Illumination device, imaging system, and control method thereof

Abstract

To make it possible to set the charge accumulation time of an image sensor to a desired value and perform imaging while suppressing the occurrence of stripes caused by light irradiated onto a subject from an illumination device.SOLUTION: The frequency F when turning on the video light 413 by PWM control is set to a value that satisfies the relationship F=1 / (t×N), where t is the charge accumulation time (shutter time) of an image sensor 103 of an imaging device 100 and N is a natural number. However, when flicker is detected from a subject, the frequency F is set to match the frequency of the detected flicker, and the charge accumulation time t of the image sensor 103 is set to a natural number multiple of the flicker period.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a technique for controlling light emission from an illumination device in an imaging system having the illumination device and an imaging device. [Background technology]

[0002] In dark places, lighting devices are used to illuminate the subject and its background when taking photographs. In this case, lighting devices such as a strobe for still photography and a video light for video photography are used, and these are either built into the imaging device (camera) or connected physically or wirelessly to the imaging device.

[0003] While video lights have traditionally used incandescent lamps as their light source, in recent years LEDs have become more common. By using LEDs as the light source, the intensity of the light shining on the subject can be easily adjusted by changing the applied voltage and using PWM control.

[0004] With PWM control, the light output is adjusted by repeatedly turning the voltage input to the LED on and off to continuously turn the LED on and off. As a result, with cameras that use CMOS sensors that acquire image signals using the rolling shutter method, it is known that, depending on the imaging conditions, striped brightness differences similar to flicker can appear in the captured image due to the light shining on the subject from the video light.

[0005] Therefore, applying conventional flicker countermeasures is considered as a method for reducing stripes that appear on a subject due to illumination from a video light. For example, Patent Document 1 discloses a technology in which flicker is detected based on multiple images obtained by driving an image sensor at a predetermined cycle, and the charge accumulation time (shutter time) in the image sensor is set to a value that reduces the effects of the detected flicker. By using this technology to control the charge accumulation time in the image sensor based on the frequency (cycle) when the video light is emitted by PWM control, it is thought that it will be possible to perform a live view display with reduced stripes. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-10317 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the above-mentioned conventional technology, the charge accumulation time of the image sensor is limited by the frequency (period) of the PWM control for illuminating the video light, and therefore, for example, it may not be possible to capture video at the desired charge accumulation time.

[0008] The present invention aims to provide an imaging system that enables imaging by setting the charge accumulation time of an imaging element to a desired value while suppressing the occurrence of stripes caused by light irradiated onto a subject from an illumination device. [Means for solving the problem]

[0009] The imaging system of the present invention is an imaging system comprising an imaging device and an illumination device connected to each other so as to be able to communicate, wherein the imaging device comprises an imaging element and a first control means for controlling the charge accumulation time in the imaging element, and the illumination device comprises a light-emitting unit and a second control means for controlling the light emission of the light-emitting unit by PWM control, wherein the first control means determines a frequency for the PWM control based on the charge accumulation time and notifies the second control means, and the second control means controls the light emission of the light-emitting unit at the frequency for the PWM control notified by the first control means. [Effects of the Invention]

[0010] According to the present invention, it is possible to perform imaging by setting the charge accumulation time of the imaging element to a desired value while suppressing the occurrence of stripes caused by light irradiated from an illumination device onto a subject. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a block diagram showing a schematic configuration of an imaging system according to an embodiment. [Figure 2] 10 is a flowchart of a photographing operation by the imaging system. [Figure 3] 10A and 10B are diagrams illustrating the relationship between charge accumulation and readout in an image sensor and photometric values. [Figure 4] 10 is a map and a determination table for determining a flicker environment. [Figure 5] 10 is a flowchart of the control of turning on the video light in S206. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Here, an imaging system according to the present invention will be described in terms of a configuration in which a lens barrel (interchangeable lens) and an illumination device are attached to an imaging device such as a digital camera.

[0013] In the following description, the term "imaging device" refers to the main body of the imaging device (device body) that includes an imaging element. However, for convenience, devices in which the taking lens is integrated with the device body, such as compact digital cameras and digital video cameras, are also included in the term "imaging device."

[0014] 1 is a block diagram showing a schematic configuration of an image capturing system 1000 according to an embodiment. The image capturing system 1000 includes an image capturing device 100, a lens barrel 300 and an illumination device 400 attached to the image capturing device 100, and an external storage medium 200 in which the image capturing device 100 is housed.

[0015] Specifically, the imaging device 100 is a digital camera capable of shooting video, and is assumed to be a mirrorless digital single-lens camera. The imaging device 100 includes a lens mount 160, an image sensor 103, a shutter 102, a shutter control unit 115, an A / D conversion unit 106, an image processing unit 107, a memory control unit 110, a D / A conversion unit 109, an image display memory 112, and a temporary storage memory 113. The imaging device 100 also includes a compression / decompression unit 111, a timing generation unit 108, an electronic viewfinder 105, a rear display unit 114, a system control unit 120, a main memory 121, a nonvolatile memory 123, an operation unit 133, a mode dial 130, and a release button 131. The imaging device 100 has a playback button 132, a power switch 134, a power control unit 124, a first camera I / F 140, a second camera I / F 150, a third camera I / F 170, a first camera connector 141, a second camera connector 151, and a third camera connector 171.

[0016] The external storage medium 200 includes a media connector 203 , a media I / F 202 , and a storage unit 201 .

[0017] The lens barrel 300 includes a camera mount 320 , a lens connector 311 , a lens I / F 310 , an imaging lens group 301 , an aperture 302 , an aperture driver 303 , a lens driver 304 , and a lens controller 305 .

[0018] The lighting device 400 includes a strobe connector 411 , a strobe I / F 410 , a strobe control unit 402 , a strobe light emitting unit 401 , a video light control unit 412 , and a video light 413 .

[0019] In the imaging device 100, the imaging element 103 is, for example, a charge-accumulating photoelectric conversion device such as a CMOS. An optical image of a subject that is incident through the lens barrel 300 and focused on the imaging surface of the imaging element 103 is converted into an analog image signal by photoelectric conversion, and the generated analog image signal is output to the A / D conversion unit 106.

[0020] The shutter 102 includes front and rear curtains, which are mechanical components, and an actuator that drives the front and rear curtains, and drives the front and rear curtains to open or block the optical path between the lens barrel 300 and the image sensor 103. Note that the shutter 102 is not limited to a mechanical configuration that drives the front and rear curtains, and may also be realized by a function that resets or reads image data captured by the image sensor 103 through electrical control. The shutter control unit 115 controls the driving of the shutter 102 (front and rear curtains) in accordance with commands from the system control unit 120.

[0021] The A / D conversion unit 106 converts the analog image signal output from the image sensor 103 into digital image data and outputs the generated digital image data to the image processing unit 107 and memory control unit 110. The image processing unit 107 performs various processes such as white balance adjustment and gradation processing on the digital image data transmitted from the A / D conversion unit 106. The memory control unit 110 controls writing and reading of various data acquired from the A / D conversion unit 106, image processing unit 107, and compression / decompression unit 111 to and from the image display memory 112 and temporary storage memory 113.

[0022] The image display memory 112 temporarily stores digital image data for display of images to be displayed on the electronic viewfinder 105 and rear display unit 114. The digital image data for display written to the image display memory 112 is sent to the D / A conversion unit 109 via the memory control unit 110. The D / A conversion unit 109 performs D / A conversion on the digital image data for display, generates analog image data for display, and supplies it to the electronic viewfinder 105 and rear display unit 114.

[0023] The temporary storage memory 113 temporarily stores image data output from the image processing unit 107 and image data read from the external storage medium 200, and is also used as a work area for the system control unit 120. The compression / decompression unit 111 reads the image data stored in the temporary storage memory 113 and compresses or decompresses the image data using a predetermined image compression method and image decompression method in accordance with various uses.

[0024] The timing generation unit 108 generates operation signals (control signals such as clock signals) to be supplied to the image sensor 103, the A / D conversion unit 106, the D / A conversion unit 109, etc. The timing generation unit 108 also controls the accumulation of charge in the image sensor 103 by controlling the reset timing of the accumulated charge in the image sensor 103. The electronic viewfinder 105 and rear display unit 114 are configured with a liquid crystal panel, an organic EL panel, etc., and display a subject image and a menu screen for making various settings of the image sensor 100, etc. The electronic viewfinder 105 is configured so that the user can check the displayed content by placing their eye against it, and the rear display unit 114 is mounted on the rear of the image sensor 100 via a vari-angle mechanism or a tilt mechanism.

[0025] The system control unit 120 controls not only the imaging device 100 but also the overall operation of the imaging system 1000. Here, a specific example of the processing executed by the system control unit 120 will be described, but the processing executed by the system control unit 120 is not limited to the following specific example.

[0026] The system control unit 120 performs photometry calculations using image data acquired by the image sensor 103, calculates the brightness value of the subject (obtains brightness information), and determines the exposure conditions for the image sensor 103. Parameters that determine the exposure conditions include aperture value, shutter speed, and shooting sensitivity (ISO sensitivity). In this way, appropriate exposure for the image sensor 103 is controlled. Furthermore, the system control unit 120 controls the positions of the lens groups in the lens barrel 300 to focus on the subject, based on the focus detection results for the subject.

[0027] The system control unit 120 controls the shutter 102 in particular when capturing still images, and controls the image sensor 103 in particular when capturing live view images or capturing moving images, thereby controlling the charge accumulation time (shutter time) at the image sensor 103. The system control unit 120 issues instructions to the strobe control unit 402 and video light control unit 412 according to the photometry calculation results, exposure conditions, and the state of the lighting device 400, to control the light emission amount and timing of the strobe light emission unit 401 and video light 413.

[0028] The system control unit 120 controls the start and end of video recording in accordance with an input signal from the operation unit 133, and can also switch the imaging range of the image sensor 103 to capture images using the pixel output of the entire image sensor or capture images by cropping out a portion of it. When capturing still images and videos, the system control unit 120 controls the display of a live view image on the electronic viewfinder 105 or rear display unit 114 to allow the user to check the subject. The system control unit 120 also detects the presence or absence of flicker in the imaging environment and its frequency using image data obtained by the image sensor 103.

[0029] Returning to the description of other components of the imaging device 100, the main memory 121 is, for example, a ROM, and stores data related to the operation of the imaging device 100, such as information on appropriate exposure for brightness values ​​(table data and program diagrams), constants for operations executed by the imaging device 100, various exposure conditions, and arithmetic expressions. The non-volatile memory 123 is, for example, an EEPROM or the like that can be electrically erased and stored, and stores various setting values ​​for the imaging system 100.

[0030] The operation unit 133 is composed of buttons, switches, dials, a touch panel, a line-of-sight detection device, a voice recognition device, or a combination of these, which input various operational instructions to the system control unit 120. Note that the operation members included in the operation unit 133 are operation members other than the mode dial 130, the release button 131, the playback button 132, and the power switch 134, which are separately shown in FIG.

[0031] The mode dial 130 is a rotary operating member used to set an arbitrary shooting mode from among a plurality of shooting modes that can be set in the imaging device 100. The imaging device 100 can be set to a still image mode for capturing still images and a video mode for recording videos. Furthermore, in each of the still image and video shooting modes, various modes are available in which exposure parameters can be set automatically or manually, such as full auto, program, aperture priority, shutter speed priority, and manual, and it is also possible to set whether or not to use flash when capturing still images.

[0032] The release button 131 is an operating member for instructing the start of preparatory operations for still image capture and video capture, and the start of actual capture. The release button 131 generates an SW1 signal with a first stroke (halfway pressed), and the system control unit 120 starts the capture preparatory operations when it detects the SW1 signal. The capture preparatory operations include focus control, exposure control, auto white balance (AWB) processing, and, in the case of video capture, exposure control such as turning on and emitting light from the video light 413 of the lighting device 400 is performed as needed. The release button 131 generates an SW2 signal with a second stroke (fully pressed). When the system control unit 120 detects the SW2 signal, it executes a series of processes (capturing processes) from exposure processing for the image sensor 103 to storage processing of image data in the external storage medium 200.

[0033] Playback button 132 is an operating member that instructs the start of playback processing in which image data is read from temporary storage memory 113 or external storage medium 200 and displayed on rear display unit 114. Power switch 134 is an operating member that switches on / off the supply of power from a power supply unit (not shown), such as a battery, to each unit of image capture device 100. Turning power switch 134 on enables power supply not only to image capture device 100 but also to lens barrel 300, external storage medium 200, and lighting device 400. Power supply control unit 124 includes a battery detection circuit, a DC-DC converter, a switch circuit used to switch current-carrying blocks, and the like, and controls the power supply from the power supply unit to each unit of image capture device 100.

[0034] The first camera I / F 140 is an interface for communicatively connecting the system control unit 120 and the external storage medium 200. The second camera I / F 150 is an interface for communicatively connecting the system control unit 120 and the lens control unit 305. The third camera I / F 170 is an interface for communicatively connecting the system control unit 120 and the strobe control unit 402 and the video light control unit 412. The lens mount 160 is a mount unit on the imaging device 100 side that engages with the camera mount 320 of the lens barrel 300 to mechanically connect the lens barrel 300 and the imaging device 100.

[0035] The first camera connector 141 is connected to the media connector 203 of the external storage medium 200. This electrically connects the image capture device 100 and the external storage medium 200, enabling the transmission of various control signals, image data, etc., and also enabling the supply of power from the image capture device 100 to the external storage medium 200. The second camera connector 151 is connected to the lens connector 311, which electrically connects the image capture device 100 and the lens barrel 300, enabling the transmission of various control signals, status signals, data signals, etc., and the supply of power from the image capture device 100 to the lens barrel 300. The third camera connector 171 is connected to the strobe connector 411, which electrically connects the image capture device 100 and the lighting device 400, enabling the transmission of various control signals, status signals, data signals, etc., and the supply of power from the image capture device 100 to the lighting device 400. The second camera connector 151 and the third camera connector 171 may be configured to perform optical communication, audio communication, etc. in addition to electrical communication.

[0036] The external storage medium 200 is a memory card, a hard disk, etc., and the storage unit 201 is composed of a semiconductor memory, a magnetic disk, etc. The media connector 203 is electrically connected to the first camera connector 141 of the imaging device 100. The media I / F 202 is an interface for connecting the external storage medium 200 and the system control unit 120 so that they can communicate with each other.

[0037] Lens barrel 300 is an optical device that is detachable from image capture device 100 and forms an optical image of a subject on image sensor 103. Camera mount 320 is a mount unit on lens barrel 300 that engages with lens mount 160 of image capture device 100 to mechanically connect lens barrel 300 and image capture device 100. Lens connector 311 is provided inside camera mount 320 and electrically connects lens barrel 300 and image capture device 100. Lens connector 311 may be configured to be capable of optical communication, audio communication, and the like in addition to electrical communication, in accordance with the configuration of second camera connector 151. Lens I / F 310 is an interface for communicatively connecting lens control unit 305 and system control unit 120.

[0038] The lens control unit 305 performs overall control of each unit of the lens barrel 300 in accordance with commands from the system control unit 120. The imaging lens group 301 is composed of multiple lenses, such as a focus lens, a zoom lens, and an image stabilization lens, and focuses incident light on the imaging surface of the image sensor 103. The lens driving unit 304 adjusts the optical axis positions of the focus lens and zoom lens in accordance with commands from the lens control unit 305, and also drives the image stabilization lens in a plane perpendicular to the optical axis. The diaphragm 302 adjusts the amount of light flux from the subject that passes through the imaging lens group 301 and enters the image sensor 103. The diaphragm 302 and the shutter 102 can be controlled in conjunction with each other. The diaphragm driving unit 303 adjusts the opening size of the diaphragm 302 in accordance with commands from the lens control unit 305.

[0039] The lighting device 400 is detachable from the imaging device 100, and emits a flash of light or illuminates (continuously emits light) the subject depending on the shooting environment. The strobe connector 411 is electrically connected to the third camera connector 171. The strobe connector 411 may be configured to be capable of optical communication, audio communication, and the like in addition to electrical communication, depending on the configuration of the third camera connector 171. The strobe I / F 410 is an interface for communicatively connecting the strobe control unit 402 and the video light control unit 412 to the system control unit 120. The strobe light emitting unit 401 is, for example, a xenon tube. The strobe control unit 402 controls the light emission of the strobe light emitting unit 401 in accordance with commands from the system control unit 120.

[0040] The video light 413 is configured with, for example, an LED. The video light control unit 412 controls the light emission of the video light 413 in accordance with commands from the system control unit 120. The light emission of the video light 413 is controlled by PWM control, and the video light control unit 412 notifies the system control unit 120 of the frequency band that can be set in the PWM control. Various settings of the lighting device 400 can be made by operating an operation unit (not shown) provided in the lighting device 400 and / or by communication from the imaging device 100.

[0041] Note that processing blocks such as the system control unit 120, image processing unit 107, strobe control unit 402, video light control unit 412, and lens control unit 305 can be realized by hardware such as an ASIC or programmable logic array (PLA). However, this is not limiting, and each processing block may be realized by a programmable processor such as a CPU or MPU executing software (a combination of software and hardware). In other words, the same hardware may be configured to function as multiple functional blocks.

[0042] Next, the imaging operation in the imaging system 1000 will be described. Fig. 2 is a flowchart illustrating the imaging operation in the imaging system 1000. Each process (step) indicated by an S number in this flowchart is realized by the system control unit 120 executing a predetermined program and comprehensively controlling the imaging system 1000. When the user turns on the power switch of the lighting device 400 and the power switch 134 of the imaging device 100 to start up the lighting device 400 and the imaging device 100, the system control unit 120 initializes the imaging system 1000, and starts processing S201 when the initialization is complete.

[0043] When the initialization of the imaging system 1000 is completed, the system control unit 120 executes live view (denoted as "LV" in FIG. 2) in S201. In live view, an image of a subject is acquired and the acquired image is displayed on the electronic viewfinder 105 or the rear display unit 114.

[0044] In S202, the system control unit 120 determines whether the live view in S201 has been "started" by turning on the power switch 134, or whether the live view has been "resumed" after being temporarily suspended due to the execution of a predetermined process. Specific examples of when the live view will be "resumed" include when video shooting ends in S209, and when predetermined processing such as still image shooting ends in S216. If the system control unit 120 determines that live view has started, it executes the process of S203, and if it determines that live view has been resumed, it executes the process of S204.

[0045] In S203, the system control unit 120 performs flicker detection processing, which will be described in detail later.

[0046] In S204, the system control unit 120 determines the control mode of the video light 413 in the lighting device 400, and branches the process depending on the determination result. The control mode of the video light 413 is an emission mode of fill light for photography, which is emitted to a subject by turning on the video light 413. Here, it is assumed that the control mode is determined to be an automatic mode in which the on / off of the video light 413 is automatically determined, a forced on mode in which the video light 413 is forced on, or a light off mode in which the video light 413 is not turned on. If the system control unit 120 determines that the automatic mode is set, it executes the process of S205; if the system control unit 120 determines that the forced on mode is set, it executes the process of S206; and if the system control unit 120 determines that the light off mode is set, it executes the process of S207.

[0047] In S205, the system control unit 120 calculates the brightness value of the subject from the live view image (frame) and determines whether it is necessary to turn on the video light 413. If the obtained brightness value is equal to or less than a predetermined threshold, the system control unit 120 determines that it is necessary to turn on the video light 413 to irradiate the subject with fill light for photography. If the system control unit 120 determines that it is necessary to turn on the video light 413 (YES in S205), it executes the processing of S206, and if it determines that it is not necessary to turn on the video light 413 (NO in S205), it executes the processing of S207.

[0048] In S206, the system control unit 120 issues an instruction to the video light control unit 412 to turn on the video light 413, which turns on the video light 413. Details of the processing in S206 will be described later.

[0049] In S207, system control unit 120 determines whether an instruction to start video shooting has been received. If system control unit 120 determines that an instruction to start video shooting has been received (YES in S207), it executes the process of S208, and if it determines that an instruction other than an instruction to start video shooting has been received (NO in S207), it executes the process of S210.

[0050] In S208, the system control unit 120 performs video shooting (video recording).

[0051] In S209, the system control unit 120 determines whether an instruction to end video shooting has been received. If the system control unit 120 determines that an instruction to end video shooting has not been received (NO in S209), it continues the processing of S208. If the system control unit 120 determines that an instruction to end video shooting has been received (YES in S209), it executes the processing of S201, thereby restarting live view.

[0052] In S210 to S212, three instructions will be given as examples of instructions other than the instruction to start video shooting, and the instructions other than these three instructions will be explained as being end instructions caused by turning off the power switch 134 of the imaging device 100.

[0053] In S210, system control unit 120 determines whether an instruction to start still image shooting has been received. If system control unit 120 determines that an instruction to start still image shooting has been received (YES in S210), it executes the process of S214, and if it determines that an instruction other than an instruction to start still image shooting has been received (NO in S210), it executes the process of S211.

[0054] In S211, system control unit 120 determines whether an instruction to display a menu has been received. If system control unit 120 determines that an instruction to display a menu has been received (YES in S211), it executes the process of S214, and if it determines that an instruction other than an instruction to display a menu has been received (NO in S211), it executes the process of S212.

[0055] In S212, the system control unit 120 determines whether an instruction to perform image playback display has been received. The image to be played back may be a still image or a video. If the system control unit 120 determines that an instruction to perform image playback display has been received (YES in S212), it executes the process of S214. If the system control unit 120 determines that an instruction other than an instruction to perform image playback display has been received (NO in S212), it executes the process of S213.

[0056] In S213, the system control unit 120 receives an instruction to turn off the power switch 134, stops all functions of the image capture system 1000, and then ends this processing.

[0057] In S214, the system control unit 120 turns off the video light 413 if it is on.

[0058] In S215, the system control unit 120 suspends the live view.

[0059] In S216, system control unit 120 executes predetermined processing in accordance with the instructions received in S210 to S212.

[0060] In S217, the system control unit 120 determines whether an instruction to end live view has been received. If the system control unit 120 determines that an instruction to end live view has been received (YES in S217), it waits until the next instruction is received. If the system control unit 120 determines that an instruction to end live view has not been received (NO in S217), it executes the process of S201, thereby restarting live view.

[0061] 2, if the live view is "resumed" in S202, the flicker detection process in S203 is not performed. However, the present invention is not limited to this; the flicker detection process in S203 may be performed regardless of whether the live view is "started" or "resumed" without performing the determination process in S202. In this case, if the video light 413 is turned on in S206, the video light 413 is turned off before the flicker detection process.

[0062] Next, the flicker detection process in S203 will be described. Fig. 3 is a diagram illustrating the relationship between the charge accumulation and readout in the image sensor 103 and the photometric value.

[0063] 3(a) is a diagram showing charge accumulation control and photometric value transitions in the image sensor 103 for flicker (flicker frequency is 100 Hz) under lighting powered by a 50 Hz commercial power source. Note that the flicker detection described below, including the example in FIG. 3(b), is also used to detect the lighting frequency of digital signage in scenes where digital signage, which is controlled to light at a predetermined frequency, is present within the imaging field of view.

[0064] To detect flicker, the image sensor 103 continuously accumulates and reads out charges at a frame rate of 600 fps (approximately 1.667 milliseconds). Here, where 'n' is a natural number, the nth charge accumulation is represented as "accumulation n," the readout of accumulation n is represented as "readout n," and the photometric value obtained from the result of readout n is represented as "AE(n)."

[0065] In Figure 3(a), charge accumulation is performed 12 times under the same exposure conditions, resulting in photometric values ​​AE(1) to AE(12). Note that, because charge accumulation in the image sensor 103 is performed over a finite period of time, photometric values ​​AE(1) to AE(12) are represented by the median value over the accumulation period. From the photometric values ​​AE(1) to AE(12), the evaluation value SAD(m) used to determine the frequency of flicker is calculated using the following equation 1.

[0066]

number

[0067] The evaluation value SAD(m) is an index of similarity and is widely used in fields such as pattern matching. 'm' is a value that indicates how many times ahead the photometric value is to be calculated for the nth photometric result AE(n) out of 12 photometric measurements. In Figure 3(a), the evaluation value SAD(m) represents the similarity with the photometric value after 1.667 × m milliseconds have elapsed, and the greater the similarity, the smaller the value of SAD(m).

[0068] For example, in a flicker environment with a frequency of 100 Hz, the flicker period is approximately 10 milliseconds, and if the charge accumulation time of the image sensor 103 is 1.667 milliseconds, then the relationship between these is 10 / 1.667 ≒ 6. This means that, as shown in FIG. 3(a), the same photometric value can be obtained over six periods, regardless of the accumulation timing of the image sensor 103. In other words, the relationship AE(n) ≒ AE(n+6) holds true for the photometric value. Due to this property, in a flicker environment with a frequency of 100 Hz, SAD(6) ≒ 0.

[0069] To detect the presence of 100 Hz flicker, SAD(3) is calculated, which indicates the similarity with the photometric value after 1.667 x 3 = 5 milliseconds have elapsed. In an environment with 100 Hz flicker, the photometric value at a timing shifted by 5 milliseconds will have an out-of-phase relationship, so SAD(3) will be larger than SAD(6). Therefore, if SAD(3) is large and SAD(6) is small, it can be determined that 100 Hz flicker is present.

[0070] Similarly, to detect flicker (flicker frequency is 120 Hz) under lighting powered by a 60 Hz commercial power supply, SAD(5) and SAD(3) can be calculated. Figure 3(b) shows the charge accumulation control and photometric value transitions in the image sensor 103 for flicker under lighting powered by a 60 Hz commercial power supply. Because the period of flicker with a frequency of 120 Hz is 8.333 milliseconds, AE(n) ≒ AE(n+5) and SAD(5) ≒ 0.

[0071] Furthermore, in the case of 120 Hz flicker, the anti-phase relationship occurs after 4.16 milliseconds, so it is desirable to determine the similarity with the photometric value after 4.16 milliseconds. However, 4.16 milliseconds is not a natural number multiple (an integer multiple excluding 0) of the charge accumulation time of 1.667 milliseconds. Therefore, SAD(3), which indicates the similarity with the photometric value after 5 milliseconds, is used as an example of a value relatively close to 4.16 milliseconds. Even in a 120 Hz flicker environment, SAD(3) indicates a photometric value that is close to the anti-phase, so SAD(3) will be larger than SAD(5).

[0072] As described above, the flicker detection process calculates SAD(6), SAD(5), and SAD(3), and detects the presence or absence of flicker and, if flicker is present, its frequency based on the relationship between these values.

[0073] 4(a) is a diagram showing an example of a map for determining whether or not a flicker with a frequency of 100 Hz has been detected. In a coordinate system in which the horizontal axis is set to SAD(3) and the vertical axis is set to SAD(6), the lower right region where SAD(3) takes a relatively large value compared to SAD(6) is set to region A, where the flicker frequency is determined to be 100 Hz. Whether or not a flicker with a frequency of 100 Hz has been detected can be determined based on whether or not the actually obtained plot of SAD(3) and SAD(6) falls within region A.

[0074] 4(b) is a diagram showing an example of a map for determining whether or not a flicker with a frequency of 120 Hz has been detected. In a coordinate system in which the horizontal axis is set to SAD(3) and the vertical axis is set to SAD(5), the lower right region where SAD(3) is relatively large compared to SAD(5) is set to region B, where the flicker frequency is determined to be 100 Hz. Whether or not a flicker with a frequency of 120 Hz has been detected can be determined depending on whether or not the actually obtained plot of SAD(3) and SAD(5) falls within region B.

[0075] Note that the boundary line separating area A from other areas in FIG. 4(a) is an example, and the bending points and slopes of the boundary line are not limited to those shown in FIG. 4(a), and the same applies to FIG. 4(b).

[0076] 4(c) is a table for finally determining the presence or absence of flicker and its frequency based on the detection results obtained from FIG. 4(a) and FIG. 4(b). If it is determined that the flicker is 100 Hz but not 120 Hz, the flicker frequency is finally determined to be 100 Hz. Similarly, if it is determined that the flicker is not 100 Hz but is 120 Hz, the flicker frequency is finally determined to be 120 Hz.

[0077] When there is no flicker and ambient light (DC) is being measured, the photometric values ​​do not change over time, so the relationship AE(1) ≒ AE(2) ≒ AE(3) ≒ ≒ ≒ AE(12) is obtained. As a result, we obtain SAD(6) ≒ SAD(5) ≒ SAD(3) ≒ 0. Therefore, the photometric values ​​of ambient light are plotted near the origin in the coordinate systems of Figures 4(a) and (b), and the flicker is determined to be neither 100 Hz nor 120 Hz. As a result, if the flicker is determined to be neither 100 Hz nor 120 Hz, it is determined to be ambient light.

[0078] It is usually difficult to imagine that a flicker is determined to be both 100 Hz and 120 Hz, but this determination can occur when the subject being acquired in AE(1) to AE(12) is not the same due to subject movement or panning, etc. In such cases, an error is considered to have occurred and it is determined to be ambient light. The above processing makes it possible to determine whether flicker is present and, if so, whether the frequency is 100 Hz or 120 Hz.

[0079] Next, the lighting control of the video light 413 in S206 will be described. Conventionally, the following information and data have been exchanged between an image capture device and a lighting device. Specifically, information such as the charge accumulation time of the image sensor, aperture value, ISO sensitivity, shooting mode, lens focal length, light emission time of the lighting device, and on / off instructions for the lighting device is sent from the image capture device to the lighting device. In addition, information such as the light emission mode, guide number, and color temperature information is sent from the lighting device to the image capture device.

[0080] In addition to this information, in this embodiment, the image capturing device 100 transmits instructions on the frequency and duty ratio (light emission amount) of PWM control when the video light 413 is turned on to the lighting device 400. On the other hand, the lighting device 400 transmits the lighting state (frequency and duty ratio of PWM control) of the video light 413 to the image capturing device 100.

[0081] 5 is a flowchart of the process of turning on the video light 413 in S206. In S501, the system control unit 120 determines whether or not flicker was detected in S203. If the system control unit 120 determines that flicker was not detected (YES in S501), it executes the process of S502, and if it determines that flicker was detected (NO in S501), it executes the process of S503.

[0082] In S502, the system control unit 120 calculates the frequency (or cycle) and duty ratio of the PWM control for turning on the video light 413 based on the charge accumulation time of the image sensor 103 during live view execution and the brightness value of the subject. A specific method for determining the frequency (or cycle) and duty ratio of the PWM control in S502 will be described later.

[0083] In S503, the system control unit 120 calculates the frequency (or cycle) and duty ratio of PWM control for turning on the video light 413 based on the charge accumulation time of the image sensor 103 during live view execution, the luminance value of the subject, and the flicker frequency detected in S203. A specific method for determining the frequency (or cycle) and duty ratio of PWM control in S503 will be described later.

[0084] When the process of S502 or S503 ends, the system control unit 120 executes the process of S504. In S504, the system control unit 120 transmits the calculation results of S502 or S503 (the frequency and duty ratio of the PWM control for turning on the video light 413) to the video light control unit 412.

[0085] In S505, the video light control unit 412 turns on the video light 413 by performing PWM control using the frequency (cycle) and duty ratio received from the system control unit 120. The video light control unit 412 notifies the system control unit 120 of the lighting state of the video light 413 (the actual frequency and duty ratio under PWM control) at regular time intervals. This completes the lighting process for the video light 413.

[0086] Next, a specific method for determining the PWM control frequency and duty ratio in S502 and S503 will be described. If the PWM control frequency for the video light 413 is 'F', the charge accumulation time of the image sensor 103 is 't', and N is a natural number, the PWM control frequency F when flicker is not detected is determined by F = 1 / (t × N). The duty ratio, which determines the light emission amount of the video light 413, is determined using known techniques so as to obtain appropriate exposure for the luminance value of the subject. This enables video shooting and live view with reduced stripes caused by the lighting of the video light 413.

[0087] If flicker is detected in S203, in this embodiment, priority is given to matching the frequency of the PWM control for the video light 413 to the frequency of the detected flicker.

[0088] For example, if the frequency of the detected flicker is 100 Hz, the system control unit 120 sets the frequency F of the PWM control for the video light 413 to 100 Hz. Then, in order to suppress the occurrence of stripes in the captured image, the system control unit 120 sets the charge accumulation time in the image sensor 103 to a natural number multiple of 1 / 100 seconds, which is the cycle corresponding to 100 Hz. Note that a method for suppressing the occurrence of such stripes is well known (for example, Japanese Patent Application Laid-Open No. 2009-213076), and therefore a detailed description thereof will be omitted. The duty ratio, which determines the light emission amount of the video light 413, is determined so as to obtain appropriate exposure for the luminance value of the subject, just as when no flicker is detected.

[0089] However, if flicker is detected in S203 and the PWM control frequency cannot be adjusted to match the frequency of the detected flicker, the setting is the same as when no flicker is detected.

[0090] If flicker is detected in S203 and the image capture device 100 is in a mode in which the shutter speed is not fixed, such as aperture priority mode, the above-described countermeasures can be taken. On the other hand, if the charge accumulation time in the image capture element 103 is fixed to a value that is not a natural number multiple of the flicker period, the system control unit 120 issues a warning. This is done by displaying a warning on the rear display unit 114 or the electronic viewfinder 105, issuing a warning sound if a speaker is provided, or displaying a warning on the display unit if the lighting device 400 has a display unit.

[0091] Furthermore, the system control unit 120 must determine the frequency F within the frequency band notified by the video light control unit 412 as being settable in PWM control. If the video light control unit 412 does not support PWM control at the frequency F calculated based on a charge accumulation time calculated based on a fixed aperture value or a predetermined fixed charge accumulation time, the system control unit 120 issues a warning. For example, this may occur if the video light control unit 412 does not have the ability to generate a pulse wave of frequency F. The warning method may be the method described above.

[0092] In the above embodiment, the system control unit 120 is configured to calculate the frequency F and duty ratio of the PWM control that turns on the video light 413. However, the present invention is not limited to this, and the video light control unit 412 may calculate and determine the frequency F (or period) and duty ratio of the PWM control that turns on the video light 413. In this configuration, the system control unit 120 transmits to the video light control unit 412 the charge accumulation time of the image sensor 103, the luminance value of the subject, and the flicker detection result in S203 (information on the presence or absence of flicker and, if flicker is detected, information on the frequency of the flicker).

[0093] When the video light control unit 412 determines the frequency F, the video light control unit 412 does not need to notify the system control unit 120 of a frequency band that can be set in PWM control, but determines the frequency F within that frequency band. The video light control unit 412 then transmits the set frequency F and information indicating whether the frequency F has been synchronized with the charge accumulation time of the image sensor 103 to the system control unit 120. If the frequency F calculated based on the charge accumulation time of the image sensor 103 is outside the settable frequency band, the video light control unit 412 further notifies the system control unit 120 of a warning. Upon receiving this warning, the system control unit 120 can be configured to issue a warning. The warning method can be the method described above.

[0094] While the present invention has been described in detail above based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the gist of the present invention are also included in the present invention. Furthermore, each of the above-described embodiments merely represents one embodiment of the present invention, and each embodiment can be combined as appropriate.

[0095] For example, in the above embodiment, a configuration was described in which the lens barrel 300 and the lighting device 400 were detachably attached to the image capture device 100, but the lens barrel 300 and the lighting device 400 may be integrally configured with the image capture device 100. In this case, the system control unit 120 also functions as the lens control unit 305, the strobe control unit 402, and the video light control unit 412. Also, while the configuration in which the lighting device 400 is physically attached to the image capture device 100 via a connector has been described, the lighting device 400 and the image capture device 100 may be connected to each other via wireless communication so as to be controllable. Furthermore, while the image capture device 100 constituting the image capture system according to the present invention has been described assuming that it is a mirrorless digital camera, the image capture device 100 is not limited to this and may be a portable device such as a digital video camera or a smartphone.

[0096] The disclosure of this embodiment includes the following configurations and methods. (Configuration 1) An imaging system comprising an imaging device and a lighting device connected to each other so as to be able to communicate, wherein the imaging device comprises an imaging element and a first control means for controlling the charge accumulation time in the imaging element, and the lighting device comprises a light-emitting unit and a second control means for controlling the light emission of the light-emitting unit by PWM control, wherein the first control means determines a frequency for the PWM control based on the charge accumulation time and notifies the second control means, and the second control means controls the light emission of the light-emitting unit at the frequency for the PWM control notified by the first control means. (Configuration 2) An imaging system comprising an imaging device and a lighting device connected to each other so that they can communicate with each other, wherein the imaging device comprises an imaging element and a first control means for controlling a charge accumulation time in the imaging element, and the lighting device comprises a light-emitting unit and a second control means for controlling the light-emitting unit by PWM control, wherein the first control means notifies the second control means of the charge accumulation time, and the second control means determines a frequency in the PWM control based on the charge accumulation time to control the light emission of the light-emitting unit. (Configuration 3) An imaging system according to configuration 1 or 2, characterized in that the frequency in the PWM control is determined by F=1 / (t×N), where 'F' is the frequency in the PWM control, 't' is the charge accumulation time, and 'N' is a natural number. (Configuration 4) The imaging system described in Configuration 3 is characterized in that the imaging device is provided with a detection means for detecting flicker, and the frequency under the PWM control is determined by F=1 / (t×N) when no flicker is detected by the detection means, and is determined to be the same frequency as the frequency of the detected flicker when a flicker is detected by the detection means. (Configuration 5) The imaging system according to configuration 4, wherein when flicker is detected by the detection means, the charge accumulation time is set to a natural number multiple of the period of the flicker. (Configuration 6) An imaging system according to configuration 4 or 5, characterized in that when flicker is detected by the detection means, if the frequency in the PWM control cannot be set to the same frequency as the frequency of the detected flicker, the frequency in the PWM control is determined by F=1 / (t×N). (Configuration 7) An imaging system according to any one of configurations 1 to 6, characterized in that it comprises a detection means for detecting luminance information from an image acquired by the imaging element, and a setting means for setting a duty ratio in the PWM control based on the luminance information. (Configuration 8) An imaging system according to any one of configurations 1 to 7, characterized in that it comprises a warning means for issuing a warning when the second control means does not correspond to the frequency in the PWM control determined based on the charge accumulation time. (Configuration 9) An imaging device comprising: an imaging element; a communication means for communicating with a lighting device; a determination means for determining a frequency for PWM control by F=1 / (t×N), where 't' is the charge accumulation time of the imaging element, 'N' is a natural number, and 'F' is the frequency for PWM control when the lighting device controls light emission by PWM control; and a notification means for notifying the lighting device of the frequency determined by the determination means using the communication means. (Configuration 10) A lighting device comprising a light-emitting unit, a control means for controlling the light-emitting unit by PWM control, a communication means for communicating with an imaging device, and an acquisition means for acquiring a charge accumulation time set in an imaging element provided in the imaging device using the communication means, wherein the control means determines the frequency in the PWM control by F=1 / (t×N), where 't' is the charge accumulation time, 'N' is a natural number, and 'F' is the frequency in the PWM control. (Configuration 11) An imaging device comprising an imaging element, a light-emitting unit that emits light toward a subject, and a control means that controls the light emission of the light-emitting unit by PWM control and also controls the charge accumulation time in the imaging element, wherein the control means determines the frequency in the PWM control by F=1 / (t×N), where 't' is the charge accumulation time, 'N' is a natural number, and 'F' is the frequency in the PWM control. (Configuration 12) A program for causing a computer to execute each step of the method for controlling an imaging system according to Configuration 9. (Method 1) A control method for an imaging system in which an imaging device and a lighting device are connected so that they can communicate with each other, comprising the steps of: setting a charge accumulation time in an imaging element of the imaging device; and determining a frequency in the PWM control by F=1 / (t×N), where 't' is the charge accumulation time, 'N' is a natural number, and 'F' is the frequency in the PWM control for emitting light from a light-emitting section of the lighting device. (Method 2) A control method for an imaging system according to claim 9, further comprising a step of detecting flicker, wherein the frequency in the PWM control is determined by F=1 / (t×N) when the flicker is not detected, and is determined to be the same as the frequency of the flicker when the flicker is detected.

[0097] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions. [Explanation of symbols]

[0098] 100 Imaging device 103 Image sensor 120 System control unit 400 lighting equipment 412 Video light control unit 413 Video Light 1000 Imaging System

Claims

1. An imaging system including an imaging device and a lighting device communicatively connected to each other, The imaging device is An imaging element; a first control means for controlling a charge accumulation time in the image sensor; The lighting device includes: A light-emitting portion; a second control means for controlling the light emission of the light emitting unit by PWM control; the first control means determines a frequency in the PWM control based on the charge accumulation time and notifies the second control means of the frequency; The imaging system according to claim 1, wherein the second control means controls light emission of the light emitting unit at the frequency of the PWM control notified by the first control means.

2. An imaging system including an imaging device and a lighting device communicatively connected to each other, The imaging device is An imaging element; a first control means for controlling a charge accumulation time in the image sensor; The lighting device includes: A light-emitting portion; a second control means for controlling the light emitting unit by PWM control, the first control means notifies the second control means of the charge accumulation time; The imaging system is characterized in that the second control means determines a frequency in the PWM control based on the charge accumulation time and controls light emission of the light emitting unit.

3. The imaging system according to claim 1 or 2, characterized in that the frequency in the PWM control is determined by F = 1 / (t x N), where 'F' is the frequency in the PWM control, 't' is the charge accumulation time, and 'N' is a natural number.

4. the imaging device includes a detection means for detecting flicker, 4. The imaging system according to claim 3, wherein the frequency under the PWM control is determined by F = 1 / (t × N) when no flicker is detected by the detection means, and is determined to be the same frequency as the frequency of the detected flicker when the detection means detects flicker.

5. 5. The imaging system according to claim 4, wherein when the detecting means detects flicker, the charge accumulation time is set to a natural number multiple of the period of the flicker.

6. 5. The imaging system according to claim 4, wherein when flicker is detected by the detection means, if the frequency under the PWM control cannot be set to the same frequency as the frequency of the detected flicker, the frequency under the PWM control is determined by F = 1 / (t × N).

7. a detection means for detecting luminance information from an image acquired by the imaging element; 3. The imaging system according to claim 1, further comprising: a setting unit that sets a duty ratio in the PWM control based on the luminance information.

8. 3. The imaging system according to claim 1, further comprising a warning unit that issues a warning when the second control unit does not correspond to the frequency in the PWM control determined based on the charge accumulation time.

9. A control method for an imaging system in which an imaging device and a lighting device are communicatively connected, comprising: setting a charge accumulation time in an image pickup element of the image pickup device; a step of determining a frequency in PWM control by F=1 / (t×N), where 't' is the charge accumulation time, 'N' is a natural number, and 'F' is the frequency in PWM control for causing the light-emitting section of the lighting device to emit light.

10. further comprising the step of detecting flicker; 10. The control method for an imaging system according to claim 9, wherein the frequency in the PWM control is determined by F=1 / (t×N) when the flicker is not detected, and is determined to be the same frequency as the frequency of the flicker when the flicker is detected.

11. An imaging element; a communication means for communicating with the lighting device; a determination means for determining a frequency in PWM control by F=1 / (t×N), where 't' is a charge accumulation time of the imaging element, 'N' is a natural number, and 'F' is a frequency in PWM control when the lighting device controls light emission by PWM control; a notification unit that notifies the lighting device of the frequency determined by the determination unit using the communication unit.

12. A light-emitting portion; a control means for controlling the light emitting unit by PWM control; a communication means for communicating with the imaging device; an acquisition unit that acquires a charge accumulation time set in an image pickup element included in the image pickup device using the communication unit, The lighting device is characterized in that the control means determines the frequency in the PWM control by F = 1 / (t x N), where 't' is the charge accumulation time, 'N' is a natural number, and 'F' is the frequency in the PWM control.

13. An imaging element; a light emitting unit that emits light toward a subject; a control unit that controls the light emission of the light emitting unit by PWM control and also controls the charge accumulation time of the image sensor, The imaging device is characterized in that the control means determines the frequency in the PWM control by F = 1 / (t x N), where 't' is the charge accumulation time, 'N' is a natural number, and 'F' is the frequency in the PWM control.

14. A program that causes a computer to execute each step of the method for controlling an imaging system according to claim 9.

Images