera 100 can be determined. The operation mode of the digital camera 100 includes a shooting mode and a playback mode. The shooting mode is an operation mode in which image data based on subject light imaged on the image sensor can be recorded on a recording medium such as a memory card by pressing the shutter button 103. The shooting mode is further subdivided into a fully automatic shooting mode, a program shooting mode, a shutter speed priority shooting mode, an aperture priority shooting mode, and a scene-specific shooting mode.

The reproduction mode is an operation mode in which an image based on the image data recorded on the recording medium can be displayed on the liquid crystal monitor 104. By operating the various operation buttons 106, more detailed settings can be made in the shooting mode and the playback mode. That is, in the shooting mode, selection of an autofocus operation method, exposure correction, white balance adjustment, settings relating to flash 102 emission, and the like can be performed. In the playback mode, the image displayed on the liquid crystal monitor 104 is enlarged or reduced, the number of images simultaneously displayed on the liquid crystal monitor 104, the image data recorded on a recording medium such as a memory card is searched, and the like. be able to.
(2. Configuration)
FIG. 2 is a block diagram of the digital camera according to the embodiment of the present invention. The imaging optical system 101 forms an image of subject light on a CCD image sensor 301 that is an imaging element. The imaging optical system 101 is composed of a plurality of lens groups. In the digital camera 100 according to the embodiment of the present invention, a zoom lens 101a, a diaphragm 101b, and a focus lens 101c are arranged in an imaging optical system 101.

  The CCD image sensor 301 outputs an image signal based on the imaged subject light. The AFE 302 interpolates the image signal output from the CCD image sensor 301, performs white balance adjustment and gamma correction, converts the image signal into image data, and outputs the image data to the preprocessing unit 305a in the signal processing LSI 305. The pre-processing unit 305 a converts the image data output from the AFE 302 into YC data, and then stores it in the SDRAM 304 via the bus 303.

  The signal processing LSI 305 includes a preprocessing unit 305a, a CPU 305b, an image processing unit 305c, and a storage unit 305d. The CPU 305b controls the entire digital camera 100. The CPU 305b monitors the operation of the shutter button 103, the mode dial 105, and various operation buttons 106. The CPU 305b can control the operations of the zoom lens 101a, the diaphragm 101b, and the focus lens 101c. The zoom lens 101a, the diaphragm 101b, and the focus lens 101c have actuators such as stepping motors for operating them, but are not shown. The CPU 305 b can change the magnification of the subject light imaged on the CCD image sensor 301 by moving the zoom lens 101 a in the optical axis direction of the imaging optical system 101. The CPU 305b can adjust the amount of subject light imaged on the CCD image sensor 301 by operating the aperture 101b. The CPU 305 b can focus the subject light on the CCD image sensor 301 by moving the focus lens 101 c in the optical axis direction of the imaging optical system 101.

  The image processing unit 305 c converts the YC data stored in the SDRAM 304 by the preprocessing unit 305 a into display data suitable for display on the liquid crystal monitor 104, and outputs the display data to the liquid crystal monitor 104 via the bus 303. The image processing unit 305c can obtain the contrast of the designated area in the YC data. The image processing unit 305c can output an evaluation value indicating the position of the person's face included in the YC data and how much the person's face is likely to be.

  The autofocus operation is started by half-pressing the shutter button 103, and shooting is performed by fully pressing the shutter button 103. Autofocus operation methods include face detection autofocus, multipoint autofocus, and single point autofocus. By operating various operation buttons 106, an autofocus operation method can be selected. In digital camera 100 according to the embodiment of the present invention, when face detection autofocus is selected as the method of autofocus operation, a method of autofocus operation that is performed when face detection autofocus fails can be selected. . Whether or not to select an autofocus operation method to be performed when face detection autofocus is unsuccessful is optional and may not be selected.

  When the YC data stored in the SDRAM 304 is YC data stored by fully pressing the shutter button 103, the image processing unit 305c converts the YC data into compressed data suitable for recording on the memory card 306, and uses the bus 303. To the memory card 306.

  The compressed data recorded on the memory card 306 is converted into display data suitable for display on the liquid crystal monitor 104 by the image processing unit 305 c and displayed on the liquid crystal monitor 104 via the bus 303.

  The storage unit 305d stores a program for operating the CPU 305b. The storage unit 305d stores a program for the CPU 305b to perform face detection autofocus, multipoint autofocus, and single point autofocus.

The signal processing LSI 305 is configured by a preprocessing unit 305a, a CPU 305b, an image processing unit 305c, and a storage unit 305d. Usually, when a non-volatile memory such as a flash memory is embedded in a signal processing LSI manufactured by a CMOS process, the cost increases. Therefore, the storage unit 305d may be configured by a flash memory different from the signal processing LSI.
(3. Operation)
(3-1. Method of autofocus operation)
The image processing unit 305c can obtain the contrast from the YC data stored in the SDRAM 304 by the preprocessing unit 305a. The CPU 305b can perform a so-called contrast-type autofocus operation by moving the focus lens 101c in the optical axis direction of the imaging optical system 101 so that the contrast is maximized.

  At this time, it is possible to select an image area for which contrast is to be obtained. In the digital camera 100 according to the embodiment of the present invention, it is possible to select the following autofocus operation method.

(1) Face Detection Autofocus The contrast of the area where the face of a person is detected is obtained. The image processing unit 305c outputs an evaluation value indicating how much the human face included in the image is likely to be a human face. When the evaluation value output from the image processing unit 305c is higher than the first threshold, the CPU 305b determines that a human face has been detected. When a plurality of human faces are detected in the image, 1) obtain the contrast of the face area of the person with the highest evaluation value, and 2) obtain the contrast of the face area of the person with the closest subject distance. 3) Find the contrast of the largest person's face area 4) Find the contrast of the person's face area most similar to the person's face stored in the storage unit 305d 5) Select with various operation buttons 106 The area of the image for which the contrast is to be determined can be selected from among the areas for which the contrast of the face area of the person is determined. This selection is performed by the user operating various operation buttons 106 in advance. If the face of a person moves, the area of the image whose contrast is to be calculated also moves.

(2) The multipoint autofocus image is divided into a plurality of areas, and the contrast of each area is obtained. Each area is called an AF area. Focusing is performed on an AF area where the peak value of contrast is maximized. FIG. 3 is a diagram for explaining the arrangement of AF areas. FIG. 3A shows an example in which 23 AF areas are provided. In FIG. 3A, the frames of all the AF areas are displayed in order to explain the arrangement of the AF areas, but actually only the frames of the focused AF areas are displayed. When the autofocus operation is completed, the frame of the AF area where the peak value of contrast is maximized is displayed. If there is another AF area where the contrast is within the depth of focus when focusing on the AF area where the contrast peak value is maximum, in addition to the frame of the AF area where the contrast peak value is maximum, the contrast The frame of the AF area where is within the depth of focus is also displayed.

(3) The contrast of the center AF area of the one-point autofocus image is obtained. FIG. 3B shows an example in which an AF area is provided at the center of the image. Regardless of the absolute value of the peak value of the contrast, focusing is performed at the position of the focus lens 101c where the contrast reaches the peak value.
(3-2. Autofocus operation)
An autofocus operation of the digital camera 100 according to the embodiment of the present invention will be described. FIG. 4 is a flowchart for explaining the autofocus operation of the digital camera according to the embodiment of the present invention. The user has selected face detection autofocus as a method of autofocus operation. In addition, an autofocus operation method that is performed when face detection autofocus fails is not selected.

  The autofocus operation is started by half-pressing the shutter button 103. The image processing unit 305c outputs an evaluation value indicating how much the human face included in the image is likely to be a human face. If the evaluation value output from the image processing unit 305c is higher than the first threshold value (Y in S101), the CPU 305b determines that a human face has been detected, and the subject light that has passed through the imaging optical system 101 is CCD. The focus lens 101c is moved in the optical axis direction of the imaging optical system 101 so as to focus on the position where the human face of the image sensor 301 is detected (S102). When a plurality of human faces are detected in the image, (3. Operation) (3-1. Method of autofocus operation) (1) The image of the image for which contrast is to be obtained as in face detection autofocus. A region can be selected.

  On the other hand, when the evaluation value output from the image processing unit 305c is lower than the first threshold value (N in S101), the CPU 305b compares the evaluation value output from the image processing unit 305c with the second threshold value (S103). .

  If the evaluation value output from the image processing unit 305c is higher than the second threshold value (Y in S103), the CPU 305b performs multipoint autofocus that places importance on the position having the highest evaluation value (S104). The following two methods are illustrated as specific methods. FIG. 5 is a diagram illustrating multi-point autofocus that places importance on the position with the highest evaluation value.

(1) AF area limitation FIG. 5A is a diagram for explaining a method for limiting an AF area for obtaining contrast. A black circle indicates a position having the highest evaluation value. In this method, the contrast is obtained for the AF area including the position having the highest evaluation value and the seven AF areas adjacent thereto. In FIG. 5A, the AF area for which the contrast is obtained is indicated by a solid line, and the AF area from which the contrast is not obtained is indicated by a broken line. The CPU 305b moves the focus lens 101c to the imaging optical system so that the subject light that has passed through the imaging optical system 101 is focused on the position of the AF area where the peak value of contrast is the highest among the AF areas for which the contrast of the CCD image sensor 301 is obtained. 101 is moved in the optical axis direction (S104).

(2) AF area weighting FIG. 5B is a diagram for explaining a method of weighting the AF area. A black circle indicates a position having the highest evaluation value. In this method, the weight of the AF area including the position having the highest evaluation value is set to 1.0, and the weight of the AF area far from the AF area including the position having the highest evaluation value is decreased. In FIG. 5B, the weight of the AF area adjacent to the AF area including the position having the highest evaluation value is set to 0.9, the weight of the AF area outside these AF areas is set to 0.7, The weight of the AF area outside these AF areas is set to 0.7, and the weight of the AF area outside these AF areas is set to 0.5. The CPU 305 b moves the focus lens 101 c to the optical axis of the imaging optical system 101 so that the subject light that has passed through the imaging optical system 101 is focused on the position of the AF area where the peak value of contrast after weighting of the CCD image sensor 301 is highest. Move in the direction (S104).

  When the evaluation value output from the image processing unit 305c is lower than the second threshold value (N in S103), the CPU 305b performs multi-point autofocus without considering the evaluation value (S105). By performing multi-point autofocus, the peak value of contrast in all AF areas can be obtained. Therefore, the CPU 305b compares the maximum contrast peak value of all AF areas with the third threshold value (S106).

  When the maximum value of the contrast peak value of all AF areas is higher than the third threshold value (Y in S106), the CPU 305b causes the subject light that has passed through the imaging optical system 101 to have the contrast peak value of the CCD image sensor 301. The focus lens 101c is moved in the direction of the optical axis of the imaging optical system 101 so as to focus on the position of the AF area where the maximum is (S104). On the other hand, when the maximum value of the contrast peak value of all AF areas is smaller than the third threshold (N in S106), the CPU 305b causes the subject light that has passed through the imaging optical system 101 to be in the center of the CCD image sensor 301. The focus lens 101c is moved in the optical axis direction of the imaging optical system so as to focus on the position of the AF area (S107).

As described above, the imaging apparatus according to the present invention has the first evaluation value indicating how likely a human face is even when the user selects face detection autofocus as the autofocus operation method. When the threshold value is lower than the threshold value, multipoint autofocus is performed with emphasis on the position having the highest evaluation value. Therefore, since multipoint autofocus is performed with an emphasis on the AF area where the possibility of the presence of a person's face is expected to a certain degree, the possibility of focusing on the position intended by the user can be improved.
(Other embodiments)
In the embodiment, the method of the autofocus operation performed when face detection autofocus fails is not selected. Here, a case will be described in which various operation buttons 106 are operated to select an autofocus operation method performed when face detection autofocus fails. In the digital camera 100 according to the embodiment of the present invention, either multi-point autofocus or single-point autofocus can be selected as the autofocus operation method performed when face detection autofocus fails. A description will be given with reference to FIG. 4 again.

(1) When multipoint autofocus is selected When multipoint autofocus is selected as the method of autofocus operation performed when the user fails face detection autofocus, the process proceeds to S105 instead of S103 according to the determination of N in S101. Branch.

(2) When one-point autofocus is selected When one-point autofocus is selected as the autofocus operation method performed when the user fails face detection autofocus, the process branches to S107 instead of S103 according to the determination of N in S101. .

  Accordingly, when the user selects face detection autofocus and does not detect a person's face, the focus position can be determined based on the method selected by the user.

  According to the present invention, it is possible to perform an appropriate autofocus operation even when the user selects face detection autofocus and does not detect a person's face. The present invention can be applied to an imaging apparatus such as a digital video camera or a camera-equipped mobile phone.

DESCRIPTION OF SYMBOLS 100 Digital camera 101 Imaging optical system 101a Zoom lens 101b Aperture 101c Focus lens 102 Flash 103 Shutter button 104 Liquid crystal monitor 105 Mode dial 106 Various operation buttons 301 CCD image sensor 302 AFE
303 Bus 304 SDRAM
305 Signal processing LSI
305a Pre-processing unit 305b CPU
305c Image processing unit 305d Storage unit 306 Memory card

Claims (5)

An optical system that includes a focus lens capable of moving back and forth in the direction of the optical axis,
An image sensor for converting the optical image into an image signal;
Focusing means for moving the focus lens forward and backward so that the optical image is focused on the image sensor;
Face detection means for outputting an evaluation value indicating the position of a person's face and how likely it is in the image based on the image signal;
Contrast calculation means for dividing an image based on the image signal into a plurality of regions and calculating contrast for each region;
When the evaluation value is higher than a first threshold value, the focusing unit is controlled so that the optical image is focused on the position of the person's face of the image sensor, and the evaluation value is the first threshold value. The optical image is focused on the position of the region where the peak value of the contrast is the highest among some of the adjacent regions including the position where the evaluation value of the imaging element is the highest. Control means for controlling the focusing means;
Comprising
An imaging apparatus characterized by that. An optical system that includes a focus lens that can advance and retreat in the direction of the optical axis and generates an optical image of the subject;
An image sensor for converting the optical image into an image signal;
Focusing means for moving the focus lens forward and backward so that the optical image is focused on the image sensor;
Face detection means for outputting an evaluation value indicating the position of a person's face and how likely it is in the image based on the image signal;
Contrast calculation means for dividing an image based on the image signal into a plurality of regions and calculating contrast for each region;
When the evaluation value is higher than a first threshold value, the focusing unit is controlled so that the optical image is focused on the position of the person's face of the image sensor, and the evaluation value is the first threshold value. The weight of the region including the position where the evaluation value of the imaging element is the highest in the optical image is the highest, and the peak value of the contrast after weighting is the highest among the plurality of regions. Control means for controlling the focusing means to focus on a position;
Comprising
An imaging apparatus characterized by that. The control means includes
When the evaluation value is lower than a second threshold value, the focusing unit is configured so that the optical image is focused on a position of a region where the peak value of the contrast is highest among the plurality of regions of the imaging element. Control,
The imaging apparatus according to claim 1 or 2, wherein The control means includes
When the maximum value of the peak value of the contrast is lower than a third threshold value, the focusing unit is controlled so that the optical image is focused on the position of the region existing in the center of the region of the image sensor. ,
The imaging apparatus according to claim 3. A selection means for selecting a method for determining a position of the image sensor for focusing the optical image;
In addition,
The control means includes
If the evaluation value is lower than the first threshold, determine the position of the imaging element to focus the optical image based on the method selected by the selection means,
The imaging apparatus according to claim 1 or 2, wherein

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