JP2014127770A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus of a simple configuration using a CMOS sensor, which renders a main subject appropriately bright when light for preliminary light emission is not contributed for the entire frame.SOLUTION: An imaging apparatus comprises an imager of a rolling shutter system, preliminary light emitting means, preliminary light emission photometric means, and photometric area determination means. The preliminary light emission photometric means measures an amount of exposure during preliminary exposure. The photometric area determination means determines a photometric area where a photometric operation is performed by using the preliminary light emission photometric means on the basis of a pick-up image being monitored. If a shutter speed for the exposure frame of the imager is higher than a strobe synchronization speed and preliminary light emission is not contributed for the photometric area determined by the photometric area determination means when the preliminary light emitting means is carried out, the shutter speed for the exposure frame during the preliminary light emission is decreased, a diaphragm corresponding to the number of steps for decreasing the shutter speed is narrowed, and then preliminary light emission is carried out. Thus, light is preliminarily emitted to the photometric area.

Description

  The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus that preliminarily determines a flash emission amount at the time of capturing a still image by preliminary light emission.

  2. Description of the Related Art Conventionally, in an imaging device such as a camera, when shooting is performed with only external light, when the main subject is underexposed, strobe shooting may be performed in which auxiliary light is emitted to capture the amount of exposure. At this time, if the main subject is underexposed, it is simply a case of shooting in a dark environment, or even in a bright environment, for example, when the background is bright but only the main subject is exposed in a backlit state. There may be a shortage.

  When the background is bright but only the main subject is underexposed, as in the latter case, the exposure time is usually shortened in order to obtain the appropriate brightness for the background, and the main subject is also set to the appropriate brightness. Therefore, take a picture with a flash. At this time, a so-called compact type camera generally uses a preliminary light emission method in which preliminary light emission is performed in advance before photographing to detect the excess or shortage of the light emission amount and the main light emission amount at the time of photographing is determined.

  On the other hand, the imaging device used in the imaging device uses a sensor that operates in a readout mode in which the exposure timing is shifted within the frame in order to perform exposure and readout sequentially for each line, such as a CMOS sensor. There is something to do. In such a sensor, if the exposure time is shorter than the time when there is preliminary light emission, the strobe light cannot be contributed to all the lines in the frame no matter what timing the light is emitted.

  In this case, since it becomes impossible to obtain a correct luminance distribution, it is difficult to obtain an appropriate light emission amount. For this reason, Patent Document 1 proposes a method in which strobe light is uniformly contributed to the entire frame surface by performing strobe light emission a plurality of times during preliminary light emission.

JP 2009-55287 A

  However, it is difficult to control the amount of light emission and the timing of light emission by applying the strobe light multiple times by software control and applying the strobe light uniformly to the entire frame by the method of Patent Document 1, and it is difficult In addition, it is expensive to realize FP light emission.

  Therefore, an object of the present invention is to provide an imaging apparatus including a CMOS sensor that can make a main subject have appropriate brightness in a state where preliminary light does not contribute to the entire frame with a simple configuration. .

  An image pickup apparatus according to the present invention is an image pickup apparatus having a function of controlling a strobe for illuminating a subject, and determines a light emission amount of a strobe light emission immediately before shooting an image sensor using a rolling shutter method and a strobe light emission. Therefore, preliminary light emission means that emits strobe light during monitoring, preliminary light emission light measurement means that measures the exposure amount of the image sensor during preliminary light emission, and a photometry area that is measured by the preliminary light emission measurement means based on the captured image being monitored When the preliminary light emission means is executed, the shutter speed of the exposure frame of the image sensor is faster than the strobe tuning speed, and preliminary light emission is performed in the photometry area determined by the photometry area determination means. If it does not contribute, slow down the shutter speed of the exposure frame during preliminary light emission so that the preliminary light emission contributes to the photometry area, and Characterized in that the preliminary light emission squeezing diaphragm corresponding to the number of stages that slow down the shutter speed.

  Further, it has a main subject detecting means for detecting a main subject based on the captured image being monitored, and the photometric area determining means determines the photometric area based on the position of the main subject detected by the main subject detecting means. Is preferred.

  Further, the main subject detection means may be a face detection means for detecting a human face.

  Further, the main subject detection means may be subject tracking means that tracks the subject specified by the user and continues to detect the position of the main subject.

  According to the present invention, it is possible to provide an imaging device including a CMOS sensor capable of setting a main subject to appropriate brightness in a state where preliminary light emission does not contribute to the entire frame with a simple configuration. .

1A is a front view, FIG. 1B is a top view, and FIG. 1C is a rear view of the digital camera according to the first embodiment of the present invention. It is a block diagram showing the system configuration | structure of the digital camera of FIG. It is a block diagram showing the structure of the signal processing part of FIG. It is a graph showing the relationship between the light emission contribution area | region which concerns on the 1st Embodiment of this invention, exposure time, and light emission time. It is a flowchart which sets the light emission timing which concerns on the 1st Embodiment of this invention. It is a graph showing the relationship between the light emission contribution area | region which concerns on the 1st Embodiment of this invention, exposure time, and light emission time. It is a flowchart which sets the light emission timing which concerns on the 2nd Embodiment of this invention.

Hereinafter, the present invention will be described based on the illustrated embodiments.
<Embodiment 1>
(Appearance structure of digital camera)
As shown in FIGS. 1A, 1B, and 1C, a release button (shutter button) 2, a power button 3, a shooting / playback switching dial 4 are provided on the upper surface side of the digital camera 1 according to the present embodiment. In the front (front) side of the digital camera 1, a lens barrel unit 6 having a photographing lens system 5, a flash light emitting unit 7 that is a flash, and an optical viewfinder 8 are provided.

  On the back side of the digital camera 1, a liquid crystal monitor (LCD) 9, an eyepiece 8a of an optical viewfinder 8, a wide-angle zoom (W) switch 10, a telephoto zoom (T) switch 11, a menu (MENU) button 12, A confirmation button (OK button) 13 and the like are provided. Further, a memory card storage unit 15 for storing a memory card 32 (see FIG. 2) for storing captured image data is provided inside the side surface of the digital camera 1.

(Digital camera system configuration)
As shown in FIG. 2, the digital camera 1 includes a CMOS 23 as a solid-state imaging device on which a subject image incident through a photographing lens system 5 of a lens barrel unit, a diaphragm unit / mechanical shutter unit 22 is formed on a light receiving surface, A signal processing unit 27 that processes electrical signals (digital RGB image signals) output from the CMOS, a motor driver 28 that drives the lens barrel unit, a CPU 29 that controls the entire camera, an SDRAM 42 that temporarily stores data, Communication driver 31, a memory card 32 that can be attached to and detached from the camera, a display controller that converts a video output signal from the signal processing unit into a signal that can be displayed on the LCD, and a display unit 33 that actually displays the LCD. Operation unit 34 that can be operated, strobe emission that can control the start / stop of light emission from the control unit Part 7 has main capacitor 36 for flash emission, and the like.

  The lens barrel unit 6 includes a photographic lens system 5 having a zoom lens, a focus lens, and the like, and an aperture unit / mechanical shutter unit 22. The drive units of the photographic lens system 5 and the aperture unit / mechanical shutter unit 22 are motors. It is driven by a driver 28. The motor driver 28 is driven and controlled by a drive signal from a CPU 29 that is a control unit of the signal processing unit.

  The CMOS 23 converts an optical image formed by the two-dimensionally arranged light receiving elements into electric charges, and outputs them as electric signals to the outside at a read signal timing transmitted from the adjacent drive unit 26. RGB primary color filters (hereinafter referred to as “RGB filters”) are arranged on a plurality of pixels constituting the CMOS, and electrical signals (digital RGB image signals) corresponding to the three primary colors of RGB are output.

  Referring to FIG. 3, the signal processing unit 27 includes a CMOS interface 40 (hereinafter referred to as “CMOS I / F”) that captures RAW-RGB data output from the CMOS, a memory controller 44 that controls the SDRAM 42, and a captured RAW. A YUV conversion unit 46 that converts RGB data into YUV format image data that can be displayed and recorded, a resize processing unit 48 that changes the image size in accordance with the size of the image data to be displayed and recorded, A display output control unit 50 for controlling display output, a data compression unit 52 for recording image data by JPEG formation, etc., and a media interface for writing image data to a memory card or reading image data written to a memory card 54 (hereinafter referred to as “media I / F”) and an operation unit Based on the operation input information from the 4, it includes a CPU29 as a control unit for performing the digital camera 1 as a whole system control or the like based on a control program 58 stored in the ROM 56.

  The SDRAM 42 stores RAW-RGB data captured by the CMOS I / F 40, and stores YUV data (YUV format image data) converted by the YUV conversion unit 46. Further, the SDRAM 42 stores the data. The compressed image data such as JPEG formation is stored. YUV of YUV data is information on luminance data (Y), color difference (difference (U) between luminance data and blue (B) data, and difference (V) between luminance data and red (R)). Is a format that expresses

  The operation unit 34 includes a release button 2, a power button 3, a photographing / playback switching dial 4, a wide angle provided on the external surface of the digital camera 1 (see FIGS. 1A, 1B, and 1C). A zoom switch 10 on the side, a zoom switch 11 on the telephoto side, a menu button 12, a confirmation button 13, and the like, and a predetermined operation instruction signal is input to the CPU 29 by the operation of the photographer.

(Digital camera monitoring and still image shooting)
Next, the monitoring operation and still image shooting operation of the digital camera 1 will be described with reference to FIGS. In the still image shooting mode, the digital camera 1 performs a still image shooting operation while executing a monitoring operation as described below.

  First, when the photographer turns on the power button 3 and sets the photographing / playback switching dial 4 to the photographing mode, the digital camera 1 is activated in the photographing mode. When the CPU 29 detects that the power button 3 is turned on and the photographing / playback switching dial 4 is set to the photographing mode, the CPU 29 outputs a control signal to the motor driver 28 so that the lens barrel unit 6 can be photographed. And the CMOS 23, the signal processing unit 27, the SDRAM 42 (see FIG. 3), the ROM 56, the liquid crystal monitor 9 and the like are activated.

  Then, by directing the photographing lens system 5 of the lens barrel unit 6 toward the subject, a subject image incident through the photographing lens system 5 is formed on the light receiving surface of each pixel of the CMOS 23. Then, an electrical signal (analog RGB image signal) corresponding to the subject image output from the light receiving element of the CMOS 23 is input to the A / D converter (ADC) 25 via the CDS / PGA 24, and the A / D converter 25. Is converted into 12-bit (RAW) RGB data.

  Referring to FIG. 3, the RAW-RGB data is taken into the CMOS I / F 40 of the signal processing unit 27 and stored in the SDRAM 42 via the memory controller. The RAW-RGB data read from the SDRAM 42 is subjected to necessary image processing, such as applying a gain divided for each block, as will be described later, and then displayed in a format that can be displayed by the YUV conversion unit 46. After being converted into certain YUV data (YUV signal), the YUV data is stored in the SDRAM 42 via the memory controller 44.

  The YUV data read from the SDRAM 42 via the memory controller 44 is sent to the display unit 33 via the display output control unit 50, and a captured image (moving image) is displayed. At the time of monitoring in which a captured image is displayed on the display unit 33 described above, one frame is read out in a time of 1/30 second by thinning out the number of pixels by the CMOS I / F 40.

  In this monitoring operation, the photographed image is only displayed on the display unit 33 functioning as an electronic viewfinder, and the release button 2 is not yet pressed (including half-pressed).

  The photographer can confirm the photographed image by displaying the photographed image on the display unit 33. Although not shown, the display output control unit 50 can output a TV video signal and display a captured image (moving image) on an external TV (television) via a video cable.

  On the other hand, as described in detail below, AF (automatic focus) evaluation value, AE (automatic exposure) evaluation value, AWB (auto white balance) are obtained from RAW-RGB data captured by the CMOS I / F 40 of the signal processing unit. An evaluation value is calculated.

  The AF evaluation value is calculated by, for example, the output integrated value of the high frequency component extraction filter or the integrated value of the luminance difference between adjacent pixels. When in the in-focus state, the edge portion of the subject is clear, so the high frequency component is the highest. By using this, at the time of AF operation (focus detection operation), AF evaluation values at each focus lens position in the photographing lens system are acquired, and AF operation is performed with the maximum point as the focus detection position. Is executed.

  The AE evaluation value and the AWB evaluation value are calculated from the integrated values of the RGB values in the RAW-RGB data. For example, the screen corresponding to the light receiving surface of all the pixels of the CMOS 23 is equally divided into 256 areas (16 horizontal divisions and 16 vertical divisions), and the RGB integration of each area is calculated.

  Then, the CPU 29 reads the calculated RGB integrated value. That is, the RAW-RGB data is transmitted from the CMOS I / F 40 to the detection unit 60, and the RGB integrated value data is created in the AE / AWB detection unit 62. The RGB data is transmitted to the SDRAM 42 via the memory controller 44. The CPU 29 reads RGB integrated data from the SDRAM 42.

  In the AE process, the brightness of each area of the screen is calculated, and an appropriate exposure amount is determined from the brightness distribution. Based on the determined exposure amount, exposure conditions (CMOS electronic shutter frequency, aperture value of the aperture unit, etc.) are set. In the AWB process, an AWB control value that matches the color of the light source of the subject is determined from the RGB distribution. By this AWB process, the white balance when the YUV conversion unit performs conversion processing to YUV data is adjusted. Note that the above-described AE process and AWB process are continuously performed during monitoring.

  When the release button 2 is pressed (half-pressed to fully pressed) during the monitoring operation described above and a still image shooting operation is started, an AF operation that is a focus position detection operation and a still image recording process are performed. .

  That is, when the release button 2 is pressed (half-pressed to fully pressed), the focus lens of the photographing lens system 5 is moved by a drive command from the CPU 29 to the motor driver. For example, contrast evaluation called so-called hill-climbing AF is performed. The AF operation of the method is executed.

  When the AF (focusing) target range is the entire region from infinity to close, the focus lens of the photographing lens system 5 moves to each focus position from close to infinity, or from infinity to close, and CMOS I / The CPU 29 reads the AF evaluation value at each focus position calculated in F40. That is, RAW-RGB data is transmitted from the CMOS I / F 40 to the detection unit 60, and AF evaluation value data is created by the AF detection unit 64. The created AF evaluation value data is transmitted to the SDRAM 42 via the memory controller 44. The CPU 29 reads AF evaluation value data from the SDRAM 42 via the memory controller 44. Then, the focus lens is moved to the in-focus position with the point where the AF evaluation value at each focus position is maximized as the in-focus position, and in-focus.

  Then, the above-described AE process is performed, and when the exposure is completed, the mechanical shutter unit 22 is closed by a drive command from the CPU 29 to the motor driver 28, and an analog RGB image signal for a still image is output from the light receiving element of the CMOS 23. . Then, as in the above monitoring, the A / D converter 25 converts the data into RAW-RGB data.

  The RAW-RGB data is taken into the CMOS I / F 40 of the signal processing unit 27, converted into YUV data by the YUV conversion unit 46, and stored in the SDRAM 42 via the memory controller 44. The YUV data is read from the SDRAM 42, converted into a size corresponding to the number of recorded pixels by the resizing processing unit 48, and compressed to image data in the JPEG format or the like by the data compression unit 52. The compressed image data in the JPEG format or the like is written back to the SDRAM 42, read out from the SDRAM 42 through the memory controller 44, and stored in the memory card 32 through the media I / F 54.

(Calculation of main light emission by preliminary light emission)
A description will be given of the main flash amount calculation means of the strobe by the preliminary light emission method.
When a photographing operation is input from the user, the CPU 29 changes the drive mode of the CMOS 23 to a drive mode for preliminary light emission. Then, the CPU 29 sends a light emission signal to the strobe light emitting unit 7 (see FIG. 1) in accordance with the exposure timing of the CMOS 23 to cause the strobe to emit light. When the frame when the strobe is emitted is fetched from the CMOS 23, the signal processing unit 27 calculates the luminance information of the frame for each grid block.

  Here, the luminance average of the photometric area determined in advance or determined based on the luminance distribution of the luminance information at the time of preliminary light emission is calculated. The CPU 29 calculates a difference of the calculated average brightness with respect to the target brightness, and based on the difference with respect to the target brightness, the preliminary light emission amount, the exposure control value during the preliminary light emission, and the exposure control value during the main light emission. The main light emission amount is calculated.

  Here, when preliminary light emission is performed with a rolling shutter in which the exposure timing is shifted for each line as in CMOS, as shown in FIG. 4A, when the exposure time is sufficiently long, all lines are under exposure. The strobe light can contribute to the entire surface of the frame. However, as shown in FIG. 4B, when the exposure time is short, there is a period in which all lines are under exposure. Therefore, even if the flash is emitted, the flash light only contributes to a part of the frame.

  Note that the main flash during shooting is not a rolling shutter, but a batch reset electronic shutter that also uses a mechanical shutter. Therefore, if the flash is emitted during exposure, the flash will always contribute to the entire frame. become.

(Description of flow)
A flow for determining the photometric area based on the face detection result and setting the light emission timing in FIG. 5 will be described.

  When the user performs a shooting operation on the camera, the camera detects the shooting operation (S501-Yes) and executes an AE process to determine the exposure time during shooting and preliminary light emission (S502). Here, it is determined whether or not the exposure time of preliminary light emission is shorter than the strobe tuning speed at the time of preliminary light emission (S503). When the exposure time of the preliminary light emission is shorter than the strobe synchronization speed (S503-Yes), the CPU (main subject detection means) (face detection means) 29 executes a process for detecting a human face in the monitoring image (S504). . When the face can be detected (S505-Yes), the CPU (photometric area determination means) sets the person's face as the photometric area, and the exposure time during the preliminary light emission contributes to the vicinity of the center of the person's face. Is corrected (S506).

  At this time, for example, in the shooting state as shown in FIG. 6, if the initial preliminary light exposure time is 1/500 second (FIG. 6A), the preliminary light is sufficiently applied to the human face. Although not hitting, the exposure time at the time of preliminary light emission is corrected to 1/250 seconds so that the human face is sufficiently exposed to light (FIG. 6B). If the exposure time is increased so that preliminary light is sufficiently applied to the face of a person, the exposure time is easily affected by the increased amount of light, resulting in poor photometric accuracy. Therefore, the aperture is narrowed down by the length of the exposure time during preliminary light emission (S507).

  The CPU (preliminary light emitting means) performs preliminary light emission in accordance with the exposure timing of the sensor with the determined exposure time and aperture value (S508). The CPU (preliminary light metering means) obtains the luminance value in the preliminary light emission through the signal processing unit, and determines the main light emission amount based on the luminance value in the preliminary light emission (S509). The main light emission is performed with the determined main light emission amount, and photographing is performed (S510).

  By doing so, even if the main subject is at the edge of the screen with preliminary light emission with the rolling shutter, the optimal flash emission amount for the main subject is determined by preliminary light emission, and shooting is performed with appropriate brightness. It becomes possible.

  In other words, by determining the flash photometry area by detecting the main subject and determining the pre-flash emission timing according to the position of the photometry area, the pre-flash light is not irradiated on the entire frame. By slowing down the shutter speed, preliminary light emission is emitted to the photometry area, and by reducing the aperture by the amount that slows down the shutter speed, the effect of external light is suppressed, so flash photography can be performed in a bright environment with a CMOS sensor camera. Even in such a case, the main subject can be set to an appropriate brightness.

<Embodiment 2>
Next, with reference to FIG. 7, a flow for determining a photometric area based on subject tracking information and setting a light emission timing will be described. The difference from the first embodiment is that a function for tracking a subject is added.

  When there is a tracking subject instruction operation by the user (S701), the CPU (subject tracking means) 29 performs subject tracking processing on the monitoring image (S702). In the subject tracking process, while subject tracking continues to be successful, tracking continues unless there is a release operation by the user. If tracking fails, the tracking process is stopped, and the tracking process is not performed unless a tracking subject instruction operation by the user is entered again (No in S703). When subject tracking continues (S703-Yes), if there is a shooting instruction from the user (S704-Yes), the CPU executes an AE process to determine the exposure time during shooting and preliminary light emission (S705). .

  Here, it is determined whether or not the exposure time of preliminary light emission is shorter than the strobe tuning speed at the time of preliminary light emission (S706). If the exposure time of the preliminary light emission is shorter than the strobe synchronization speed (S706-Yes), the CPU 29 sets the tracking subject as the photometry area, and corrects the exposure time during the preliminary light emission so that the preliminary light emission contributes near the center line of the tracking subject. (S707). Then, the aperture is narrowed by the length of the exposure time so that the preliminary emission light is sufficiently applied to the tracking subject (S708).

  The CPU 29 (see FIG. 3) performs preliminary light emission in accordance with the exposure timing of the CMOS 23 with the determined exposure time and aperture value (S709). The CPU 29 acquires the luminance value in the preliminary light emission through the signal processing unit 27, and determines the main light emission amount based on the luminance value in the preliminary light emission (S710). The main light emission is performed with the determined main light emission amount, and photographing is performed (S711).

  In this way, even when the main subject is at the edge of the screen and the exposure time is short with the rolling shutter, the optimal flash output for the main subject is determined by preliminary flash and the appropriate brightness is achieved. It becomes possible to shoot with.

  In other words, by determining the flash photometry area by detecting the main subject and determining the pre-flash emission timing according to the position of the photometry area, the pre-flash light is not irradiated on the entire frame. By slowing down the shutter speed, preliminary light emission is emitted to the photometry area, and by reducing the aperture by the amount that slows down the shutter speed, the effect of external light is suppressed, so flash photography can be performed in a bright environment with a CMOS sensor camera. Even in such a case, the main subject can be set to an appropriate brightness.

1 Digital camera (imaging device)
7 Strobe flash unit (strobe)
22 Aperture
23 CMOS (imaging device)
29 CPU (preliminary light emission means, preliminary light emission photometry means, photometry area determination means, main subject detection means)

Claims (4)

An imaging apparatus having a function of controlling a strobe that irradiates a subject,
A rolling shutter image sensor;
Preliminary light emission means for emitting a strobe during monitoring in order to determine the light emission amount of the strobe light immediately before taking a still image with strobe light emission,
Preliminary light-emission metering means for measuring the exposure amount of the image sensor at the time of preliminary light emission;
Photometric area determining means for determining a photometric area to be measured by the preliminary light-emission photometric means based on a captured image being monitored;
When executing the preliminary light emission means, the shutter speed of the exposure frame of the image sensor is faster than the strobe tuning speed,
And, if the preliminary light emission does not contribute to the photometric area determined by the photometric area determination means, the shutter speed of the exposure frame at the time of preliminary light emission is slowed so that the preliminary light emission contributes to the photometric area,
An image pickup apparatus that performs preliminary light emission by narrowing an aperture corresponding to the number of steps for reducing the shutter speed.   A main subject detecting unit for detecting a main subject based on a captured image being monitored; and the photometric region determining unit determines a photometric region based on a position of the main subject detected by the main subject detecting unit. The imaging apparatus according to claim 1.   The imaging apparatus according to claim 2, wherein the main subject detection unit is a face detection unit that detects a human face.   The imaging apparatus according to claim 2, wherein the main subject detection unit is a subject tracking unit that continues to detect the position of the main subject by tracking the subject specified by the user.

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