JP2016012812A - Imaging apparatus, control method, program, and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire an excellent image, even when photographing is performed under a light source causing a flicker.SOLUTION: An imaging apparatus includes a shutter which is changeable between a first state for shielding an imaging element from light and a second state not for shielding the imaging element from the light, setting means which sets the exposure time of the imaging element, calculation means which calculates the light quantity change characteristics of the light from a photometric target on the basis of the photometric result of photometric means, generation means which generates a reference signal according to a timing in which the light quantity change period of the light from the photometric target satisfies a predetermined condition on the basis of the light quantity change characteristics calculated by the calculation means, and decision means which decides a start timing for starting operation for changing the state of the shutter when performing photographing according to the timing in which the predetermined condition is satisfied from the first state to the second state on the basis of the reference signal generated by the generation means and the exposure time set by the setting means.

Description

  The present invention relates to an imaging apparatus, and more particularly to a technique for suppressing the effect of flicker generated under an artificial light source such as a fluorescent lamp.

  In recent years, the sensitivity of imaging devices such as digital cameras and mobile phones has been increasing. For this reason, even in a relatively dark environment such as a room, it has become possible to acquire a bright image with reduced blur by shooting with a high shutter speed (short exposure time).

  In addition, fluorescent lamps that are widely used as indoor light sources cause flicker, which is a phenomenon in which illumination light periodically fluctuates due to the influence of the commercial power supply frequency. When shooting with such a flickering light source (hereinafter referred to as a flicker light source) at a high shutter speed, exposure unevenness or color unevenness occurs in one image, or a plurality of images shot continuously. Variations in exposure and color temperature may occur between images.

  In order to solve such a problem, Patent Document 1 detects a flicker state of illumination light, and adjusts the imaging timing so that the center of the exposure time substantially coincides with the timing at which the amount of illumination light exhibits a maximum value. Has been proposed.

JP 2006-222935 A

  However, Patent Document 1 describes that the exposure start time is adjusted so that the maximum value of the amount of illumination light and the center of the exposure period substantially coincide with each other, but no specific method is described. Therefore, a good image cannot be acquired when it cannot be adjusted to an appropriate exposure start time according to the shooting conditions.

  Therefore, an object of the present invention is to make it possible to obtain a good image even when shooting under a light source in which flicker occurs.

  In order to achieve the above object, an imaging apparatus according to the present invention includes an imaging element, a shutter that can be changed between a first state in which the imaging element is shielded from light and a second state in which the imaging element is not shielded. A setting means for setting an exposure time of the image sensor; a photometry means; a calculation means for calculating a light quantity change characteristic of light from the photometry target based on a photometry result of the photometry means; and a light quantity calculated by the calculation means Based on the change characteristics, a generating unit that generates a reference signal in accordance with a predetermined timing of a light amount change period of light from the photometric object, a reference signal generated by the generating unit, and an exposure set by the setting unit Start of starting an operation to change the state of the shutter from the first state to the second state when shooting is performed at the predetermined timing based on time And having a determining means for determining a timing, a.

  According to the present invention, it is possible to obtain a good image even when shooting under a light source in which flicker occurs.

1 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention. It is a figure explaining the process which ICPU112 transmits the signal according to the calculation result of a light quantity change characteristic to the camera microcomputer 101. FIG. It is a figure which shows the timing which the flicker reference signal corresponding to the peak timing of a flicker light source is transmitted. It is a figure which shows the timing at which the flicker reference signal corresponding to the bottom timing of a flicker light source is transmitted. It is a figure explaining the process in which the camera microcomputer 101 controls a shutter based on the signal transmitted from ICPU112. It is a figure which shows the shutter start timing according to a shutter speed. It is a figure which shows the shutter start timing according to a shutter speed.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of an imaging apparatus according to the present embodiment. The imaging apparatus according to the present embodiment includes a camera body 100 and a lens unit 200 that can be attached to and detached from the camera body 100.

  First, the configuration of the camera body 100 will be described. A microcomputer CPU (hereinafter, camera microcomputer) 101 controls each part of the camera body 100. The memory 102 is a memory such as a RAM or a ROM connected to the camera microcomputer 101.

  The image sensor 103 is an image sensor such as a CCD or CMOS including an infrared cut filter, a low-pass filter, and the like, and photoelectrically converts a light beam incident through the lens unit 200 and outputs an image signal.

  The shutter 104 travels in a light shielding state in which the image sensor 103 is shielded from a light beam incident through the lens unit 200 and a retracted state in which the light beam incident through the lens unit 200 is guided to the image sensor 103. That is, the shutter 104 can be changed between a first state in which the image sensor 103 is shielded from light and a second state in which the image sensor 103 is not shielded.

  The half mirror 105 is movable between a position for guiding the light beam incident through the lens unit 200 to the image sensor 103 (mirror up state) and a position for guiding it to the photometric sensor 108 (mirror down state). In other words, the half mirror 105 changes the optical path of the light beam that has entered through the lens unit 200 between the state leading to the image sensor 103 and the state leading to the photometric sensor 108. Further, when it is at a position to be guided to the photometric sensor 108, the light beam incident through the lens unit 200 is imaged on the focus plate 106.

  The display element 107 is a display element using PN liquid crystal or the like, and displays a frame (AF frame) indicating a focus detection area used for automatic focus adjustment control (AF control). The photometric sensor 108 uses not only photometry but also subject face detection and subject tracking based on the output image signal by using a charge storage type imaging device that accumulates charges according to the amount of incident light such as a CCD or CMOS. Flicker detection can be performed. The pentaprism 109 guides the light beam incident through the lens unit 200 reflected by the half mirror 105 to the photometric sensor 108 and an optical finder (not shown). The focus detection circuit 110 performs focus detection for AF control, and a part of the light beam incident through the lens unit 200 and passing through the half mirror 105 is guided by the AF mirror 111.

  The CPU 112 is a CPU for driving control of the photometric sensor 108 and image processing / calculation (hereinafter referred to as ICPU). Based on an output signal (image signal) from the photometric sensor 108, photometry, subject face detection, and subject tracking are performed. Performs various calculations related to The ICPU 112 also determines the timing at which the light amount change period and the amount of light from the photometric target satisfy a predetermined condition based on the output signal (image signal) from the photometric sensor 108 (for example, the timing at which the light amount becomes maximum or minimum The light quantity change characteristic such as The memory 113 is a memory such as a RAM or a ROM connected to the ICPU 112. In the present embodiment, a configuration in which the ICPU 112 is provided separately from the camera microcomputer 101 will be described. However, a configuration in which processing executed by the ICPU 112 is executed by the camera microcomputer 101 may be used.

  The operation unit 114 includes a release button for the user to instruct the camera body 100 to start a shooting preparation operation or a shooting operation, and a setting button for the user to make various settings for the camera body 100. The operation unit 114 includes a power switch for the user to turn on / off the power of the camera body 100, a mode dial for the user to select an operation mode of the camera body 100 from a plurality of modes, a touch panel, and the like. .

  Next, the configuration of the lens unit 200 will be described. The lens CPU 201 (hereinafter referred to as LPU) controls each part of the lens unit 200, for example, a focus lens, a zoom lens, a diaphragm driving unit, and the like, and transmits information about the lens to the camera microcomputer 101.

  Next, FIG. 2 shows a process in which the ICPU 112 calculates a light amount change period and a light amount satisfying a predetermined condition as a light amount change characteristic of light from a photometric object, and transmits a signal according to the calculation result to the camera microcomputer 101. It explains using. The flowchart of FIG. 2 is started in response to the power supply of the camera body 100 being turned on.

  First, when the power of the camera body 100 is turned on and the ICPU 112 is activated, the ICPU 112 determines whether or not there is a photometric request from the camera microcomputer 101 in step S100. If it is determined in step S100 that there is a photometric request, the process proceeds to step S101, and the ICPU 112 performs normal photometry. In this normal photometry, the ICPU 112 causes the photometry sensor 108 to perform accumulation for a predetermined time, and performs photometry calculation based on the obtained image signal. Then, the photometric value is transmitted to the camera microcomputer 101 as a photometric result.

  In step S102, the ICPU 112 causes flicker detection accumulation and readout operations to be performed. In this flicker detection accumulation and readout operation, the ICPU 112 accumulates the number of times and the number of accumulations of the photometric sensor 108 so that an image signal that can calculate the light amount change period and the amount of light satisfying a predetermined condition is obtained. To control. For example, the accumulation time for one time is set to a time shorter than the light quantity change period of the flicker light source, and the photometric sensor 108 performs accumulation for a plurality of times continuously for a period longer than one period of the light quantity change period. In order to accurately calculate the light amount change period of the flicker light source, it is desirable that the period of continuous accumulation of a plurality of floors (flicker detection accumulation period) is two or more periods of the light amount change period.

  Next, the ICPU 112 calculates the light amount change cycle of light from the photometric object and the timing at which the light amount satisfies a predetermined condition based on a plurality of image signals read out by performing flicker detection accumulation (hereinafter referred to as flicker detection calculation). ). In this flicker detection calculation, it is determined by calculation whether the light amount change period of the light from the photometric object corresponds to no flicker, 10 ms (100 Hz), or 8, 33 ms (12 Hz).

  The light quantity change cycle can be obtained by using the image signal obtained in step S102. For example, the luminance components of a plurality of image signals are compared, and the cycle is obtained from the difference in the accumulation timings of the pair that minimizes the difference. What should I do? Further, if the difference does not exceed a predetermined value even when the luminance signal is compared between any of the image signals, the flicker may be eliminated. The ICPU 112 transmits information relating to the light quantity change period indicating the obtained flicker presence / absence, the light quantity change period of the flicker light source, and the like to the camera microcomputer 101.

  Further, in step S103, the ICPU 112 calculates the timing when the light amount satisfies a predetermined condition when there is flicker. In the present embodiment, the following description is given for the case where the light intensity is maximized as the timing at which the light intensity satisfies a predetermined condition (peak timing). However, even when the light intensity is the minimum (bottom timing), Good. Note that the peak timing calculation method is not particularly limited. For example, by using a plurality of image signals including the image signal having the maximum luminance component and the image signals before and after the image signal obtained in step S102, the peak timing is estimated. Also good.

  Next, in step S104, the ICPU 112 generates a flicker reference signal based on the light quantity change characteristic calculated in step S103, and transmits it to the camera microcomputer 101. This flicker reference signal is transmitted to the camera microcomputer 101 in synchronization with the peak timing of the light quantity change period of the flicker light source. FIG. 3 is a diagram illustrating the timing at which the flicker reference signal is transmitted. In FIG. 3, the flicker detection accumulation period is made equal to the length of two periods of the light quantity change period. FIG. 3 also shows the execution timing of steps S102, 103, and 104.

  As shown in FIG. 3, the ICPU 112 causes flicker detection accumulation to be performed in accordance with the first light quantity change cycle and the second light quantity change cycle, and then performs flicker detection calculation. Since the flicker detection calculation shows the peak timing of the light amount of the flicker light source, the ICPU 112 transmits a flicker reference signal to the camera microcomputer 101 in synchronization with the peak timing of the light amount of the flicker light source that comes after the flicker detection calculation.

  FIG. 3 shows an example in which the flicker reference signal is transmitted in synchronization with the peak timing of the light amount of the flicker light source, but when the flicker reference signal is transmitted in synchronization with the bottom timing of the light amount of the flicker light source, FIG. The flicker reference signal is transmitted as shown in FIG.

  Next, a process in which the camera microcomputer 101 controls the shutter based on a signal transmitted from the ICPU 112 will be described with reference to FIG. The flowchart of FIG. 5 is started in response to the power supply of the camera body 100 being turned on. First, when the power of the camera body 100 is turned on and the camera microcomputer 101 is activated, the camera microcomputer 101 determines in step S200 whether or not the user has operated the release button to instruct the start of the shooting preparation operation. If it is determined that an instruction to start the shooting preparation operation has been issued, the camera microcomputer 101 transmits a photometry request to the ICPU 112 in step S201.

  After transmitting the photometry request of the ICPU 112 in step S201, the camera microcomputer 101 determines whether or not a photometry value has been received from the ICPU 112 in step S202.

  When the photometric value is received from the ICPU 112, the camera microcomputer 101 calculates an exposure control value (exposure calculation) such as an aperture value, shutter speed (exposure time), and photographing sensitivity based on the received photometric value in step S203. . The exposure calculation method is determined by a known method using a program diagram stored in advance in the memory 102.

  Next, in step S <b> 204, the camera microcomputer 101 determines whether information related to the light amount change period has been received from the ICPU 112.

  When the information regarding the light quantity change period is received, the camera microcomputer 101 determines the presence or absence of flicker based on the received information in step S205. If it is determined that there is flicker (if the received information regarding the light quantity change period includes the light quantity change period of the flicker light source), the process proceeds to step S206. If it is determined that there is no flicker, the process proceeds to step S208.

  If it is determined that there is flicker, the camera microcomputer 101 determines in step S206 whether a flicker reference signal has been received. When the flicker reference signal is received, the camera microcomputer 101 stores the time when the flicker reference signal is received in the memory 102 in step S207. Next, in step S <b> 208, the camera microcomputer 101 determines whether or not the user has issued a shooting operation start instruction by operating the release button. If it is determined that a shooting operation start instruction has been issued, the process proceeds to step S209. If it is not determined that a shooting operation start instruction has been issued, the process returns to step S200.

  In step S209, the camera microcomputer 101 calculates a start timing (hereinafter referred to as shutter start timing) for starting an operation for changing the state of the shutter 104 from the first state to the second state. Here, a method for calculating the shutter start timing will be described with reference to FIGS. In this embodiment, as shown in FIGS. 6 and 7, it is assumed that a delay time represented by the shutter travel characteristic T_ShutterResponse occurs after the shutter start signal is transmitted until the shutter 104 actually starts moving. This delay time is caused by the mechanical mechanism of the shutter 104, and the shutter travel characteristic T_ShutterResponse is measured before factory shipment and stored in the memory 102 in advance. Instead of changing the state of the shutter 104, the image sensor 103 is controlled to change the exposure start timing for each region. When a so-called electronic shutter is used, this T_ShutterResponse may be ignored.

  FIG. 6 is a diagram showing a case in which the shutter start timing is controlled so that the center of the exposure period comes at the timing when one period of the light amount change period has elapsed after receiving the flicker reference signal.

  When the camera microcomputer 101 receives the flicker reference signal synchronized with the peak timing (A) of the light quantity change, as shown by B and C in FIGS. 6 and 7, an integer of the separately received light quantity change period (flicker period λ). It is estimated that the peak timing comes after the double time has elapsed. When the shutter start timing is controlled so that the timing indicated by B is at the center of the exposure period, a shutter start signal is output as shown in FIG. Similarly, when the shutter start timing is controlled so that the timing indicated by C is at the center of the exposure period, a shutter start signal is output as shown in FIG.

When the shutter start timing is controlled so that the timing indicated by B is at the center of the exposure period, the shutter start timing Tstart (1) for transmitting the shutter start signal is calculated by the following equation (1).
Tstart (1) = Tbase + (λ × 1) − (Tv / 2) − (T_Run / 2) −T_ShutterResponse (1)

  Here, Tbase is the time when the flicker reference signal is received, λ is the light amount change period, Tv is the shutter speed calculated in step S203, and T_Run is the shutter 104 moving from one end of the imaging region of the image sensor 103 to the other end. This is the time it takes to do.

  When the shutter start timing is controlled so that the timing indicated by C is at the center of the exposure period, (λ × 1) in equation (1) may be changed to (λ × 2). Similarly, when the shutter start timing is controlled so that the nth (n is a natural number) peak timing after receiving the flicker reference signal is at the center of the exposure period, (λ × 1) in equation (1) May be changed to (λ × n). Since the release time lag can be suppressed as n becomes smaller, the camera microcomputer 10 stores Tstart (n) calculated from the smallest n in the memory 102 after the time when the calculation of the shutter start timing is started.

  Further, as can be seen from the equation (1), the shutter start timing differs depending on the shutter speed, and FIGS. 6 and 7 show when the shutter speed is 1/1000 second and 1/200.

  Next, in step S210, the camera microcomputer 101 stands by until the time indicated by the shutter start timing stored in the memory 102 in step S209 is reached. As can be seen from the above-described equation (1), the calculated shutter start timing is an interval of the light quantity change period λ, and therefore the standby time in step S210 is equal to the light quantity change period λ even at the longest.

  When the time indicated by the shutter start timing stored in the memory 102 is reached, the camera microcomputer 101 starts the operation of outputting the shutter start signal and changing the state of the shutter 104 from the first state to the second state. Instruct.

  The change of the state of the shutter 104 is started, and in step S212, the camera microcomputer 101 returns to step S200 when exposure corresponding to the shutter speed calculated in step S203 has elapsed and exposure is completed.

  As described above, according to the present invention, it is possible to acquire a good image while suppressing the release time lag regardless of the shutter speed, even if shooting is performed under a light source where flicker occurs.

  In the present embodiment, the configuration including the camera microcomputer 101 and the ICPU 112 has been described. However, even if the configuration does not include the ICPU 112, the camera microcomputer 101 may execute the process executed by the ICPU 112.

  In this embodiment, the shutter start timing is controlled so that the peak timing of the light quantity change cycle is at the center of the exposure period. However, depending on the running characteristics of the shutter 104, the peak timing of the light quantity change period is set at the center of the exposure period. A better image can be obtained if it is not. Therefore, the peak timing of the light quantity change period may be shifted from the center of the exposure period based on the running characteristics of the shutter 104.

  In this embodiment, the shutter start timing is controlled so that the peak timing of the light amount change period is at the center of the exposure period. However, if the light amount change rate is less than a predetermined value, a relatively good image is obtained. It is done. Therefore, if the exposure period is included in a period in which the change rate of the light amount is less than a predetermined value, the shutter start timing may be controlled so that a predetermined timing other than the peak timing of the light amount change period is at the center of the exposure period. Good.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of this embodiment is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads out and executes the program. It is processing to do.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

DESCRIPTION OF SYMBOLS 100 Camera body 101 Camera microcomputer 103 Image pick-up element 104 Shutter 108 Photometric sensor 112 ICPU

Claims (9)

An image sensor;
A shutter that can be changed between a first state in which the image sensor is shielded from light and a second state in which the image sensor is not shielded;
Setting means for setting an exposure time of the image sensor;
Photometric means;
A calculating means for calculating a light quantity change characteristic of light from a photometric object based on a photometric result of the photometric means;
Generating means for generating a reference signal in accordance with a timing at which a light quantity change period of light from the photometric target satisfies a predetermined condition, based on the light quantity change characteristic calculated by the calculating means;
Based on the reference signal generated by the generation unit and the exposure time set by the setting unit, the state of the shutter when shooting is performed in accordance with the timing satisfying the predetermined condition is set to the first state. And an deciding means for deciding a start timing for starting an operation for changing to the second state.   The imaging apparatus according to claim 1, wherein the timing that satisfies the predetermined condition is a peak timing of a light amount change cycle of light from the photometric target.   The imaging apparatus according to claim 1, wherein the timing that satisfies the predetermined condition is a bottom timing of a light amount change cycle of light from the photometric target.   Further comprising output means for outputting a signal for starting an operation of changing the state of the shutter from the first state to the second state based on the start timing determined by the determining means. The imaging apparatus according to any one of claims 1 to 3, wherein the imaging apparatus is characterized.   5. The imaging apparatus according to claim 1, further comprising a storage unit that stores a time when the reference signal is generated by the generation unit.   6. The start timing is determined based on a time stored in the storage unit, a light amount change period of light from the photometric object, and an exposure time set by the setting unit. Imaging device. A control method for an imaging apparatus, comprising: an imaging element; and a shutter that can be changed between a first state in which the imaging element is shielded from light and a second state in which the imaging element is not shielded.
A setting step for setting an exposure time of the image sensor;
Metering step,
Based on the photometric result of the photometric step, a calculation step for calculating a light quantity change characteristic of light from the photometric object;
A generation step for generating a reference signal in accordance with a timing at which a light amount change period of light from the photometric target satisfies a predetermined condition based on the light amount change characteristic calculated in the calculation step;
Based on the reference signal generated in the generation step and the exposure time set in the setting step, the state of the shutter when shooting is performed in accordance with the timing satisfying the predetermined condition is set to the first state And a determination step for determining a start timing for starting an operation for changing to the second state.   A program for causing a computer to execute the control method according to claim 7.   A computer-readable storage medium storing a program for causing a computer to execute the control method according to claim 7.

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