JP2010012911A - Luminescence control method of on-vehicle camera and its auxiliary light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for reducing thermal storage by luminescence of an auxiliary light source and for executing effective luminescence control in an electric power saving manner. <P>SOLUTION: The on-vehicle camera and its auxiliary light source include an imaging device 3 for picturing interior of an automobile by the on-vehicle camera, a lighting device 4 for radiating light to an imaging area of the imaging device 3 and a light-emission control device 2 for controlling a luminescence signal to the lighting device 4 by detecting brightness values of various sensors and a pictured image. The light-emission control device 2 generates the luminescence signal for synchronizing with an exposure signal of an imaging device 3 and supplies it to the lighting device 4 in the case that a mean radiance value of the pictured image is less than a predetermined threshold value and detection signals of the various sensor indicate possibility of risk on its own vehicle. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vehicle-mounted camera and a light emission control method for an auxiliary light source mounted on the vehicle-mounted camera.

  A technique is known in which an in-vehicle camera is used to image the vicinity of a vehicle or a passenger compartment, and the captured image is used for various controls. In general, these in-vehicle cameras are equipped with an auxiliary light source for ensuring imaging illuminance, and there is a problem that a problem is caused by the generated heat.

  In this regard, in the technique described in Patent Document 1, heat storage is reduced by synchronizing the light emission of the auxiliary light source with the video capture timing of the in-vehicle camera.

JP 2005-271836 A

  However, in such a technique, since the in-vehicle camera continues to capture images, the auxiliary light source needs to emit light at every video capture timing.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a technique for reducing heat storage due to light emission of an auxiliary light source and performing efficient and power-saving light emission control.

  In order to solve the problems described above, an in-vehicle camera according to the present invention includes an imaging unit for imaging a predetermined area, an auxiliary light source of the imaging unit, and an image captured by the imaging unit having a predetermined brightness or less. And a control means for controlling the light emission timing of the auxiliary light source when the detection signal of the sensor for detecting the traveling state of the moving object indicates a risk of an accident. It is characterized by providing.

  As described above, according to the present invention, it is possible to execute efficient and power-saving light emission control.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of the in-vehicle camera 1 according to the first embodiment.

  The in-vehicle camera 1 includes an imaging device 3 that images a vehicle interior with a solid-state imaging device, an illumination device 4 that irradiates light to an imaging region of the imaging device 3, a light emission control device 2 that outputs a light emission signal to the illumination device 4, and Is provided.

  The imaging device 3 has an exposure control circuit (not shown) that generates an exposure signal having a constant or variable period, and images a predetermined area with an exposure time determined by the exposure signal. Then, the captured image is output to the light emission control device 2 and an exposure signal is provided in accordance with the request of the light emission control device 2.

  Specifically, the imaging device 3 is an image sensor configured by a solid-state imaging element such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS). The solid-state imaging device is exposed at the same cycle as the frequency in accordance with an exposure signal generated by an exposure control circuit included in the imaging device 3, and outputs an image signal.

  Further, for example, as illustrated in FIG. 2, the imaging device 3 according to the present embodiment is installed on a ceiling or the like of the passenger seat and images the vicinity of the passenger seat. Furthermore, the imaging device 3 has sensitivity in at least the infrared spectrum region, and can receive reflected light of near-infrared light irradiated by the illumination device 4 described later. In addition, it is good also as a structure which receives only the near-infrared light which the illuminating device 4 irradiates using the filter which permeate | transmits the wavelength range of infrared light.

  In addition, the installation position and the number of the imaging devices 3 are not limited to the above, and any number may be installed at any position. For example, the driver seat, the rear seat, and the periphery of the vehicle can be installed at a position where the imaging region is used.

  Moreover, the captured image by the imaging device 3 is output to another in-vehicle system via the image processing device 5, for example. The image processing device 5 performs processing such as noise removal, contour enhancement, binarization processing, and the like on the image signal received from the imaging device 3 via the interface unit 25. And the said image is supplied to the apparatus which performs various control regarding a vehicle including other vehicle-mounted systems, for example, various passenger protection means. As the occupant protection means, there is an air bag or the like that reduces the impact on the occupant during a collision.

  The illumination device 4 receives a light emission signal from the light emission control device 2 and irradiates the imaging region of the imaging device 3 with near infrared light.

  Specifically, the illumination device 4 includes a light source (for example, LED; light emitting diode) that can irradiate near infrared light, and is based on a light emission signal from the light emission control device 2 that is synchronized with an exposure signal of the imaging device 3. Near-infrared light is irradiated at the light emission timing.

  In addition, the illuminating device 4 which concerns on this embodiment is integral with the imaging device 3, and has an irradiation area which can irradiate the imaging area of the imaging device 3. FIG. Note that the illumination device 4 and the imaging device 3 may be provided separately as long as the imaging region of the imaging device 3 can be irradiated.

  The light emission control device 2 includes a control unit 20, a storage unit 24, and an interface unit (hereinafter referred to as I / F unit) 25.

  The control unit 20 includes an image processing unit 21 that detects a luminance value of a captured image, a situation determination unit 22 that determines the necessity of light emission of the illumination device 4 based on the luminance value and a detection signal from the sensor, and the imaging device 3. And a light emission control unit 23 for generating a light emission signal synchronized with the exposure signal from.

  When the image processing unit 21 receives a captured image from the imaging device 3 according to the frame rate, the image processing unit 21 converts the image into digital data and stores the digital data in a frame memory (not shown) of the storage unit 24. Then, a luminance value is detected for the vertical line 9 at the horizontal axis center point of this image, and this value is output to the situation determination unit 22.

  The detected luminance value may be detected in any way, such as an average value of luminance values for each pixel constituting the vertical line 9 or an integrated value thereof. Here, the pixel group constituting the vertical line 9 is detected. The average luminance value of. Of course, other than the vertical line 9, for example, the luminance value of all the pixels or the luminance value of another specific area may be used.

  Based on the average luminance value of the vertical line 9 and the detection signal from the sensor, the situation determination unit 22 determines the necessity of light emission of the illumination device 4 during the capture (exposure) of the next frame executed by the imaging device 3. To do.

Specifically, the situation determination unit 22 first compares the average luminance value with a predetermined threshold Th ₁ stored in advance in the storage unit 24.

Note that the predetermined threshold Th ₁ defines the brightness at which a captured image that does not cause a problem in subsequent processing performed using the captured image of the imaging device 3, such as face recognition, can be acquired. In such a case, the average luminance value in the vertical line 9 is set in advance. Therefore, the situation determining section 22, when the average brightness value is less than the threshold value Th _1, it is determined that it is necessary to light emission of the lighting device 4.

  The necessity of light emission can also set a suitable determination condition depending on whether or not a detection signal of a sensor included in the host vehicle indicates a possibility that the host vehicle is dangerous. Hereinafter, an example in which detection signals from the vehicle speed sensor 71 and the brake sensor 72 according to the present embodiment are used will be described.

  The vehicle speed sensor 71 generates a pulse signal corresponding to the rotational speed and outputs it at a constant cycle. The vehicle speed sensor 71 may be any sensor that can detect the vehicle speed, and may be a wheel speed sensor that detects the rotation speed of each wheel, or a rotation that detects the rotation speed of the axle connected to the wheel. It may be a sensor.

  The brake sensor 72 detects the depression state of the brake pedal by the driver and outputs a detection signal corresponding to the state. For example, an on signal is output when the driver depresses the brake pedal, and an off signal is output when the driver releases the brake pedal by releasing his / her foot from the brake.

  The situation determination unit 22 calculates the vehicle speed v based on the detection signal from the vehicle speed sensor 71, and compares the vehicle speed v with a predetermined threshold value stored in advance in the storage unit 24.

  The predetermined threshold value may be determined in any way, and may be determined on the assumption that, for example, the brake is stepped on at a distance of 20 km or more which is considered to have a high risk of accident.

  Therefore, when the vehicle speed v is greater than the threshold value, the situation determination unit 22 acquires a detection signal from the brake sensor 72 and determines whether an on (brake) signal is detected. When the ON signal is detected, it is determined that the lighting device 4 needs to emit light, and the light emission control unit 23 is requested to start signal processing.

  Even when it is considered that the host vehicle is stopped from the vehicle speed signal, the situation determination unit 22 requests the light emission control unit 23 to start signal processing because there is a risk of collision from another vehicle.

  As an initial operation, the light emission control unit 23 generates a light emission signal whose initial state is maintained at a low level by a light emission signal generation circuit (not shown), and always outputs it to the illumination device 4. The LED provided in the illumination device 4 emits light when the light emission signal is High, and does not emit light when the Light signal is Low.

  Further, the light emission control unit 23 supplies a light emission signal synchronized with the exposure signal to the illumination device 4 for the next one cycle of the exposure signal (that is, the next exposure time).

  Specifically, when receiving a signal processing start request from the situation determination unit 22, the light emission control unit 23 first requests the imaging device 3 to output an exposure signal and receives the input of the signal.

  Next, the light emission control unit 23 sets the light emission signal to High based on the next rising edge of the exposure signal, and sets the light emission signal to Low based on the falling edge. After that, the Low state is maintained until there is a light emission request again.

  The storage unit 24 stores a captured image from the imaging device 3. In addition, information necessary for executing various processes, for example, each threshold value is stored in advance.

  The I / F unit 25 connects the light emission control device 2 to other devices so as to be able to transmit and receive information. The communication may be performed by any means.

  Here, the hardware configuration of the light emission control device 2 will be described. FIG. 8 is a block diagram showing an electrical configuration of the light emission control device 2.

  As shown in FIG. 8, the light emission control device 2 is a main part of a computer, and a CPU (Central Processing Unit) 201 that centrally controls each device, a memory 202 that stores various data in a rewritable manner, Is provided. Further, the light emission control device 2 includes an external storage device 203 that stores various programs, data generated by the program, and a communication device 204 that communicates with an external device. Each of these devices is connected to the CPU 201 via a signal line 205 such as a bus.

  For example, the CPU 1 executes various processes by loading a program stored on the external storage device 203 onto the memory 202 and executing the program.

  Processing in the light emission control device 2 configured as described above will be described with reference to the flowchart shown in FIG. FIG. 3 is a flowchart showing a flow of processing in which the light emission control device 2 controls light emission of the LEDs included in the illumination device 4.

  When the supply of power is started, the light emission control device 2 starts acquiring a captured image from the imaging device 3 and starts supplying a light emission signal whose initial state is maintained at a low level to the illumination device 4. Start.

  When receiving the captured image from the imaging device 3, the image processing unit 21 calculates an average luminance value of a predetermined region (S101).

  Specifically, when the image processing unit 21 acquires a captured image according to the frame rate of the imaging device 3, for the vertical line 9 at the horizontal axis center point of the image, the image processing unit 21 calculates an average luminance value of a pixel group constituting the vertical line 9. Then, this value is output to the situation determination unit 22.

The situation determination unit 22 compares the average luminance value with the threshold Th ₁ (S102).

Specifically, when receiving the average luminance value from the image processing unit 21, the situation determination unit 22 reads a predetermined threshold value Th ₁ stored in advance in the storage unit 24 and compares it with the average luminance value. If it is smaller than Th ₁ (YES), the process proceeds to step 103, and if the average luminance value is not smaller than the threshold Th ₁ (NO), the process is terminated.

When the average luminance value is smaller than the threshold Th ₁ (YES), the situation determination unit 22 compares the vehicle speed with a predetermined threshold (S103).

  Specifically, the situation determination unit 22 acquires a detection signal from the vehicle speed sensor 71 to calculate the vehicle speed v, and reads and compares a predetermined threshold value stored in advance in the storage unit 24. If the vehicle speed v is greater than the threshold (YES), the process proceeds to step 104, and if the average luminance value is not greater than the threshold (NO), the process proceeds to step 107.

  When the vehicle speed v is greater than the threshold value in step 103 (YES), the situation determination unit 22 detects whether or not the brake signal is on (S104).

  Specifically, the situation determination unit 22 acquires a detection signal of the brake sensor 72 and determines whether or not an on signal is detected. When the ON signal is detected (YES), the situation determination unit 22 requests the light emission control unit 23 to start signal processing and proceeds to step 105. If no ON signal is detected (NO), the process is terminated.

  When the vehicle speed v is not greater than the threshold value in step 103 (NO), the situation determination unit 22 detects whether or not the host vehicle is stopped (S107).

  Specifically, when it is determined from the vehicle speed signal in the vehicle speed sensor 71 that the host vehicle is stopped (YES), the situation determination unit 22 requests the light emission control unit 23 to start signal processing, and step 105 Proceed to If it is determined that the host vehicle is not stopped (NO), the process is terminated.

  Upon receiving a signal processing start request, the light emission control unit 23 requests the imaging apparatus 3 to output an exposure signal and receives the signal (S105).

  Next, the light emission control unit 23 supplies the light emission signal synchronized with the exposure signal to the illumination device 4 (S106).

  Specifically, the light emission control unit 23 sets the light emission signal to High based on the next rising edge of the exposure signal, sets the light emission signal to Low based on the falling edge, and outputs the light emission signal to the illumination device 4. Then, it returns to step 103 and repeats a process.

  The first embodiment of the present invention has been described above. In addition, this invention is not restrict | limited to the said embodiment, A various deformation | transformation is possible within the range of the technical idea of this invention.

  For example, a detection signal is obtained from a steering angle sensor that detects a steering angle, an acceleration sensor that detects acceleration, an angular velocity sensor that detects angular velocity, a radar device that detects surrounding obstacles, and the like. It is possible to determine the necessity of light emission based on the driving situation. For example, when the steering angle or acceleration changes greatly, or when the distance to the obstacle is short, the light emission control unit 23 may be requested to start signal processing.

  Moreover, it is good also as a structure which detects the brightness of a vehicle interior by the illumination intensity sensor which detects the illumination intensity of a room interior instead of calculating the average luminance value of a captured image.

  According to such a configuration, the light emission of the lighting device 4 is controlled according to the light emission conditions corresponding to various situations that are considered to have a high possibility of danger to the host vehicle, and more reliable illumination around the vehicle and in the passenger compartment is achieved. Is possible.

  With the configuration as described above, the in-vehicle camera 1 according to the present embodiment suggests that there is a possibility that the detection signal from the sensor may pose a danger to the host vehicle when the amount of light necessary for processing is insufficient. In this case, the lighting device is caused to emit light and the light-off state is normally maintained, so that power consumption and heat storage of the lighting device can be suppressed, and efficient operation is possible.

  Next, the in-vehicle camera 10 according to the second embodiment of the present invention will be described. The in-vehicle camera 10 monitors the temperature in the imaging device 30 and varies the light emission time of the LED for each cycle in order to reduce the influence of the luminescent heat on the imaging device 30.

  The in-vehicle camera 10 according to the second embodiment includes an imaging device 30 having a temperature sensor 31, a lighting device 4 that emits light to an imaging region of the imaging device 30, and a light emission control device that supplies a light emission signal to the lighting device 4. 200.

  Hereinafter, a different part is demonstrated compared with the vehicle-mounted camera 1 concerning 1st embodiment.

  The imaging device 30 has substantially the same configuration as the imaging device 3 according to the first embodiment, but differs in that it includes a temperature sensor 31.

  The temperature sensor 31 is, for example, a control register mounted on a solid-state imaging device, and may be any device as long as the temperature status can be monitored.

  The light emission control device 200 includes a control unit 201, a storage unit 240, and an I / F unit 25.

  The control unit 201 acquires captured images at regular intervals and detects the luminance value, and the situation in which the lighting time of the lighting device 4 is specified based on the temperature status and the luminance value of the imaging device 30. The determination part 220 and the light emission control part 230 which produces | generates the light emission signal match | combined with the specified light emission time are provided.

  The image processing unit 210 executes substantially the same processing as in the first embodiment, but here, the image output from the imaging device 30 is acquired and stored at regular intervals (for example, every 10 frames). Store in the unit 240. Further, the average luminance value of the vertical line 9 of the image is calculated and output to the situation determination unit 220.

  The situation determination unit 220 identifies the light emission time of the illumination device 4 based on the temperature status of the imaging device 30 and the average luminance value of the vertical line 9.

  Specifically, the situation determination unit 220 first requests the imaging device 30 to provide the latest temperature status monitored by the temperature sensor 31, and the temperature is equal to or higher than a predetermined threshold value stored in advance in the storage unit 240. Judge whether there is.

  Although this predetermined threshold value may be determined in any way, here, the temperature when the imaging device 30 stores heat by light emission, for example, about 50 ° C. is set.

  When the temperature of the imaging device 30 is equal to or higher than the threshold, the situation determination unit 220 modulates the light emission time of the LED for each period, that is, the High pulse width (duty ratio) of the light emission signal.

  The pulse width modulation is executed based on the average luminance value detected by the image processing unit 210 with reference to, for example, a modulation table 221 as shown in FIG.

The modulation table 221 is stored in advance in the storage unit 240, and includes an average luminance value storage area 221a and a duty ratio storage area 221b. In the average luminance value storage area 221a, information for determining the range of the average luminance value in stages is stored, and the duty ratio of the light emission signal corresponding to the range is stored in the duty ratio storage area 221b (here, The relationship between the threshold values is Th ₁ > Th ₂ > Th ₃ ).

  The range of the average luminance value and the corresponding duty ratio may be determined in any way, but the exposure time is not greatly affected by reducing the light emission time of the LED, that is, it does not affect the subsequent processing. It is desirable that the captured image can be acquired.

For example, when the average luminance value is high enough that an auxiliary light source is unnecessary (for example, Th ₁ or more as described above), the light emission time having a short (High pulse width c) is selected, and the processing described later is as shown in FIG. A light emission signal C is generated. In this case, the LED may stop emitting light by generating a light emission signal whose duty ratio is 0%, that is, at a low level. When the average luminance value is lower than Th ₁ , the duty ratio of the High pulse widths a and b is selected based on the average luminance value, and the light emission signals A and B are generated.

  Specifically, when the temperature of the imaging device 30 is equal to or higher than the threshold value, the situation determination unit 220 belongs to which range the average luminance value detected by the image processing unit 210 is stored in the average luminance value storage area 221a. And the corresponding duty ratio is acquired from the duty ratio storage area 221b and output to the light emission control unit 230.

  The light emission control unit 23 receives an exposure signal from the imaging device 30 as an initial operation, generates a light emission signal synchronized with the signal, and supplies the light emission signal to the illumination device 4.

  When the light emission control unit 23 receives the duty ratio from the situation determination unit 220, the light emission control unit 23 modulates the pulse width of the light emission signal currently being output to a pulse width corresponding to the duty ratio, and generates a light emission signal as shown in FIG. Generate.

  Note that the light emission control unit 23 may further execute a phase or amplitude modulation process in order to generate a more suitable light emission signal upon exposure of the imaging device 30.

  Processing in the light emission control device 200 configured as described above will be described with reference to the flowchart shown in FIG. FIG. 7 is a flowchart showing a flow of processing in which the light emission control device 200 controls the light emission of the LED included in the lighting device 4.

  When the supply of power is started, the light emission control device 200 acquires a captured image from the image pickup device 3 at a constant period, and starts generating and supplying a light emission signal synchronized with the supply of the exposure signal, Start this flow.

  First, the situation determination unit 220 requests the imaging device 30 to provide the latest temperature status monitored by the temperature sensor 31, and acquires this (S201).

  Next, the situation determination unit 220 determines whether or not the temperature of the imaging device 30 is equal to or higher than a predetermined threshold stored in advance in the storage unit 240 (S202). When the temperature of the imaging device 30 is equal to or higher than a predetermined threshold (YES), a luminance value calculation request is output to the image processing unit 210 and the process proceeds to Step 203. When the temperature is not equal to or higher than the predetermined threshold (NO), The process ends.

  When the temperature of the imaging device 30 is equal to or higher than the predetermined threshold (YES in step 202), when the image processing unit 210 receives a luminance value calculation request, the pixels constituting the vertical line 9 for the latest acquired captured image The average luminance value of the group is calculated (S203) and supplied to the situation determination unit 220.

  When the situation determination unit 220 is supplied with the average luminance value, the situation determination unit 220 refers to the modulation table 221 stored in the storage unit 240 and identifies the range to which the average luminance value belongs and the corresponding duty ratio. (S204). Then, the specified duty ratio is output to the light emission control unit 230.

  When receiving the provision of the duty ratio, the light emission control unit 230 generates a light emission signal obtained by modulating the pulse width of the currently output light emission signal to a pulse width corresponding to the duty ratio, and supplies the light emission signal to the lighting device 4. (S205).

  The second embodiment of the present invention has been described above.

  With the configuration as described above, the in-vehicle camera 10 according to the present embodiment suitably controls the light emission time of the lighting device 4 even when the imaging device 30 is affected by the light emission heat of the lighting device 4. Thus, it is possible to prevent a failure due to heat storage.

  Moreover, you may apply the vehicle-mounted camera 10 concerning 2nd embodiment to the vehicle-mounted camera 1 concerning 1st embodiment. According to such a configuration, it is possible to more efficiently control both the lighting and extinguishing and the light emission time during lighting.

  Furthermore, the vehicle-mounted camera 10 may be configured to specify the duty ratio based on the temperature value detected by the temperature sensor without using the average luminance value. According to such a configuration, it is possible to reduce the load due to image processing and perform processing at a higher speed of light.

  In the above embodiment, the configuration of the in-vehicle camera mounted on the automobile has been described. However, the present invention can also be applied to other moving bodies such as aircraft and ships.

FIG. 1 is a block diagram showing the configuration of the in-vehicle camera 1 according to the first embodiment. FIG. 2 is a schematic diagram illustrating a captured image of the imaging device 3. FIG. 3 is a flowchart showing a flow of processing in which the light emission control device 2 controls the light emission of the LED included in the illumination device 4. FIG. 4 is a block diagram showing the configuration of the in-vehicle camera 1 according to the second embodiment. FIG. 5 is a schematic diagram of the modulation table 221. FIG. 6 is a timing chart showing LED light emission control. FIG. 7 is a flowchart showing a flow of processing in which the light emission control device 200 controls the light emission of the LED included in the lighting device 4. FIG. 8 is a block diagram showing an electrical configuration of the light emission control device 2.

Explanation of symbols

1.10: In-vehicle camera, 2.200: Light emission control device, 3.30: Imaging device, 4: Illumination device, 5 ... Image processing device, 71: Vehicle speed sensor, 72: Brake sensor, 20.201: Control unit, 21/210: Image processing unit, 22/220: Status determination unit, 23/230: Light emission control unit, 24/240: Storage unit, 25: Interface unit

Claims (7)

Imaging means for imaging a predetermined area;
An auxiliary light source of the imaging means;
When the image picked up by the image pickup means is less than or equal to a predetermined brightness, and when the detection signal of the sensor for detecting the traveling state of the moving body is an indication of the risk of an accident,
And a control means for controlling the light emission timing of the auxiliary light source. The in-vehicle camera according to claim 1,
The sensor detects the speed of the moving body and that the brake device is operated,
The control means, when the luminance value is less than or equal to a first threshold value,
An in-vehicle camera, wherein the auxiliary light source is caused to emit light when it is detected that the speed of the moving body is equal to or higher than a second threshold and the brake device is operated. The in-vehicle camera according to claim 1 or 2,
The sensor detects the speed of the moving body and that the brake device is operated,
The control means, when the luminance value is less than or equal to a first threshold value,
An in-vehicle camera that emits the auxiliary light source when detecting that the moving body is stopped. The vehicle-mounted camera according to any one of claims 1 to 3,
The vehicle-mounted camera, wherein the control unit causes the auxiliary light source to emit light at a light emission timing synchronized with an exposure timing of the imaging unit. Imaging means for imaging a predetermined area;
An auxiliary light source of the imaging means;
A sensor for detecting the temperature of the imaging means;
And a control unit that controls a light emission time of the auxiliary light source when a temperature detected by the sensor is equal to or higher than a predetermined temperature. The in-vehicle camera according to claim 5,
The control means further detects a luminance value of an image captured by the imaging means,
When the detected temperature of the sensor is equal to or higher than a third threshold value,
The in-vehicle camera, wherein the auxiliary light source emits light for a predetermined light emission time corresponding to the luminance value. A method for controlling light emission of an auxiliary light source included in an in-vehicle camera,
Imaging a predetermined area;
Detecting a luminance value of the captured image;
Obtaining a detection signal of a sensor for detecting a traveling state of a moving object when the luminance value is equal to or lower than a predetermined brightness;
And a step of causing the auxiliary light source to emit light at a light emission timing synchronized with an exposure timing when a detection signal of the sensor indicates a risk of an accident. Light emission control method of light source.

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