Imaging apparatus, control method thereof, and program

Abstract

To provide an imaging apparatus, a control method thereof, and a program, capable of reducing an influence of a flicker while maintaining a degree of freedom of imaging.SOLUTION: An imaging apparatus 100 having an imaging element 103 for imaging a subject image formed via an optical system, comprises: a flicker detection part 112 that detects a frequency and a phase of a flicker; a comparison part (S304) that compares a curtain speed that is a time when a shutter travels from an upper part to a lower part of the imaging element 103 with a flicker period time as a time of one period of the flicker; and imaging control parts (S305 and S306) that image a subject by performing control of an imaging accumulation time in the case where the curtain speed is longer than the flicker period time, and image the subject by performing control of imaging timing on the basis of the frequency and the phase of the flicker detected in the case where the curtain speed is shorter than or is equivalent to the flicker period time.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an imaging apparatus capable of reducing the effect of flicker, and a control method and program therefor. [Background technology]

[0002] When capturing still images, videos, etc. under a flickering light source, the effects of the flicker may appear in the image as uneven brightness or stripes. Various methods for reducing the effects of this flicker are well known. For example, Patent Document 1 discloses a technique for reducing uneven brightness and stripes by capturing an image with an accumulation time of "(n / (detection frequency (Hz))" (seconds) for the period of the detected flicker. Patent Document 2 discloses a technique for capturing an image at a timing that is less susceptible to the effects of flicker, based on the period and phase of the detected flicker. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-42352 A [Patent Document 2] JP 2016-152537 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, according to the method disclosed in Patent Document 1, although the effect of flicker is certainly reduced, the accumulation time used for imaging is limited. This causes problems such as a decrease in the degree of freedom of imaging. Also, according to the method disclosed in Patent Document 2, although imaging is possible with any accumulation time regardless of the frequency of the flicker, it is necessary as a prerequisite that the curtain speed of the shutter used for imaging is faster than the time of one cycle of the detected flicker.

[0005] In recent years, the causes of flicker are not only due to the "50 / 60 (Hz)" power supply frequency, but also due to light sources that flicker at higher frequencies, such as LED power supplies and liquid crystal panels, and these are on the rise. For this reason, there is also the problem that the prerequisites disclosed in Patent Document 2 are increasingly not met.

[0006] An object of the present invention is to provide an imaging apparatus capable of reducing the influence of flicker while maintaining the degree of freedom in imaging, and a control method and program therefor. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, an imaging apparatus of the present invention is an imaging apparatus having an imaging element which captures an image of a subject formed via an optical system, and is characterized in comprising: a flicker detection unit which detects the frequency and phase of a flicker; a comparison unit which compares a curtain speed, which is the time it takes for a shutter to travel from the top to the bottom of the imaging element, with a flicker cycle time, which is the time for one cycle of the flicker; and an imaging control unit which, when the curtain speed is longer than the flicker cycle time, controls an imaging accumulation time to capture an image of the subject, and, when the curtain speed is shorter than or equal to the flicker cycle time, controls the imaging timing based on the detected flicker frequency and phase to capture an image of the subject.

[0008] In addition, another aspect of the imaging device of the present invention is an imaging device that, in response to a strobe imaging instruction, successively obtains a dimming non-emission image and a dimming emission image before actual imaging, identifies the subject area from the brightness difference between both images, calculates the amount of actual light emission, and enables actual imaging of the subject, and is characterized in having a flicker detection unit that detects the frequency and phase of flicker, and an imaging control unit that, when a time that satisfies a specified condition exists, controls the dimming accumulation time to make that time the accumulation time for dimming, thereby enabling actual imaging, and in other cases, controls the dimming timing based on the frequency and phase of the flicker, thereby enabling actual imaging. Effect of the Invention

[0009] According to the present invention, it is possible to obtain an effect of reducing the influence of flicker while maintaining the degree of freedom in imaging. [Brief description of the drawings]

[0010] [Figure 1] 1 is a block diagram showing an example of the configuration of an imaging device according to an embodiment of the present invention. [Diagram 2] 1A to 1C are diagrams illustrating a method for reducing flicker under a flickering light source and the effect of the reduction method on an image. [Diagram 3] 5 is a flowchart showing a flicker reduction imaging process according to the first embodiment of the present invention. [Figure 4] FIG. 2 is a schematic explanatory diagram of a flow from light control calculation to imaging in strobe imaging. [Diagram 5] FIG. 11 is a schematic explanatory diagram of a storage time constraint of a light control image used during light control calculation. [Figure 6A] 1A and 1B are diagrams illustrating a dimming problem under a flickering light source and a method for reducing flicker. [Figure 6B] 1A and 1B are diagrams illustrating a dimming problem under a flickering light source and a method for reducing flicker. [Figure 7A] 1A and 1B are diagrams illustrating a dimming problem under a flickering light source and a method for reducing flicker. [Figure 7B] 1A and 1B are diagrams illustrating a dimming problem under a flickering light source and a method for reducing flicker. [Figure 8] 11 is a flowchart showing a flicker reduction imaging process during dimming. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the configurations described in the following embodiments are merely examples, and the technical scope of the present invention is not limited to the configurations described in the embodiments. First, a first embodiment of the present invention will be described.

[0012] <Figure 1: Block diagram> FIG. 1 is a block diagram showing an example of the configuration of an imaging device 100 according to an embodiment of the present invention. The imaging device 100 has a lens group 101, an imaging element 103, a signal processing unit 104, a recording processing unit 105, a lens control unit 102, and a camera control unit 107. The camera control unit 107 is connected to an exposure control unit 111, a flicker detection unit 112, a light control calculation unit 113, an operation unit 108, an imaging timing calculation unit 109, an accumulation time calculation unit 110, and a strobe control unit 114. The camera control unit 107 is configured to be able to control each of these connected units and to receive notifications of detection results, calculation results, etc. in each unit. In addition, the strobe control unit 114 controls the blinking of the light emitting unit 115. Note that the recording medium 106 in FIG. 1 is a storage device that records image data from the signal processing unit 104, and is detachable from the imaging device 100.

[0013] <Lens group 101: lens control unit 102: imaging element 103> The lens group 101 has multiple lenses and includes a mechanism for controlling exposure by an "aperture" and a mechanism for performing focusing and zooming operations, and forms an optical image of a subject on the image sensor 103 from incident light. The image sensor 103 converts the light of the formed optical image into an electric signal, and multiple pixels are arranged in a matrix, and conversion to an electric signal is performed for each image. The electric signal converted by the image sensor 103 is output to a signal processing unit 104. The lens control unit 102 performs drive control of the "aperture" included in the lens group 101, and the camera control unit 107 executes control of the accumulation time in the image sensor 103, control of the amplification rate of the electric signal, and the like. This controls the exposure of the captured image, etc.

[0014] <Signal processing unit 104> The signal processing unit 104 performs brightness correction such as gain correction, color correction such as white balance correction, and other signal processing on the obtained electrical signal (image signal), and outputs image data to the recording processing unit 105.

[0015] <Recording processing unit 105: recording medium 106: operation unit 108: camera control unit 107> The recording processing unit 105 records the image signal in a recordable format on a recording medium 106 such as a smart card. The camera control unit 107 functions as a controller that controls the flow of this series of image processing. The camera control unit 107 also has a function of accepting an operation from a user via an operation unit 108, and calculating imaging setting values ​​related to zoom, focus, and brightness of an imaged image according to a set imaging mode and brightness of a subject. The camera control unit 107 notifies the calculated imaging setting values ​​to the lens control unit 102, the exposure control unit 111, and the like, and the lens control unit 102 and the exposure control unit 111 control corresponding control positions, members related to control states, and the like according to the notified imaging setting values. The camera control unit 107 also performs various controls required for the imaging device 100, and is configured to be able to execute required control, required calculation, and other processes by, for example, the CPU expanding a program stored in a recording medium such as a ROM into a RAM and executing it. The required control, required calculation, and other processes include those according to the present invention.

[0016] <Image capture timing calculation unit 109: Storage time calculation unit 110: Flicker detection unit 112:> The flicker detection unit 112 inputs the captured images accumulated by the image sensor 103, and determines and detects the frequency and phase of the flicker from the periodicity of the luminance change of the previous and next images. The imaging timing calculation unit 109 determines the timing to perform imaging according to the frequency and phase of the flicker detected by the flicker detection unit 112, and notifies the camera control unit 107. The camera control unit 107 performs imaging based on the notified timing. The accumulation time calculation unit 110 calculates an accumulation time that is N times (N is a natural number) the frequency of the flicker detected by the flicker detection unit 112, and notifies the camera control unit 107. The camera control unit 107 notifies the exposure control unit 111 of the notified accumulation time, and performs imaging. Note that the "accumulation time" is the charge accumulation time of the image sensor 103, and is also called the "imaging accumulation time" or "imaging accumulation time".

[0017] <Light control calculation unit 113: Strobe control unit 114: Light emission unit 115> The light control calculation unit 113 calculates the "main light emission amount" required for imaging from the difference between an image captured with the light emission unit 115 emitting light and an image captured without emitting light. The main light emission amount is notified to the strobe control unit 114 by the camera control unit 107, and the strobe control unit 114 controls the light emission amount of the light emission unit 115. Note that the imaging timing calculation unit 109, the accumulation time calculation unit 110, the exposure control unit 111, the flicker detection unit 112, and the light control calculation unit 113 may be configured to be included in the camera control unit 107.

[0018] First Embodiment First, the relationship between flicker and "curtain speed" and its effect on imaging results will be described with reference to Fig. 2, and then the process flow of a flicker reduction method according to an embodiment of the present invention will be described with reference to Fig. 3. Note that "curtain speed" is the time it takes for a mechanical shutter to move up and down. In this embodiment, it is the time it takes for the shutter to travel from the top to the bottom of the sensor (image sensor 103).

[0019] (Figure 2: Flicker reduction method and its effect on the image) FIG. 2(A) is an explanatory diagram of detecting the frequency and phase of a flickering light source and controlling to capture an image at a timing that is less susceptible to the effects of flickering. In this case, the "curtain speed," which is the time it takes for the shutter to travel from the top of the sensor (image sensor 103) to the bottom of the sensor, is shorter than one period of the flickering. Therefore, by capturing an image so that the accumulation center of the captured image and the timing when the flickering light source (flicker) are at their brightest coincide with each other, the center of the screen becomes the brightest, and the brightness gradually decreases from the center to the top and bottom of the screen. Therefore, an image with reduced brightness unevenness within the screen can be captured, as shown in FIG. 2(D). The "accumulation center of gravity" is the center of gravity of the captured image, and in the example of FIG. 2, it corresponds to the intersection of the diagonals of the parallelogram that represents the captured image.

[0020] On the other hand, Fig. 2(B) is an explanatory diagram of imaging under a flickering light source with a higher frequency than the light source in Fig. 2(A). The curtain speed is longer than one period of the flicker. For this reason, even if the accumulation center of gravity and the timing of the brightest light source are aligned, an image with uneven brightness and stripes caused by the flicker will be captured, as shown in Fig. 2(E).

[0021] In such a case, as shown in FIG. 2(C), image capturing is performed so that the accumulation time is "(one cycle time of flicker) × N times (N is a natural number)" instead of synchronizing the image capturing timing. This allows electric charges to be accumulated with the same exposure amount for all pixels of the image capturing element 103, so that the effect of flicker can be reduced. Also, in the example of FIG. 2(C), image capturing is performed with the accumulation time being "(one cycle time of flicker) × 1 time", that is, the accumulation time being the same as the flicker. As a result, as shown in FIG. 2(F), it is possible to prevent the occurrence of uneven brightness and stripes due to the effect of flicker.

[0022] <FIG. 3: Flowchart showing flicker reduction imaging processing of the first embodiment> The flow of the above process will be described with reference to the flowchart in Fig. 3. The progress of the series of processes shown in Fig. 3 is controlled by the camera control unit 107. First, when an image capture instruction is received, the process proceeds to step S301, where the presence or absence of flicker and the frequency and phase of the flicker are detected by the flicker detection unit 112. Next, in step S302, if flicker is not detected (No), flicker reduction processing is not required, so the process proceeds to step S307 and image capture is performed.

[0023] On the other hand, if flicker is detected (Yes), the process proceeds to step S303. In S303, the flicker detection unit 112 stores the time of one cycle of the detected flicker for the variable "FLKCycle." Specifically, the time of one cycle of the flicker is stored in a storage device such as a RAM provided inside the flicker detection unit 112, linked to the variable "FLKCycle."

[0024] Next, in step S304, the time of one cycle associated with "FLKCycle" is compared with the "curtain speed" of the shutter used for imaging (comparison unit). If the curtain speed is shorter or equal (Yes), the process proceeds to step S305. Then, in step S305, imaging timing calculation unit 109 calculates and controls imaging timing taking into account the phase of the flicker, and then in step S307, imaging is performed according to an imaging instruction from camera control unit 107. Here, an example of "calculating imaging timing taking into account the phase" is to control so as to align the phase of the rising start point of the flicker waveform with the passing point where the shutter passes over the top of image sensor 103. In this example, specifically, it is to align the time of the rising start point of the flicker waveform with the passing time where the shutter passes over the top of image sensor 103.

[0025] On the other hand, if it is determined in step S304 that the "curtain speed" is longer (No), the process proceeds to step S306, where the accumulation time calculation unit 110 calculates the accumulation time to be used for imaging. The object here is to reduce the detected flicker. Therefore, an accumulation time that is N times the detection frequency (for example, in the case of a 100 (Hz) light source, the time for one cycle of flicker is 10 (msec), so 10, 20, 30 (msec), etc.) is calculated, and imaging is performed in step S307. Then, imaging ends.

[0026] As described above, a shooting method that is effective for reducing flicker can be selected according to the flicker frequency and curtain speed. For example, when shooting under a 100 Hz flicker light source and the curtain speed is "3 (msec)", the condition "one cycle time of flicker ≧ curtain speed" is met. Therefore, the user can shoot an image with a flicker reduction effect at any accumulation time without limiting the accumulation time to "10 × N (msec)".

[0027] Conversely, if the flicker light source has a higher frequency of 1000 (Hz) compared to a curtain speed of "3 (msec)", the condition "one cycle time of flicker ≧ curtain speed" is not met. Therefore, if the accumulation time arbitrarily set by the user is "1 / 800 (sec)", no flicker reduction effect can be obtained. The camera control unit 107 determines this and changes the arbitrary accumulation time "1 / 800 (sec)" to "1 / 1000 (sec)" so that the flicker reduction effect can be obtained.

[0028] Note that when flicker is detected, whether or not to prioritize the flicker reduction effect (such as by shifting the imaging timing or fine-tuning an arbitrary accumulation time) may be selected by the user, or may be determined by the imaging device 100. Also, in the first embodiment, the explanation has been given using an explanatory diagram assuming a slit rolling shutter, but even in the case of a global shutter, control can be executed according to the processing flow shown in Fig. 3.

[0029] In addition, in the case of a global shutter, it is possible to perform only the imaging timing control of S305 in Fig. 3. When a global shutter is used, it is suitable for timing control because it does not use a shutter that sequentially captures image information, but rather acquires images at the same time for all pixels.

[0030] <Second embodiment> Below, an overview of normal flash imaging will be described with reference to Fig. 4, and the conditions of the accumulation time used in the light control calculation during flash imaging will be described with reference to Fig. 5. After that, a method of reducing the influence on the light control calculation under a flickering light source, which is a feature of this embodiment, will be described with reference to Figs. 6 to 8.

[0031] (Figure 4: An explanatory diagram of the flow from light control calculation to imaging with a strobe) 4 is an explanatory diagram of the flow from an imaging instruction for flash imaging to light control calculation and actual imaging. When a user gives an imaging instruction to the imaging device 100 via the operation unit 108, the light control calculation unit 113 performs light control calculation to calculate the amount of main flash light to be used in actual imaging. The light control calculation finds the difference in luminance between an image without flash light and an image with flash light, and calculates the amount of light required to properly image the subject.

[0032] For example, image 4a is an image without a flash, and both the subject and the background are dark. In contrast, image 4b ​​was captured with a flash, and the exposure remains the same because the strobe light does not reach the background, but the strobe light reaches the subject, resulting in an image in which only the subject is exposed (an image with improved brightness). Image 4c is the brightness difference between these two images, and areas with a difference are shown as "whiter" and areas without a difference are shown as "blacker." The area where the brightness difference occurs is determined to be the subject area to be enhanced (in other words, increased brightness) by strobe imaging, and the light control calculation is carried out to calculate the amount of actual light emitted to appropriately enhance the subject.

[0033] (Fig. 5: An explanation of the storage time constraints for the dimming image used during dimming calculation) Next, referring to Figure 5, four cases are shown where the accumulation time of the light emission image for dimming is changed. In order to illuminate the entire screen evenly with strobe light, it is necessary to fire the strobe at a timing when the accumulation times of the upper and lower parts of the screen overlap (hereinafter referred to as the "fully open shutter section"). When the strobe emission time required for dimming calculation is constant, the accumulation time of the light emission image for dimming must ensure at least this time. For this reason, the accumulation time when "strobe emission time for dimming = fully open shutter section" becomes the "shortest accumulation time" for dimming.

[0034] Figure 5(A) is an explanatory diagram of the relationship between strobe emission and imaging at that time. Next, Figure 5(B) shows a case where the accumulation time is a little longer than that of Figure 5(A). The dimming strobe emission is completed during the "fully open shutter section", and the conditions for a dimming emission image are met. Figure 5(C) shows a case where the accumulation time is even longer than that of Figure 5(B). Although the condition that the "fully open shutter section" is longer than the strobe emission time is met, if the accumulation time is too long, then the effect of the strobe emission will be diluted by the effect of external light (ambient light), and there is a possibility that the dimming calculation will not be performed correctly.

[0035] In this case, as shown in Figure 5(D), it is necessary to increase the amount of strobe light emitted to capture an image, but there may be cases where the amount of strobe light emitted itself has a limit, and even if the limit is not reached, increasing the amount of light emitted will result in new problems such as increased power consumption. Therefore, the accumulation time for dimming light images is set to an upper limit based on the amount of light emitted that (1) allows correct dimming calculation and (2) is acceptable in terms of power consumption, and this is the "longest accumulation time" for dimming.

[0036] (Fig. 6A, Fig. 6B, Fig. 7A, Fig. 7B: Dimming problem under flickering light source, and explanation of flicker reduction method) Based on the explanations of Fig. 4 and Fig. 5(A) to Fig. 5(D), the dimming control under a flickering light source, which is a feature of this embodiment, will be explained with reference to Fig. 6A, Fig. 6B, Fig. 7A, and Fig. 7B. Fig. 6A is an explanatory diagram for explaining the effect on an image used for dimming calculation when strobe imaging is performed under a flickering light source.

[0037] When a flash image capture command is issued, a dimming non-emission image 6a and a dimming emission image 6b are continuously captured and stored before the actual capture, and the subject area is identified from the brightness difference between the two images to calculate the "main flash amount." If we look at the two images, as shown in 6a and 6b, both have stripes of uneven exposure due to the influence of the flicker light source. Furthermore, since each image was captured at a different phase of the light source's blinking cycle, the positions of the stripes that appear on the screen are also different. Image 6c is the result of taking the brightness difference between these two images, and a striped brightness difference area has occurred outside the subject area. Note that, as in Figure 4, areas with larger brightness differences are shown as "white" and areas with smaller brightness differences are shown as "black." If the "main flash amount" that provides the correct exposure for the area with the brightness difference is determined, the brightness difference of the stripes in these background areas will also be large and will be included in the calculation, making it impossible to calculate the appropriate "main flash amount" for the subject.

[0038] In response to this problem, FIG. 6B captures the dimming non-light image 6d and dimming light image 6e with the accumulation time set to "(one cycle time of flicker) × N times (N is a natural number)". Then, the dimming non-light image 6d and dimming light image 6e are not affected by flicker, and images without stripes of exposure unevenness can be obtained. The image 6f from which the brightness difference is taken can extract only the subject area to be subjected to the dimming calculation, making it possible to perform appropriate dimming calculation. Therefore, the camera control unit 107 can continuously obtain the dimming non-light image 6d and dimming light image 6e before the actual imaging in response to a flash imaging instruction, identify the subject area from the brightness difference between the two images 6d and 6e, and obtain the actual light emission amount. As a result, when the camera control unit 107 gives an instruction to the flash control unit 114, the flash control unit 114 controls the light emission unit 115 to irradiate the subject with the actual light emission amount and perform the actual imaging.

[0039] However, depending on the flicker frequency, it is not always possible to set the accumulation time as shown in Fig. 6B. Figs. 7A and 7B show examples of strobe imaging under a flicker light source with a lower frequency than Figs. 6A and 6B. It can be seen that the frequency of the flicker light source shown in the upper part of Figs. 7A and 7B is lower than the frequency of the flicker light source shown in the upper part of Figs. 6A and 6B.

[0040] The principle behind the occurrence of exposure unevenness in the dimming non-illuminated image 7a and the dimming illuminated image 7b in Fig. 7A is the same as that explained in Fig. 6A, so a duplicate explanation will be omitted. Since the dimming non-illuminated image 7a is darker toward the top of the screen and the dimming illuminated image 7b is darker toward the bottom of the screen, it can be seen that a large brightness difference occurs not only in the subject area but also in the top and bottom of the background area in the brightness difference image 7c.

[0041] In response to this, if the same countermeasure as in Figure 6B is taken, for example, a 100 Hz flickering light source requires at least 10 msec of accumulation time. However, if the maximum accumulation time for dimming is set at an upper limit of 6 msec, as described above, it is not possible to set an accumulation time of 10 msec, and it is not possible to obtain an image with reduced flicker effects. In such a case, as shown in Figure 7B, the accumulation time remains at an arbitrary value that satisfies the dimming condition, and timing control is performed so that the start of accumulation of the dimming non-emission image 7d and the dimming emission image 7e are in phase with the light source blinking cycle.

[0042] For example, under a 100 (Hz) flickering light source, accumulation of the dimming light-emission image 7e begins "10 x N (msec): N is a natural number" after accumulation of the dimming non-emission image 7d begins. By doing this, exposure unevenness in the background area still occurs, but the exposure unevenness is in the same position and to the same degree because the phase of the light source is aligned with the start of accumulation, and is offset when the brightness difference is taken. As a result, it is possible to extract only the subject area that is the target of the dimming calculation, as in image 6f, making it possible to perform appropriate dimming calculation.

[0043] (Figure 8: Flowchart showing flicker reduction imaging process when dimming) The flow of processing up to the selection of the method described above will be described with reference to the flowchart in Fig. 8. The progress of the processing shown in Fig. 8 is controlled by the camera control unit 107. First, when an image capture instruction is given via the operation unit 108, the process proceeds to step S801, where the flicker detection unit 112 detects the presence or absence of flicker and its frequency.

[0044] Next, in step S802, if flicker is not detected (No), the process proceeds to step S808, where light control calculation and strobe imaging are performed (step S809). On the other hand, in step S802, if flicker is detected (Yes), the process proceeds to step S803.

[0045] In step S803, the "shortest accumulation time" required for the light control calculation is stored in the variable "ETTLTmin". Next, in step 804, the "longest accumulation time" usable for the light control calculation is acquired and stored in the variable "ETTLTmax". For example, both the "shortest accumulation time" in step 803 and the "longest accumulation time" in step 804 are obtained by the accumulation time calculation unit 110 and notified to the camera control unit 107. In addition, both the "shortest accumulation time" and the "longest accumulation time" may be predetermined for each type of the imaging device 100. Furthermore, while one of the "shortest accumulation time" and the "longest accumulation time" is predetermined for each type of the imaging device 100, there are imaging devices 100 in which the other can be accommodated by being obtained by the accumulation time calculation unit 110. In this case, the other obtained by the accumulation time calculation unit 110 is notified to the camera control unit 107. In this way, the "shortest accumulation time" and the "longest accumulation time" are obtained and stored in the variables "ETTLTmin" and "ETTLTmax". The variables "ETTLTmin" and "ETTLTmax" are stored in the RAM or the like inside the camera control unit 107. When the "shortest accumulation time" and the "longest accumulation time" are determined in advance, the following process is executed. For example, the CPU of the camera control unit 107 reads out the predetermined "shortest accumulation time" and / or "longest accumulation time" from the ROM, and stores the corresponding variables "ETTLTmin" and / or "ETTLTmax" in association with the "shortest accumulation time" and / or "longest accumulation time" in the RAM.

[0046] Next, step S805 is a process for selecting a method for reducing the effect of flicker. If there is a time "N (N is a natural number)" that satisfies "(one cycle time of flicker) × N" for which a flicker reduction effect can be obtained and is equal to or greater than "ETTLTmin" and equal to or less than "ETTLTmax" (Yes), the process proceeds to step S806. Then, in step S806, this accumulation time is adopted as the accumulation time for the image for dimming. This is the method described above with reference to FIG. 6B.

[0047] On the other hand, if there is no "N" that satisfies the condition (No), the process proceeds to step S807. In step S807, the camera control unit 107 controls the accumulation timing of the image for dimming. This is the method described above with reference to FIG. 7B. The timing control here means controlling the interval between the start of accumulation of two images to be "(one cycle time of flicker)×N (N is a natural number)". After step S806 or S807 is completed, the process proceeds to step S808. In step S808, the dimming calculation unit 113 performs dimming calculation to calculate the amount of main light emission. Then, in S809, the strobe control unit 114 causes the light emission unit 115 to emit light with the amount of main light emission calculated in step S808, performs strobe imaging, and the imaging ends.

[0048] As described above, even under a flickering light source, it is possible to perform appropriate light control calculations for the subject to be imaged without being affected by flicker. It is possible to reduce the effects of flicker using either the method shown in Fig. 6B or Fig. 7B. However, if the required accumulation time can be controlled, it is preferable to prioritize the accumulation time control method. This is because accumulation time control makes it possible to capture non-emission and emission images for light control continuously in time, which is advantageous for imaging moving objects.

[0049] 6B or 7B may be selected by a user using an instruction unit such as a dedicated button, or may be selected by an existing operation unit 108 or a special operation of the operation unit 108. An example of the special operation is simultaneous pressing of multiple operators provided in advance.

[0050] In addition, in the imaging timing control method, Fig. 7B shows an example in which the start of accumulation of the light control image is set to the darkest timing of the flicker blinking. That is, as shown in Fig. 7B, the start point is set to the lowest point of the brightness (see vertical axis) of the flicker light source. However, since the start of accumulation between images only needs to be N times the time of one cycle of the flicker, the start timing can be any timing.

[0051] <Additional Note> The disclosure of this embodiment includes the following configuration, method, and program. (Configuration 1) An imaging device having an image sensor for capturing an object image formed through an optical system, a flicker detection unit that detects the frequency and phase of a flicker; a comparison unit that compares a shutter speed, which is a time required for a shutter to travel from the top to the bottom of the image sensor, with a flicker cycle time, which is a time required for one cycle of the flicker; and an imaging control unit that, when the curtain speed is longer than the flicker cycle time, controls an imaging accumulation time to image the subject, and, when the curtain speed is shorter than or equal to the flicker cycle time, controls an imaging timing based on a frequency and a phase of the detected flicker to image the subject. (Configuration 2) The device according to configuration 1, characterized in that the image capturing and accumulation time is controlled so that the image capturing and accumulation time becomes "(one cycle time of flicker)×N times (N is a natural number)". (Configuration 3) The device according to configuration 1 or 2, characterized in that the imaging timing is controlled so as to align the phase of a rising start point of a flicker waveform with a passing point at which the shutter passes over the image sensor. (Configuration 4) An imaging device that, in response to a strobe imaging instruction, continuously acquires a dimming non-emission image and a dimming emission image before actual imaging, identifies a subject area from a luminance difference between the two images, calculates a main emission amount, and enables actual imaging of a subject, a flicker detection unit that detects the frequency and phase of a flicker; and an imaging control unit that, when a time that satisfies a predetermined condition exists, controls the dimming accumulation time to set that time as an accumulation time for dimming so as to enable actual imaging, while in other cases, controls the dimming timing based on the frequency and phase of the flicker so as to enable actual imaging. (Configuration 5) The time period during which the predetermined condition is satisfied is The imaging device described in configuration 4 is characterized in that the time is longer than the shortest accumulation time required for dimming and shorter than the longest accumulation time usable for dimming, and also satisfies "(one cycle time of flicker) x N (N is a natural number)." (Configuration 6) The imaging device described in configuration 4 or 5, characterized in that the control of the dimming timing controls the interval between the start of accumulation of the two images to be a time of "(one cycle time of flicker) x N (N is a natural number)". (Configuration 7) 6. The imaging device according to configuration 4 or 5, wherein the light adjustment timing is controlled so that the start of accumulation of both images is in phase with the blinking cycle of a light source of the flicker. (Configuration 8) The imaging device described in configuration 7, characterized in that the dimming timing is controlled so that accumulation of the dimming light-emission image starts after "(one cycle time of flicker) x N (N is a natural number)" from the start of accumulation of the dimming non-emission image. (Method 1) 1. A method for controlling an imaging apparatus having an imaging element that captures a subject image formed through an optical system, comprising the steps of: a flicker detection step of detecting a frequency and a phase of a flicker; a comparison step of comparing a shutter speed, which is a time required for a shutter to travel from the top to the bottom of the image sensor, with a flicker cycle time, which is a time required for one cycle of the flicker; and an imaging control step of controlling an imaging accumulation time to image the subject when the curtain speed is longer than the flicker cycle time, and controlling an imaging timing to image the subject based on a frequency and a phase of the detected flicker when the curtain speed is shorter than or equal to the flicker cycle time. (Method 2) A method for controlling an imaging device, which, in response to a strobe imaging instruction, continuously acquires a dimming non-emission image and a dimming emission image before actual imaging, identifies a subject area from a luminance difference between the two images, calculates an actual light emission amount, and enables actual imaging of a subject, comprising: a flicker detection step of detecting a frequency and a phase of a flicker; and an imaging control step of controlling a dimming accumulation time to set the time as an accumulation time for dimming when a time that satisfies a predetermined condition exists, thereby enabling actual imaging, while otherwise controlling a dimming timing based on a frequency and a phase of the flicker to enable actual imaging. (Program 1) A program for causing a computer to execute a control method for an imaging device having an imaging element that captures a subject image formed through an optical system, comprising: The control method includes: a flicker detection step of detecting a frequency and a phase of a flicker; a comparison step of comparing a shutter speed, which is a time required for a shutter to travel from the top to the bottom of the image sensor, with a flicker cycle time, which is a time required for one cycle of the flicker; and an imaging control step of controlling an imaging accumulation time to image the subject when the curtain speed is longer than the flicker cycle time, and controlling an imaging timing to image the subject based on a frequency and a phase of the detected flicker when the curtain speed is shorter than or equal to the flicker cycle time. (Program 2) A program for causing a computer to execute a control method for an imaging device that, in response to a strobe imaging instruction, continuously acquires a dimming non-emission image and a dimming emission image before actual imaging, identifies a subject area from a luminance difference between the two images, calculates an actual light emission amount, and enables actual imaging of a subject, The control method includes: a flicker detection step of detecting a frequency and a phase of a flicker; and an imaging control process for controlling the dimming accumulation time to set the time as an accumulation time for dimming when a predetermined condition exists, thereby enabling actual imaging, and otherwise controlling the dimming timing based on the frequency and phase of the flicker to enable actual imaging.

[0052] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment, and various modifications and changes are possible within the scope of the gist of the present invention. For example, the present invention can be realized by supplying a program that realizes one or more functions of the above-mentioned embodiment to a system or device via a network or a recording medium, and having a computer processor of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions. [Explanation of symbols]

[0053] 100 Imaging device 101 Lens Group 102 Lens control unit 103 Image sensor 104 Signal Processing Section 105 Recording processing section 106 Recording media 107 Camera control unit 108 Operation section 109 Shooting timing calculation unit 110 Accumulation time calculation unit 111 Exposure control section 112 Flicker detection section 113 Light control calculation unit 114 Strobe control unit 115 Light-emitting part

Claims

1. An imaging device having an image sensor for capturing an object image formed through an optical system, a flicker detection unit that detects the frequency and phase of a flicker; a comparison unit that compares a shutter speed, which is a time required for a shutter to travel from the top to the bottom of the image sensor, with a flicker cycle time, which is a time required for one cycle of the flicker; and an imaging control unit that, when the curtain speed is longer than the flicker cycle time, controls an imaging accumulation time to image the subject, and, when the curtain speed is shorter than or equal to the flicker cycle time, controls an imaging timing based on a frequency and a phase of the detected flicker to image the subject.

2. 2. The device according to claim 1, wherein the image pickup accumulation time is controlled so that the image pickup accumulation time becomes "(one period of flicker)×N (N is a natural number)".

3. 3. The device according to claim 1, wherein the imaging timing is controlled so as to align a phase between a rising edge of a flicker waveform and a passing point at which the shutter passes over the imaging element.

4. An imaging device that, in response to a strobe imaging instruction, continuously acquires a dimming non-emission image and a dimming emission image before actual imaging, identifies a subject area from a luminance difference between the two images, calculates a main emission amount, and enables actual imaging of a subject, a flicker detection unit that detects the frequency and phase of a flicker; and an imaging control unit that, when a time that satisfies a predetermined condition exists, controls the dimming accumulation time to set that time as an accumulation time for dimming so as to enable actual imaging, while in other cases, controls the dimming timing based on the frequency and phase of the flicker so as to enable actual imaging.

5. The time period during which the predetermined condition is satisfied is The imaging device according to claim 4, characterized in that the time is equal to or longer than the shortest accumulation time required for dimming and equal to or shorter than the longest accumulation time usable for dimming, and also satisfies "(one cycle time of flicker) x N (N is a natural number)".

6. 6. The imaging device according to claim 4, wherein the light adjustment timing is controlled so that the interval between the start of accumulation of the two images becomes "(one cycle time of flicker) x N (N is a natural number)".

7. 6. The imaging apparatus according to claim 4, wherein the light adjustment timing is controlled so that the start of accumulation of both images is in phase with a blinking cycle of a light source of the flicker.

8. The imaging device according to claim 7, characterized in that the dimming timing is controlled so that accumulation of the dimming light emission image starts after "(one cycle time of flicker) x N (N is a natural number)" from the start of accumulation of the dimming non-light emission image.

9. 1. A method for controlling an imaging apparatus having an imaging element that captures a subject image formed through an optical system, comprising the steps of: a flicker detection step of detecting a frequency and a phase of a flicker; a comparison step of comparing a shutter speed, which is a time required for a shutter to travel from the top to the bottom of the image sensor, with a flicker cycle time, which is a time required for one cycle of the flicker; and an imaging control step of controlling an imaging accumulation time to image the subject when the curtain speed is longer than the flicker cycle time, and controlling an imaging timing to image the subject based on a frequency and a phase of the detected flicker when the curtain speed is shorter than or equal to the flicker cycle time.

10. A method for controlling an imaging device, which, in response to a strobe imaging instruction, continuously acquires a dimming non-emission image and a dimming emission image before actual imaging, identifies a subject area from a luminance difference between the two images, calculates an actual light emission amount, and enables actual imaging of a subject, comprising: a flicker detection step of detecting a frequency and a phase of a flicker; and an imaging control step of controlling a dimming accumulation time to set the time as an accumulation time for dimming when a time that satisfies a predetermined condition exists, thereby enabling actual imaging, while otherwise controlling a dimming timing based on a frequency and a phase of the flicker to enable actual imaging.

11. A program for causing a computer to execute a control method for an imaging device having an imaging element that captures a subject image formed through an optical system, comprising: The control method includes: a flicker detection step of detecting a frequency and a phase of a flicker; a comparison step of comparing a shutter speed, which is a time required for a shutter to travel from the top to the bottom of the image sensor, with a flicker cycle time, which is a time required for one cycle of the flicker; and an imaging control step of controlling an imaging accumulation time to image the subject when the curtain speed is longer than the flicker cycle time, and controlling an imaging timing to image the subject based on a frequency and a phase of the detected flicker when the curtain speed is shorter than or equal to the flicker cycle time.

12. A program for causing a computer to execute a control method for an imaging device that, in response to a strobe imaging instruction, continuously acquires a dimming non-emission image and a dimming emission image before actual imaging, identifies a subject area from a luminance difference between the two images, calculates an actual light emission amount, and enables actual imaging of a subject, The control method includes: a flicker detection step of detecting a frequency and a phase of a flicker; and an imaging control process for controlling the dimming accumulation time to set the time as an accumulation time for dimming when a predetermined condition exists, thereby enabling actual imaging, and otherwise controlling the dimming timing based on the frequency and phase of the flicker to enable actual imaging.

Images