JP2020173374A - Image capturing device - Google Patents

Abstract

To provide a flash light-emitting image capturing device capable of providing a good captured image with a face in focus by performing facial detection on an object image obtained by emitting flash light and measuring distance to a zone with the detected face even if the face of a person, the main object, is dark in the scene.SOLUTION: An image capturing device provided herein is configured to perform facial detection on an object image obtained by emitting flash light and measure distance to a zone with a detected face even if the face of a person, the main object, is dark in the scene.SELECTED DRAWING: Figure 2

Description

The present invention has a means for focusing on a subject, performs pre-flash and photometry of a strobe, and has a method of detecting a face from a photometric image in an imaging device that controls main light emission using this photometric value. The present invention relates to an imaging device for accurately focusing a face by performing detection.

Conventionally, there is known an imaging device that performs photometry and face detection by focusing on a subject before shooting, acquiring an image signal with a photometric sensor, and processing the image signal.

In an imaging device that performs pre-flash and photometry of a strobe and controls the main flash using this photometric value, an imaging device that detects the face of the subject in the image captured during pre-flash of the strobe and improves the photometric accuracy is known. There is.

Patent Document 1 discloses a method in which an image is acquired by a photometric sensor, a face is detected from the acquired image, and the position where the face is detected is used as a main AF point for distance measurement.

Patent Document 2 discloses a method of performing face detection from an image at the time of pre-flash of a strobe to improve the accuracy at the time of main strobe flash. It discloses a method of determining the main emission amount by using the distance measurement information obtained by measuring the distance to the subject and the brightness of the detected face region in the pre-emission.

Patent Document 3 also discloses a method of illuminating and improving a subject in order to solve a problem that cannot be detected because the subject has low brightness.

Japanese Patent No. 5832153 Japanese Unexamined Patent Publication No. 2005-184508 Japanese Unexamined Patent Publication No. 2015-219274

In the prior art disclosed in Patent Document 1, there is a problem that face detection cannot be performed accurately and the face cannot be focused in a scene where the brightness of the face region of the subject cannot be detected. For example, in the night view 301 where there is a building with a window light in the distant view as shown in FIG. 3, when shooting a person 302 whose face area is so dark that the face cannot be detected, the AF point corresponding to the distant view is the window light in the distant view. Is a point light source and has a high contrast, so that a large ranging signal can be easily obtained in a known ranging operation. On the other hand, the ranging point corresponding to the face of a person has a very dark brightness in the face area and low contrast, so that the ranging signal becomes small, and as a result, a large ranging signal is obtained. Is determined as the main AF point, and there is a problem that the person's face 303 is not in focus.

In the prior art disclosed in Patent Document 2 above, there is a problem that it is not possible to focus on the face because it is not disclosed where to focus on the subject from the obtained distance measurement information. Especially in a scene where the brightness of the face region is so dark that the face cannot be detected when the subject is not exposed to the strobe illumination, the face can be detected only after the subject is exposed to the strobe illumination. Therefore, in the distance measuring operation for measuring the distance to the subject prior to the pre-flash, there is a problem that the face position of the subject cannot be determined and the face cannot be focused.

In the prior art disclosed in Patent Document 3 above, it is necessary to use a high-illuminance light source when the subject is at a long distance or when the brightness other than the face region is high. Not preferable from the viewpoint of power consumption. A portable photographing device is premised on being driven by a battery, and a lighting device that consumes a large amount of power has a problem that a large number of batteries are required.

Therefore, an object of the present invention is to detect a face by performing face detection from a subject image irradiated by a flash of a strobe, which consumes less power than normal lighting, even if the face of a person who is the main subject is dark. It is an object of the present invention to provide a strobe light emitting image pickup device capable of obtaining a good image captured image focused on a face by performing distance measurement on the area.

In order to achieve the above object, the imaging device according to the present invention is
It is an imaging device that focuses on the subject at the time of shooting and also performs pre-flash before the main flash.
A means of moving the lens focal length to a position that is the first coefficient multiple of the lens focal length,
After moving to the lens focal position, a means for acquiring a subject captured image by the first light emission, and
A face area detecting means for detecting a face area in the subject captured image, and
A main subject determining means for determining the face area as the main subject,
A distance measuring means for measuring the distance to the main subject, and
A main subject focusing means for focusing the main subject from the distance to the main subject,
Luminance difference acquisition means for acquiring the difference between the subject brightness not due to light emission and the subject brightness due to the second light emission,
An arithmetic means for calculating the third amount of light emission according to the photometric value of the second light emission, and
A control means that controls the strobe based on the third light emission amount calculated by the calculation means to control shooting.
It is characterized by having.

According to the present invention, even if the face of a person who is the main subject is a dark scene, the face is detected from the subject image by the light emission of the strobe, and the face is focused on the face which is the main subject by measuring the distance to the detected area. It is possible to provide a strobe light emitting imaging device that can obtain a good captured image that matches the above.

Device configuration Shooting flow A scene where the distant view is bright and the person is dark Lens focal length and lens focal position when performing face detection

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram of an imaging device according to the present embodiment.

The imaging device according to the present embodiment includes a camera device 10, a lens device 11, and a strobe device 12. The camera device 10 and the lens device 11 are configured such that the lens device is detachable via a mount portion. The camera device 10 and the lens device 11 may be integrated. The camera device 10 and the strobe device 12 are configured such that the strobe device can be attached to and detached from the accessory shoe portion. The camera device 10 and the strobe device 12 may be integrated.

101 is a camera control unit, 102 is a non-volatile memory, 103 is a temporary storage memory, 104 is a main mirror, 105 is a focus plate, 106 is a pentaprism, 107 is a finder, 108 is a photometric sensor, 109 is a sub mirror, and 110 is a focus detection sensor. , 111 is a shutter, 112 is an imaging element, 113 is an image processing unit, 114 is a recording medium, 115 is a shutter button, 116 is a setting button, 151 is a strobe control unit, 152 is a xenon tube, 153 is a charging circuit, and 154 is a strobe. The light emitting capacitor, 155 is a light emitting circuit, 156 is an external dimming sensor, 157 reflecting plate, and 158 are contacts.

The camera control unit 101 controls the operation of the entire camera. The camera control unit 101 is composed of a microcomputer, and a non-volatile memory 102 and a temporary storage memory 103 are connected to the camera control unit 101. The non-volatile memory 102 stores programs and set values, and the temporary storage memory 103 stores images being calculated, calculation results, and control values. The camera control unit 101 communicates with the lens control unit 202 and the strobe control unit 151 through the contact 203 and the contact 158 to transmit instructions and receive information.

When the main mirror 104 is in the viewfinder observation state shown in FIG. 1, it reflects a part of the luminous flux of the subject light that has passed through the photographing lens 201. The luminous flux reflected by the main mirror 104 is imaged by the focus plate 105, changed the direction of the image by the pentaprism 106, and guided to the finder 107 to reach the photographer's eyes. This allows the photographer to confirm the subject image. The subject image imaged by the focus plate 105 is guided to the photometric sensor 108 near the viewfinder 107. The photometric sensor 108 is an area type sensor capable of global shutter operation. The subject image formed on the photometric sensor 108 is photoelectrically converted into an electrical image signal and output to the camera control unit 101 as luminance information. The photometric sensor 108 is an area-type sensor having tens of thousands or more pixels, and can measure light by dividing the screen area. The photometric sensor 108 may output the luminance information to the image processing unit 113, perform various calculations on the image processing unit 113, and output the result to the camera control unit 101.

In order to calculate the subject brightness and analyze the scene, the camera control unit 101 or the image processing unit 113 divides the screen area into, for example, 9 × 7 blocks, and based on the signal of the pixels included in each block, the brightness information for each block. Is calculated. The brightness information of the block is obtained, for example, by averaging the brightness of all the pixels in the block. Further, the photometric sensor 108 may have R pixels, G pixels, and B pixels and can recognize colors. The image processing unit 113 has a function of detecting the face of a person who is the main subject as the main subject by determining the feature points of the shape such as the eyes, nose, and mouth of the face in the captured image, and the number of detected faces. -The area position, size, etc. are output to the camera control unit 101.

The main mirror 104 is composed of a half mirror, and the light flux that has passed through the main mirror 104 without being reflected is reflected by the sub mirror 109 and guided to the focus detection sensor 110. The subject image formed on the focus detection sensor 110 is photoelectrically converted into an electrical image signal and transmitted to the camera control unit 101. The camera control unit 101 performs a focus detection calculation by a phase difference detection method based on the image signal of the subject image from the focus detection sensor 110, and based on the calculated defocus amount and focusing distance information such as the defocus direction, The position of the focus lens in the image pickup lens 201 is changed via the lens control unit 202 to drive the focus lens to the in-focus position. Further, the camera control unit 101 drives an aperture (not shown) via the lens control unit 202.

At the time of imaging, the camera control unit 101 retracts the main mirror 104 and the sub mirror 109 and changes the optical path so that the subject image is formed on the image sensor 112.

A shutter 111 is arranged on the front surface of the image sensor 112. The shutter 111 is a focal plane shutter.

As the image sensor 112, a CMOS image sensor or the like having several million or more imaging pixels is used. The light of the subject that has passed through the image pickup lens 201 forms a subject image on the image pickup element 112. The image sensor 112 receives this light and performs photoelectric conversion. The electric charge converted from light indicates the brightness, is stored in each pixel, and is read out as a voltage by a transistor in the pixel. The read voltage is converted into a digital signal and transferred to the image processing unit 113.

The image processing unit 113 is a processor specialized in image processing. The captured image transferred from the image pickup element 112 is developed, processed in various ways, encoded, and then output to the recording medium 114. Further, the calculation result of the image is output to the camera control unit 101.

Reference numeral 115 denotes a shutter button, and SW1 and SW2 are formed by a two-stage switch. When SW1 is on, shooting preparation is started, and when SW2 is on, shooting is started. Reference numeral 116 denotes a setting button, which is a means for the photographer to input settings for selecting the operation of the camera. It consists of mechanical buttons or touch sensors.

Reference numeral 151 denotes a strobe control unit, which controls each strobe unit and communicates with the camera control unit 101 via the contact point 158 to receive an operation instruction or transmit various information.

The charge circuit 155 controls the electric charge charged in the strobe light emitting capacitor 154 by the charging circuit 153, and the xenon tube 152 emits light. The light emitted is collected by the reflector 157 and irradiates the subject. Reference numeral 156 is an external dimming sensor that measures the brightness of the subject without using the light transmitted through the lens 201.

Here, a method for detecting the face before the distance measuring operation will be described.

Since it is before the distance measurement operation, the distance to the subject is unknown, and the focusing of the imaging optical system cannot be expected. In order to detect the face at this time, the image obtained by the photometric optical system is used. The photometric optical system such as an interchangeable-lens single-lens reflex camera and the imaging optical system have different optical systems, and the size of the sensor is different. The sensor of the photometric optical system has a larger image plane than the sensor of the imaging optical system. small. If the same subject angle of view is taken in these two optical systems, the optical system with a small sensor has a larger image magnification and a larger F value than the optical system with a large sensor. Therefore, it is known that the blurring of the image on the sensor is proportional to the sensor size.

Therefore, the image of the photometric optical system with a small sensor has a deeper depth of focus and is closer to pan focus than the image of a system with a large sensor, so that the subject image is less likely to be blurred.

Since the size of an adult's face is 12 to 16 centimeters, the distance to the subject in a human image is, for example, 1 meter to 100 f. Since the photometric optical system having a small sensor as described above is close to pan focus and used like a fixed focus camera, the lens focal position when detecting a face is moved to an intermediate position 50f in the range of 1 meter to 100f, for example. By placing the subject in this focal position, a subject in the range of 1 meter to 100 f can be put in the depth of focus, and face detection can be performed even if the distance to the subject is unknown.

Further, the range of light of the strobe device 12 included in the photographing device is finite. Considering that it is the operation of the pre-light emission before the main light emission, the light amount of the pre-light emission is, for example, about 1/10 of the light amount of the main light emission, and the reach is further reduced in consideration of the power consumption. The reach is determined by the amount of light emitted by the strobe device of the photographing device, the lens F value, and the ISO sensitivity of the image pickup. It is said to be 10 meters. Therefore, since the distance that can sufficiently irradiate the subject is within 10 meters, it is premised that the face of the person who is the main subject in this range is detected. If the lens focal length at the time of face detection is, for example, 50f, the lens focal length is, for example, 200 mm or less in order to keep the lens focal length within, for example, 10 meters of the photographable distance. Therefore, the lens focal position at the time of face detection is set to 50 f, and is fixed at 10 meters for 200 mm or more, for example.

Further, when the focal length of the attached lens is sufficiently short, there is little blurring and there is no problem in detecting the subject. Therefore, if the focal length of the lens is equal to or less than the threshold value, the lens position may be any distance at the time of face detection, and it is not necessary to drive the lens focal length again. For example, if the lens focal length is 35 mm or less, the lens focal position at the time of face detection is not changed.

When performing lens focal length and face detection under these assumptions, the lens focal length is as shown in FIG. In the region 401, the lens focal length at the time of face detection is not changed when the lens focal length is 35 mm or less.

Based on this premise, in order to achieve the above object, when the photographing operation is started, the lens focal length is moved from the focal length of the mounted lens as shown in FIG. First, constant photometry is performed to determine if there is a low-brightness region where face detection is not possible. If there is a low-brightness area where face detection is not possible, the strobe device flashes. A person's face is detected from the subject image acquired by the photometric optical system. If there is no low-brightness region where face detection is not possible, a person's face is detected from the subject image under constant light. When the time until the main shooting exceeds the threshold value, face detection may be performed again.

Next, by performing distance measurement and focusing operations on the area of the face, a good captured image in focus on the face can be obtained. After moving the lens to the focal position, pre-emission is performed to determine the amount of light emitted, and the reflected light of the subject is measured. The amount of the main emission is determined from the measured value of the reflected light, and the main emission and shooting are performed.

Next, photography using a strobe in the present embodiment will be described with reference to the flow chart of FIG.

The shooting operation is performed according to each step in FIG.

In step S201, the state of SW1 of the shutter button 115 is monitored. If SW1 of the shutter button 115 is turned on, the process returns to step S202, and if it is off, the process returns to step S201.

In step S202, photometry is performed using the photometric detection sensor 108.

In step S203, in order to calculate the subject luminance from the photometric image obtained in step S202, the screen area is divided into blocks, and the luminance information for each block is calculated based on the signal of the pixel included in each block.

In step S204, if the focal length of the lens 203 is equal to or greater than the threshold value, the process proceeds to step S205. If it is equal to or less than the threshold value, the process proceeds to step S206.

In step S205, the lens 203 is driven to set the lens focal position to 50f.

In step S206, it is determined whether or not there is a block whose block brightness value obtained in step S203 is smaller than the brightness threshold value 1. If there is, the process proceeds to step S207. If not, the process proceeds to step S208.

In step S207, the strobe device 12 is made to emit light.

In step S208, the photometric detection sensor 108 is used to acquire a subject image illuminated by the light emitted by the strobe device 12.

In step S209, face detection is performed on the face detection image.

In step S210, it is determined whether or not a face has been detected. If a face is detected, the process proceeds to step S211. If no face is detected, the process proceeds to step S213.

In step S211 the detected face area position is determined.

In step S212, the main AF point is determined based on the position of the face obtained in step 211, and the process proceeds to step S214.

In step S213, the main AF point is determined by AF without using the face position information.

In step S214, the focal position 2 is detected at the main focusing point.

In step S215, the lens 203 is driven to the focal position 2 at the main focusing point.

In step S216, it is determined whether the elapsed time from step S210 exceeds the threshold value. If it exceeds the limit, the process returns to step S202.

In step S217, the state of SW2 of the shutter button 115 is monitored. If SW2 of the shutter button 115 is turned on, the process returns to step S217, and if it is off, the process returns to step S216.

In step S218, the external light is metered (2).

In step S219, pre-flash is performed.

In step S220, pre-emission metering (3) is performed.

In step S221, the dimming region is determined from the pre-emission photometric result.

In step S222, the photometric image AE (3) -AE (2) calculation that draws external light is performed in order to calculate the subject brightness due to the pre-flash, and the flash emission amount of the strobe is determined.

In step S223, the main shooting and the main light emission are performed.

In step S224, the image processing unit 113 performs development processing and image processing on the data captured by the image sensor 112, and compresses and encodes the data.

In step S225, the image data is recorded on the recording medium 114.

In step S226, shooting ends.

As described above, even if the face of the person who is the main subject is dark, the face is focused by detecting the face from the subject image by the light emission of the strobe and measuring the distance to the detected area. A good captured image can be provided.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and modifications can be made within the scope of the gist thereof.

10 camera device, 11 lens device, 12 strobe device

Claims (6)

It is an imaging device that focuses on the subject at the time of shooting and also performs pre-flash before the main flash.
A means of moving the lens focal length to a position that is the first coefficient multiple of the lens focal length,
After moving to the lens focal position, a means for acquiring a subject captured image by the first light emission, and
A face area detecting means for detecting a face area in the subject captured image, and
A main subject determining means for determining the face area as the main subject,
A distance measuring means for measuring the distance to the main subject, and
A main subject focusing means for focusing the main subject from the distance to the main subject,
Luminance difference acquisition means for acquiring the difference between the subject brightness not due to light emission and the subject brightness due to the second light emission,
An arithmetic means for calculating the third amount of light emission according to the photometric value of the second light emission, and
A control means that controls the strobe based on the third light emission amount calculated by the calculation means to control shooting.
An imaging device characterized by having. The imaging apparatus according to claim 1, wherein the first coefficient multiple of the lens focal length is 50 f. The imaging device according to claim 1, wherein an image for detecting a face is acquired by a photometric optical system different from the imaging optical system. The imaging device according to claim 1, wherein when the focal length of the imaging lens is smaller than the first threshold value, the subject image is acquired by the first emission without moving. The imaging device according to claim 1, wherein when a time exceeding a certain threshold value has elapsed from the detection of the face to the actual shooting, the face detection image is acquired and detected again. The imaging device according to claim 1, wherein the first light emission is performed only when a region having a brightness or less required for detecting a face is present in the subject image.