JP6501463B2 - Image pickup apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging apparatus such as a digital camera and a control method thereof, and more particularly to a technology 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 sensors of digital cameras, it has become possible to take photographs without blur at high shutter speeds even in relatively dark environments such as indoors. Here, in a fluorescent lamp widely used as an indoor light source, a phenomenon called flickering of illumination light periodically occurs 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 causing flicker (hereinafter referred to as "flicker light source"), the effects of the flicker cause variations in image exposure and color temperature for each frame, and within one frame. Uneven exposure or color unevenness may occur.

  Here, the change in brightness is small near the peak of the flicker light amount. Therefore, a flicker removal system has been proposed that detects a flicker synchronization signal so as to detect a flicker cycle and a phase, and perform exposure in accordance with the peak timing of the light amount from the flicker light source (hereinafter referred to as "flicker light amount"). (See Patent Document 1).

JP 2004-193922 A

  However, the fluctuation of the frequency of the commercial power source is said to be 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. Therefore, in the flicker removal system described in Patent Document 1, as time passes from the flicker detection, the relationship between the flicker synchronization signal and the peak timing of the flicker light amount deviates due to the influence of the fluctuation of the frequency of the commercial power supply.

  FIG. 9 is a view schematically showing the relationship among the flicker light amount, the flicker synchronization signal, and the shutter operation, and the luminance distribution in a photographed image (an image of one frame) 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. FIGS. 9A, 9B, and 9C respectively show states when about 100 ms (milliseconds), 200 ms, and 300 ms have elapsed since the flicker detection. From FIG. 9, even if flicker detection is performed once to calculate the timing of the flicker synchronization signal, the peak timing of the flicker light amount deviates from the timing of the shutter operation with the passage of time from the flicker detection, so that the luminance is obtained. It turns out that it will become a photography image from which distribution differs.

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

An imaging apparatus according to the present invention is an imaging apparatus including an imaging unit, and a detection unit that detects a flicker based on a plurality of outputs by accumulation and readout of a plurality of charges using the imaging unit. A detection unit configured to detect a timing at which the flicker cycle and the light amount of the flicker become a predetermined value based on a plurality of outputs by accumulation and readout of the first number of charges using the imaging unit; A second flicker detecting a timing at which the light quantity of the flicker becomes a predetermined value based on a plurality of outputs by accumulation and readout of a second number of times less than the first number of times using the imaging means and detection, can be performed and when it is detected flicker by the first flicker detection, the imaging instruction of the exposure for imaging a subject And executes the second flicker detection timing overlapping the period until the exposure start in response to the imaging instruction.

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

FIG. 1 is a diagram showing a schematic configuration of a digital camera according to an embodiment of the present invention. It is a flowchart of imaging | photography control with the digital camera of FIG. It is a figure which shows transition of the charge accumulation control of the photometry sensor with respect to the flicker light source made to light with each power supply of frequency 50 Hz and 60 Hz, and an output photometry value. It is a figure explaining an example of the method of calculating the peak timing (phase) of flicker light volume. It is a figure which shows the relationship (timing) of a flicker synchronization signal and a shutter start signal. It is a 1st figure which shows the imaging | photography sequence from the switch SW2 of shutter switch of the digital camera of FIG. 1 being turned on until imaging operation by an image pick-up element is performed. It is a 2nd figure which shows the imaging | photography sequence from the switch SW2 of the shutter switch of the digital camera of FIG. FIG. 3 is a view for explaining the relationship between the aperture operation in step S210 of FIG. FIG. 7 is a view schematically showing the relationship between the flicker light amount, the flicker synchronization signal, and the shutter operation, and the luminance distribution in a photographed image obtained by the shutter operation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. Here, a so-called digital camera is taken as an imaging device according to the present invention. However, the present invention is not limited to this, and may be various electronic devices having a camera function. 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 mobile computer with a camera function, a mobile game machine with a camera function, or the like.

<Schematic Configuration of Digital Camera>
FIG. 1 is a view 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, which 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 imaging device 103, a shutter 104, a half mirror 105, a focusing plate 106, a display device 107, and a photometric sensor (AE sensor) 108. The camera body 100A further includes a pentaprism 109, an optical finder (not shown), an AF (automatic focusing) 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 in which the CPU 101 develops a program, and a RAM that temporarily stores image data and the like. The LPU 122 is a CPU in the lens barrel, transmits distance information and the like to the subject to the CPU 101, and performs drive control and the like of the lens 121 based on an instruction from the CPU 101. The imaging element 103 is an image sensor such as a CCD sensor or a CMOS sensor including an infrared cut filter, a low pass filter, and the like. The shutter 104 is closed when not photographing and shields the imaging element 103 from light, and is opened during photographing and guides incident light (light flux) having passed through the lens barrel 100 B to the imaging element 103.

  A half mirror 105 provided on the front side (subject side) of the image sensor 103 reflects a part of light incident through the lens 121 at the time of non-shooting, and forms an optical image on a focusing plate 106. The display element 107 displays an AF distance measurement frame such as PN liquid crystal and shows the photographer through an optical finder to which position of the object the control of the AF operation is performed. The photometric sensor 108 is composed of an imaging device such as a CCD or a COMS, and in the present embodiment, performs face detection, tracking, photometry, flicker detection and the like using an output signal from the photometric sensor 108. In the present embodiment, although the photometric sensor 108 is used as the flicker detection means, the image sensor 103 for performing the main photographing can also be used as the flicker detection means.

  The pentaprism 109 guides the subject image of the focusing plate 106 to the photometric sensor 108 and the optical finder. The photometric sensor 108 is looking at an object image formed on the focusing plate 106 via the pentagonal prism 109 from an oblique position. The AF mirror 111 guides a part of the light beam which has entered from the lens barrel 100 B and passed 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 luminous flux.

  The ICPU 112 is a CPU that performs drive control of the photometric sensor 108, photometric calculation, object recognition processing such as face detection calculation and tracking calculation, and various calculation processing such as flicker detection calculation. The memory 113 includes a ROM for storing programs executed by the ICPU 112, variables, and the like, a work area for the ICPU 112 to deploy a program, and a RAM for temporarily storing calculation results. In the present embodiment, the ICPU 112, which is a dedicated CPU, is provided for the photometric sensor 108. However, drive control of the photometric sensor 108, image processing, and calculation may be performed by the CPU 101.

  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 which is turned on by half pressing (first stroke) and a switch SW2 which 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 focusing control based on the output from the AF sensor 110 are performed. Further, when the switch SW2 is turned on, the main photographing is performed. In the main photographing, an optical image formed on the image pickup element 103 is converted to an analog electric signal by the image pickup element 103, and the analog electric signal is converted to digital image data by an image processing unit (not shown). Are stored in the storage means of

<Shooting control method with digital camera>
FIG. 2 is a flowchart of shooting control in the digital camera 100. Each process shown in FIG. 2 is realized by controlling the operation of each component of the digital camera 100 by the CPU 101 developing a program stored in the ROM into the RAM. Note that among the processing illustrated in FIG. 2, there is processing that is substantially executed by the ICPU 112 under the control of the CPU 101, and the processing subject is described as the ICPU 112.

  When the digital camera 100 is powered on, the CPU 101 acquires lens information in step S201. 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 of the diaphragm operation and the operation speed from the acquired lens information.

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

  Here, since the frequency at which the light and dark of the flicker light source changes is twice the power supply frequency, the frequency is 100 Hz in a region where the frequency of the commercial power supply is 50 Hz, and the period 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 period is 8.33 ms. In order to cope with 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, even if the power supply frequency is either 50 Hz or 60 Hz, light of approximately one cycle of flicker is accumulated, so that a stable photometric value can be obtained even under a flicker light source.

  In step S 202, the ICPU 112 further determines the aperture value AV, the shutter speed TV, and the ISO sensitivity, which are the exposure conditions, using the 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 readout in the photometric sensor 108 for flicker detection. In this 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

  The details of FIG. 3 will be described together with the contents of the process of step S204 later, and a method of driving the photometric sensor 108 at about 600 fps will be described here. The frequency of 600 fps is a common multiple of the expected power source frequency of the flicker light source (100 Hz and 120 Hz). In recent years, with single-lens reflex cameras, image signals are acquired by the photometric sensor 108 immediately before shooting, face detection and subject tracking are performed by processing the acquired image signals, and photometry is further performed based on the image signals. There is something that At this time, for example, when face detection is performed, a linear output photometric sensor such as a CCD or a CMOS provided with at least about QVGA pixels is required.

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

  In the case where the photometric sensor 108 is a CCD, in general, the CCD can not perform partial readout, and therefore it is preferable to drive at high speed by pseudo reduction of the number of readout lines by pixel addition. For example, in a sensor in which the pixel array has a stripe shape, 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, the frame rate can be set to about 600 fps by performing 9 pixel addition, and the image obtained in that case becomes one in which the number of pixels in the vertical direction is 1/9. When the photometric sensor 108 is a CMOS, partial readout can be performed relatively easily. Therefore, it is preferable to adjust the total time of accumulation and readout to be about 1.667 ms by so-called thinning readout.

  It returns to the explanation of FIG. In step S204 after step S203, the ICPU 112 performs flicker detection calculation. FIG. 3A is a diagram showing the charge accumulation control of the photometric sensor 108 and the transition of the output photometric value with respect to the flicker light source which is turned on by the power supply having a frequency of 50 Hz. The nth (n: natural number) charge accumulation is described as "accumulation n", the readout of accumulation n is "read n", and the photometric value obtained from the result of readout n is "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.

  The flicker emission period in the case where the power supply frequency is 50 Hz is about 10 ms, and "10 ÷ 1.667 ≒ 6". Therefore, as shown in FIG. The same photometric value is obtained. That is, the relationship of "AE (n) = AE (n + 6)" is obtained.

  FIG. 3B is a diagram showing the charge accumulation control of the photometric sensor 108 and the transition of the output photometric value with respect to the flicker light source which is turned on by the power supply having a frequency of 60 Hz. As in the case of the power supply frequency of 50 Hz, when the power supply frequency is 60 Hz, the flicker emission period 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 five 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.

  An evaluation value F50 under a flicker light source having a power supply frequency of 50 Hz and an evaluation value F60 under a flicker light source having a power supply frequency of 60 Hz are respectively defined as Formula 1 and Formula 2 below.

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

  Here, it is conceivable that both of the evaluation values F50 and F60 exceed the threshold F_th due to the panning operation of the digital camera 100 and the movement of the subject. In this case, the magnitudes of the evaluation values F50 and F60 are compared. In the case of "F50 ≧ F_th and F60 ≧ F_th", when "F50 ≦ F60", it is judged that the power supply frequency is under a flicker light source of 50 Hz, and in the case of "F50> F60" It is determined that the power supply frequency is under the flicker light source of 60 Hz. However, in this case, 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 if the flicker exists. As a method of determining the phase of the flicker light, for example, a method of calculating the peak timing at which the flicker light amount becomes maximum can be used by interpolating the photometric values obtained by 12 consecutive charge accumulation and readout.

  FIG. 4 is a diagram for explaining an example of a method of calculating the peak timing of the flicker light amount. In FIG. 4, the point at which the maximum output is obtained among the photometric values AE (1) to AE (12) is P2 [t (m), AE (m)], and the photometric point immediately before that is P1 [t It is assumed that (m-1) and AE (m-1)], and the next photometric point is P1 [t (m + 1) and AE (m + 1)]. A straight line passing a point (P1 in the example of FIG. 4) having a smaller value of the photometric values AE (m-1) and AE (m + 1) and the point P2 is determined as "L1 = at + b". Then, passing through a point (P3 in the example of FIG. 4) which takes a larger value of the photometric values AE (m-1) and AE (m + 1), a straight line with an inclination of -a is taken as L2, and an intersection point Ask for From this intersection point, it is possible to calculate the peak timing t_peak when the flicker metering start time is set as the reference (0 ms) and the photometric value AE_peak at the peak timing t_peak. 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 flicker, and is generated at every flicker emission cycle in the present embodiment.

  FIG. 5 is a diagram showing the relationship (timing) between the flicker synchronization signal and the shutter start signal, and exemplifies the case where the shutter speed is 1/1000 sec and the case where the shutter speed is 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 start of operation is "T_ShutterResponse (hereinafter referred to as" T_SR ")", that is, the shutter 104 actually starts traveling after the time "T_SW + T_SR" has elapsed from the flicker synchronization signal. Further, the time during which the shutter 104 runs from end to end of the image sensor 103 is taken as "T_Run".

  The change in the flicker light amount 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 approximately at the center of the time T_Run (that is, the exposure time) from the start of the front curtain travel of the shutter 104 to the end of the rear curtain travel. , Adjust the timing of issuing the shutter start signal.

  In step S204, the flicker emission cycle T and the peak timing t_peak are known. The flicker synchronization signal generation timing t_Flickr (hereinafter referred to as “t_F”) is represented by “t_F = t_peak−T_SR− (T_Run + TVmax) / 2 + T × n” with reference to the start of photometry for flicker detection (0 ms). Ru. Here, n is a natural number, and TVmax is a shutter speed which is the boundary between the execution / non-execution of the flicker countermeasure. As described above, it is preferable to use a flicker synchronization signal in which the generation timing t_F changes 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 of one cycle or more from the flicker light source, so that the exposure variation caused by the flicker becomes smaller. Therefore, in the present embodiment, it is considered to take measures against flicker 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 of approximately one cycle from the flicker light source as charge, so stable exposure is possible even under the flicker light source. You can get it. Therefore, in the present embodiment, a countermeasure against flicker is taken when the shutter speed is faster than 8 ms (= 1/125 sec), and 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 from the start of the front curtain travel of the shutter 104 to the end of the rear curtain travel It can be set to be at the center of time. Thus, the waiting time T_SW set for each shutter speed may be stored in the memory 113 as a table. Table 2 shows an example of a table showing 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 pressed the shutter switch fully). When the SW2 is not turned on (NO in S205), the CPU 101 returns the process to step S202, and updates the flicker emission cycle and the phase to the latest information. At this time, in the present embodiment, one flicker detection process is repeated for one normal photometry, but the flicker detection process in steps S203 and S204 is performed only once for a plurality of normal photometry. You may do so.

  On the other hand, when the SW 2 is turned on (YES in S206), the 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 SW 2 is turned on, that is, until the imaging operation by the imaging device 103 is performed. If the CPU 101 can not perform the flicker detection process (NO in S207), the process proceeds to step S208. If the flicker detection process can be performed (YES in S207), the CPU 101 advances the process to step S209.

  Here, the determination as to whether to execute the flicker detection process in step S207 will be described with reference to FIG. 6 and FIG. FIG. 6 and FIG. 7 are diagrams showing a photographing sequence representing the relationship between the operation of the half mirror 105, the aperture and the shutter 104 from when the switch SW2 is turned on until the photographing operation by the image pickup device 103 is performed.

  FIG. 6A shows a shooting sequence at the time of normal shooting without taking a countermeasure against flicker. In normal shooting, when the switch SW2 is turned on, the CPU 101 drives a mirror-up motor (not shown in FIG. 1) based on the switch-on signal of the switch SW2 to mirror up the half mirror 105 (the front surface of the imaging device 103). ) Is started. 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, a timer (clocking means (shown in FIG. 1) provided in the camera main body 100A has a time (mirror-up stable time) from the mirror-up instruction until the bounce is settled and the photographing becomes possible. (Not shown))).

  Further, based on the on signal of SW2, the CPU 101 instructs the LPU 122 to have the aperture set as the imaging condition. In FIGS. 6 and 7, communication between the CPU 101 and the LPU 122 is described as “lens communication”. The LPU 122 drives the diaphragm so as to attain the diaphragm state instructed by the CPU 101, and when the diaphragm driving is finished, notifies the CPU 101 of the fact and ends the diaphragm operation.

  The CPU 101 uses a timer to measure the time (release stable time) from when the switch SW2 is turned on until the shutter front curtain travels. The measurement of the release stabilization time is performed in order to prevent variation in the time from the turning on of the switch SW2 to the photographing by the image pickup device 103, which enables stable photographing.

  Normal photographing can be performed at the time when these three times of mirror-up stabilization time, aperture driving time, and release stabilization time are finished. In the example of FIG. 6A, since the release stabilization time ends the slowest, the photographing operation by the imaging element 103 is started at the end of the release stabilization time.

  FIG. 6B shows a shooting sequence in the case of performing flickerless shooting. Note that flicker-less imaging refers to imaging that obtains a stable imaging output without being affected by flicker under the flicker light source by taking the above-mentioned countermeasure against flicker. Since the aperture operation takes time even in flickerless shooting, when the switch 2 is turned on, the same operation as the normal shooting in FIG. 6A is performed. Note that the description of the aperture operation here is omitted because it is redundant.

  On the other hand, since the mirror-up operation is quick to complete, the mirror-up stable time is reversely calculated from the front curtain traveling start timing of the shutter 104 to determine the start time of the mirror-up operation. Note that since the diaphragm 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 by comparing the diaphragm drive time and the release stabilization time. You can calculate back from the completion time of.

  In flickerless photography, the start of the mirror-up operation is not immediately after the switch SW2 is turned on, and the light path to the photometric sensor 108 is secured after the switch SW2 is turned on, thereby securing a time for performing flicker detection. It becomes possible. The flicker detection executable time can be obtained by “[flicker detection executable time] = [release stabilization time] − [mirror up stabilization time]” in the case of “diaphragm drive time ≦ release stable time”. In addition, in the case of "diaphragm drive time> release stable time", it can be obtained by "[flicker detection executable time] = [diaphragm drive time]-[mirror up stabilization time]".

  Some digital cameras can accelerate the shooting start time by performing shooting when the diaphragm driving time and the mirror-up stabilization time are completed, even if there is variation in the release time lag. In that case, the flicker detection executable time is determined by the diaphragm drive time, and can be obtained by “[Flicker detection executable time] = [diaphragm drive time] − [mirror up stabilization time]”.

  In order to perform the flicker detection process within the flicker detection feasible time and update the flicker synchronization signal, it is sufficient if six charge accumulation and readout can be performed as shown in FIG. However, in this case, since it is not possible to detect the flicker light emitting cycle T by 12 times of charge accumulation, the flicker light emitting cycle T uses the result of detection previously. When only the calculation of the peak timing t_peak of the flicker light amount due to the six charge accumulation is performed, the calculation time is shorter than in the case where the calculation of the flicker light emission period T is also performed, so flicker detection is completed in a short time. It is possible to

  When it is possible to store 12 charges during the flicker detection enable time and to calculate the flicker emission period T in addition to the calculation of the peak timing t_peak, both of them The operation may be performed. In addition, when the photometric value shows a change that alternately repeats rising and falling so as to indicate the peak timing t_peak of the flicker light amount, the peak timing t_peak may be calculated before reaching the number of times of charge accumulation of six times. It is possible. Therefore, when only the peak timing t_peak is obtained, it is possible to complete the charge accumulation before reaching the six charge accumulation times without being limited to the above six charge accumulation times.

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

  In step S208, the CPU 101 does not perform flicker detection, performs a photographing operation using flicker information detected before that, and then ends this processing. On the other hand, in step S209, the ICPU 112 performs charge storage and readout operations for flicker detection as described with reference to FIGS. 6 (b) and 7. Although the process of step S209 is the same as the process of step S203, only the peak timing t_peak of the flicker light amount may be calculated by six charge accumulations so that the process is completed in the flicker detection enable time. .

  In step S210, the CPU 101 multiplies the photometric value obtained by the readout in step S209 by a gain according to the diaphragm drive. FIG. 8 is a diagram for explaining the relationship between the aperture operation and the gain to be multiplied by the photometric value, and in this case, the case of the lens with the aperture stop F2.8 is illustrated. In FIG. 8, the gain applied to the storage n is represented by Gain (n).

  In the photographing sequence at the time of flicker-less photographing, as shown in FIG. 6B and FIG. 7, after the lens communication between the CPU 101 and the LPU 122 is performed, the diaphragm drive is started. Therefore, when the diaphragm drive is started, the diaphragm operates at a speed as shown in FIG. 8, and the light amount reaching the photometric sensor 108 is reduced. That is, since the diaphragm drive is executed during charge accumulation for flicker detection, the photometric value is calculated to be lower than the charge accumulation for flicker detection in step S203 performed by turning on SW1. Therefore, the photometric value is corrected to the same photometric value as the charge accumulation for flicker detection by multiplying the photometric value by a gain according to the diaphragm drive so as to cancel out this light amount decrease. When the lens barrel 100B is a so-called interchangeable lens that can be attached to and removed from the camera body 100A, the lens communication time, the aperture value, the maximum aperture value, the diaphragm driving speed, etc. differ for each lens barrel 100B. . Therefore, it is necessary to obtain the correction amount gain in accordance with the lens barrel 100B mounted on the camera body 100A.

  In step S211, the ICPU 112 performs flicker detection calculation using the photometric value obtained in step S210, and the processing content is the same as the processing content of step S204. In step S211, whether to calculate the peak timing of the flicker or to calculate the period is changed in accordance with the number of times of charge accumulation 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 of step S205. After step S212, the CPU 101 advances the process to step S208 to perform a photographing operation, and then terminates the present process, whereby the digital camera 100 returns to the photographing standby state.

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

100 Digital Camera 100A Camera Body 100B Lens Barrel 101 CPU
103 image sensor 104 shutter 105 half mirror 107 display element 108 photometric sensor 112 ICPU
122 LPU

Claims (10)

Imaging means,
An imaging apparatus comprising: detection means for detecting flicker based on a plurality of outputs obtained by accumulating and reading out electric charges a plurality of times using the imaging means;
The detection unit detects a timing at which the flicker cycle and the light amount of the flicker become a predetermined value, based on a plurality of outputs by accumulation and readout of the first number of charges using the imaging unit. And second detecting a timing at which the light amount of the flicker becomes a predetermined value based on a plurality of outputs by accumulation and readout of a second number of charges smaller than the first number using the imaging means. Flicker detection, and when flicker is detected by the first flicker detection, a period from an imaging instruction of a main exposure for imaging a subject to an exposure start according to the imaging instruction An imaging device characterized in that the second flicker detection is performed at a timing when the second flicker detection is performed ; Comprising a generation means to generate a flicker synchronous signal corresponding to the previous northern timing the detection means detects,
The generation means generates a flicker synchronization signal corresponding to the timing obtained by the second flicker detection when the second flicker detection is performed, and does not execute the second flicker detection. the imaging apparatus according to claim 1, characterized that you generate flicker synchronous signal corresponding to the timing obtained by the first flicker detection that is executed first. The generation means may generate the flicker based on the period of the flicker detected by the first flicker detection and the timing detected by the first flicker detection or the second flicker detection. The imaging device according to claim 2, which generates a synchronization signal. 4. The image pickup apparatus according to claim 2, further comprising an adjustment unit configured to adjust a time from the flicker synchronization signal to the start of the main exposure in accordance with a shutter speed at the time of performing the main exposure. The predetermined value is a peak timing at which the light amount in the light amount change period of the flicker becomes maximum,
5. The system according to claim 4 , wherein the adjusting means adjusts a time from the flicker synchronization signal to the start of the main exposure so that the peak timing is included in the exposure time of the main exposure. Imaging device. A shutter for adjusting an exposure time at which the subject is imaged;
The adjustment means is a time obtained by adding a release time lag until the shutter is actually started to be started from the flicker synchronization signal until a signal for starting the traveling of the shutter is generated. The image pickup apparatus according to claim 5 , wherein the adjustment is performed. It has an imaging element used for the main exposure, which is different from the imaging means,
A mirror disposed on the front side of the imaging element;
And driving means for retracting the mirror from the front of the imaging device before the start of traveling of the shutter.
It said detecting means, and executes the second flicker detection if it can complete the detection of the pre-Kita timing before starting an operation for retracting the mirror from the front of the imaging device The imaging device according to claim 6 . A diaphragm for controlling the incidence of light on the imaging device;
8. The image pickup device according to claim 7 , further comprising correction means for correcting an output from said image pickup means used for detection of flicker by said detection means in accordance with driving of said diaphragm performed immediately before said main exposure. apparatus. The detection unit is configured to detect the first flicker based on a plurality of outputs by accumulation and readout of charges using the imaging unit at frequencies of common multiples of a plurality of power supply frequencies of the flicker light source expected to be generated. Perform 2 flicker detection,
  The imaging apparatus according to any one of claims 1 to 8, wherein the first number and the second number correspond to integer multiples of the flicker cycle. A control method of an image pickup apparatus comprising an image pickup means, comprising:
It has a detection step of detecting flicker based on a plurality of outputs by accumulation and readout of a plurality of times of charge using the imaging means,
In the detecting step, a first flicker detection is performed to detect a timing at which the flicker cycle and the light amount of the flicker become a predetermined value based on a plurality of outputs by accumulation and readout of the first number of charges using the imaging unit. And second detecting a timing at which the light amount of the flicker becomes a predetermined value based on a plurality of outputs by accumulation and readout of a second number of charges smaller than the first number using the imaging means. Flicker detection, and when flicker is detected by the first flicker detection, a period from an imaging instruction of a main exposure for imaging a subject to an exposure start according to the imaging instruction And controlling the second flicker detection at a timing overlapping with the control signal.