JP2010183459A - Image capturing apparatus and method of controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a scene blackening a background in flash photographing a low-brightness scene. <P>SOLUTION: An image capturing apparatus (100) enables imaging using a flash (111). The image capturing apparatus includes a brightness detection means (106) obtaining the brightness information of image data acquired by imaging by an image sensing means, a motion detection means (115) detecting the quantity of a subject move in the image from image data, and a control unit (102) deciding whether the emission of the flash is required on the basis of the brightness information. The image capturing apparatus further includes a shutter setting-range changer (116) changing the longest limitation of exposure time on the basis of the quantity of the subject move when deciding photographing using the flash, and an AE processing unit (109) obtaining exposure conditions containing the exposure time on the basis of the brightness information of the image data and the longest limitation of the exposure time. The shutter setting-range changer makes the longest limitation longer with the reduction of the quantity of the subject move. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image pickup apparatus and a control method thereof, and more particularly to an image pickup apparatus capable of photographing using a flash and a control method thereof.

  In photographing with a digital camera, when photographing a person in a scene such as a night view, since the amount of light hitting the subject is small, it is generally performed to compensate for the shortage of the amount of light with a flash.

  Here, in general, the shutter speed at the time of flash emission in the dark is set slightly faster than that at the time of non-light emission in consideration of camera shake and subject shake as described in Patent Document 1, for example.

Japanese Patent Laid-Open No. 08-006113

  However, if a faster shutter speed is set when flashing in a dark scene, the exposure will be forcibly changed, and the background will be blacked out, resulting in an image where only the subject is floating. There was a case.

  The present invention has been made in view of the above problems, and an object of the present invention is to reduce scenes in which the background is obscured during flash photography of low-luminance scenes.

  In order to achieve the above object, an imaging apparatus of the present invention capable of imaging using a light-emitting device comprises: luminance detection means for obtaining luminance information of image data obtained by imaging by an imaging means; and the image data, Motion detection means for detecting the amount of movement of a subject included in the image, determination means for determining whether or not the light emitting device needs to emit light based on luminance information obtained by the luminance detection means, and the light emission by the determination means A change unit that changes a maximum exposure time limit based on the amount of movement of the subject when it is determined to perform shooting using the apparatus; and luminance information of image data obtained by imaging by the imaging unit And an exposure control means for obtaining an exposure condition including the exposure time based on the maximum limit of the exposure time changed by the changing means. The changing means has a smaller movement amount of the subject. , The longer the maximum limit.

  Also, the control method of the present invention for an imaging device capable of imaging using a light emitting device includes a luminance detection step for obtaining luminance information of image data obtained by imaging by an imaging means, and the image data includes the luminance detection step. A motion detection step for detecting the amount of movement of the subject to be detected, a determination step for determining whether or not the light emitting device needs to emit light based on the luminance information obtained in the luminance detection step, and the determination step for using the light emitting device. And changing the maximum exposure time limit based on the amount of movement of the subject, the luminance information of the image data obtained by the imaging means, and the change An exposure control step for obtaining an exposure condition including an exposure time based on the longest limit of the exposure time changed by the step, and in the changing step, the smaller the amount of movement of the subject, The length limit for longer.

  According to another configuration, the imaging device of the present invention capable of imaging using a light emitting device includes a luminance detection unit that obtains luminance information of image data obtained by imaging by the imaging unit, and the imaging device. Based on the brightness information obtained by the brightness detecting means, a shake detecting means for detecting the amount of movement, a judging means for judging whether or not the light emitting device needs to emit light, and the judging means for photographing using the light emitting device. When it is determined to be performed, based on the amount of movement of the imaging device, a changing unit that changes a maximum exposure time limit, luminance information of image data obtained by the imaging unit, and the changing unit Exposure control means for obtaining an exposure condition including the exposure time based on the changed maximum limit of the exposure time, and the change means makes the maximum limit longer as the amount of movement of the imaging device is smaller. That.

  In addition, the control method of the present invention for an imaging device capable of imaging using a light emitting device includes a luminance detection step for obtaining luminance information of image data obtained by imaging by an imaging means, and a motion amount of the imaging device. Based on the blur detection step, the luminance information obtained by the luminance detection step, a determination step for determining whether or not the light emitting device needs to emit light, and the determination step is determined to perform photographing using the light emitting device. A change step for changing the maximum exposure time limit based on the amount of movement of the image pickup device, the luminance information of the image data obtained by the image pickup means, and the exposure changed by the change step. And an exposure control step for obtaining an exposure condition including an exposure time based on the longest limit of time. In the changing step, the smaller the amount of motion of the imaging device, the longer the longest limit.

  According to the present invention, it is possible to reduce the number of scenes in which the background is obscured during flash photography of a low brightness scene.

1 is a block diagram showing a schematic configuration of a digital camera according to a first embodiment of the present invention. It is a flowchart for demonstrating the imaging operation of the digital camera in the 1st Embodiment of this invention. It is a figure for demonstrating the effect of the 1st Embodiment of this invention. It is a block diagram which shows schematic structure of the digital camera concerning the 2nd Embodiment of this invention. It is a flowchart for demonstrating the imaging operation of the digital camera in the 2nd Embodiment of this invention.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

<First Embodiment>
In this embodiment, a case where a digital camera is used as an imaging device will be described. FIG. 1 is a block diagram showing a functional configuration of the digital camera according to the present embodiment.

Configuration of Imaging Device In the first embodiment, a case where a digital camera is used as the imaging device will be described. FIG. 1 is a block diagram illustrating a functional configuration of the digital camera 100 according to the first embodiment.

  An operation unit 101 includes switches and buttons that are operated by an operator of the digital camera 100 to input various instructions. The operation unit 101 also includes a shutter button. When the shutter button is half-pressed, SW1 is turned on, and the control unit 102 is notified from the operation unit 101. When the shutter button is fully pressed, SW2 is turned on, and the control unit 102 is notified from the operation unit 101. As an example of processing executed by half-pressing (SW1 ON) and full-pressing (SW2 ON), there is processing for capturing a captured image by locking the focus and exposure by half-pressing and then continuously pressing fully.

  Reference numeral 103 denotes an image pickup device represented by a CCD or CMOS sensor, and reference numeral 108a denotes a lens. In FIG. 1, it is represented by a single lens for the sake of convenience, but actually it is composed of a plurality of lenses including a focus lens. An exposure mechanism 109a includes a mechanical shutter. The image sensor 103 receives incident light through the lens 108a and the exposure mechanism 109a, and accumulates electric charges according to the amount of light. The accumulated charge is read out to the shift register and sequentially read out as a voltage signal by the transfer pulse.

  The A / D conversion unit 104 performs sampling, gain adjustment, A / D conversion, and the like on the analog image signal output from the image sensor 103, and outputs digital image data.

  The image processing unit 105 performs various kinds of image processing on the digital image data output from the A / D conversion unit 104, and outputs processed digital image data. For example, digital image data received from the A / D conversion unit 104 is converted into YUV image data and output.

  Reference numeral 102 denotes a control unit that controls the operation of each unit of the digital camera 100 shown in FIG. 1 and controls each unit in accordance with an instruction from the operation unit 101.

  The luminance detection unit 106 uses the digital image data output from the A / D conversion unit 104 to obtain luminance information for each predetermined block.

  The subject detection unit 115 detects a subject such as a face from the digital image data. The information related to the detected subject (subject information) includes the position on the screen, the range, and the reliability (probability as the shape of the face). The subject detection unit 115 holds subject information in time series and compares the subject information before and after to determine whether the subject is moving in the screen, and calculates the position, range, and amount of motion of the subject. Such information is also included in the subject information.

  The shutter setting range changing unit 116 sets a settable range of the shutter speed (exposure time) during main exposure based on information obtained from the luminance detection unit 106 and the subject detection unit 115. For example, the luminance of the entire angle of view is acquired from the screen division luminance integrated value obtained by the luminance detector 106, and the photometric value is acquired. When a face is detected by the subject detection unit, the time-series coordinate fluctuation amount of the face is held. The shutter speed can be set from 1/60 to 1/2000 when the fluctuation amount is large, within a range where proper exposure is possible based on the photometric value, and the shutter speed is 1 to 1/2000 when the fluctuation amount is small. It can be set with.

  The shutter range set here is transmitted to the AE processing unit 109.

  Reference numeral 108 denotes an AF processing unit that performs focus adjustment by controlling the focus lens. Reference numeral 109 denotes an AE processing unit which controls the exposure mechanism 109a. When it is determined that the flash is necessary, the EF processing unit 110 is instructed to flash on. When the EF processing unit 110 receives a flash-on instruction, the EF processing unit 110 calculates a light emission amount based on the luminance information obtained by the luminance detection unit 106, and transmits an appropriate light emission amount to the flash unit 111 (light emitting device) to emit light.

  The display unit 107 is configured with a small liquid crystal screen or the like, and displays an image according to the image data processed by the image processing unit 105.

  The format conversion unit 112 converts the format of the digital image data (image data) output from the image processing unit 105 into a format such as JPEG and outputs it to the image recording unit 113. The image recording unit 113 performs processing for recording the format-converted image data received from the format conversion unit 112 in a memory (not shown) in the digital camera 100, an external memory inserted in the digital camera 100, or the like.

  The external connection unit 114 functions as an interface for connecting the digital camera 100 to an external device such as a PC (personal computer) or a printer.

Process Flow Next, the operation of the digital camera 100 having the above configuration in the first embodiment will be described.

  FIG. 2 is a flowchart showing the imaging operation of the digital camera 100 according to the first embodiment, which is executed when the power switch included in the operation unit 101 is turned on and the imaging mode is selected.

  In a state where the power switch is ON, when power is supplied to each part of the digital camera 100, the shutter included in the exposure mechanism 109a opens, and light enters the image sensor 103 through the lens 108a and the exposure mechanism 109a. (Step S201). In this state, the electric charge accumulated for a predetermined time by the electronic shutter control is read (step S202), and is output to the A / D converter 104 as an analog image signal. The A / D conversion unit 104 performs sampling, gain adjustment, A / D conversion, and the like on the analog image signal output from the image sensor 103 and outputs the digital image data to the image processing unit 105. The image processing unit 105 performs various types of image processing on the digital image data, and outputs processed digital image data.

  The processed digital image data is converted into a format suitable for display by the format conversion unit 112 and displayed on the display unit 107. As described above, by sequentially displaying the image data sequentially obtained at a predetermined frame rate on the display unit 107, an electronic viewfinder (EVF) function can be realized.

  In step S203, the luminance detection unit 106 divides the digital image data obtained in step S202 into blocks and calculates an average value for each region, thereby calculating an average luminance value (luminance information) for each block.

  In step S204, the subject detection unit 115 detects a subject such as a face from the digital image data obtained in step S202, and acquires subject position and area information. The information acquired here includes, for example, face center coordinates, face size, gender, face reliability information, and the like. If it is not the face detection timing, the previous subject information is held as it is. Here, the subject information also holds past information in time series, and detects the amount of movement of the subject by comparing with the latest information.

  Note that the subject detection described above is not limited to face detection, but a specification that identifies a subject and detects the amount of change in that region, such as moving object detection by pattern matching, in-focus position by AF, and user designation by a touch panel. Those that do not deviate are also included.

  Next, the state of the shutter button included in the operation unit 101 is checked. If the shutter button is not pressed and SW1 is OFF (NO in step S205), the process returns to step S201 and the above processing is repeated. On the other hand, if SW1 is ON, the process proceeds to step S206, and preparation for actual photographing is started.

  In step S206, focus adjustment processing (AF control) is performed. In the focus adjustment process, an edge in the screen is detected based on the digital signal of the subject area detected in the immediately preceding step S204, and is calculated from the focal length information of the focus lens operated in the AF processing unit 108. Obtained distance information. Then, based on the obtained distance, the focus lens of the lens 108a is controlled to adjust the focus.

  Next, exposure control processing (AE control) is performed in step S207. The AE processing unit 109 calculates a photometric value from the average luminance value (luminance information) for each block obtained by the luminance detection unit 106 in the immediately preceding step S203, and sets an exposure condition for bringing the screen luminance to an appropriate level. calculate. If it is determined that the screen brightness is dark and the brightness is insufficient, it is determined that the flash is emitted (step S208).

  When the process for determining whether flash light emission is necessary is completed, the state of SW2 is determined in step S209. If SW2 is OFF, the process returns to step S205, and if SW1 is ON, the above-described process is repeated. If it is determined that SW1 is also OFF, the process returns to step S201. On the other hand, if SW2 is ON, the process proceeds to step S210.

  In step S210, it is confirmed whether or not the flash is determined to be emitted in step S208. If no light is emitted, the process proceeds to step S216, and the exposure condition obtained in the immediately preceding step S207 is set as the exposure condition for the main photographing. .

  If it is determined in step S210 that the flash is to be emitted, it is determined from the subject information whether the subject has moved (step S211). Here, the coordinates of the detected face are acquired for a certain period, and when the average value of the obtained fluctuation amount of the coordinates exceeds a certain threshold value, it is regarded as moving.

  When the flash is emitted, since it is necessary to synchronize the light emission time of the xenon tube and the exposure time, an upper limit is usually set for the shutter speed (the upper limit is 1/500 seconds in the first embodiment). Further, since camera shake is a concern when the shutter speed is too slow, a normal lower limit (the maximum limit of exposure time) is also set (the lower limit is 1/60 seconds in the first embodiment). If the shutter speed during non-light emission is set within 1/60 to 1/500 seconds, the background will not be blackened even if the flash is emitted under the same conditions. However, if the shutter speed when no light is emitted is longer than 1/60 seconds, the shutter speed is forcibly changed to 1/60 seconds, resulting in blackening of the background.

  Therefore, in the first embodiment, when the subject is moving, it is determined that image blurring occurs, and the lower limit of the shutter speed during light emission is set to 1/60 seconds (step S213). When the subject is stationary, it is determined that image blur does not occur, and the lower limit of the shutter speed during light emission is set to 1 second so that the brightness of the background can be captured more (step S212).

  In this way, in the case of a low-luminance subject whose shutter speed is longer than 1/60 seconds, the scene is analyzed, and the flash is emitted by changing the lower limit of the shutter speed according to the subject's movement. Reduce scenes with black backgrounds.

  After setting the lower limit of the shutter speed at the time of light emission in step S212 or S213, the exposure condition at the time of actual photographing is calculated (step S214). Then, the control unit 102 controls the EF processing unit 110 to cause the flash unit 111 to perform pre-light emission, and performs processing such as calculation of the light emission amount and weighting of the EF frame. Then, the main light emission amount calculated by the pre-light emission is calculated (step S215).

  In actual photographing, photographing is performed in the same procedure as in steps S201 and S202 described above under the exposure condition and main light emission amount set in steps S214 and S215, or the exposure condition set in step S216, and image data is acquired. . Then, the format conversion unit 112 converts the format of the obtained image data into a format such as JPEG and outputs it to the image recording unit 113. The image recording unit 113 records the format-converted image data in a predetermined memory, and ends the process.

  FIG. 3 is a diagram for explaining an example of an effect obtained by controlling the shutter speed described above.

  FIG. 3A shows a night scene where the subject is moving. In this case, if the shutter speed is decreased to prevent the background from being blacked out, the subject is blurred as shown in FIG. Therefore, when the subject is moving, by limiting the lower limit of the shutter speed to 1/60 second, as shown in FIG. Shoot.

  On the other hand, FIG. 3D shows a case where the scene is also a night scene and the subject is stationary. In this case, even if the shutter speed is decreased, the subject does not blur much. Therefore, by increasing the lower limit of the shutter speed to 1 second (FIG. 3 (e)), the background black is compared with the case where the lower limit of the shutter speed is limited to 1/60 second (FIG. 3 (f)). Crushing can be eliminated (mitigated).

  As described above, according to the first embodiment, in the case of a low-luminance subject, it is possible to reduce background blackout by changing the lower limit of the shutter speed according to the movement of the subject.

  In the first embodiment, the average value of the amount of variation of the subject is compared with a threshold value to determine whether or not the subject is moving, and 2 is set as the lower limit of the shutter speed according to the determined presence or absence of the motion. One of the lower limits was determined. However, the present invention is not limited to this, and any of the three or more lower limits is set such that the lower the subject movement amount, the lower the shutter speed lower limit (that is, the longer the maximum exposure time limit). You may make it change.

<Second Embodiment>
Configuration of Imaging Device As an imaging device according to the second embodiment, the configuration of a digital camera 100 ′ is shown in FIG. The configuration illustrated in FIG. 4 is a configuration in which a camera motion detection unit 218 configured to detect the motion of the digital camera 100 ′ is added to the configuration illustrated in FIG. Since the other configuration is the same as the configuration of FIG. 1, the same reference numerals are given, and the description thereof is omitted here. The camera motion detection unit is not particularly limited to the gyro sensor as long as the camera motion amount and direction are known, such as an acceleration sensor or an HV sensor.

Process Flow Next, the operation of the digital camera 100 ′ having the above-described configuration in the second embodiment will be described with reference to the flowchart of FIG.

  The processing in the second embodiment is performed in steps S501 to S507 in consideration of the camera motion obtained by the camera motion detection unit 218 as compared to the first embodiment described with reference to FIG. However, it is different. Therefore, in the following description, the same step number is attached to the same process as in FIG. 2, and the description is omitted as appropriate.

  In the second embodiment, in addition to the luminance information (step S203) and the subject information (step S204), the motion information of the digital camera 100 'is acquired from the camera motion detection unit 218 in step S501. The camera motion detection unit 218 acquires angular velocity information in the camera rotation direction from the gyro sensor, and acquires the fluctuation amount for a certain period. Then, an average value of the obtained fluctuation amounts is calculated, and it is determined that the camera is moving when a certain threshold value is exceeded.

  Then, when both SW1 and SW2 are turned on and it is determined in step S210 that the flash is emitted, it is determined from the subject information obtained in step S204 whether the subject is moving (step S502). Here, the coordinates of the detected face are acquired for a certain period, and it is considered that the subject is moving when the average value of the obtained fluctuation amount of the coordinates exceeds a certain threshold value TH11.

  If the subject is moving (NO in step S502), it is determined that image blurring occurs, and the lower limit of the shutter speed during light emission is set to 1/60 seconds (step S507).

  On the other hand, when the subject is stationary, the camera is determined to be stationary. If the camera shake amount, which is the amount of camera movement, is smaller than an arbitrary threshold value TH21, it is determined that the camera is stationary, and the lower limit of the shutter speed during light emission is set to 1 second (step S504). ). Even when the camera shake amount is greater than or equal to the threshold value TH21 (NO in step S503), if it is less than the arbitrary threshold value TH22 (YES in step S505), it is determined that the camera movement is small and stable. To do. Then, the lower limit of the shutter speed during light emission is set to 1/8 second (step S506).

  As described above, according to the second embodiment, in the case of a low-luminance subject, it is possible to reduce the background blackout by changing the lower limit of the shutter speed according to the subject movement and the camera movement. It becomes.

  In the second embodiment, the amount of camera shake is compared with two threshold values to determine the degree of blurring, and one of the three lower limits is set as the lower limit of the shutter speed according to the determined state of movement. It was changed to. However, the present invention is not limited to this, and the lower the shutter speed lower limit (that is, the longer the maximum exposure time limit) may be changed as the camera movement amount is smaller. The lower limit may not be three.

  In the second embodiment, the case where the lower limit of the shutter speed is set according to the amount of movement of the subject and the amount of movement of the camera has been described. However, the lower limit of the shutter speed is set only according to the amount of movement of the camera. Also good.

  In the first and second embodiments, the lower limit of the shutter speed is set according to the amount of movement of the subject. However, the lower limit of the shutter speed is set according to whether or not the subject is detected by the subject detection unit. It doesn't matter. For example, if the subject is not detected by the subject detection unit, the same control as when the amount of movement of the subject is small may be performed.

  In addition, although the flash unit which is a light emitting device is built in the digital camera, an external flash device which can be attached to and detached from the digital camera may be used as the light emitting device.

106 luminance detection unit 110 EF processing unit 111 flash unit 115 subject detection unit 116 shutter setting range change unit 218 camera motion detection unit

Claims (5)

An imaging device capable of imaging using a light emitting device,
Luminance detection means for obtaining luminance information of image data obtained by imaging by the imaging means;
Motion detection means for detecting a motion amount of a subject included in the image from the image data;
Determining means for determining whether or not the light emitting device needs to emit light based on the luminance information obtained by the luminance detecting means;
Changing means for changing a maximum limit of exposure time based on the amount of movement of the subject when it is determined by the determining means to perform shooting using the light emitting device;
Exposure control means for obtaining an exposure condition including an exposure time based on the luminance information of the image data obtained by imaging by the imaging means and the longest limit of the exposure time changed by the changing means,
The imaging device according to claim 1, wherein the changing means makes the longest limit longer as the amount of movement of the subject is smaller. Further comprising a shake detection means for detecting the amount of movement of the imaging device,
The imaging apparatus according to claim 1, wherein the changing unit makes the longest limit longer as the amount of motion of the imaging apparatus is smaller. An imaging device capable of imaging using a light emitting device,
Luminance detection means for obtaining luminance information of image data obtained by imaging by the imaging means;
Blur detection means for detecting the amount of motion of the imaging device;
Determining means for determining whether or not the light emitting device needs to emit light based on the luminance information obtained by the luminance detecting means;
Changing means for changing the maximum exposure time limit based on the amount of movement of the imaging device when it is determined by the determining means to perform photographing using the light emitting device;
Exposure control means for obtaining an exposure condition including an exposure time based on the luminance information of the image data obtained by imaging by the imaging means and the longest limit of the exposure time changed by the changing means,
The changing device makes the longest limit longer as the amount of movement of the imaging device is smaller. An imaging device control method capable of imaging using a light emitting device,
A luminance detection step for obtaining luminance information of image data obtained by imaging by an imaging means;
A motion detection step of detecting a motion amount of a subject included in the image from the image data;
A determination step of determining whether light emission of the light emitting device is necessary based on the luminance information obtained by the luminance detection step;
A change step of changing a maximum limit of exposure time based on the amount of movement of the subject when it is determined by the determination step that shooting using the light emitting device is performed;
An exposure control step for obtaining an exposure condition including an exposure time based on luminance information of image data obtained by imaging by the imaging means and a maximum limit of the exposure time changed by the changing step;
In the changing step, the longest limit is made longer as the amount of movement of the subject is smaller. An imaging device control method capable of imaging using a light emitting device,
A luminance detection step for obtaining luminance information of image data obtained by imaging by an imaging means;
A shake detection step of detecting the amount of motion of the imaging device;
A determination step of determining whether light emission of the light emitting device is necessary based on the luminance information obtained by the luminance detection step;
A change step of changing the maximum exposure time limit based on the amount of movement of the imaging device when it is determined by the determination step that shooting using the light emitting device is performed;
An exposure control step for obtaining an exposure condition including an exposure time based on luminance information of image data obtained by imaging by the imaging means and a maximum limit of the exposure time changed by the changing step;
In the changing step, the longest limit is made longer as the movement amount of the imaging device is smaller.

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