JP2016039579A - Imaging apparatus, control method, program, and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a good image even when photographing under a light source in which flicker occurs.
An imaging unit, a photometric unit, a setting unit that sets an exposure time of the imaging unit, and a calculating unit that calculates a light quantity change characteristic of light from a subject based on a plurality of photometric results of the photometric unit Control means for controlling the timing of exposure by the imaging means based on the light quantity change characteristic calculated by the calculation means, and the calculation means is based on the exposure time set by the setting means. Thus, the frequency of calculating the light amount change characteristic when performing continuous shooting is changed.
[Selection] Figure 2

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, in the technique described in Patent Document 1, each imaging timing of a plurality of continuous images is adjusted based on the phase of the maximum value of the amount of illumination light detected before the start of continuous imaging of the plurality of images. The following problems occur.

  In general, it is known that the commercial power supply frequency fluctuates about ± 0,2 Hz with respect to the reference frequency. That is, the flicker cycle of the flicker light source fluctuates about ± 0,4 Hz with respect to the reference flicker cycle. For this reason, if the elapsed time after flicker detection becomes longer, the peak timing of the light amount of the flicker light source obtained from the detection result of the flicker tends to be shifted from the peak timing of the light amount of the actual flicker light source.

  Therefore, in the technique described in Patent Document 1, the later the imaging in the continuous imaging, the more easily the peak timing obtained from the detection result is shifted from the actual peak timing, and it is difficult to suppress the influence of flicker.

  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 unit, a photometric unit, a setting unit that sets an exposure time of the imaging unit, and a subject based on a plurality of photometric results of the photometric unit. Calculation means for calculating the light quantity change characteristic of the light, and control means for controlling the timing of performing exposure by the imaging means based on the light quantity change characteristic calculated by the calculation means. The frequency of calculating the light quantity change characteristic when performing continuous shooting is changed based on the exposure time set by the setting means.

  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 flowchart figure which shows the operation | movement for performing imaging | photography which reduced the influence of the flicker of the imaging device which concerns on embodiment of this invention. It is a figure which shows the accumulation | storage timing of the electric charge for flicker detection, and the read-out timing of an image signal. It is a figure which shows the relationship between the number of vertical pixel additions, and reading time. It is a figure explaining an example of the method of calculating the timing of the peak of the light quantity of a flicker light source. It is a figure which shows the relationship between the light quantity change of a flicker light source, and the generation timing of a flicker synchronizing signal and a shutter start signal. It is a figure which shows the table which linked | related the value of T_ShutterWait and the value of shutter speed. It is a figure which shows the operation | movement sequence of the photometry sensor 108 and ICPU112 between the frames of continuous imaging | photography. It is a figure which shows the timing calculation of the feature point of the flicker under the flicker light source of commercial power supply 50Hz. It is a figure which shows the timing calculation of the feature point of the flicker under the flicker light source of commercial power supply 60Hz.

  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.

  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 subject satisfy a predetermined condition based on the output signal (image signal) from the photometric sensor 108 (for example, the timing at which the amount of light becomes maximum and the amount of light is minimized). The light quantity change characteristic such as (timing) is calculated. 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, an operation for performing photographing with reduced influence of flicker will be described with reference to FIG. FIG. 2 is a flowchart illustrating an operation for performing imaging with reduced influence of flicker of the imaging apparatus according to the present embodiment.

  When the power of the camera body 100 is turned on by the user's operation on the power switch, a photometric operation is performed in step S101. In the photometric operation, charge is accumulated and the image signal is read by the photometric sensor 108, and the ICPU 112 performs a calculation related to photometry (hereinafter referred to as photometric calculation) based on the obtained image signal to obtain a photometric value.

  Note that this photometric operation is performed when the accumulation time of the photometric sensor 108 is set to be approximately an integral multiple of the flicker cycle so that the photometric value does not vary due to the change in the light amount of the flicker light source even under a flicker light source. Good. Here, the frequency at which the light amount of the flicker light source changes (hereinafter referred to as the flicker frequency) is twice the commercial power supply frequency. Therefore, in the region where the commercial power supply frequency is 50 Hz, the flicker frequency is 100 Hz. 10 ms. Similarly, in an area where the commercial power supply frequency is 60 Hz, the flicker frequency is 120 Hz and the light quantity change period is 8,33 ms.

  In order to deal with these two types of flicker frequencies, the accumulation time of the photometric sensor 108 is set to a time substantially equal to the average value of 10 ms and 8,33 ms, for example, 9 ms. Then, regardless of whether the commercial power supply frequency is 50 Hz or 60 Hz, the accumulation time of the photometric sensor 108 is substantially equal to one cycle of the light amount change of the flicker light source, and a stable photometric value can be obtained even under the flicker light source.

  Further, based on the obtained photometric value, the camera microcomputer 101 sets an aperture value Av, which is an exposure control value, a shutter speed (exposure time) Tv, and an ISO sensitivity (photographing sensitivity) Sv. In determining Av, Tv, and Sv, the camera microcomputer 101 determines the program using a program diagram stored in advance in the memory 102.

  Next, in step S102, as shown in FIG. 3, the photometric sensor 108 accumulates a plurality of charges for flicker detection and reads out an image signal. FIG. 3 is a diagram showing the charge accumulation timing for flicker detection and the image signal readout timing. Accumulation / readout is continuously performed 12 times at a cycle of 600 fps and about 1,667 ms. This 600 fps is a value equal to the least common multiple of the flicker frequencies (100 Hz and 120 Hz) assumed in advance. In addition, by accumulating 12 times at 600 fps, the accumulation is performed in a period of 20 ms as a whole, and the light quantity change of the flicker light source is included in two cycles regardless of whether the commercial power supply frequency is 50 Hz or 60 Hz. become.

  Here, a method for driving the photometric sensor 108 at 600 fps (cycle of 1,667 ms) will be described.

  In this embodiment, based on the image signal output from the photometry sensor 108, not only photometry but also subject face detection, subject tracking, flicker detection, and the like are performed. In order to accurately detect the face of the subject, the number of pixels of the photometric sensor 108 needs to be a certain number, for example, the number of pixels equivalent to QVGA. In order to read out all pixel signals of an image sensor having a number of pixels that can accurately detect the face of the subject at a frame rate of 600 fps or more, the circuit configuration becomes complicated and the cost increases.

  Therefore, the frame rate is set to 600 fps (cycle of 1,667 ms) by reading out all pixel signals for the image signal for detecting the face of the subject and performing pixel addition reading and thinning-out reading for the image signal for detecting flicker. Adjust to.

  In the case of using a CCD for the photometric sensor 108, it is preferable to shorten the readout time by artificially reducing the number of readout lines by pixel addition readout by adding and reading out pixel signals. For example, by performing vertical pixel addition with a CCD having a stripe arrangement, there is an effect of shortening the readout time as shown in FIG. FIG. 4 is a diagram showing the relationship between the number of vertical pixel additions and the readout time. A CCD in which the readout time is 6,25 ms when all pixel signals are read out without adding pixel signals (the number of vertical pixel additions is 1). Will be described as an example. In the case of a CCD having the characteristics shown in FIG. 4, by adding nine pixels, the readout time is 1,66 ms, and the frame rate can be about 600 fps. The image signal read out at this time has 1/9 the number of pixels in the vertical direction as compared with the image signal read out without adding the pixel signals. However, in flicker detection, the photometric values between the image signals are compared. Therefore, there is no problem even if the image signal has a reduced number of pixels in the vertical direction.

  In the case where a CMOS is used for the photometric sensor 108, it is preferable to adjust so that the total time of accumulation and readout becomes a period of about 1,667 ms by so-called thinning readout in which horizontal lines for reading out pixel signals are limited.

  This completes the description of the method for driving the photometric sensor at about 600 fps (about 1,667 ms cycle).

  When the accumulation of the charge for flicker detection and the reading of the image signal are finished in step S102, the ICPU 112 performs a flicker detection calculation based on the read image signal in step S103.

  FIG. 3A shows changes in charge accumulation timing, image signal readout timing, and photometric value when the commercial power supply frequency is 50 Hz. The n-th accumulation is “accumulation n”, the readout of the accumulation n is “read n”, and the photometric value obtained from the result of the readout n is “AE (n)”. Note that although one photometric value is obtained by each accumulation, the light quantity of the flicker light source is not constant during the accumulation period. Therefore, the photometric value obtained by each accumulation is regarded as a value corresponding to the light amount of the flicker light source at the central point in each accumulation period.

  When the commercial power supply frequency is 50 Hz, the light amount change period of the flicker light source is about 10 ms and 10 ÷ 1,667≈6. Therefore, as shown in FIG. Accumulation is performed at substantially the same timing. That is, the relationship of AE (n) ≈AE (n + 6) is established.

  Similarly, when the commercial power supply frequency is 60 Hz, the light amount change period of the flicker light source is about 8,33 ms and is 8,33 ÷ 1,667≈5. Therefore, as shown in FIG. Accumulation is performed at a timing when the amount of light of the flicker light source is approximately equal in period. That is, AE (n) ≈AE (n + 5).

  On the other hand, AE (n) is substantially constant regardless of n if the light source has no change in light quantity. Therefore, an evaluation value is calculated using the following equations (1) and (2) based on a plurality of photometric values obtained by accumulation for flicker detection.

  Flicker is obtained by comparing the evaluation value F50 and the evaluation value F60 with a predetermined threshold value F_th, with the evaluation value calculated using the equation (1) as F50 and the evaluation value calculated using the equation (2) as F60. Perform detection. Specifically, in the case of F50 <F_th and F60 <F_th, it can be said that all of a plurality of photometric values obtained by accumulating for flicker detection are substantially equal, and therefore it is determined that no flicker occurs. In the case of F50 <F_th and F60 ≧ F_th, a plurality of photometric values obtained by accumulating for flicker detection are substantially equal in six cycles and not substantially equal in five cycles. It can be said. Therefore, it is determined that a flicker with a light quantity change period of 10 ms is generated (under a flicker light source with a commercial power supply frequency of 50 Hz).

  In the case of F50 ≧ F_th and F60 <F_th, a plurality of photometric values obtained by accumulating for flicker detection are substantially equal in five cycles and are not substantially equal in six cycles. It can be said. Therefore, it is determined that a flicker with a light amount change period of 8,33 ms is generated (under a flicker light source with a commercial power supply frequency of 60 Hz).

  It should be noted that the photometric value may change greatly to satisfy F50 ≧ F_th and F60 ≧ F_th when panning or other imaging device movement or subject movement occurs during flicker detection accumulation. Conceivable. In that case, flicker detection is performed by comparing F50 and F60.

  Specifically, when F50 ≧ F_th, F60 ≧ F_th, and F50 ≦ F60, it is determined that a flicker with a light quantity change period of 10 ms occurs (under a flicker light source with a commercial power supply frequency of 50 Hz). On the other hand, when F50 ≧ F_th, F60 ≧ F_th, and F50> F60, it is determined that a flicker with a light quantity change period of 8,33 ms is generated (under a flicker light source with a commercial power supply frequency of 60 Hz). Note that when F50 ≧ F_th, F60 ≧ F_th, and F50 = F60, the light amount change period of the flicker light source cannot be determined, and therefore it may be determined that no flicker occurs or flicker cannot be detected.

  In addition, when F50 ≧ F_th and F60 ≧ F_th, the light amount change period of the flicker light source is determined. However, when F50 ≧ F_th and F60 ≧ F_th, the flicker detection accuracy is low, so the flicker detection accumulation is performed again. May be.

  Further, in step S103, the ICPU 112 obtains the timing of the flicker feature point when the light source is under the flicker light source. FIG. 5 is a diagram for explaining an example of a method for calculating the peak timing of the light quantity of the flicker light source, which is an example of the timing of the flicker feature point.

  The point where the maximum value is obtained among AE (1) to AE (12) is P2 (t (m), AE (m)), and the point of the previous photometric result is P1 (t (m-1). ), AE (m−1)), and the point of the next photometric result is P3 (t (m + 1), AE (m + 1)). Then, a straight line passing through two points AE (m−1) and AE (m + 1) (P1 in the example of FIG. 5) and point P2 is obtained as L1 = at + b, and the larger of AE1 and AE3 is determined. It passes through the point (P3 in the example of FIG. 5), and the straight line with the inclination −a is L2. When the intersection of L1 and L2 is obtained, the peak timing t_peak when the accumulation start time for flicker detection is set to 0 ms and the peak photometric value AE_peak corresponding to the light quantity at the peak can be calculated.

  In FIG. 5, as an example of a method for calculating the timing of the flicker feature point, the method for calculating the timing at which the light amount becomes the maximum (peak) in the change in the amount of flicker light is described, but the light amount is the minimum (bottom). You may calculate the timing which becomes.

  In step S104, the camera microcomputer 101 generates a flicker synchronization signal from the flicker frequency obtained in step S103 and the light amount change timing. As shown in FIG. 6, the flicker synchronization signal is a signal that is generated every cycle of the light amount change of the flicker light source and synchronized with a predetermined timing of the light amount change of the flicker light source. FIG. 6 is a diagram showing the relationship between the change in the amount of light of the flicker light source and the generation timing of the flicker synchronization signal and the shutter start signal.

  In FIG. 6, a time lag from the shutter start signal until the shutter 104 actually travels and starts to expose the first line of the imaging region of the image sensor 103 is defined as T_ShutterResponse. In addition, the time T_Run from the start of exposure of the first line in the imaging region of the image sensor 103 to the start of exposure of the last line is defined as T_Run. Note that when the exposure of all the imaging regions of the imaging element 103 is started simultaneously, T_Run = 0 may be set.

The flicker synchronization signal generation timing t_Flicker is expressed by the following expression (3) when the accumulation start time for flicker detection is set to 0 ms.
t_Flicker = t_peak−T_ShutterResponse− (T_Run + TVmax) / 2 + T × n (3)

  Here, the light quantity change period T of the flicker light source and the peak timing t_peak when the flicker detection accumulation start time is set to 0 ms are calculated in step S103. n is a natural number, and TVmax is a shutter speed that is a threshold value for determining whether or not to perform shutter control to reduce the influence of flicker, and is set in advance.

  When the shutter speed is slower than 1/100 second, exposure is performed in a period of one cycle or more of the light amount change period of the flicker light source, so that the influence of flicker is reduced. Even if the exposure period is less than one period of the light quantity change period of the flicker light source, if the exposure period is close to one period of the light quantity change period of the flicker light source, the effect of flicker is relatively high. It is thought that there are few. Therefore, in this embodiment, when the shutter speed is faster than 8 ms, shutter control for reducing the influence of flicker is performed, and TVmax = 1/125 (seconds).

Further, the camera microcomputer 101 sets T_ShutterWait, which is a wait time from the flicker synchronization signal to the shutter start signal instructing the start of running of the shutter 104. The camera microcomputer 101 changes T_ShutterWait for each shutter speed, and the timing at which the light quantity change of the flicker light source is small comes to the center of the time from the start of exposure of the first line in the imaging region of the image sensor 103 to the end of exposure of the last line. To control. For example, T_ShutterWait is set as shown in Expression (4).
T_ShutterWait = (TVmax−TV) / 2 (4)
(However, TV <1/125)

  By setting T_ShutterWait as described above, control is performed so that the peak timing of the light amount of the flicker light source is at the center of the time from the start of exposure of the first line to the end of exposure of the last line in the imaging region of the image sensor 103. it can. FIG. 7 is a view showing a table in which the value of T_ShutterWait and the value of the shutter speed are associated with each other, and the table shown in FIG. 7 may be stored in the memory 102 or the like in advance.

  As described above, the example in which the timing of the peak of the light amount of the flicker light source is calculated in step S103 and the generation timing of the flicker synchronization signal is set based on the timing of the peak of the light amount of the flicker light source has been described. However, when the bottom timing of the light amount of the flicker light source is calculated in step S103, the generation timing of the flicker synchronization signal may be set based on the bottom timing of the light amount of the flicker light source.

  Thereafter, in step S105, the camera microcomputer 101 determines whether or not the switch SW2 for instructing the user to start the shooting operation is turned on by operating the release button. If the switch SW2 is not turned on, the process returns to step S101, and the series of operations in steps S101 to S104 is repeated to update the flicker light source light quantity change period and the flicker light source peak timing to the latest. To go. If the series of operations in steps S101 to S104 are repeated with a cycle of about 100 ms, for example, even if the fluctuation of the light amount change cycle of the flicker light source is about ± 0, 4 Hz, the deviation of the light amount change cycle within 100 ms is a maximum of ± It is about 0.4ms. Therefore, it is possible to perform shutter control that accurately reduces the influence of flicker, regardless of when the switch SW2 is turned on.

  Instead of repeating the operations in steps S101 to S104 in the same way, the photometric operation performed in step S101 and the flicker detection operation performed in steps S102 to S104 may be performed at different periods. As described above, a period of about 100 ms is sufficient for the flicker detection operation. However, in order to improve the responsiveness to a change in luminance of the subject, the photometry operation is performed with a period shorter than the period of the flicker detection operation, for example, about 50 ms. You may make it perform.

  If the switch SW2 is ON, the process proceeds to step S106. In step S106, the camera microcomputer 101 generates a shutter start signal by delaying the first flicker synchronization signal after SW2 is turned on by T_ShutterWait according to the determined shutter speed. Thereafter, the shutter 104 is driven according to the generated shutter start signal, and photographing is performed.

  As described above, as shutter control for reducing the influence of flicker, the shutter start signal is delayed by T_ShutterWait according to the shutter speed with respect to the flicker synchronization signal. Therefore, as shown in FIG. 6, even when the shutter speed is 1/1000 second or 1/200 second, the peak timing of the light amount of the flicker light source is from the start of exposure of the first line of the imaging region of the image sensor 103. It comes to the center of the time until the end of the exposure of the last line. In this way, by controlling the shooting timing based on the timing of the flicker feature points, it is possible to reduce exposure unevenness in one image due to the influence of the flicker. When shooting is completed, the camera microcomputer 101 determines in step S107 whether continuous shooting (continuous shooting) is performed. Whether or not continuous shooting is performed may be determined based on whether or not the state where SW2 is ON is maintained, or based on whether or not the continuous shooting mode is selected as the operation mode. You may judge.

  When continuous shooting is not performed, the process returns to S101, and when continuous shooting is performed, the process proceeds to step S108.

  In step S108, the camera microcomputer 101 determines the presence or absence of flicker (whether the amount of light from the subject is periodically changing). Here, the determination result in step S103 may be used. If there is no flicker, the process proceeds to step S115 and the first inter-frame sequence is performed. If there is flicker, the process proceeds to step S109.

  In step S109, the camera microcomputer 101 determines whether the shutter speed is faster than a predetermined value (exposure time is shorter than the predetermined value). In this embodiment, in order to fix the exposure condition at the time of continuous shooting to the exposure condition of the first frame, in step S109, the shutter speed determined in step S101 is compared with a predetermined value. If the exposure condition during continuous shooting is set for each frame, for example, the same photometry operation as in step S101 is performed after step S107, and the shutter speed set based on the obtained photometry value and a predetermined value are set. Compare with the above.

  When the shutter speed is faster than a predetermined value, it is difficult to suppress the influence of flicker if the exposure timing and the peak timing of the light amount of the flicker light source are shifted. Therefore, when the shutter speed is faster than the predetermined value, the process proceeds to step S110 and the second inter-frame sequence is performed.

  If the shutter speed is not faster than the predetermined value, even if the exposure timing deviates from the peak timing of the light amount of the flicker light source, the effect of flicker is small and the process proceeds to step S111. In step S111, the camera microcomputer 101 sets a detection cycle Tf that is a cycle for performing flicker detection. It should be noted that the setting of the detection cycle Tf may be executed only when the process proceeds to step S111 for the first time in a series of continuous shooting, and the process of step S111 may be omitted thereafter.

  In step S112, the camera microcomputer 101 determines whether the current time matches the detection cycle Tf. The detection period Tf in steps S111 and S112 does not indicate the time interval for performing flicker detection, but indicates the frequency at which flicker detection is performed with respect to the number of shootings, for example, once every 10 times. If the detection cycle Tf = 10, it is determined in step S112 immediately before performing the 10th frame of continuous shooting that the current time matches the detection cycle Tf. If the detection cycle Tf = 10, it is determined that the current time matches the detection cycle Tf in step S112 immediately before the 10 × n frame (n is a natural number) is shot.

  If they match, the process proceeds to S113 and the second inter-frame sequence is performed. If they do not match, the process proceeds to Step S114 and the first inter-frame sequence is performed.

  Here, the first inter-frame sequence and the second inter-frame sequence will be described with reference to FIG. 8A and 8B are diagrams showing the operation sequence of the photometric sensor 108 and the ICPU 112 between the frames for continuous shooting. FIG. 8A shows the first inter-frame sequence, and FIG. 8B shows the second inter-frame sequence. Each is shown.

  First, the operation sequence of the photometric sensor 108 and the ICPU 112 in the first inter-frame sequence will be described with reference to FIG.

  The half mirror 105 that has been in the mirror-up state to guide the light beam to the image sensor 103 at the time of shooting moves to the mirror-down state to guide the light beam to the photometric sensor 108 after shooting. Immediately after moving from the mirror-up state to the mirror-down state, the half mirror 105 bounces (hereinafter referred to as a mirror bounce) due to an impact associated with the movement stop. When the mirror bounds converge and the half mirror 105 is in a stable mirror-down state, the photometric sensor 108 accumulates charges (hereinafter referred to as AE and tracking accumulation) and an image for obtaining an image signal used for photometry and subject tracking. Read the signal. The readout of the image signal accompanying the AE and tracking accumulation is preferably short in order to increase the frame speed (continuous shooting speed) of continuous shooting. Therefore, when the CCD is used for the photometric sensor 108, the above-described pixel addition reading is performed, and when the CMOS is used, the above-described thinning-out reading is performed. Then, the ICPU 112 performs calculation related to subject tracking (hereinafter referred to as tracking calculation) and photometry calculation based on the obtained image signal.

  The photometric sensor 108 accumulates electric charges (hereinafter referred to as accumulation for face detection) and reads out the image signal for obtaining an image signal used for detecting the face of the subject after reading out the image signal associated with AE and tracking accumulation. In order to perform face detection with high accuracy, the readout of the image signal accompanying the face detection accumulation is performed by setting the pixel addition number of the pixel addition readout and the number of thinned lines for the thinning readout rather than the readout of the image signal accompanying the accumulation for AE and tracking. Reduce. In the present embodiment, all pixel readout is performed without performing pixel addition readout or thinning readout. Then, the ICPU 112 performs a calculation related to the face detection of the subject (hereinafter referred to as a face detection calculation) based on the obtained image signal. The result of the face detection calculation is used for the following tracking calculation and photometry calculation. For example, the tracking calculation is performed using the face area of the subject detected by the face detection calculation as a tracking target, or the photometric calculation is performed by increasing the weight of the face area of the subject detected by the face detection calculation.

  Here, in order to increase the frame speed (continuous shooting speed) of continuous shooting, the face detection accumulation is preferably performed in parallel with the tracking calculation and the photometry calculation by the ICPU 112. In addition, since the image signal reading accompanying the face detection accumulation may be performed in a state where the light beam is not guided to the photometric sensor 108, a half mirror is used in order to increase the frame speed (continuous shooting speed) of continuous shooting. This is preferably performed while moving 105 to the mirror-up state.

  When the mirror bound after movement converges and the half mirror 105 is in a stable mirror-up state, the next photographing (exposure) is performed.

  That is, in the first inter-frame sequence, accumulation of charges for flicker detection and reading of image signals (hereinafter referred to as flicker detection accumulation / reading) are not performed between shootings, and flicker is not newly detected. , Flicker feature point timing is not calculated.

  Next, the operation sequence of the photometric sensor 108 and the ICPU 112 in the second inter-frame sequence will be described with reference to FIG.

  When the mirror bound converges and the half mirror 105 is in a stable mirror-down state, the photometric sensor 108 accumulates charges for flicker detection and reads out image signals (hereinafter referred to as flicker detection accumulation / readout). The flicker detection accumulation / reading is performed by a method similar to the method described in step S102 in FIG.

  Note that it is unlikely that the light source changes to another light source having a different flicker frequency during continuous shooting, and the frequency serving as a reference for the flicker frequency during continuous shooting may be considered constant. Therefore, the number of times of accumulation of charges for flicker detection may be less than the number of times performed in step S102 of FIG. 2 as long as the peak timing of the light amount of the flicker light source can be calculated. For example, the calculation of the peak timing of the light amount of the flicker light source only needs to have an accumulation count corresponding to at least one cycle of the light amount change period of the flicker light source. If the flicker light amount change period is about 8,33 ms, the peak timing of the light amount of the flicker light source can be accurately calculated by accumulating 5 times or more, and about 10 ms if accumulating. As described above, in the second inter-frame sequence, by performing simple flicker detection accumulation for calculating the timing of the peak of the light quantity of the flicker light source, the frame speed (continuous shooting speed) for continuous shooting is reduced. Can be suppressed.

  Then, the ICPU 112 performs flicker detection calculation based on the obtained image signal. This flicker detection calculation is performed by the same method as described in step S103 of FIG. As described above, the reference frequency of the flicker frequency during continuous shooting may be considered to be constant. Therefore, here, the peak timing of the light amount of the flicker light source is determined without determining the light amount change period of the flicker light source. You may calculate only. At this time, the timing of the flicker feature point represented by the latest detection result among the detection results is calculated.

  After the end of the flicker detection calculation, the camera microcomputer 101 updates the flicker synchronization signal to the latest one based on the detection result of the flicker detection calculation. That is, the shooting timing is controlled based on the latest flicker feature point timing calculated after the previous shooting.

  When the flicker detection accumulation / readout is completed, the photometric sensor 108 performs AE, tracking accumulation, and image signal readout. Here, in order to increase the frame speed (continuous shooting speed) for continuous shooting, the AE and tracking accumulation are preferably performed in parallel with the flicker detection calculation by the ICPU 112.

  The subsequent face detection accumulation and various calculations are the same as when there is no flicker described with reference to FIG.

  After the photometry calculation is completed, the camera microcomputer 101 generates a shutter start signal by delaying the latest flicker synchronization signal by T_ShutterWait according to the shutter speed determined based on the latest photometry calculation result. Take a picture.

  The details of the timing calculation of the flicker feature points will be described below with reference to FIGS. FIG. 9 is a diagram showing the timing calculation of the characteristic points of the flicker under the flicker light source of the commercial power supply 50 Hz. 9A shows the case where the flicker detection accumulation is started at the bottom timing of the light amount of the flicker light source, and FIG. 9B shows the flicker detection accumulation started at the peak timing of the light amount of the flicker light source. Shows the case. FIG. 10 is a diagram showing the timing calculation of the flicker feature point under the flicker light source of commercial power supply 60 Hz. 10A, when flicker detection accumulation starts at the bottom timing of the light amount of the flicker light source, FIG. 10B starts flicker detection accumulation at the peak timing of the light amount of the flicker light source. Shows the case.

  Since the light quantity change period of the flicker light source at commercial power supply 50 Hz is about 10 ms, as shown in FIG. 9A, when flicker detection accumulation is started at the bottom timing of the light quantity of the flicker light source, accumulation 1 to 6 is performed. The photometric values before and after the peak can be obtained. In this case, the timing of the peak of the light amount of the flicker light source is calculated by the same method as described in S103. That is, when the output signal that has the maximum value among the plurality of output signals is not the output signal that is obtained first or last, the output signal that is the maximum value and the output signal that is obtained before and after the output signal that is the maximum value Based on this, the timing at which the light quantity becomes maximum in the flicker light quantity change is calculated.

  However, when accumulation for flicker detection is started at the timing of the peak of the light amount of the flicker light source, AE (1) and AE (6) in AE (1) to AE (6) have the maximum photometric value AE (max). (In the case of FIG. 9B, AE (1) is AE (max)). In such a case, since there is no photometric value before or after the peak, the method described in S103 cannot calculate the peak timing of the light amount of the flicker light source.

  Therefore, first, the minimum photometric value AE (min) among AE (1) to AE (6) is calculated. In the case of FIG. 9B, AE (4) = AE (min). After calculating AE (min), 6 is added to the index of the photometric values (AE (1) to AE (3) in FIG. 9B) obtained before that point, and AE (7) to AE (9 ). In the case of FIG. 9B, the output signal having the maximum value among the plurality of output signals is the output signal obtained at the beginning of the plurality of output signals. In such a case, an output signal that is the maximum value, an output signal that is obtained immediately after the output signal that is the maximum value, and an output signal that is obtained after a time corresponding to the flicker cycle from the output signal that is the maximum value. Based on this, the timing at which the light quantity becomes the maximum in the light quantity change of the flicker is calculated. Assuming that the light quantity change period of the flicker light source is substantially constant, it is considered that AE (1) to AE (3) are substantially equal to the photometric values AE (7) to AE (9) after each one period. Therefore, even if AE (1) to AE (3) are substituted for AE (7) to AE (9), the influence on the calculation result is small. By doing so, even in the case as shown in FIG. 9B, the peak of the light amount of the flicker light source can be obtained from the photometric values before and after the maximum photometric value AE (max) by the method described in S103. Timing can be calculated.

  As in the case similar to FIG. 9B, the output signal having the maximum value among the plurality of output signals may be the output signal obtained at the end of the plurality of output signals. In such a case, the output signal obtained immediately before the output signal that becomes the maximum value, the output signal that becomes the maximum value, the output signal that is obtained only by the time corresponding to the flicker cycle before the output signal that becomes the maximum value, Based on the above, the timing at which the light quantity becomes maximum during the flicker light quantity change is calculated.

  Further, the timing of the peak of the light amount of the flicker light source can be calculated by using the same method even under a flicker light source with a commercial power supply of 60 Hz.

  As shown in FIG. 10A, when the maximum photometric value is AE (3) and the photometric values before and after the peak can be obtained with the accumulations 1 to 6, the flicker light source of the flicker light source can be obtained by the same method as described in S103. What is necessary is just to calculate the peak timing of the light quantity. On the other hand, as shown in FIG. 10 (b), when the maximum photometric value is AE (1) and accumulation 1-6 cannot be obtained before and after the peak, the flicker light source is obtained by the same method as 9 (b). What is necessary is just to calculate the timing of the peak of the light quantity.

  The same concept may be used when calculating the bottom timing of the light amount of the flicker light source. That is, the maximum value and the minimum value in the description of FIGS. 9 and 10 may be replaced.

  After performing the first inter-frame sequence or the second inter-frame sequence as described above, in step S116, the camera microcomputer 101 performs photographing at the exposure timing set based on the latest flicker synchronization signal. When shooting is completed, the camera microcomputer 101 determines in step S117 whether continuous shooting (continuous shooting) is continued. Whether or not continuous shooting is continued may be determined based on whether or not the state in which SW2 is turned on is maintained.

  When the continuous shooting is continued, the process proceeds to step S108, and when the continuous shooting is not performed, this flow is finished.

  As described above, the timing of the peak of the light amount of the flicker light source can be accurately calculated even if the number of times is less than the number of times of accumulation for flicker detection. For this reason, during continuous shooting, frames for continuous shooting are calculated by performing accumulation for calculating the timing of the peak of the light amount of the flicker light source with a smaller number of times than the number of accumulations for flicker detection. A good image can be taken while suppressing a decrease in speed.

  Also, by changing the execution frequency of the flicker detection operation according to the shutter speed, even if the exposure timing and the peak timing of the light amount of the flicker light source are deviated, the effect of flicker is small, so that the decrease in the frame speed can be suppressed. it can.

  It should be noted that control is performed to switch between performing the first inter-frame sequence or performing the second inter-frame sequence according to the shutter speed only when a specific mode is set according to the operation of the operation unit 114 by the user. You may make it perform.

  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.

  For example, in the above embodiment, the ICPU 112 performs photometry or light amount change characteristic calculation of light from the subject based on the output signal (image signal) from the photometry sensor 108. However, the photometry sensor and light amount change characteristic calculation are performed. May be provided separately.

  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.

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

Claims (9)

Imaging means;
Photometric means;
Setting means for setting an exposure time of the imaging means;
Calculating means for calculating a light quantity change characteristic of light from the subject based on a plurality of photometric results of the photometric means;
Control means for controlling the timing of performing exposure by the imaging means based on the light amount change characteristic calculated by the calculating means,
The imaging device is characterized in that, based on the exposure time set by the setting unit, the frequency of calculating the light quantity change characteristic when performing continuous shooting is changed.   The calculating means calculates the light quantity change characteristic before performing continuous shooting, and determines that the light quantity of the light from the subject is changing periodically, the exposure time set by the setting means The imaging apparatus according to claim 1, wherein the frequency of calculating the light quantity change characteristic is changed based on continuous shooting.   3. The imaging apparatus according to claim 2, wherein the calculation unit calculates the light quantity change characteristic between the continuous shootings when the exposure time set by the setting unit is shorter than a predetermined value. .   The calculation means calculates the light amount change characteristic before performing continuous shooting, and determines that the light amount of light from the subject does not change periodically, the light amount between consecutive shootings The imaging apparatus according to claim 2, wherein the change characteristic is not calculated.   5. The control unit according to claim 1, wherein the control unit controls a timing at which the imaging unit performs exposure based on the latest light amount change characteristic calculated by the calculation unit. 6. Imaging device.   The calculation means calculates a light amount change period of the light from the subject and a timing at which the light from the subject satisfies a predetermined condition before performing continuous shooting, and light from the subject is transmitted during the continuous shooting. 6. The imaging apparatus according to claim 1, wherein a timing satisfying the condition is calculated. An image pickup apparatus control method comprising an image pickup means and a photometry means,
A setting step for setting an exposure time of the imaging means;
A calculation step of calculating a light amount change characteristic of light from the subject based on a plurality of photometric results of the photometric means;
A control step for controlling the timing of performing exposure by the imaging means based on the light amount change characteristic calculated by the calculation step;
The method of controlling an imaging apparatus, wherein the calculating step changes the frequency of calculating the light quantity change characteristic when performing continuous shooting based on the exposure time set in the setting step.   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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