Patent Publication Number: US-2023156341-A1

Title: Gating camera, sensing system for vehicle, and lighting unit for vehicle

Description:
TECHNICAL FIELD 
     The present invention relates to a gated camera. 
     BACKGROUND ART 
     For automatic driving and automatic control on light distribution of a headlamp, an object identification system that senses a position and a type of an object present around a vehicle is used. The object identification system includes a sensor and an arithmetic processing device that analyzes an output of the sensor. The sensor is selected from a camera, light detection and ranging or laser imaging detection and ranging (LiDAR), a millimeter wave radar, an ultrasonic sonar, and the like in consideration of use, required accuracy, and cost. 
     It is not possible to obtain depth information from a general monocular camera. Therefore, when a plurality of objects located at different distances overlap one another, it is difficult to separate them from one another. 
     As a camera from which the depth information is obtained, a time of flight camera (TOF camera) is known. The time of flight (TOF) camera projects infrared light by a light emitting device, measures a flight time until reflected light returns to an image sensor, and obtains a TOF image in which the flight time is converted into distance information. 
     An active sensor (hereinafter, referred to as gated camera or gating camera in the present description) has been proposed in place of the TOF camera (Patent Literatures 1 and 2). The gated camera divides an imaging range into a plurality of ranges, and performs imaging by changing an exposure timing and an exposure time for each range. Accordingly, a slice image is obtained for each target range, and each slice image merely includes the object included in the corresponding range. 
     Citation List 
     Patent Literature 
     
         
         Patent Literature 1: JP2009-257981A 
         Patent Literature 2: WO2017/110417A1 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     1. The present inventors have recognized that, at the time of operating a gated camera, noise in horizontal stripes may randomly occur in an output image (sensor image) of an image sensor, and an image quality of a slice image may be deteriorated. 
     An aspect of the present invention has been made in such a situation, and an exemplary object thereof is to provide a gated camera capable of preventing deterioration in a slice image. 
     2. The gated camera includes an image sensor and an image processing device that processes an output image (sensor image) of the image sensor. Here, the image sensor and the image processing device are often connected by a serial interface, and a transmission speed of the sensor image during this connection becomes a bottleneck, a time required to generate one slice image becomes long, and a frame rate of the gated camera is limited. 
     An aspect of the present invention has been made in such a situation, and an exemplary object thereof is to provide a gated camera capable of shortening a generation time of a slice image. 
     3. Since the gated camera in the related art performs one exposure for one light emission, merely the slice image of one range is generated for each light emission. Therefore, in order to sense all of N ranges, a set of light emission and exposure is required N times, and a sensing time becomes long. When light emission and exposure are repeatedly integrated a plurality of times at the time of imaging a distant range, the sensing time becomes further longer. 
     An aspect of the present invention has been made in such a situation, and an exemplary object thereof is to provide a gated camera capable of shortening a sensing time. 
     Solution to Problem 
     1. A gated camera according to an aspect of the present invention divides a depth direction into a plurality of ranges and generates a plurality of slice images corresponding to the plurality of ranges. The gated camera includes an illumination device configured to radiate probe light, an image sensor, a controller configured to control a light emission timing of the illumination device and an exposure timing of the image sensor, and an image processing device configured to generate the slice images based on a sensor image transmitted from the image sensor. The image processing device selects M (M ≥ 2) pixel values in ascending order of pixel values for each line of the sensor image, calculates an average value of the M pixel values, and subtracts the average value from each pixel value of the corresponding line. 
     2. An aspect of the present invention relates to a gated camera configured to divide a depth direction into a plurality of ranges and generate a plurality of slice images corresponding to the plurality of ranges. The gated camera includes an illumination device configured to radiate probe light, an image sensor including a plurality of pixels, a controller configured to control a light emission timing of the illumination device and an exposure timing of the image sensor, and an image processing device configured to generate the slice images based on a sensor image transmitted from the image sensor. A resolution of the sensor image transmitted from the image sensor to the image processing device is lower as the range is closer. 
     3. An aspect of the present invention relates to a gated camera configured to divide a depth direction into a plurality of ranges and generate a plurality of slice images corresponding to the plurality of ranges. The gated camera includes an illumination device configured to radiate probe light, an image sensor including a plurality of pixels, and a controller configured to control a light emission timing of the illumination device and an exposure timing of the image sensor. The plurality of pixels of the image sensor are classified into a plurality of pixel groups, and the controller exposes the plurality of pixel groups at different timings with respect to one light emission of the illumination device. 
     Advantageous Effects of Invention 
     According to a first aspect of the present invention, an image quality of a slice image can be improved. According to a second aspect of the present invention, a generation time of a slice image can be shortened. According to a third aspect of the present invention, a sensing time can be shortened. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a block diagram of a sensing system according to a first embodiment. 
         FIG.  2    is a diagram showing a basic operation of a gated camera. 
         FIG.  3 A  and  FIG.  3 B  are diagrams showing slice images obtained by the gated camera. 
         FIG.  4    is a diagram showing a noise in a sensor image S1. 
         FIG.  5    is a diagram showing noise cancellation by an image processing device. 
         FIGS.  6 A and  6 B  are diagrams showing sensor images before and after noise subtraction processing. 
         FIGS.  7 A and  7 B  are diagrams showing sensor images before and after noise subtraction processing. 
         FIG.  8    is a block diagram of a sensing system according to a second embodiment. 
         FIG.  9    is a diagram showing a basic operation of a gated camera. 
         FIGS.  10 A and  10 B  are diagrams showing slice images obtained by the gated camera. 
         FIG.  11    is a diagram showing an example of control on a resolution of the sensor image S 1  depending on a range. 
         FIG.  12 A  is a diagram showing a certain traveling scene, and  FIG.  12 B  is a diagram showing sensor images Slx and Sly obtained in the traveling scene in  FIG.  12 A . 
         FIG.  13 A  is a time chart showing an operation of the gated camera, and  FIG.  13 B  is a time chart showing an operation of a gated camera according to a comparative technique. 
         FIG.  14    is a diagram showing another example of control on the resolution of the sensor image S l  depending on the range. 
         FIG.  15    is a diagram showing still another example of control on the resolution of the sensor image S l  depending on the range. 
         FIG.  16    is a block diagram of a gated camera according to a second modification. 
         FIG.  17    is a diagram showing exposure of the gated camera according to the second modification. 
         FIG.  18    is a time chart showing an operation of the gated camera according to the second modification. 
         FIG.  19    is a block diagram of a sensing system according to a third embodiment. 
         FIG.  20    is a time chart showing an operation of the gated camera in  FIG.  19   . 
         FIGS.  21 A and  21 B  are diagrams showing slice images obtained by the gated camera in  FIG.  19   . 
         FIGS.  22 A to  22 D  are diagrams showing examples of pixel groups. 
         FIG.  23    is a block diagram of the sensing system. 
         FIGS.  24 A and  24 B  are diagrams showing an automobile including the gated camera. 
         FIG.  25    is a block diagram showing a vehicle lamp including an object detection system. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Overview of Embodiments 
     An overview of some exemplary embodiments of the present invention will be described. As an introduction of the detailed description to be described later, this overview is intended to simplify and describe some concepts of one or more embodiments for the purpose of basic understanding of the embodiments, and does not limit the scope of the invention or disclosure. In addition, this overview is not a comprehensive overview of all conceivable embodiments, and is not intended to limit components that are essential to the embodiments. For convenience, “one embodiment” may be used to refer to one embodiment (example or modification) or a plurality of embodiments (example or modification) disclosed in the present description. 
     This overview is not an extensive overview of all conceivable embodiments, and does not intend to specify an important component of all embodiments or to draw a range of a part or all of aspects. As an introduction of the detailed description to be presented later, one of the purposes is to present some concepts of one or more embodiments in a simplified form. 
     1. A gated camera according to an embodiment divides a depth direction into a plurality of ranges, and generates a plurality of slice images corresponding to the plurality of ranges. The gated camera includes an illumination device configured to radiate probe light, an image sensor, a controller configured to control a light emission timing of the illumination device and an exposure timing of the image sensor, and an image processing device configured to generate the slice images based on a sensor image transmitted from the image sensor. The image processing device selects M (M ≥ 2) pixel values in ascending order of pixel values for each line of the sensor image, calculates an average value of the M pixel values, and subtracts the average value from each pixel value of the corresponding line. 
     According to this configuration, noise in horizontal stripes can be reduced, and an image quality can be improved. 
     In an embodiment, M may be 2% to 8% of the number of pixels of the corresponding line. 
     2. A gated camera according to an embodiment divides a depth direction into a plurality of ranges, and generates a plurality of slice images corresponding to the plurality of ranges. The gated camera includes an illumination device configured to radiate probe light, an image sensor including a plurality of pixels, a controller configured to control a light emission timing of the illumination device and an exposure timing of the image sensor, and an image processing device configured to generate the slice images based on a sensor image transmitted from the image sensor. A resolution of the sensor image transmitted from the image sensor to the image processing device is lower as the range is closer. 
     In a case where the same subject is imaged by the gated camera, when the subject is present in a distant range, the subject is small, that is, the subject is imaged at a low resolution, and when the subject is present in a close range, the subject is large, that is, the subject is captured at a high resolution. Therefore, as the distance to the subject is shorter, in other words, as the range is closer, by reducing the resolution of the sensor image transmitted from the image sensor to the image processing device, it is possible to shorten a transmission time of the sensor image and shorten a generation time of the slice images while maintaining the resolution necessary for the subsequent processing. 
     In an embodiment, the image sensor may be capable of specifying presence or absence of transmission for each line for the plurality of pixels, and the number of lines to be skipped is larger as the range is closer. 
     In an embodiment, the image sensor may be capable of specifying presence or absence of transmission for each column for the plurality of pixels, and the number of columns to be skipped is larger as the range is closer. 
     In an embodiment, the image sensor may be capable of specifying presence or absence of transmission for each of the plurality of pixels, and the number of pixels to be skipped is larger as the range is closer. 
     In an embodiment, the image sensor exposes all of the pixels in all of the ranges. 
     In an embodiment, the image sensor merely exposes pixels to be transmitted in each range. 
     In an embodiment, the plurality of pixels of the image sensor are classified into a plurality of groups. The controller exposes the plurality of groups at different timings with respect to one light emission of the illumination device. Accordingly, the plurality of ranges can be imaged in parallel. 
     In an embodiment, the image processing device scales the sensor image transmitted from the image sensor such that slice images having same aspect ratio are obtained for each range. The scaling may use interpolation processing or thinning-out processing. 
     A gated camera according to an embodiment divides a depth direction into a plurality of ranges, and generates a plurality of slice images corresponding to the plurality of ranges. The gated camera includes an illumination device configured to radiate probe light, an image sensor including a plurality of pixels, and a controller configured to control a light emission timing of the illumination device and an exposure timing of the image sensor. The plurality of pixels of the image sensor are classified into a plurality of pixel groups, and the controller exposes the plurality of pixel groups at different timings with respect to one light emission of the illumination device. 
     According to an embodiment, images of a plurality of ranges can be generated for one light emission. Therefore, a sensing time required to generate the slice images of all of the ranges can be shortened. 
     In an embodiment, when number of the plurality of pixel groups is n (n ≥ 2), an i-th pixel group may include an (i+n×j)-th (j is an integer) line. 
     In an embodiment, when number of the plurality of pixel groups is n (n ≥ 2), an i-th pixel group may include an (i+n×j)-th (j is an integer) column. 
     In an embodiment, the gated camera may further include an image processing device configured to generate the slice images based on a sensor image transmitted from the image sensor. The sensor image generated for each of the pixel groups is transmitted as a unit from the image sensor to the image processing device. 
     Embodiment 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. The same or equivalent components, members, and processing shown in the drawings are indicated by the same reference numerals, and repeated description thereof will be appropriately omitted. In addition, the embodiments are not intended to limit the scope of the present invention and are merely for illustration, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention. 
     First Embodiment 
       FIG.  1    is a block diagram of a sensing system  10  according to a first embodiment. The sensing system  10  is mounted on a vehicle such as an automobile or a motorcycle, and detects an object OBJ present around the vehicle. 
     The sensing system  10  mainly includes a gated camera  20 . The gated camera  20  includes an illumination device  22 , an image sensor  24 , a controller  26 , and an image processing device  28 . Imaging by the gated camera  20  is performed by dividing a depth direction into a plurality of N (N ≥ 2) ranges RNG 1  to RNGN. Adjacent ranges may overlap each other in the depth direction at boundaries thereof. 
     The illumination device  22  radiates probe light L1 toward the front of the vehicle in synchronization with a light emission timing signal S l  supplied from the controller  26 . The probe light L1 is preferably infrared light, but is not limited thereto, and may be visible light or ultraviolet light having a predetermined wavelength. 
     The image sensor  24  includes a plurality of pixels, can perform exposure control in synchronization with an exposure timing signal S 2  supplied from the controller  26 , and generates a sensor image SI. The image sensor  24  has sensitivity to the same or similar wavelength as that of the probe light L 1 , and images reflected light (return light) L 2  reflected by the object OBJ. A sensor image obtained for an i-th range RNGi is indicated by SIi. 
     The controller  26  controls a radiation timing (light emission timing) of the probe light L 1  by the illumination device  22  and an exposure timing by the image sensor  24 . The controller  26  can be implemented by a combination of a processor (hardware) such as a central processing unit (CPU), a micro processing unit (MPU), or a microcomputer and a software program executed by the processor (hardware). 
     The image sensor  24  and the image processing device  28  are connected via a serial interface, and the sensor image SIi imaged by the image sensor  24  is transmitted to the image processing device  28 . The image processing device  28  generates a slice image IMGi based on the sensor image SIi transmitted from the image sensor  24 . 
       FIG.  2    is a diagram showing a basic operation of the gated camera  20 .  FIG.  2    shows a state in which the i-th range RNGi is sensed. The illumination device  22  emits light during a light emission period τ1 between times t0 and t1 in synchronization with the light emission timing signal S1.An uppermost stage shows a diagram of light beams in which a horizontal axis indicates time and a vertical axis indicates distance. A distance from the gated camera  20  to a front boundary of the range RNGi is indicated by dMINi, and a distance from the gated camera  20  to a rear boundary of the range RNGi is indicated by dMAXi. 
     A round-trip time TMINi until the light that departs from the illumination device  22  at a certain time reaches the distance dMINi and the reflected light returns to the image sensor  24  is TMINi = 2 × dMINi/c. c is the speed of light. 
     Similarly, a round-trip time TMAXi until the light that departs from the illumination device  22  at a certain time reaches the distance dMAXi and the reflected light returns to the image sensor  24  is TMAXi = 2 x dMAXi/c. 
     When it is desired to image merely the object OBJ included in the range RNGi, the controller  26  generates the exposure timing signal S 2  so as to start the exposure at a time t2 = t0 + TMINi and end the exposure at a time t3 = t1 + TMAXi. This is one exposure operation. 
     At the time of imaging the i-th range RNGi, a plurality of sets of light emission and exposure may be performed. In this case, the controller  26  may repeat the above exposure operation a plurality of times at a predetermined cycle τ2. 
       FIGS.  3 A and  3 B  are diagrams showing slice images obtained by the gated camera  20 . In the example of  FIG.  3 A , an object (pedestrian) OBJ 2  is present in a range RNG 2 , and an object (vehicle) OBJ 3  is present in a range RNG 3 .  FIG.  3 B  shows a plurality of slice images IMG 1  to IMG 3  obtained in the situation of  FIG.  3 A . When the slice image IMG 1  is imaged, since the image sensor is exposed merely by the reflected light from the range RNG 1 , no object image is captured in the slice image IMG 1 . 
     When the slice image IMG 2  is imaged, since the image sensor is exposed merely by the reflected light from the range RNG 2 , merely the object image OBJ 2  is captured in the slice image IMG 2 . Similarly, when the slice image IMG 3  is imaged, since the image sensor is exposed merely by the reflected light from the range RNG 3 , merely the object image OBJ 3  is captured in the slice image IMG 3 . In this way, according to the gated camera  20 , it is possible to separately image an object for each range. 
     Image processing in the image processing device  28  will be described.  FIG.  4    is a diagram showing noise in the sensor image SI. The sensor image S 1  includes noise in horizontal stripes along lines. The lines in which noise occurs are random, and noise levels are also random. 
     The image processing device  28  calculates an average value of M (M ≥ 2) pixel values having small pixel values for each line of the sensor image SI, and subtracts the average value from the pixel values of the pixels included in the corresponding line. 
     M is preferably 2% to 8% of the number of pixels of the corresponding line, and can be set to, for example, about 5%. 
       FIG.  5    is a diagram showing noise cancellation by the image processing device  28 .  FIG.  5    shows processing on one line. With reference to line data which is a collection of pixel values of a certain line, M pixel values are selected in ascending order of pixel values. In this example, M = 8, and pixel values  10 ,  10 ,  11 ,  11 ,  12 ,  13 ,  14 , and  15  are selected. The image processing device  28  calculates an average value AVE (12 in this example) of the selected M pixel values. Then, the average value AVE is subtracted from the corresponding line data of the original sensor image SI. 
       FIGS.  6 A and  6 B  are diagrams showing sensor images before and after noise subtraction processing.  FIGS.  7 A and  7 B  are diagrams showing sensor images before and after noise subtraction processing. In  FIGS.  6 A and  6 B , an image not including an object (subject) is taken as a target, and in  FIGS.  7 A and  7 B , an image including an object is taken as a target. In this example, the average value of the number of pixels M corresponding to 5% of each line is calculated. It can be seen that merely background noise can be suitably removed both when an image does not include an object and when an image includes an object. 
     Second Embodiment 
       FIG.  8    is a block diagram of the sensing system  10  according to a second embodiment. The sensing system  10  is mounted on a vehicle such as an automobile or a motorcycle, and detects the object OBJ present around the vehicle. 
     The sensing system  10  mainly includes the gated camera  20 . The gated camera  20  includes the illumination device  22 , the image sensor  24 , the controller  26 , and the image processing device  28 . Imaging by the gated camera  20  is performed by dividing a depth direction into the plurality ofN (N ≥ 2) ranges RNG 1  to RNGN. Adjacent ranges may overlap each other in the depth direction at boundaries thereof. 
     The illumination device  22  radiates the probe light L1 toward the front of the vehicle in synchronization with the light emission timing signal S 1  supplied from the controller  26 . The probe light L1 is preferably infrared light, but is not limited thereto, and may be visible light or ultraviolet light having a predetermined wavelength. 
     The image sensor  24  includes a plurality of pixels, can perform exposure control in synchronization with the exposure timing signal S 2  supplied from the controller  26 , and generates the sensor image SI. The image sensor  24  has sensitivity to the same or similar wavelength as that of the probe light L 1 , and images the reflected light (return light) L 2  reflected by the object OBJ. A sensor image obtained for the i-th range RNGi is indicated by SIi. 
     The controller  26  controls a radiation timing (light emission timing) of the probe light L1 by the illumination device  22  and an exposure timing by the image sensor  24 . 
     The image sensor  24  and the image processing device  28  are connected via a serial interface, and the sensor image SIi imaged by the image sensor  24  is transmitted to the image processing device  28 . The image processing device  28  generates the slice image IMGi based on the sensor image Sli transmitted from the image sensor  24 . 
       FIG.  9    is a diagram showing a basic operation of the gated camera  20 .  FIG.  9    shows a state in which the i-th range RNGi is sensed. The illumination device  22  emits light during the light emission period τ1 between the times t0 and t1 in synchronization with the light emission timing signal S1. An uppermost stage shows a diagram of light beams in which a horizontal axis indicates time and a vertical axis indicates distance. A distance from the gated camera  20  to a front boundary of the range RNGi is indicated by dMINi, and a distance from the gated camera  20  to a rear boundary of the range RNGi is indicated by dMAXi. 
     The round-trip time TMINi until the light that departs from the illumination device  22  at a certain time reaches the distance dMINi and the reflected light returns to the image sensor  24  is TMINi = 2 × dMINi/c. c is the speed of light. 
     Similarly, the round-trip time TMAXi until the light that departs from the illumination device  22  at a certain time reaches the distance dMAXi and the reflected light returns to the image sensor  24  is TMAXi = 2 × dMAXi/c. 
     When it is desired to image merely the object OBJ included in the range RNGi, the controller  26  generates the exposure timing signal S 2  so as to start the exposure at the time t2 = t0 + TMINi and end the exposure at the time t3 = tl + TMAXi. This is one exposure operation. 
     At the time of imaging the i-th range RNGi, a plurality of sets of light emission and exposure may be performed. In this case, the controller  26  may repeat the above exposure operation a plurality of times at the predetermined cycle τ2. 
       FIGS.  10 A and  10 B  are diagrams showing slice images obtained by the gated camera  20 . In the example of  FIG.  10 A , the object (pedestrian) OBJ 2  is present in the range RNG 2 , and the object (vehicle) OBJ 3  is present in the range RNG 3 .  FIG.  10 B  shows the plurality of slice images IMG 1  to IMG 3  obtained in the situation of  FIG.  10 A . When the slice image IMG 1  is imaged, since the image sensor is exposed merely by the reflected light from the range RNG 1 , no object image is captured in the slice image IMG 1 . 
     When the slice image IMG 2  is imaged, since the image sensor is exposed merely by the reflected light from the range RNG 2 , merely the object image OBJ 2  is captured in the slice image IMG 2 . Similarly, when the slice image IMG 3  is imaged, since the image sensor is exposed merely by the reflected light from the range RNG 3 , merely the object image OBJ 3  is captured in the slice image IMG 3 . In this way, according to the gated camera  20 , it is possible to separately image an object for each range. 
     Return to  FIG.  1   . In the present embodiment, a resolution (that is, the number of pixels) of the sensor image SI transmitted from the image sensor  24  to the image processing device  28  changes according to the range. Specifically, the resolution of the sensor image SI is lower (the number of pixels is smaller) as the range is closer, and the resolution of the sensor image S 1  is higher (the number of pixels is larger) as the range is farther. In the present embodiment, in all of the ranges, all of the pixels of the image sensor  24  are exposed, merely necessary pixels are read out from all of the pixels, and unnecessary pixels are thinned out to generate the sensor image SI. The controller  26  generates a control signal S 3  indicating a pixel to be transmitted for each range, and supplies the control signal S 3  to the image sensor  24 . 
     The controller  26  can be implemented by a combination of a processor (hardware) such as a central processing unit (CPU), a micro processing unit (MPU), or a microcomputer and a software program executed by the processor (hardware). 
       FIG.  11    is a diagram showing an example of control on the resolution of the sensor image SI depending on the range. Hatched pixels indicate valid pixels (valid lines) constituting the sensor image S 1 , and blank pixels indicate invalid pixels (invalid lines) that are not transmitted. In this example, the resolution, in the vertical direction, of the sensor image SI to be transmitted, that is, the number of lines, is controlled according to the range. For example, in the farthest range, all of the lines of the image sensor  24  are valid, and all of the pixels are transmitted as valid pixels. As the range is closer, a ratio (number) of lines to be thinned out increases, and the number of valid pixels decreases. 
       FIG.  12 A  is a diagram showing a certain traveling scene, and  FIG.  12 B  is a diagram showing sensor images SIx and SIy obtained in the traveling scene in  FIG.  12 A . 
     In the traveling scene of  FIG.  12 A , a preceding vehicle OBJ 1  is present at a position close to an own vehicle on a traveling lane, and an oncoming vehicle OBJ 2  is present at a position far from the own vehicle on an oncoming lane. The preceding vehicle OBJ 1  is included in an x-th range RNGx, and the oncoming vehicle OBJ 2  is included in a y-th range RNGy. 
     The preceding vehicle OBJ 1  in the range RNGx is captured in the sensor image SIx in  FIG.  12 B , and the oncoming vehicle OBJ 2  in the range RNGy is captured in the sensor image SIy. Horizontal lines in  FIG.  12 B  indicate effective lines constituting a sensor image. 
     The resolution of the sensor image SI in each range may be determined so as to cross the same number of valid lines when the same object (in this example, vehicle) is captured. 
       FIG.  13 A  is a time chart showing the operation of the gated camera  20 .  FIG.  13 B  is a time chart showing an operation of a gated camera according to a comparative technique. 
     First, the comparative technique will be described with reference to  FIG.  13 B . In the comparative technique, the sensor images SI 1  to SI 3  having the same resolution are transmitted for all of the ranges. In this case, all the sensor images SI 1 , SI 2 , and SI 3  have the same transmission time, and a time required for sensing the three ranges RNG 1  to RNG 3  included in one cycle becomes long. 
     Next, the operation of the gated camera  20  according to the second embodiment will be described with reference to  FIG.  13 A . In this example, the number of ranges is three, and the range RNG 1  covers 0 to 25 m, the range RNG 2  covers  25  to 50 m, and the range RNG 3  covers  50  to 100 m. For the farthest third range RNG 3 , all of the lines are valid. Since the distance of the second range RNG 2  is substantially half the distance of the third range RNG 3 , the resolution of the sensor image SI is set to ½. Since the distance of the first range RNG 1  is ¼ of the distance of the third range RNG 3 , the resolution of the sensor image S 1  is set to ¼. In this case, specifically, in the sensor image SI 3 , all lines of the image sensor are set as valid lines. In the sensor image SI 2 , a valid line is selected at a ratio of one line per two lines, and in the sensor image SI 1 , a valid line is selected at a ratio of one line per four lines. 
     Since the numbers of pixels of the sensor images SI 1 , SI 2 , and SI 3  are proportional to the number of lines, a relation of about 1: 2: 4 is established. Therefore, the transmission time of the sensor image SI 1  is shortened to ¼ of the transmission time of the sensor image SI 3 , and the transmission time of the sensor image SI 2  is shortened to ½ of the transmission time of the sensor image SI 3 . Therefore, the time required for sensing the three ranges RNG 1  to RNG 3  included in one cycle can be shortened. 
     The sensor images SI 1  and SI 2  generated by the line skip as described above are crushed in the vertical direction compared to the sensor image SI 3  and have different aspect ratios. Therefore, the image processing device  28  may generate the slice images IMG 1  to IMG 3  by equalizing the aspect ratios of the sensor images SI 1  to SI 3  by image processing. 
     For example, the image processing device  28  may complement, by image processing, invalid lines thinned out at the time of transmission for a sensor image SIj. In this case, all of the slice images IMG 1  to IMG 3  can have the same resolution. 
     When a vertical resolution of the sensor image SIj is X times (X &lt; 1) at the time of transmission, the image processing device  28  may set the resolution in a horizontal direction to X times. That is, the image processing device  28  may generate the slice image IMGi by thinning out a plurality of columns of the received sensor image Slj. 
     In the above description, the resolution of the sensor image in the vertical direction is variable, but the present invention is not limited thereto.  FIG.  14    is a diagram showing another example of control on the resolution of the sensor image SI depending on the range. In this example, the resolution, in the horizontal direction, of the sensor image SI to be transmitted, that is, the number of columns is controlled according to the range. For example, in the farthest range, all columns of the image sensor  24  are valid, and all pixels are transmitted as valid pixels. As the range is closer, the ratio (number) of the columns to be thinned out increases, and the number of valid pixels decreases. 
       FIG.  15    is a diagram showing still another example of control on the resolution of the sensor image SI depending on the range. In this example, the resolutions, in the horizontal direction and the vertical direction, of the sensor image SI to be transmitted are controlled according to the range. 
     Next, a modification of the gated camera  20  will be described. 
     First Modification 
     In the above description, regardless of the range, the resolution of the sensor image SI is controlled by performing exposure on all pixels of the image sensor  24  and selecting a line or a column to be read, but the present invention is not limited thereto. Depending on the specifications of the image sensor  24 , presence or absence of exposure can be controlled for each line, each column, or each pixel. When the image sensor  24  having such a specification is adopted, merely the valid pixels to be transmitted may be exposed in each range. 
     Second Modification 
     When the image sensor  24  capable of performing exposure control for each pixel is used as in the first modification, it is possible to divide the pixels (lines/columns) into a plurality of groups in a range in which a utilization rate of the pixels (lines/columns) is low and to use the groups for imaging in different ranges.  FIG.  16    is a block diagram of the gated camera  20  according to a second modification. For one light emission of the illumination device  22 , a first pixel group (line group or column group) of the image sensor  24  is exposed at a first timing, and a second pixel group (line group or column group) of the image sensor  24  is exposed at a second timing. A sensor image formed by the first pixel group and the sensor images SIi and SIj formed by the second pixel group are images obtained by imaging different ranges RNGi and RNGj. 
     The controller  26  generates the light emission timing signal SI for the illumination device  22 , generates an exposure timing signal S2A for the first pixel group such that an object in the certain range RNGi is exposed, and generates an exposure timing signal S2B for the second pixel group such that an object in the another range RNGj is exposed. 
       FIG.  17    is a diagram showing exposure of the gated camera  20  according to the second modification. In this example, the utilization rate of pixels (lines) at the time of imaging in one range is 50%. All of the pixels constituting the image sensor  24  are classified, for each row, into the first pixel group of odd-numbered lines and the second pixel group of even-numbered lines, and are subjected to exposure control at different timings. 
       FIG.  18    is a time chart showing an operation of the gated camera  20  according to the second modification. The first pixel group is assigned to the i-th range RNGi which is relatively close, and the second pixel group is assigned to the j-th range RNGj (j &gt; i). The illumination device  22  emits light during the light emission period τ1 between the times t0 and t1 in synchronization with the light emission timing signal S1. An uppermost stage shows a diagram of light beams in which a horizontal axis indicates time and a vertical axis indicates distance d. A distance from the gated camera  20  to a front boundary of the range RNGi is indicated by dMINi, and a distance from the gated camera  20  to a rear boundary of the range RNGi is indicated by dMAXi. Similarly, a distance from the gated camera  20  to a front boundary of the range RNGj is indicated by dMINj, and a distance from the gated camera  20  to a rear boundary of the range RNGi is indicated by dMAXj. 
     Therefore, in order to image an object OBJi included in the range RNGi, the exposure timing signal S2A is generated such that the exposure of the first pixel group is started at the time t2 = t0 + TMINi and the exposure is ended at the time t3 = t1 + TMAXi. 
     In order to image an object OBJj included in the range RNGj using the same probe light, the exposure timing signal S2B is generated such that the exposure of the second pixel group is started at a time t4 = t0 + TMINj and the exposure is ended at a time t5 = t1 + TMAXj. 
     
       
         
           
             TMINj 
             = 
             2 
             × 
             dMINj 
             / 
             c 
           
         
       
     
     
       
         
           
             TMAXj 
             = 
             2 
             × 
             dMAXj 
             / 
             c 
           
         
       
     
     The two ranges RNGi and RNGj to be simultaneously imaged may be adjacent to each other (j = i + 1). 
     According to this modification, the transmission time can be shortened by lowering the resolution of the sensor image S 1  at the time of imaging a close range. 
     In addition, since images of two ranges can be obtained by one light emission of the illumination device  22 , a utilization efficiency of hardware resources is improved. 
     When generalized, in a situation where the utilization efficiency of the pixels is 1/N, it is also possible to classify the pixels of the image sensor  24  into N pixel groups and perform imaging in N ranges. In addition, the classification on the pixel group is not limited to a line unit, and may be a column unit or a pixel unit. 
     Third Embodiment 
       FIG.  19    is a block diagram of the sensing system  10  according to a third embodiment. The sensing system  10  is mounted on a vehicle such as an automobile or a motorcycle, and detects the object OBJ present around the vehicle. 
     The sensing system  10  mainly includes the gated camera  20 . The gated camera  20  includes the illumination device  22 , the image sensor  24 , the controller  26 , and the image processing device  28 . Imaging by the gated camera  20  is performed by dividing a depth direction into a plurality of N (N ≥ 2) ranges RNG 1  to RNGN and generating a slice image for each range. Adjacent ranges may overlap each other in the depth direction at boundaries thereof. 
     The image sensor  24  includes a plurality of pixels, and can individually control the exposure timing for each pixel, for each line, or for each column. The plurality of pixels are classified into a plurality of pixel groups. In the following description, it is assumed that the number of pixel groups is two, and the pixel groups are referred to as a first pixel group and a second pixel group. 
     For one light emission of the illumination device  22 , the gated camera  20  exposes the first pixel group (line group or column group) of the image sensor  24  at a first timing and exposes the second pixel group (line group or column group) of the image sensor  24  at a second timing. A sensor image formed by the first pixel group and the sensor images Sli and Slj formed by the second pixel group are images obtained by imaging different ranges RNGi and RNGj. 
     Specifically, the controller  26  exposes the first pixel group and the second pixel group at different timings for one light emission of the illumination device  22 . 
     The controller  26  can be implemented by a combination of a processor (hardware) such as a central processing unit (CPU), a micro processing unit (MPU), or a microcomputer and a software program executed by the processor (hardware). 
     The image sensor  24  and the image processing device  28  may be connected via a serial interface, and the sensor image SIi imaged by the first pixel group of the image sensor  24  and the sensor image S1j imaged by the second pixel group of the image sensor  24  may be transmitted as separate images. The image processing device  28  generates the slice image IMGi based on the sensor image Sli transmitted from the image sensor  24 . Image processing in the image processing device  28  is not particularly limited, and for example, interpolation processing or thinning processing for changing an aspect ratio may be performed. 
     At the time of imaging the i-th range RNGi and the j-th range RNGj, a plurality of sets of light emission and exposure may be performed. In this case, the controller  26  may repeat the light emission and the exposure operation a plurality of times. In this case, the image processing device  28  may generate one slice image IMGi by combining a plurality of sensor images Sli obtained for the same range RNGi. 
     The configuration of the gated camera  20  is as described above. Next, an operation thereof will be described. 
       FIG.  20    is a time chart showing the operation of the gated camera  20  in  FIG.  19   . The first pixel group is assigned to the i-th range RNGi which is relatively close, and the second pixel group is assigned to the j-th range RNGj (j &gt; i). The illumination device  22  emits light during the light emission period τ1 between the times t0 and t1 in synchronization with the light emission timing signal S1. An uppermost stage shows a diagram of light beams in which a horizontal axis indicates time and a vertical axis indicates distance d. A distance from the gated camera  20  to a front boundary of the range RNGi is indicated by dMINi, and a distance from the gated camera  20  to a rear boundary of the range RNGi is indicated by dMAXi. Similarly, a distance from the gated camera  20  to the front boundary of the range RNGj is indicated by dMINj, and a distance from the gated camera  20  to the rear boundary of the range RNGi is indicated by dMAXj. 
     The round-trip time TMINi until the light that departs from the illumination device  22  at a certain time reaches the distance dMINi and the reflected light returns to the image sensor  24  is TMINi = 2 × dMINi/c. c is the speed of light. 
     Similarly, the round-trip time TMAXi until the light that departs from the illumination device  22  at a certain time reaches the distance dMAXi and the reflected light returns to the image sensor  24  is TMAXi = 2 × dMAXi/c. 
     When it is desired to image merely the object OBJ included in the range RNGi, the controller  26  generates the exposure timing signal so as to start the exposure at the time t2 = t0 + TMINi and end the exposure at the time t3 = t1 + TMAXi. This is one exposure operation. 
     Therefore, in order to image the object OBJi included in the range RNGi, the exposure timing signal S2A is generated such that the exposure of the first pixel group is started at the time t2 = t0 + TM INi and the exposure is ended at the time t3 = t1 + TMAXi. 
     In order to image the object OBJj included in the range RNGj using the same probe light, the exposure timing signal S2B is generated such that the exposure of the second pixel group is started at the time t4 = t0 + TMINj and the exposure is ended at the time t5 = t1 + TMAXj. 
     
       
         
           
             TMINj 
             = 
             2 
             × 
             dMINj 
             / 
             c 
           
         
       
     
     
       
         
           
             TMAXj 
             = 
             2 
             × 
             dMAXj 
             / 
             c 
           
         
       
     
     The two ranges RNGi and RNGj to be simultaneously imaged may be adjacent to each other (j = i + 1). 
       FIGS.  21 A and  21 B  are diagrams showing slice images obtained by the gated camera  20  in  FIG.  19   . In the example of  FIG.  21 A , an object (pedestrian) OBJ 2  is present in the range RNG 2 , and an object (vehicle) OBJ 3  is present in the range RNG 3 .  FIG.  21 B  shows the plurality of slice images IMG 1  to IMG 3  obtained in the situation of  FIG.  21 A . When the slice image IMG 1  is imaged, since the image sensor is exposed merely by the reflected light from the range RNG 1 , no object image is captured in the slice image IMG 1 . 
     It is assumed that the range RNG 2  is assigned to the first pixel group and the range RNG 3  is assigned to the second pixel group. At this time, since the first pixel group is exposed merely by the reflected light from the range RNG 2 , merely the object image OBJ 2  is captured in the sensor image SI 2 . Similarly, since the second pixel group is exposed merely by the reflected light from the range RNG 3 , merely the object image OBJ 3  is captured in the sensor image SI 3 . In this way, according to the gated camera  20 , it is possible to separately image an object for each range. 
     Since images of the two ranges RNGi and RNGj can be obtained by one light emission of the illumination device  22 , a sensing time required for imaging all of the ranges can be shortened. In addition, in a system in which merely one range is imaged by one light emission, reflected light from an object other than the range to be imaged is wasted, but in the present embodiment, reflected light from an object in another range is also detected, and thus, the utilization efficiency of energy is increased. 
     Next, division of pixel groups will be described.  FIGS.  22 A to  22 D  are diagrams showing examples of the pixel groups. In  FIG.  22 A , the pixels are assigned to the first pixel group and the second pixel group every other line. When the number of the plurality of pixel groups is n (n ≥ 2), an i-th pixel group includes an (i+n×j)-th (j is an integer) line. This example is suitable for an image sensor capable of controlling the exposure timing for each line. 
     In  FIG.  22 B , the pixels are assigned to the first pixel group and the second pixel group every other column. When the number of pixel groups is n (n ≥ 2), the i-th pixel group includes an (i+n×j)-th (j is an integer) column. This example is suitable for an image sensor capable of controlling the exposure timing for each column. 
     In  FIG.  22 C , a left half of all of the pixels is sorted to the first pixel group, and a right half of all of the pixels is sorted to the second pixel group. As a modification, an upper half of all of the pixels may be sorted to the first pixel group, and a lower half of all of the pixels may be sorted to the second pixel group. 
     In  FIG.  22 D , the number of pixel groups is four. All of the pixels are divided into blocks each including four adjacent pixels, and a first pixel group to a fourth pixel group are formed by selecting one pixel from each block. 
     The techniques described in the first to third embodiments can be implemented in any combination. 
     Application 
       FIG.  23    is a block diagram of the sensing system  10 . The sensing system  10  includes an arithmetic processing device  40  in addition to any gated camera  20  described in the first to third embodiments. The sensing system  10  is mounted on a vehicle such as an automobile or a motorcycle, and determines a type (also referred to as category or class) of the object OBJ present around the vehicle. 
     A plurality of slice images IMG 1  to IMGN corresponding to a plurality of ranges RNG 1  to RNGN are generated by the gated camera  20 . In the i-th slice image IMGi, merely an object included in the corresponding range RNGi is captured. 
     The arithmetic processing device  40  can identify the type of the object based on the plurality of slice images IMG 1  to IMGN corresponding to the plurality of ranges RNG 1  to RNGN obtained by the gated camera  20 . The arithmetic processing device  40  includes a classifier  42  implemented based on a learned model generated by machine learning. The arithmetic processing device  40  may include a plurality of classifiers  42  optimized for each range. An algorithm of the classifier  42  is not particularly limited, and you only look once (YOLO), single shot multi box detector (SSD), region-based convolutional neural network (RCNN), spatial pyramid pooling (SPPnet), Faster R-CNN, deconvolution-SSD (DSSD), Mask R-CNN, or the like can be adopted, or an algorithm developed in the future can be adopted. 
     The arithmetic processing device  40  can be implemented by a combination of a processor (hardware) such as a central processing unit (CPU), a micro processing unit (MPU), or a microcomputer and a software program executed by the processor (hardware). The arithmetic processing device  40  may be a combination of a plurality of processors. Alternatively, the arithmetic processing device  40  may be implemented merely by hardware. Functions of the arithmetic processing device  40  and functions of the image processing device  28  may be implemented in the same processor. 
       FIGS.  24 A and  24 B  are diagrams showing an automobile  300  including the gated camera  20 . Reference is made to  FIG.  24 A . The automobile  300  includes headlamps (lamps)  302 L and  302 R. In the automobile  300  in  FIG.  24 A , one illumination device  22  is provided at the center of the vehicle, and the image sensor  24  is built in one or both of the left and right headlamps  302 L and  302 R. A position of the illumination device  22  is not particularly limited, and for example, the illumination device  22  may be provided in a front bumper (C1) or a front grille (C2), or may be attached to a rear side (C3) of a rear-view mirror inside a front window. In addition, a position of the controller  26  is not particularly limited, and the controller  26  may be provided in an engine room, in a vehicle interior, or in a head lamp. 
     Reference is made to  FIG.  24 B . The illumination device  22  includes a plurality of (for example, two) light sources  22 A and  22 B. The plurality of light sources  22 A and  22 B emit light at the same timing, and the emitted light forms one probe light. The plurality of light sources  22 A and  22 B are built in the left and right headlamps  302 L and  302 R. 
     The image sensor  24  is built in one or both of the headlamps  302 L and  302 R. Alternatively, the image sensor  24  may be provided outside the headlamps  302 L and  302 R, and may be provided, for example, in the vicinity of the illumination device  22 . 
       FIG.  25    is a block diagram showing a vehicle lamp  200  including an object detection system  210 . The vehicle lamp  200  constitutes a lamp system  310  together with a vehicle-side ECU  304 . The vehicle lamp  200  includes a light source  202 , a lighting circuit  204 , and an optical system  206 . Further, the vehicle lamp  200  is provided with the object detection system  210 . The object detection system  210  corresponds to the above sensing system  10 , and includes the gated camera  20  and the arithmetic processing device  40 . 
     Information on the object OBJ detected by the arithmetic processing device  40  may be used for light distribution control on the vehicle lamp  200 . Specifically, a lamp-side ECU  208  generates an appropriate light distribution pattern based on the information on a type and a position of the object OBJ generated by the arithmetic processing device  40 . The lighting circuit  204  and the optical system  206  operate so as to obtain the light distribution pattern generated by the lamp-side ECU  208 . 
     In addition, the information on the object OBJ detected by the arithmetic processing device  40  may be transmitted to the vehicle-side ECU  304 . The vehicle-side ECU may perform automatic control based on the information. 
     Although the present invention has been described using specific words and phrases based on the embodiments, the embodiments merely show one aspect of principles and applications of the present invention, and many modifications and changes in arrangement can be made in the embodiment without departing from the spirit of the present invention defined in the claims. 
     INDUSTRIAL APPLICABILITY 
     The present invention relates to a gated camera.