JP2016039596A - Imaging device and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform stable exposure free from fluctuation of power supply frequency, under a flicker light source that is lighted by a power supply of a predetermined frequency.SOLUTION: A digital camera 100 includes an imaging element 103, a photometric sensor 108 for metering the amount of light impinging on the imaging element 103 through a barrel 100B, and an ICPU112 for detecting whether or not the light from a flicker light source is contained in the incident light. When the fact that the light from a flicker light source is contained in the incident light is detected, the ICPU112 generates a flicker synchronization signal by detecting the phase of the light from the flicker light source, e.g., the peak timing t_peak of the amount of flicker light, immediately before exposure of main shooting, and adjusts the time until exposure of main shooting is started from the flicker synchronization signal, so that the peak timing t_peak is included in the exposure time when performing main shooting.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an imaging apparatus such as a digital camera and a control method therefor, and more particularly to a technique for detecting flicker when photographing under an artificial light source such as a fluorescent lamp and performing exposure at a timing with little change in brightness due to flicker. .

  In recent years, with the increase in sensitivity of image pickup elements of digital cameras, it has become possible to take a blur-free photograph at a high shutter speed even in a relatively dark environment such as a room. Here, in a fluorescent lamp that is widely used as an indoor light source, a phenomenon called flicker in which illumination light periodically fluctuates due to the influence of the frequency of a power source (generally, a commercial power source). In high-speed shutter shooting under a light source that generates flicker (hereinafter referred to as “flicker light source”), the image exposure and color temperature vary from frame to frame due to the effect of flicker, and within one frame. Exposure unevenness and color unevenness may occur.

  Here, the change in brightness is small near the peak of the flicker light amount. Therefore, a flicker removal system that detects the flicker period and phase and generates a flicker synchronization signal so as to perform exposure according to the peak timing of the light amount from the flicker light source (hereinafter referred to as “flicker light amount”) is proposed. (See Patent Document 1).

JP 2004-193922 A

  However, it is said that the fluctuation of the frequency of the commercial power supply is about ± 0.2 Hz in a short time, and the fluctuation of the flicker frequency of the flicker light source is about ± 0.4 Hz. For this reason, in the flicker removal system described in Patent Document 1, when the time has elapsed since flicker detection, the relationship between the flicker synchronization signal and the peak timing of the flicker light amount shifts due to the influence of fluctuations in the frequency of the commercial power supply.

  FIG. 9 is a diagram schematically illustrating the relationship between the flicker light amount, the flicker synchronization signal, and the shutter operation, and the luminance distribution in a captured image (one frame image) obtained by the shutter operation. 9A to 9C, the time from the flicker synchronization signal to the shutter operation is constant, and the shutter speed (exposure time) is also constant. 9A, 9B, and 9C show states when about 100 ms (milliseconds), 200 ms, and 300 ms have elapsed since flicker detection, respectively. From FIG. 9, even if flicker detection is performed once and the timing of the flicker synchronization signal is calculated, the peak timing of the flicker light amount and the timing of the shutter operation are shifted with the passage of time from flicker detection. It can be seen that the captured images have different distributions.

  An object of the present invention is to provide a technique capable of performing stable exposure regardless of fluctuations in power supply frequency under a flicker light source that is lit by a power supply having a predetermined frequency.

  An image pickup apparatus according to the present invention includes an image pickup element, a photometric unit that measures the amount of incident light that passes through an optical system and enters the image pickup element, and whether the incident light includes light from a flicker light source. And an image pickup apparatus that detects whether or not the incident light includes light from a flicker light source. A phase of light from the flicker light source is detected immediately before exposure.

  According to the present invention, stable exposure can be performed under a flicker light source regardless of fluctuations in the power supply frequency, and a stable imaging output can be obtained.

1 is a diagram illustrating a schematic configuration of a digital camera according to an embodiment of the present invention. 2 is a flowchart of shooting control in the digital camera of FIG. 1. It is a figure which shows transition of the charge accumulation control of a photometry sensor with respect to the flicker light source turned on with each power supply whose frequency is 50 Hz, and 60 Hz, and an output photometric value. It is a figure explaining an example of the method of calculating the peak timing (phase) of flicker light quantity. It is a figure which shows the relationship (timing) of a flicker synchronizing signal and a shutter start signal. FIG. 3 is a first diagram illustrating a photographing sequence from when the shutter switch SW2 of the digital camera of FIG. 1 is turned on until a photographing operation is performed by the image sensor. FIG. 6 is a second diagram illustrating a photographing sequence from when the shutter switch SW2 of the digital camera of FIG. 1 is turned on until a photographing operation by the image sensor is performed. It is a figure explaining the relationship between the aperture operation in step S210 of FIG. 2 and the gain applied to the photometric value. It is a figure which shows typically the luminance distribution in the picked-up image obtained by the relationship between a flicker light quantity, a flicker synchronizing signal, and shutter operation | movement, and shutter operation | movement.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, a so-called digital camera is taken up as the imaging apparatus according to the present invention. However, the present invention is not limited to this, and various electronic devices having a camera function may be used. For example, the imaging device according to the present invention may be a mobile communication terminal with a camera function such as a mobile phone or a smartphone, a portable computer with a camera function, a portable game machine with a camera function, or the like.

<Schematic configuration of digital camera>
FIG. 1 is a diagram showing a schematic configuration of a digital camera 100 according to an embodiment of the present invention. The digital camera 100 generally includes a camera body 100A and a lens barrel 100B. The lens barrel 100B that is an imaging optical system may be integrated with the camera body 100A, or may be detachable from the camera body 100A.

  The camera body 100A includes a CPU 101, a memory 102, an image sensor 103, a shutter 104, a half mirror 105, a focus plate 106, a display element 107, and a photometric sensor (AE sensor) 108. The camera main body 100A includes a pentaprism 109, an optical finder (not shown), an AF (automatic focus) sensor 110, an AF mirror 111, an ICPU 112, and a memory 113. The lens barrel 100B includes a plurality of lenses 121, a diaphragm (not shown), and an LPU 122.

  The CPU 101 is a microcomputer that controls each unit of the digital camera 100. The memory 102 includes a ROM that stores programs executed by the CPU 101, variables, and the like, a work area where the CPU 101 develops programs, and a RAM that temporarily stores image data and the like. The LPU 122 is a CPU in the lens barrel, transmits distance information to the subject to the CPU 101, and performs drive control of the lens 121 based on a command from the CPU 101. The image sensor 103 is an image sensor such as a CCD sensor or a CMOS sensor including an infrared cut filter and a low-pass filter. The shutter 104 is closed when not photographing to shield the image sensor 103, and is opened during photographing and guides incident light (light beam) that has passed through the lens barrel 100B to the image sensor 103.

  The half mirror 105 provided on the front surface side (subject side) of the image sensor 103 reflects a part of the light incident through the lens 121 when not photographing, and forms an optical image on the focus plate 106. The display element 107 displays an AF distance measurement frame such as a PN liquid crystal, and indicates to the photographer through the optical viewfinder which position of the subject is controlled by the AF operation. The photometric sensor 108 includes an image sensor such as a CCD or a COMS. In the present embodiment, face detection, tracking, photometry, flicker detection, and the like are performed using an output signal from the photometric sensor 108. In the present embodiment, the photometric sensor 108 is used as the flicker detection unit, but the image sensor 103 for performing the main photographing can also be used as the flicker detection unit.

  The pentaprism 109 guides the subject image on the focusing screen 106 to the photometric sensor 108 and the optical viewfinder. The photometric sensor 108 views the subject image formed on the focus plate 106 via the pentaprism 109 from a position in the oblique direction. The AF mirror 111 guides part of the light beam incident from the lens barrel 100 </ b> B and passing through the half mirror 105 to the AF sensor 110. The AF sensor 110 performs distance measurement for focusing on the subject based on the received light flux.

  The ICPU 112 is a CPU that performs various calculation processes such as subject recognition processing such as drive control of the photometric sensor 108, photometry calculation, face detection calculation and tracking calculation, and flicker detection calculation. The memory 113 includes a ROM that stores programs executed by the ICPU 112, variables, and the like, a work area where the ICPU 112 develops programs, and a RAM that temporarily stores calculation results. In this embodiment, the ICPU 112, which is a dedicated CPU, is provided for the photometric sensor 108. However, the CPU 101 may be configured to perform drive control, image processing, and calculation of the photometric sensor 108.

  Although not shown in FIG. 1, the digital camera 100 includes a power switch and a shutter switch. The shutter switch includes a switch SW1 that is turned on by half pressing (first stroke) and a switch SW2 that is turned on by full pressing (second stroke). When the switch SW1 is turned on, exposure control based on the output from the photometric sensor 108 and automatic focus control based on the output from the AF sensor 110 are executed. Further, when the switch SW2 is turned on, the actual photographing is performed. In the actual photographing, an optical image formed on the image sensor 103 is converted into an analog electric signal by the image sensor 103, and the analog electric signal is converted into digital image data by an image processing unit (not shown), and a memory card (not shown) or the like. Is stored in the storage means.

<Shooting control method with digital camera>
FIG. 2 is a flowchart of shooting control by the digital camera 100. Each process shown in FIG. 2 is realized by the CPU 101 developing the program stored in the ROM in the RAM and controlling the operation of each component of the digital camera 100. 2 includes a process that is substantially executed by the ICPU 112 under the control of the CPU 101. The process will be described on the assumption that the operation subject is the ICPU 112.

  When the power of the digital camera 100 is turned on, in step S201, the CPU 101 acquires lens information. The lens information can be acquired from the LPU 122 by serial communication between the CPU 101 and the LPU 122, and the CPU 101 can know the start timing and operating speed of the aperture operation from the acquired lens information.

  In step S202, the ICPU 112 performs a normal photometry operation. In the normal photometry in step S202, the photometric value does not vary with respect to a change in brightness due to flicker even under a flicker light source. For this reason, the charge accumulation time in the photometric sensor 108 is set to, for example, approximately an integral multiple of the period in which the brightness of the flicker light source changes.

  Here, since the frequency at which the brightness of the flicker light source changes is twice the power supply frequency, the frequency of the commercial power supply is 50 Hz in an area where the frequency of the commercial power supply is 50 Hz, and the cycle is 10 ms. Similarly, in a region where the frequency of the commercial power supply is 60 Hz, the frequency is 120 Hz and the cycle is 8.33 ms. In order to correspond to these two types of frequencies, the charge accumulation time in the photometric sensor 108 is set to about 9 ms, which is between 10 ms and 8.33 ms. In that case, since the light for one cycle of flicker is accumulated regardless of whether the power supply frequency is 50 Hz or 60 Hz, a stable photometric value can be obtained even under a flicker light source.

  In step S202, the ICPU 112 further determines the aperture value AV, the shutter speed TV, and the ISO sensitivity, which are exposure conditions, using a program diagram stored in advance in the memory 113 based on the obtained photometric value. .

  In step S203, the ICPU 112 performs charge accumulation and reading in the photometric sensor 108 for flicker detection. In the present embodiment, in step S203, as shown in FIG. 3, charge accumulation and readout by the photometric sensor 108 are continuously performed at a frequency of 600 fps (frames per second) (= period of about 1.667 ms). Do it once.

  The details of FIG. 3 will be described later when the details of the processing in step S204 are described later, and here, a method of driving the photometric sensor 108 at about 600 fps will be described. The frequency of 600 fps is a frequency that is a common multiple of the expected power supply frequency (100 Hz and 120 Hz) of the flicker light source. In recent single-lens reflex cameras, an image signal is acquired by the photometric sensor 108 immediately before shooting, and the acquired image signal is processed to perform face detection and subject tracking, and then perform photometry based on the image signal. There is something. At this time, for example, when performing face detection, a linear output type photometric sensor such as a CCD or CMOS having at least the number of pixels of about QVGA is required.

  In order to read out all the pixels of a CCD or CMOS having a number of pixels of QVGA or more at a frame rate of about 600 fps or more, there are a method of increasing the driving frequency and a method of arranging a large number of A / D converters. However, these methods have a problem that the circuit configuration becomes complicated, a problem that costs increase, and a problem that it is not easy technically. Therefore, it is considered to adjust the frequency to 600 fps by reading out the total number of pixels when performing face detection or subject tracking, and performing pixel addition reading or thinning-out reading when performing flicker detection.

  When the photometric sensor 108 is a CCD, the CCD generally cannot perform partial readout, and therefore it is preferable to drive the CCD at high speed by a pseudo decrease in the number of readout lines by pixel addition. For example, in a sensor having a striped pixel arrangement, the readout time (1 V time) can be shortened by performing vertical pixel addition as shown in Table 1 below. In the example of Table 1, by adding 9 pixels, the frame rate can be about 600 fps, and the image obtained in that case is one in which the number of pixels in the vertical direction is 1/9. Further, when the photometric sensor 108 is a CMOS, partial reading can be performed relatively easily. Therefore, it is preferable to adjust so that the total time of accumulation and reading is about 1.667 ms by so-called thinning-out reading.

  Returning to the description of FIG. In step S204 after step S203, the ICPU 112 performs flicker detection calculation. FIG. 3A is a diagram illustrating the transition of the charge accumulation control of the photometric sensor 108 and the output photometric value with respect to the flicker light source that is turned on with a power supply having a frequency of 50 Hz. The n-th (n: natural number) charge accumulation is described as “accumulation n”, the readout of the accumulation n is described as “read n”, and the photometric value obtained from the result of the readout n is described as “AE (n)”. Since charge accumulation is performed in a finite time, the acquisition time of the photometric value AE (n) shown in FIG. 3A is represented by the median value during the accumulation period.

  When the power supply frequency is 50 Hz, the flicker emission cycle is about 10 ms and is “10 ÷ 1.667≈6”. Therefore, as shown in FIG. The same photometric value is obtained. That is, the relationship “AE (n) = AE (n + 6)” is established.

  FIG. 3B is a diagram illustrating the transition of the charge accumulation control of the photometric sensor 108 and the output photometric value with respect to the flicker light source that is turned on by a power source having a frequency of 60 Hz. Similarly to the case where the power supply frequency is 50 Hz, when the power supply frequency is 60 Hz, the flicker emission cycle is about 8.33 ms, which is “8.33 / 1.667≈5”. That is, as shown in FIG. 3B, the same photometric value is obtained in a cycle of 5 times, and the relationship of “AE (n) = AE (n + 5)” is obtained. Note that AE (n) is always constant regardless of n under a light source where flicker does not occur.

  Assume that an evaluation value F50 under a flicker light source with a power supply frequency of 50 Hz and an evaluation value F60 under a flicker light source with a power supply frequency of 60 Hz are defined as the following Expression 1 and Expression 2, respectively.

At this time, when the relationship of “F50 <F_th and F60 <F_th” is established using the predetermined threshold value F_th, it can be determined that there is no flicker (not under the flicker light source). Further, when the relationship of “F50 <F_th and F60 ≧ F_th” is established, it can be determined that the flicker light source has a power supply frequency of 50 Hz. Furthermore, when the relationship of “F50 ≧ F_th and F60 <F_th” is established, it can be determined that the flicker light source has a power frequency of 60 Hz.

  Here, there may be a case where both the evaluation values F50 and F60 exceed the threshold value F_th due to the panning operation of the digital camera 100 and the movement of the subject. In this case, the evaluation values F50 and F60 are compared in magnitude. In the case of “F50 ≧ F_th and F60 ≧ F_th”, in the case of “F50 ≦ F60”, it is determined that the power source frequency is under the flicker light source with 50 Hz, and in the case of “F50> F60”, The power source frequency is determined to be under a flicker light source having a frequency of 60 Hz. However, in this case, the flicker detection may be performed again on the assumption that the reliability of the flicker detection result is low.

  In step S204, the ICPU 112 further obtains the phase of the flicker light when flicker is present. As a method for obtaining the phase of the flicker light, for example, a method can be used in which a photometric value obtained by twelve consecutive charge accumulations and readouts is interpolated to calculate a peak timing at which the flicker light quantity becomes maximum.

  FIG. 4 is a diagram for explaining an example of a method for calculating the peak timing of the flicker light amount. In FIG. 4, the point where the maximum output is obtained among the photometric values AE (1) to AE (12) is P2 [t (m), AE (m)], and the previous photometric point is P1 [t (M-1), AE (m-1)], and the next photometric point is P1 [t (m + 1), AE (m + 1)]. A straight line passing through the point (P1 in the example of FIG. 4) and the point P2 that takes a small value among the photometric values AE (m−1) and AE (m + 1) is obtained as “L1 = at + b”. Then, it passes through a point (P3 in the example of FIG. 4) that takes a large value among the photometric values AE (m−1) and AE (m + 1), and a straight line having an inclination of −a is L2, and the intersection of the straight lines L1 and L2 Ask for. From this intersection, the peak timing t_peak when the flicker metering start time is set as a reference (0 ms), and the photometric value AE_peak at the peak timing t_peak can be calculated. Although the peak timing of the flicker light amount is calculated here, the bottom timing of the flicker light amount may be calculated.

  In step S205 after step S204, the ICPU 112 generates a flicker synchronization signal from the flicker frequency and phase (for example, peak timing t_peak) obtained in step S204, and outputs the flicker synchronization signal to the CPU 101. The flicker synchronization signal is a signal synchronized with a predetermined timing of the flicker, and is generated every flicker light emission period in this embodiment.

  FIG. 5 is a diagram showing the relationship (timing) between the flicker synchronization signal and the shutter start signal, and illustrates the case where the shutter speed is 1/1000 sec and 1/200 sec. 5, the waiting time from the flicker synchronization signal to the shutter start signal for the shutter 104 to start the shutter operation is “T_ShutterWait” (hereinafter referred to as “T_SW”). The release time lag until the operation starts is “T_ShutterResponse (hereinafter referred to as“ T_SR ”).” That is, after the time of “T_SW + T_SR” has elapsed from the flicker synchronization signal, the shutter 104 actually starts running. Further, the time during which the shutter 104 runs from end to end of the image sensor 103 is “T_Run”.

  The change in the amount of flicker light is small before and after the peak timing t_peak. Therefore, the waiting time T_SW is changed for each shutter speed so that the peak timing of the flicker light amount comes to approximately the center of the time T_Run (that is, the exposure time) from the start of the front curtain travel to the end of the rear curtain travel. The timing for issuing the shutter start signal is adjusted.

  In step S204, the flicker emission period T and the peak timing t_peak are known. The flicker synchronization signal generation timing t_Flicker (hereinafter referred to as “t_F”) is expressed by “t_F = t_peak−T_SR− (T_Run + TVmax) / 2 + T × n” with the time of the start of photometry for flicker detection as a reference (0 ms). The Here, n is a natural number, and TVmax is a shutter speed serving as a boundary between execution / non-execution of flicker countermeasures. As described above, it is preferable that the flicker synchronization signal is such that the generation timing t_F changes at every peak timing t_peak.

  By the way, when the shutter speed TV is slower than 1/100 sec (= 10 ms), the exposure includes light for one cycle or more from the flicker light source, so that the exposure variation due to the flicker is reduced. Therefore, in the present embodiment, it is considered that countermeasures against flicker are taken only when the shutter speed TV is faster than 1/100 sec. In addition, when the shutter speed TV is around 1/111 (≈9 ms), the photometric sensor 108 accumulates light for approximately one cycle from the flicker light source as electric charge, so that stable exposure is performed even under the flicker light source. Can be obtained. Therefore, in the present embodiment, when the shutter speed is faster than 8 ms (= 1/125 sec), flicker countermeasures are taken. Therefore, in the following description, TVmax = 1/125 sec (= 8 ms).

  When the waiting time T_SW is “T_SW = (TVmax−TV) / 2 and TV <1/125”, the peak timing t_peak of the flicker light amount is from the start of the front curtain travel of the shutter 104 to the end of the rear curtain travel. Can be set to be at the center of the time. The waiting time T_SW set for each shutter speed in this way may be stored in the memory 113 as a table. Table 2 shows an example of a table indicating the relationship between the shutter speed and the waiting time T_SW.

  In step S206 following step S205, the CPU 101 determines whether the switch SW2 is turned on (whether the user has fully pressed the shutter switch). If SW2 is not turned on (NO in S205), the CPU 101 returns the process to step S202, and updates the flicker emission cycle and phase to the latest information. At this time, in the present embodiment, a sequence in which one flicker detection process is repeated for one normal metering is performed, but the flicker detection process in steps S203 and S204 is performed only once for a plurality of normal metering. You may make it perform.

  On the other hand, if SW2 is turned on (YES in S206), CPU 101 advances the process to step S207. In step S207, the CPU 101 determines whether or not the flicker detection process can be completed within a predetermined time after the SW2 is turned on, that is, before the photographing operation by the image sensor 103 is performed. If the flicker detection process cannot be performed (NO in S207), the CPU 101 advances the process to step S208. If the flicker detection process can be executed (YES in S207), the CPU 101 advances the process to step S209.

  Here, whether or not the flicker detection process can be performed in step S207 will be described with reference to FIGS. FIG. 6 and FIG. 7 are diagrams illustrating a photographing sequence representing the relationship among the operations of the half mirror 105, the diaphragm, and the shutter 104 from when SW2 is turned on until the photographing operation by the image sensor 103 is performed.

  FIG. 6A shows a shooting sequence during normal shooting without taking measures against flicker. In normal shooting, when SW2 is turned on, the CPU 101 drives a mirror-up motor (not shown in FIG. 1) based on the SW2 on signal, thereby causing the mirror up operation of the half mirror 105 (the front surface of the image sensor 103). Evacuation) starts. When the mirror up operation is completed, the half mirror 105 bounces in the up state and then becomes stable. In order to perform stable photographing, the time (mirror up stabilization time) from when the mirror up instruction is given until the bounce is settled to become ready for photographing (mirror up stabilization time) is determined by a timer (timer means (see FIG. 1 in FIG. 1)). (Not shown)).

  Further, the CPU 101 instructs the LPU 122 to set the aperture set as the photographing condition based on the SW2 ON signal. In FIG. 6 and FIG. 7, communication between the CPU 101 and the LPU 122 is described as “lens communication”. The LPU 122 drives the diaphragm so that the diaphragm state instructed by the CPU 101 is obtained, and when the diaphragm driving is completed, the LPU 122 notifies the CPU 101 of this and terminates the diaphragm operation.

  The CPU 101 measures the time (release stable time) from when SW2 is turned on until the shutter front curtain travels (time for release stabilization). The measurement of the release stabilization time is performed so that there is no variation in the time from when SW2 is turned on to when the image is picked up by the image sensor 103, thereby enabling stable shooting.

  The normal photographing can be performed at the time when these three times of the mirror up stabilization time, the aperture driving time, and the release stabilization time are completed. In the example of FIG. 6A, since the release stabilization time ends the latest, the photographing operation by the image sensor 103 is started at the end of the release stabilization time.

  FIG. 6B shows a shooting sequence when performing flickerless shooting. Note that flickerless shooting refers to shooting that obtains a stable imaging output without being affected by flicker under a flicker light source by taking the above-described countermeasure against flicker. Since the aperture operation takes time even in flickerless shooting, when SW2 is turned on, the same operation as in normal shooting in FIG. 6A is performed. Note that the description of the diaphragm operation is omitted because it overlaps.

  On the other hand, since the mirror-up operation is quick to complete, the mirror-up operation start time is determined by calculating the mirror-up stabilization time from the timing of starting the first curtain travel of the shutter 104. Since the aperture drive time can be determined from the lens information of the lens 121 and the aperture value set in the shooting conditions, the measurement start time of the mirror up stabilization time is longer than the aperture drive time and the release stabilization time. Can be calculated from the completion time.

  In flickerless shooting, since the mirror-up operation is not started immediately after SW2 is turned on, an optical path to the photometric sensor 108 is secured after SW2 is turned on, thereby securing time for performing flicker detection. It becomes possible. The flicker detection feasible time is obtained by “[flicker detection feasible time] = [release stable time] − [mirror up stable time]” when “aperture driving time ≦ release stable time”. Further, when “aperture driving time> release stable time”, “[flicker detection possible time] = [aperture driving time] − [mirror up stable time]” is obtained.

  In some digital cameras, even when the release time lag varies, it is possible to advance the shooting start time by performing shooting when the aperture driving time and the mirror up stabilization time are completed. In this case, the flicker detection feasible time is determined by the aperture driving time, and is obtained by “[flicker detection feasible time] = [aperture driving time] − [mirror up stabilization time]”.

  In order to perform the flicker detection process and update the flicker synchronization signal within the flicker detection feasible time, it is sufficient that the charge accumulation and reading can be performed six times as shown in FIG. However, in this case, since the flicker emission period T cannot be detected by 12 times of charge accumulation, the previously detected result is used for the flicker emission period T. When only calculating the peak timing t_peak of the flicker light amount due to six times of charge accumulation, the calculation time is shorter than when calculating the flicker light emission period T, etc., so the flicker detection is completed in a short time. It becomes possible to make it.

  In addition, in the case where the charge can be accumulated 12 times during the flicker detection feasible time and the flicker emission period T can be calculated in addition to the calculation of the peak timing t_peak, both of these can be performed. An operation may be performed. In addition, when the photometric value shows a change in which the rise and fall are alternately repeated such that the flicker light quantity represents the peak timing t_peak, the peak timing t_peak can be calculated before the number of charge accumulations reaches six. Is possible. Therefore, when only the peak timing t_peak is obtained, the charge accumulation is not limited to the above six times of charge accumulation, and it is also possible to complete the charge accumulation before reaching the six times of charge accumulation.

  FIG. 7 is a diagram showing a shooting sequence when SW2 is turned on when the flicker detection process of steps S203 to S205 is being executed when SW1 is turned on. In this case, if the CPU 101 continues the flicker detection started when the SW1 is turned on even after the SW2 is turned on, whether or not the remaining processing can be completed within the flicker detection executable time. Determine whether. When it is determined that the flicker detection is completed, the CPU 101 continues the flicker detection process, and when it is determined that the flicker detection is not completed, the CPU 101 interrupts the flicker detection process. The other sequences are the same as the sequence in FIG.

  In step S208, the CPU 101 does not perform flicker detection, performs a shooting operation using flicker information detected before that time, and then ends this processing. On the other hand, in step S209, the ICPU 112 performs charge accumulation and reading operations for flicker detection as described with reference to FIGS. The process in step S209 is the same as the process in step S203, but only the peak timing t_peak of the flicker light amount may be calculated by accumulating the charge six times so that the process is completed within the flicker detection feasible time. .

  In step S210, the CPU 101 multiplies the photometric value obtained by the reading in step S209 by a gain corresponding to the aperture drive. FIG. 8 is a diagram for explaining the relationship between the aperture operation and the gain applied to the photometric value. Here, a case of a lens having an open aperture F2.8 is illustrated. In FIG. 8, the gain applied to the accumulation n is represented by Gain (n).

  In the shooting sequence at the time of flickerless shooting, as shown in FIGS. 6B and 7, the aperture driving is started after the lens communication between the CPU 101 and the LPU 122 is performed. Therefore, when aperture driving is started, the aperture operates at a speed as shown in FIG. 8, and the amount of light reaching the photometric sensor 108 decreases. That is, the aperture driving is executed during the charge accumulation for flicker detection, and therefore the photometric value is calculated lower than the charge accumulation for flicker detection in step S203 executed when SW1 is turned on. Therefore, by multiplying the photometric value by a gain corresponding to the aperture drive so as to cancel out the decrease in the amount of light, the photometric value is corrected to the same as the charge accumulation for flicker detection. When the lens barrel 100B is a so-called interchangeable lens that is detachable from the camera body 100A, the lens communication time, the open aperture value, the maximum aperture value, the aperture drive speed, and the like are different for each lens barrel 100B. . Therefore, it is necessary to obtain the correction amount gain according to the lens barrel 100B attached to the camera body 100A.

  In step S211, the ICPU 112 performs a flicker detection calculation using the photometric value obtained in step S210, and the processing content is the same as the processing content in step S204. In step S211, whether to perform the flicker peak timing calculation or the cycle calculation is changed according to the number of charge accumulations performed in step S209.

  In step S212, the ICPU 112 generates a flicker synchronization signal based on the flicker peak timing obtained in step S211, and the processing content is the same as the processing content in step S205. After step S212, the CPU 101 advances the process to step S208 to perform a shooting operation, and thereafter ends the present process, whereby the digital camera 100 returns to the shooting standby state.

  As described above, according to the present embodiment, it is possible to perform charge accumulation, reading, and calculation in the photometric sensor 108 for flicker detection after SW2 is turned on. That is, since it is possible to generate a flicker synchronization signal immediately before photographing, a stable imaging output can be obtained even under a flicker light source.

100 Digital Camera 100A Camera Body 100B Lens Barrel 101 CPU
DESCRIPTION OF SYMBOLS 103 Image pick-up element 104 Shutter 105 Half mirror 107 Display element 108 Photometric sensor 112 ICPU
122 LPU

Claims (7)

An image sensor;
Photometric means for measuring the amount of incident light that passes through the optical system and enters the image sensor;
An image pickup apparatus comprising: a detection unit that detects whether the incident light includes light from a flicker light source using the photometry unit;
The detection means detects the phase of the light from the flicker light source immediately before the exposure of the main photographing when it detects that the incident light contains light from the flicker light source. apparatus. Generating means for generating a flicker synchronization signal corresponding to the phase of light from the flicker light source detected by the detection means;
2. The imaging according to claim 1, further comprising: an adjusting unit that adjusts a time from the flicker synchronization signal to the start of exposure of the main shooting in accordance with a shutter speed at the time of performing the main shooting. apparatus.   The adjustment means until the exposure of the main photographing is started from the flicker synchronization signal so that the peak timing at which the light amount from the flicker light source is maximized is included in the exposure time when performing the main photographing. The imaging apparatus according to claim 2, wherein the time is adjusted. A shutter for controlling exposure to the image sensor;
The adjustment means sets a release time lag from the shutter start signal until the shutter actually starts running during a period from the flicker synchronization signal to generation of a shutter start signal for causing the shutter to start a shutter operation. The imaging apparatus according to claim 3, wherein the added time is adjusted. A mirror that is disposed on the front side of the image sensor, controls the incidence of light to the image sensor and guides a part of the incident light to the photometric means with respect to the image sensor;
Drive means for retracting the mirror from the front surface of the image sensor until the shutter starts to travel,
The detection means can detect the phase of the light from the flicker light source when the detection of the phase of the light from the flicker light source can be completed before the operation of retracting the mirror from the front surface of the image sensor is started. The imaging apparatus according to claim 4, wherein detection is performed. A diaphragm for controlling the incidence of light on the image sensor;
The detection means detects whether the incident light contains light from a flicker light source using the photometry means in response to driving of the diaphragm performed immediately before the exposure of the main photographing. 6. The imaging apparatus according to claim 5, wherein a correction is applied to a photometric value obtained by the photometric means. A method for controlling an imaging apparatus,
A photometric step for measuring the amount of incident light that passes through the optical system and enters the image sensor;
A first detection step of detecting whether or not light from a flicker light source is included in the incident light in the photometric step;
A generation step of generating a flicker synchronization signal corresponding to the phase of the light from the flicker light source when the incident light contains light from the flicker light source in the first detection step;
A determination step of determining whether or not the detection of the phase of the light from the flicker light source can be completed within a predetermined time when an instruction to start main photographing by the image sensor is given;
A second detection step of detecting the phase of the light from the flicker light source when it is determined in the determination step that the detection of the phase of the light from the flicker light source can be completed;
An update step of updating the flicker synchronization signal based on the phase of light from the flicker light source detected in the second detection step;
An adjustment step of adjusting a time from the flicker synchronization signal updated in the update step to the start of the exposure of the main shooting according to the shutter speed at the time of performing the main shooting;
And a photographing step for performing the main photographing after the time adjusted in the adjusting step has elapsed.