JP5938269B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging apparatus and a control method thereof, and more particularly to a focus display technique.

  Focusing on a specific subject by automatic focus detection based on the contrast evaluation value of the focus detection region including a specific subject such as a human face among a plurality of focus detection regions with fixed positions and sizes An imaging device is known (Patent Document 1).

JP 2010-39200 A

  Focus detection based on contrast evaluation values (contrast AF) is in principle difficult to focus on low-contrast subjects. For this reason, when focus detection is performed on a focus detection region including a part of a person's face, it is easy to capture the contrast of the contour, not the center of the face. As a result, focus detection cannot be performed at the center part of the face such as the eyes and mouth (focus distance cannot be detected), and focus detection may be performed only in the focus detection region including the part that forms the face contour such as the ear.

  In order to clearly indicate to the user the focus detection area where the focus has been detected, focus display is known in which a frame-shaped index is superimposed on the EVF image. However, in the case of the above-described example, even if an index is displayed because focus detection has been performed in the focus detection area corresponding to the contour part of the face, the index cannot be detected in the focus detection area corresponding to the center part of the face. It may happen that it is not displayed.

  In this case, there is a problem that it is difficult to determine whether or not the face is in focus because the index is not displayed for the focus detection area at the center part of the face. In particular, when the face part is underexposed and the background is bright as in a backlight scene, or when the face part is overexposed due to direct sunlight, an event in which focus is detected only at the contour part is likely to occur.

  The present invention has been made in view of such a problem of the prior art, and an imaging apparatus that performs automatic focus detection based on contrast evaluation values in a plurality of focus detection areas whose positions and sizes are fixed, and a control method therefor An object of the present invention is to realize an appropriate in-focus display.

The above-described object is to provide a focus detection unit that detects a focus distance based on a contrast evaluation value of an image for each of a plurality of focus detection areas that are set in advance and have a fixed position and size, and a specific subject from the image. An object detection means for detecting the area of the image, a determination means for determining the final focus distance based on the focus distance detected by the focus detection means, and the focus distance detected by the focus detection means is the final focus distance. When there is a focus detection area including a specific subject area among the focus detection areas existing within the depth of field, all of the focus detection areas including the specific subject area are included. depending on the focus detection area, the image pickup apparatus characterized by having a focus display means performs a display indicating that it is focused by superimposing displays a frame indicating a focus detection area on the image It is achieved.

  ADVANTAGE OF THE INVENTION According to this invention, an appropriate focus display can be implement | achieved in the imaging device which performs automatic focus detection based on the contrast evaluation value in the several focus detection area where the position and the magnitude | size were fixed, and its control method. .

1 is a block diagram illustrating an example of a functional configuration of a digital camera as an example of an imaging apparatus according to an embodiment of the present invention. 1 is a block diagram showing an example of the functional configuration of the camera DSP in FIG. The figure which shows typically the example of the several focus detection area set to the digital camera which concerns on embodiment of this invention. The figure which shows the state which expanded the face part among FIG. Flowchart for explaining a focus detection operation in a digital camera according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings.
<Configuration of digital camera>
FIG. 1 is a block diagram illustrating a functional configuration example of a digital camera as an example of an imaging apparatus according to an embodiment of the present invention. Note that the present invention relates to an arbitrary imaging device using a plurality of focus detection areas whose sizes and positions are fixed and contrast AF, and an arbitrary device including such an imaging device (a mobile phone including a camera, a mobile phone, It can be applied to information terminals, computer equipment, and the like.

  As shown in FIG. 1, the digital camera 100 includes a system controller 129 that is configured by a CPU, an MPU, and the like and controls the entire camera operation, and a lens controller 107 that controls the entire optical system under the system controller 129. FIG. 1 shows only the focus lens 101 that can change the in-focus distance among the lenses constituting the optical system, but a variable magnification lens and a fixed lens (not shown) are also provided. In the present embodiment, a drive command, a stop command, a drive amount, and a required drive speed for the focus lens 101 are transmitted from the system controller 129 to the lens controller 107. Further, the lens controller 107 receives from the system controller 129 a drive amount and drive speed for aperture control of the aperture 102 and a transmission request for various data on the lens side. The optical system (components 101 to 108) is not limited to the configuration built in the digital camera 100, and may be in the form of an interchangeable lens.

  In the automatic focus detection operation, the system controller 129 issues a lens drive command that instructs the lens controller 107 about the drive direction, drive amount, and drive speed of the focus lens 101. When the lens controller 107 receives a lens driving command from the system controller 129, the lens controller 107 controls the lens driving mechanism 103 through the lens driving control unit 104. The lens drive mechanism 103 has, for example, a stepping motor as a drive source, and drives the focus lens 101 along the optical axis.

  The amount of movement of the focus lens 101 is sent to the lens controller 107 through a lens position information detection unit 109 configured by, for example, a pulse encoder that detects the amount of rotation of the stepping motor. The output of the lens position information detection unit 109 is connected to a hardware counter (not shown) in the lens controller 107. As a result, when the focus lens 101 is driven, a number of pulses corresponding to the driving amount is output from the lens position information detection unit 109, and the pulses are counted by the counter of the lens controller 107. The lens controller 107 can access the internal hardware counter register and read the stored counter value as the position information of the focus lens 101.

Upon receiving the aperture control command from the system controller 129, the lens controller 107 controls the aperture drive mechanism 105 that drives the aperture 102 via the aperture drive control unit 106, and the aperture 102 according to the drive amount received by the aperture control command. To control.

  The lens controller 107 is connected to a memory 108 in which at least a part of the area is nonvolatile. The memory 108 stores performance information such as a focal length (angle of view) of a variable magnification lens (not shown), an open aperture value of the aperture 102, and an aperture drive speed that can be set.

  A light beam incident from the aperture of the diaphragm 102 reaches the image sensor 112 through the optical filter 111 from the aperture of the focal plane shutter 110 that is a mechanical shutter. The optical filter 111 has an infrared filter function that cuts infrared light from incident light and guides visible light to the image sensor 112, and an optical low-pass filter function.

  The focal plane shutter 110 includes, for example, a front curtain and a rear curtain that use a spring as a drive source, and controls exposure and light shielding of the image sensor 112. The shutter control unit 114 controls the driving of the front and rear curtains of the focal plane shutter 110 according to a control signal from the system controller 129. The shutter charge mechanism 113 performs spring charge for the next operation after the focal plane shutter 110 travels.

  Further, the system controller 129 displays a program diagram in which the relationship between the subject brightness obtained from the output of a predetermined photometric area in the image sensor 112 and the charge accumulation time, exposure sensitivity, and aperture value of the image sensor 112 is determined, for example. It is stored in the EEPROM 122.

  The timing generator 118 generates a timing signal and determines the drive timing of the entire imaging system. The driver 117 generates a drive signal for each pixel of the image sensor 112 based on the timing signal from the timing generator 118. The image sensor 112 converts a light beam incident on each pixel at the time of exposure into an electric charge, and generates an electric signal (image signal) for each pixel.

  An image signal generated by the image sensor 112 is amplified by a correlated double sampling / automatic gain control (CDS / AGC) circuit 115 and converted into a digital image signal by an A / D converter 116. The digital image signal output from the A / D converter 116 is input to the selector 121. The selector 121 switches the output destination of the digital image signal among the camera DSP 126, the video memory 120, and the memory controller 127 based on a signal from the system controller 129.

  All the digital image signals input to the memory controller 127 are transferred to the DRAM 128 which is a frame memory. By periodically transferring the digital image signal transferred to the DRAM 128 to the video memory 120 via the selector 121 (at a predetermined frame rate), the monitor display unit 119 can function as an electronic viewfinder.

  In addition to the system controller 129, the camera DSP 126 is connected to a timing generator 118, an A / D converter 116, a video memory 120, and a work memory 125 through a selector 121.

  At the time of capturing an image for recording, the system controller 129 reads a digital signal for one frame from the DRAM 128, performs image processing with the camera DSP 126, and then temporarily stores it in the work memory 125. Then, the system controller 129 compresses the image data stored in the work memory 125 in a predetermined format such as the JPEG format by the compression / decompression circuit 124 and records it in the external nonvolatile memory 123. Usually, a detachable recording medium such as a semiconductor memory card, a magnetic disk, or an optical disk is used for the non-volatile memory 123, but any non-volatile recording medium can be used. Moreover, both a detachable recording medium and a non-detachable recording medium may be used.

  The operation switch 131 connected to the system controller 129 is an input device group for a user to input setting values, instructions, and the like to the digital camera 100, and includes an arbitrary input device. The display unit 130 is a display device such as a liquid crystal panel, an LED (light emitting diode), or an organic EL panel, and displays information related to the operating state of the digital camera 100. SW1 132 and SW2 133 are two switches included in the release switch. SW1 132 is pressed when the release button is pressed halfway (pressed one step), and SW2 133 is pressed when pressed fully (pressed two steps). , Turn on each.

  When SW1 132 is turned on, the system controller 129 starts photographing preparation operations such as photometry (determination of exposure conditions) and focus detection. When SW2 133 is turned on, the system controller 129 starts a photographing operation (charge accumulation and charge readout operation) for recording a still image. The live view mode switch 134 controls on / off of the live view display that causes the monitor display unit 119 to function as an EVF. The moving image switch 135 is a switch for instructing the start of moving image shooting. During moving image shooting, the system controller 129 repeatedly executes charge accumulation and charge readout at a predetermined frame rate (for example, 30 frames / second). Note that the operation during moving image shooting is basically the same as the shooting operation during live view display.

  The digital camera 100 according to the present embodiment is set to record a still image as an initial setting when the power is turned on (still image mode), but is switched to a setting to record a moving image (moving image mode) by operating the moving image switch 135. When the moving image switch 135 is operated in the moving image mode, the setting is returned to the still image mode.

Next, a functional configuration example and operation of the camera DSP 126 will be described using the block diagram of FIG.
The image signal read from the image sensor 112 is amplified by the CDS / AGC circuit 115 as described above, converted into a digital image signal by the A / D converter 116 , and input to the camera DSP 126 via the selector 121.

  The camera DSP 126 calculates a contrast evaluation value used for contrast AF and detects a specific subject from the digital image signal. Here, it is assumed that the specific subject is a human face. However, an arbitrary subject that can be detected from an image by a known technique such as pattern matching can be set as a specific subject.

  In order to calculate the contrast evaluation value, the digital image signal input to the camera DSP 126 is input to the focus detection area extraction unit 202 via the DSP internal memory 201. The focus detection area extraction unit 202 extracts an image in the focus detection area from the digital image signals for the entire screen, and supplies the image to the contrast evaluation value calculation unit 203.

  In the digital camera 100 of the present embodiment, a plurality of focus detection areas whose positions and sizes are fixed are set in advance. The position and size of the focus detection area are set in advance for the focus detection area extraction unit 202 by the system controller 129. The contrast evaluation value calculation unit 203 extracts a predetermined frequency component by digital filter calculation for the image in the focus detection region for each of the plurality of focus detection regions, and outputs it to the system controller 129 as a contrast evaluation value. The face area detection unit 204 serving as a subject detection unit extracts an image area that appears to be a person's face by extracting feature points of the person's face from the digital image signals for the entire screen input via the DSP internal memory 201. (Face region) is detected. A technique for detecting a specific subject such as a person's face from an image is generally used, and a face area can also be detected using a known technique in this embodiment. The face area detection unit 204 outputs information (position, size, etc.) of the detected face area to the system controller 129.

Next, the focus detection area will be described.
FIG. 3 is a diagram schematically illustrating an example of a plurality of focus detection areas used by the digital camera 100 of the present embodiment. In FIG. 3, the full screen (imaging field of view) 301 includes a person 302 as a main subject, a tree 303 positioned far from the main subject, and a hedge 304 positioned in front of the main subject. As a plurality of focus detection areas, a total of 24 focus detection areas 305 are set by dividing the area excluding the peripheral portion of the screen into six equal parts in the horizontal direction and four equal parts in the vertical direction. Each of the plurality of focus detection areas 305 has a fixed position and size, and focus detection can be performed for each focus detection area. The system controller 129 determines which focus detection area is finally focused. In the example of FIG. 3, for each of the person 302, the tree 303, and the hedge 304, there is no focus detection area that encompasses the entirety, and the plurality of focus detection areas partially include one or more subject areas. doing.

  In the present specification, “including” a subject or a subject region means overlapping with the subject region (that is, including at least a part of the subject or the subject region).

  When the digital camera 100 is activated, it enters a shooting standby state in the still image mode, and the system controller 129 starts a live view display operation. When the release button is pressed halfway in the shooting standby state and the SW1 131 is turned on, the system controller 129 executes a focus detection operation for 24 focus detection areas as part of the shooting preparation operation.

  FIG. 4 is an enlarged view of the area around the person in FIG. 3, and is a view for explaining a focus display method when a face is a specific subject. FIG. 4 shows focus detection areas 401 to 406 including a face area among the plurality of focus detection areas 305. Among these focus detection areas 401 to 406, the focus detection area 403 does not include a face outline and includes a center part of the face such as eyes, but the other focus detection areas include a face outline.

  When a plurality of focus detection areas whose positions and sizes are fixed and a person as a specific subject are in a positional relationship as shown in FIG. 4, focus detection areas 401, 402, 404, and 405 including a face outline are used. Focus detection is easy. Note that the focus detection area 406 is easily detected by the focus, although it depends on the contrast of the boundary with the body area. On the other hand, the focus detection region 403 that does not include an outline often includes only the degree of contrast components in the eyes and eyebrows. If the face area is underexposed, such as in a backlight scene, or the face area is overexposed, such as when direct sunlight is reflected from the face, the contrast of the focus detection area 403 (and 406) is further Lower. On the other hand, the focus detection areas 401, 402, 404, and 405 including the face outline and the background are more easily detected.

  For this reason, when performing display (focus display) indicating the focus detection area where the focus detection has been successful, the focus detection areas 401, 402, 404, and 405 are displayed in focus, and the focus detection areas 403 and 406 are in focus. A situation can occur where no indication is made.

<Focus detection operation>
Next, the focus detection operation in the present embodiment will be described using the flowchart of FIG. Unless specifically described, the following operations are executed based on the control of the system controller 129.

  As described above, the focus detection operation is executed as one of the shooting preparation operations started when the SW1 131 is turned on in the shooting standby state of the still image mode. In the shooting preparation operation, other operations such as determination of exposure conditions are also performed. However, the operations are not directly related to the present invention, and the description thereof is omitted because a known technique can be applied. Only the focus detection operation will be described.

  As described above, in the shooting standby state, the live view display operation is executed at a frame rate of 30 to 60 frames / second, and it is necessary for generating images for display such as image processing as well as shooting and display. Assume that processing is being performed.

  First, in step S501, the system controller 129 performs a known focus detection (focus scan) based on a contrast evaluation value for a focus detection area (focused AF frame) for which focus detection is to be performed. Then, the system controller 129 performs focus detection for each AF frame of interest, and detects the focus distance (the position of the focus lens 101 corresponding to the focus state). Here, the focus AF frame is all of the focus detection areas or a plurality of specific focus detection areas (so-called zone AF frames) among the 24 focus detection areas. When the in-focus distance is detected for each AF frame of interest, the system controller 129 advances the process to S502.

In step S <b> 502, the system controller 129 determines whether the final focus distance can be determined according to a predetermined condition (for example, priority is given to a close focus distance) from the focus distance detected in each AF frame of interest. If there is only one AF frame of interest, the focus distance detected there is set as the final focus distance. If it is determined that the final focus distance can be determined, the system controller 129 proceeds to S503, and if it is determined that the final focus distance cannot be determined, the process returns to S501 and repeats the processing from the focus scan again.

  In step S503, the system controller 129 issues a command for moving the focus lens 101 to a position corresponding to the determined final focusing distance to the lens controller 107, and displays a display indicating in-focus on the display unit 130, and the process proceeds to step S504. Proceed.

  In step S504, the system controller 129 detects whether or not there is another focus detection area whose in-focus distance is within the depth of field of the final in-focus distance, and stores the detection result. Then, the system controller 129 advances the process to S505.

  In step S <b> 505, the face area detection unit 204 applies face area detection processing to the image signal captured for live view display. For example, when the system controller 129 receives an output from the face area detection unit 204, the process proceeds to S506.

  In step S <b> 506, the system controller 129 determines whether a face area has been detected based on, for example, an output from the face area detection unit 204. The system controller 129 proceeds to S507 if it is determined that a face area has been detected, and proceeds to S509 if it is determined that it has not been detected.

  In step S507, the system controller 129 determines whether at least one of the focus detection area in which the final focus distance determined in step S502 is detected and the other focus detection area detected in step S504 overlap the face area (including the face area). Is determined). If it is determined that the face area is included in one or more of the focused focus detection areas, the system controller 129 proceeds to S508, and any of the focused focus detection areas changes the face area. If it is determined that it is not included, the process proceeds to S509.

  In step S508, the system controller 129 determines that the face area is included within the depth of field, performs in-focus display for all focus detection areas including the face area, and ends the focus detection process.

  In step S509, the system controller 129 performs in-focus display on the focus detection area in which the final focus distance is detected and the other focus detection areas having the focus distance within the depth of field, and ends the focus detection process. .

  If the focus detection area in focus can be grasped by the user, the focus display method is not particularly limited. For example, the live view image displayed on the electronic viewfinder is focused. An index such as a mark or a frame representing a focus detection area can be superimposed and displayed. This in-focus display can be realized by the system controller 129 reading out the index GUI data from, for example, the EEPROM 122 and writing it into the video memory 120 through the selector 121.

  As described above, according to the present embodiment, when one or more focus detection areas including a specific subject area have a focus distance within the depth of field, all the areas including the specific subject area are included. In-focus display is performed on the focus detection area. Therefore, even if the focus detection is successful for the focus detection region including the face contour portion and the focus detection fails in the focus detection region not including the face contour portion, all the focus including the face region is included. The user can be informed that the detection area is in focus.

(Modification)
In this embodiment, in S507, it is determined whether or not there is a focus detection area including a face area which is a specific subject area. However, if there is a focus detection area including a region of another subject that is considered to be equal in distance to the specific subject, the focus display may be performed on all the focus detection regions including the region of the specific subject. .

  For example, as shown in FIG. 3, when the specific subject is a person's face, the body part continuous to the person's face is also present at substantially the same distance as the face. Therefore, when there is at least one focus detection region including the body region where the detected focus distance exists within the depth of field, the face region is also included within the depth of field. Therefore, the focus display may be performed on all focus detection areas including the face area. By performing such an operation, even when focus detection cannot be performed at the center of the face such as the eyes and eyebrows, it is possible to display that the face is substantially in focus after focusing on the body area. become.

In this case, in step S507, the system controller 129 estimates the body area from the position of the face area from the face detection result, and the focus detection that overlaps with the body area where the detected focus distance exists within the depth of field. The presence or absence of an area is also detected. If there is a focus detection area that overlaps with the face area and / or the body area in which the detected focus distance exists within the depth of field, the system controller 129 determines in S508 that all of the focus detection areas overlap with the face area. In-focus display is performed on the focus detection area. Note that if there is a focus detection area that overlaps with the body area where the detected focus distance is within the depth of field, the focus detection area is also displayed in focus.

(Other embodiments)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (4)

Focus detection means for detecting a focus distance based on a contrast evaluation value of an image for each of a plurality of focus detection areas that are set in advance and have a fixed position and size;
Subject detection means for detecting a specific subject region from the image;
Determining means for determining a final focusing distance based on the focusing distance detected by the focus detection means;
When there is a focus detection area that includes the area of the specific subject among the focus detection areas in which the focus distance detected by the focus detection unit exists within the depth of field of the final focus distance , Out of the plurality of focus detection areas, all the focus detection areas including the specific subject area are in focus by superimposing and displaying a frame representing the focus detection area on the image. In-focus display means for displaying
An imaging device comprising: The subject detection means further detects a region of another subject that is considered to be equal in distance to the specific subject;
The focus display means includes a focus that includes the area of the other subject in the focus detection area where the focus distance detected by the focus detection means is within the depth of field of the final focus distance. When there is a detection area, the focus distance detected by the focus detection means includes the area of the specific subject among the focus detection areas existing within the depth of field of the final focus distance. Even when there is no focus detection area, a frame representing the focus detection area is superimposed on the image for all focus detection areas including the specific subject area among the plurality of focus detection areas . The imaging apparatus according to claim 1, wherein a display indicating that the subject is in focus is performed.   The imaging apparatus according to claim 2, wherein the subject detection unit detects a person's face as the specific subject and detects the person's torso as the other subject. A focus detection step of detecting a focus distance based on a contrast evaluation value of an image for each of a plurality of focus detection areas having a fixed position and size fixed in advance;
A subject detection step of detecting a specific subject area from the image;
A determination step of determining a final focus distance based on the focus distance detected in the focus detection step;
When there is a focus detection area that includes the area of the specific subject among focus detection areas in which the focus distance detected in the focus detection step exists within the depth of field of the final focus distance , Out of the plurality of focus detection areas, all the focus detection areas including the specific subject area are in focus by superimposing and displaying a frame representing the focus detection area on the image. An in-focus display process for displaying
A method for controlling an imaging apparatus, comprising: