Distance measuring device and distance measuring method

Abstract

To provide a distance measuring device and distance measuring method that can reduce a required memory capacity while maintaining distance measurement accuracy and resolution.SOLUTION: A distance measuring device comprises: a light receiving unit which has multiple pixels that detect pulse light reflected by an object within a measurement target area; a binning processing unit which converts multiple signals output from multiple unit regions each including at least one pixel into multiple signals corresponding to multiple pixel blocks each including at least two unit regions; a data storage unit which stores information for each pixel block that represents the relationship between a class determined according to the time from pulse light emission to detection by the light receiving unit and a frequency on the basis of the multiple signals output from the binning processing unit; a reflected light determination unit which extracts from the information a candidate of the class including the signal by reflected light from the object for each unit region; and a distance calculation unit which calculates the distance to the object corresponding to each unit region on the basis of the candidate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a distance measuring device and a distance measuring method. [Background technology]

[0002] One distance measurement technology is called flash LiDAR (Light Detection and Ranging), which irradiates a predetermined area including the object to be measured with light from a surface light source, detects the light reflected from the object, and measures the distance to the object based on the relationship between the timing of light emission from the surface light source and the timing of detection of the light reflected from the object.

[0003] In flash LiDAR, distance measurement accuracy is improved by emitting light from a surface light source multiple times and accumulating the reflected light. The reflected light is accumulated by generating histogram information that shows the relationship between distance and frequency, but the memory capacity required for processing increases in proportion to the number of pixels in the light-receiving section. The memory capacity required for processing can be reduced by performing a process known as binning, which treats multiple pixels as a single pixel, but simple binning cannot avoid a decrease in resolution.

[0004] Patent Document 1 discloses a technique for calculating high-resolution distance by taking the difference between a binned distance histogram and a distance histogram excluding the output of some regions. Patent Document 2 discloses a technique for estimating high-resolution distance information by extracting contour information from a high-resolution image and correcting low-resolution distance information based on the extracted contour information. Patent Document 3 discloses a technique for performing pseudo-high-resolution distance measurement by shifting the binned region at intervals narrower than the region itself. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-180941 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-071976 [Patent Document 3] Japanese Patent Publication No. 2020-118570 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the techniques described in Patent Documents 1, 2 and 3 do not necessarily achieve both a reduction in memory capacity and an increase in resolution.

[0007] An object of the present invention is to provide a distance measuring device and a distance measuring method that can reduce the required memory capacity while maintaining the accuracy and resolution of distance measurement. [Means for solving the problem]

[0008] According to one disclosure of this specification, there is provided a distance measuring device having a light receiving unit having a plurality of pixels that detect pulsed light emitted from a light emitting unit and reflected by an object in a measurement target area; a binning processing unit that converts a plurality of signals output from a plurality of unit areas each including at least one of the pixels into a plurality of signals corresponding to a plurality of pixel blocks each including at least two unit areas; a data storage unit that stores, for each pixel block, information representing the relationship between a class determined according to the time from when the pulsed light is emitted to when it is detected by the light receiving unit and a frequency indicating the number of times the pulsed light is detected, based on the plurality of signals output from the binning processing unit; a reflected light determination unit that extracts from the information, for each of the plurality of unit areas, class candidates including signals due to reflected light from the object; and a distance calculation unit that calculates the distance to the object corresponding to each of the plurality of unit areas based on the candidates.

[0009] According to another disclosure of the present specification, there is provided a distance measuring device having a light receiving unit having a plurality of pixels that detect pulsed light emitted from a light emitting unit and reflected by an object in a measurement target area; a binning processing unit that converts a plurality of first signals output from the plurality of pixels into a plurality of second signals having a spatial resolution lower than that of the plurality of first signals; a data storage unit that stores, for each of a plurality of first unit areas corresponding to the plurality of second signals, information indicating the relationship between a class determined according to the time from when the pulsed light is emitted to when it is detected by the light receiving unit and a frequency indicating the number of times the pulsed light is detected, based on the plurality of second signals output from the binning processing unit; a reflected light determination unit that extracts from the information, for each of a plurality of second unit areas corresponding to a plurality of signals having a spatial resolution higher than that of the plurality of second signals, class candidates including signals due to reflected light from the object; and a distance calculation unit that calculates the distance to the object corresponding to each of the plurality of second unit areas based on the candidates.

[0010] Furthermore, according to yet another disclosure of the present specification, there is provided an information processing device having an input unit that receives signals output from a plurality of pixels that detect pulsed light emitted from a light emitting unit and reflected by an object in a measurement area; a binning processing unit that converts the plurality of signals output from a plurality of unit areas, each including at least one of the pixels, into a plurality of signals corresponding to a plurality of pixel blocks, each including at least two unit areas; a data storage unit that stores, for each of the pixel blocks, information indicating a relationship between a class determined according to a time from when the pulsed light is emitted to when it is detected and a frequency indicating the number of times the pulsed light is detected, based on the plurality of signals output from the binning processing unit; a reflected light determination unit that extracts, for each of the plurality of unit areas, class candidates including signals due to reflected light from the object from the information; and a distance calculation unit that calculates a distance to the object corresponding to each of the plurality of unit areas based on the candidates.

[0011] Furthermore, according to yet another disclosure of the present specification, there is provided a distance measurement method in which pulsed light emitted from a light-emitting unit and reflected by an object in a measurement target area is detected by a plurality of pixels, and the distance to the object is calculated based on signals detected by the plurality of pixels, the method comprising: converting a plurality of signals output from a plurality of unit areas, each of which includes at least one of the pixels, into a plurality of signals corresponding to a plurality of pixel blocks, each of which includes at least two unit areas; accumulating, for each pixel block, information representing the relationship between a class determined according to the time from when the pulsed light is emitted to when it is detected by a light-receiving unit and a frequency indicating the number of times the pulsed light is detected, extracting from the information, for each of the plurality of unit areas, a class candidate including a signal due to the reflected light from the object; and calculating, based on the candidate, the distance to the object corresponding to each of the plurality of unit areas. [Effects of the Invention]

[0012] According to the present invention, in a distance measuring device and a distance measuring method, it is possible to reduce the memory capacity required while maintaining the accuracy and resolution of distance measurement. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a block diagram showing a schematic configuration of a distance measuring device according to a first embodiment of the present invention. [Figure 2] FIG. 1 is a timing diagram illustrating the basic operation of a LiDAR system. [Figure 3] FIG. 1 is a diagram illustrating an example of a histogram generated in a LiDAR system. [Figure 4] 4 is a flowchart (part 1) showing the operation of the distance measuring device according to the first embodiment of the present invention. [Figure 5] 4 is a flowchart (part 2) showing the operation of the distance measuring device according to the first embodiment of the present invention. [Figure 6] 6 is a flowchart (part 3) showing the operation of the distance measuring device according to the first embodiment of the present invention. [Figure 7]10 is a flowchart (part 4) showing the operation of the distance measuring device according to the first embodiment of the present invention. [Figure 8] 3 is a diagram showing an example of the structure of entries held in a data storage unit of a distance calculation unit in the distance measuring device according to the first embodiment of the present invention. FIG. [Figure 9] 10 is a flowchart (part 1) showing the operation of the distance measuring device according to the second embodiment of the present invention. [Figure 10] 10 is a flowchart (part 2) showing the operation of the distance measuring device according to the second embodiment of the present invention. [Figure 11] 10 is a flowchart (part 3) showing the operation of the distance measuring device according to the second embodiment of the present invention. [Figure 12] FIG. 10 is a diagram showing an example of the structure of entries held in a data storage unit of a distance calculation unit in a distance measuring device according to a second embodiment of the present invention. [Figure 13] FIG. 2 is a diagram illustrating the positional relationship between a pixel of interest and surrounding pixels. [Figure 14] FIG. 10 is a diagram (part 1) showing an example of the operation of the distance measuring device according to the second embodiment of the present invention. [Figure 15] 10A and 10B are diagrams showing an example of a low-resolution histogram acquired in a first period and an example of a low-resolution histogram of ambient light acquired in a second period. [Figure 16] FIG. 10 is a diagram (part 2) showing an example of the operation of the distance measuring device according to the second embodiment of the present invention. [Figure 17] FIG. 10 is a diagram (part 3) showing an example of the operation of the distance measuring device according to the second embodiment of the present invention. [Figure 18] FIG. 10 is a diagram (part 4) showing an example of the operation of the distance measuring device according to the second embodiment of the present invention. [Figure 19] FIG. 10 is a diagram showing an example of the configuration of a data area of ​​a data storage unit in a distance measuring device according to a fourth embodiment of the present invention. [Figure 20] FIG. 10 is a diagram illustrating an example of the configuration of a moving body according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] As mentioned above, distance measurement devices such as flash LiDAR improve distance measurement accuracy by emitting light from a light source multiple times and accumulating the reflected light. The reflected light is accumulated by generating histogram information that shows the relationship between distance and frequency, but the memory capacity required for processing increases in proportion to the number of pixels in the light-receiving section. While the memory capacity required for processing can be reduced by performing a process known as binning, which treats multiple pixels as a single pixel, simple binning cannot avoid a decrease in resolution.

[0015] Patent Document 1 discloses a technique for calculating high-resolution distance by calculating the difference between a binned distance histogram and a distance histogram in which the output of some regions is excluded. However, the method described in Patent Document 1 requires storing multiple distance histograms in which the output of some regions is excluded. Therefore, this method requires a memory capacity equivalent to the memory capacity required for the distance histogram with the resolution before binning.

[0016] Patent Document 2 discloses a technique for estimating high-resolution distance information by extracting contour information from a high-resolution image and correcting low-resolution distance information based on the extracted contour information. However, the method described in Patent Document 2 sometimes fails to obtain contours in the image when the object and background are similar in color, resulting in an erroneous distance estimation.

[0017] Patent Document 3 discloses a technology for performing pseudo-high-resolution distance measurement by shifting the binning area at intervals narrower than the actual area. However, the method described in Patent Document 3 merely shifts the phase of the binned pixels, and does not improve the essential distance resolution.

[0018] [First embodiment] A ranging device and ranging method according to a first embodiment of the present invention will be described with reference to Figs. 1 to 8. Fig. 1 is a block diagram showing a schematic configuration of a ranging device according to this embodiment. Fig. 2 is a timing chart showing the basic operation of a LiDAR system. Fig. 3 is a diagram showing an example of histogram information. Figs. 4 to 7 are flowcharts showing the operation of the ranging device according to this embodiment. Fig. 8 is a diagram showing an example configuration of entries held in a data storage unit of a distance calculation unit in the ranging device according to this embodiment.

[0019] First, the schematic configuration of the distance measuring device according to this embodiment will be described with reference to FIG. 1. As shown in FIG. 1, the distance measuring device 100 according to this embodiment includes a light emitting unit 10, a time counting unit 20, a control unit 30, a light receiving unit 40, a distance calculation unit 50, a binning processing unit 60, a low-resolution histogram processing unit 70, and an output unit 80. The light receiving unit 40 includes a plurality of light receiving elements 42 arranged two-dimensionally. For simplicity of illustration, FIG. 1 shows only two of the plurality of light receiving elements 42 that make up the light receiving unit 40. The distance calculation unit 50 includes a data storage unit 52 and a reflected light determination unit 54. The low-resolution histogram processing unit 70 includes a data storage unit 72 and a reflected light determination unit 74.

[0020] The control unit 30 is connected to the light emitting unit 10 and the time counting unit 20. Each of the light receiving elements 42 of the light receiving unit 40 is connected to a distance calculation unit 50 and a binning processing unit 60. Note that in FIG. 1, the distance calculation unit 50 is shown divided into multiple blocks corresponding to the multiple light receiving elements 42 in order to visually show that the distance calculation unit 50 processes the signals output from each of the multiple light receiving elements 42. The time counting unit 20 is connected to the distance calculation unit 50 and a low-resolution histogram processing unit 70. The binning processing unit 60 is connected to a data accumulation unit 72 of the low-resolution histogram processing unit 70. The data accumulation unit 72 is connected to a reflected light determination unit 74 of the low-resolution histogram processing unit 70. The reflected light determination unit 74 is connected to the distance calculation unit 50. The distance calculation unit 50 is connected to an output unit 80.

[0021] The light-emitting unit 10 has a light-emitting element (not shown) and serves to emit pulsed light (irradiation light 12), such as laser light, emitted from the light-emitting element toward the measurement target area. The light-emitting element constituting the light-emitting unit 10 may be, for example, a light-emitting diode (LED) or a laser diode (LD), which is capable of high-speed modulation. The light-emitting element may be a vertical cavity surface-emitting laser (VCSEL) or a surface-emitting element in which these elements are arranged in an array. The light-emitting unit 10 is preferably configured to irradiate the measurement target area with a uniform amount of light, and may further include an optical element, such as a lens, for optically converting the light emitted from the light-emitting element and irradiating the measurement target area with the light.

[0022] The light receiving unit 40 detects light incident from the measurement target area. The light incident on the light receiving unit 40 includes ambient light in the measurement target area as well as light (reflected light 14) of the irradiated light 12 reflected by an object 110 in the measurement target area. The light receiving element 42 converts the incident optical signal into an electrical signal and outputs it to the distance calculation unit 50 and the binning processing unit 60. A pulse signal corresponding to the reflected light 14 is superimposed on the electrical signal output from the light receiving element 42 to the distance calculation unit 50. For example, a single photon avalanche diode (SPAD) sensor or a complementary metal oxide semiconductor (CMOS) sensor can be used as the light receiving element 42. The light receiving unit 40 may further include an optical element, such as a lens, for efficiently guiding the reflected light 14 to the light receiving element 42.

[0023] The number of light receiving elements 42 included in the light receiving unit 40 is not particularly limited, but for convenience of explanation, the present embodiment assumes that the light receiving unit 40 has a total of 256 light receiving elements 42 arranged two-dimensionally, 16 horizontally and 16 vertically. In this specification, the horizontal direction of the light receiving unit 40 is represented by the X axis, and the vertical direction of the light receiving unit 40 is represented by the Y axis, and each light receiving element 42 may be represented by an XY coordinate. The two light receiving elements 42 shown in FIG. 1 may be, for example, the light receiving element 42 arranged at coordinates (0,0) and the light receiving element 42 arranged at coordinates (1,0) out of the 256 light receiving elements 42.

[0024] The control unit 30 generates a light emission control signal for controlling the timing of emitting pulsed light in the light emitting unit 10, and transmits the generated light emission control signal to the light emitting unit 10. The control unit 30 also generates a count control signal synchronized with the light emission control signal, and transmits the generated count control signal to the time count unit 20.

[0025] The time count unit 20 starts counting time in response to a count control signal from the control unit 30, and counts up the time count value by one at regular intervals. The time count unit 20 sequentially transmits the time count values ​​to the distance calculation unit 50 and the low-resolution histogram processing unit 70.

[0026] The binning processor 60 is a functional block that performs pixel binning, a process of combining signals from two or more pixels (here, photodetectors 42) into a signal from a larger pixel block. While pixel binning reduces resolution, it increases the probability of receiving reflected light 14, thereby extending the measurable distance. Upon receiving pulse signals from each of the photodetectors 42 in the photodetector unit 40, the binning processor 60 performs pixel binning on these signals, outputting a smaller number of signals than the signals received from the photodetector unit 40. For convenience of explanation, in this embodiment, pixel binning is performed for each 4×4 photodetector block. For example, if pixel binning is performed for each 4×4 photodetector block on signals from the photodetector unit 40, which consists of a total of 256 photodetectors 42 (16×16), signals from a total of 16 pixel blocks (4×4) are obtained. The number of pixels to be binned can be set arbitrarily.

[0027] The data storage unit 72 of the low-resolution histogram processing unit 70 generates histogram information for each pixel block after binning processing based on signals from the binning processing unit 60 and the time count unit 20, and stores the generated histogram information. The histogram information here represents the relationship between time classes (hereinafter referred to as "light-receiving time bins") and the frequency of each bin. The light-receiving time bins are classified according to the time (time count value from the time count unit 20) from the time when pulsed light is emitted from the light-emitting unit 10 to the time when a pulse signal is output from the light-receiving element 42 in response to the incidence of reflected light 14. For example, if the time count value is counted up in 1-nanosecond increments and the light-receiving time bins are set at 10-nanosecond intervals, the light-receiving time bin number corresponding to the pulse signal from the light-receiving element 42 can be calculated by dividing the time count value by 10. Each time the data storage unit 72 receives a pulse signal during a predetermined period, it increments the light-receiving count value (frequency) of the light-receiving time bin corresponding to the received pulse signal by 1. In this way, by counting the number of times a pulse signal is detected in each bin for each pixel after binning processing, histogram information for each pixel after binning processing can be generated.

[0028] The reflected light determination unit 74 of the low-resolution histogram processing unit 70 determines the presence or absence of reflected light 14 for each pixel block after binning processing based on the histogram information generated by the data accumulation unit 72 and outputs the determination result to the distance calculation unit 50. The reflected light determination unit 74 determines whether reflected light 14 can be determined upon receiving a pulse signal from the binning processing unit 60. For example, it can set the unit to a state in which reflected light 14 cannot be determined for a certain period of time within a frame, and then set the unit to a state in which reflected light 14 can be determined thereafter. If reflected light 14 can be determined, the unit determines the presence or absence of reflected light 14 for each pixel after binning processing and outputs a signal according to the determination result. For example, the reflected light determination unit 74 outputs a high-level signal (1) if reflected light 14 is present, and outputs a low-level signal (0) if reflected light 14 is not present. In addition to the above method, the determination of whether or not the reflected light 14 can be determined can also be made, for example, based on whether or not the light reception count value of the kth bin from the top is equal to or greater than a certain value compared to the average light reception count value of the other bins.

[0029] Various criteria can be applied to the determination of the presence or absence of reflected light 14 in the reflected light determination unit 74. For example, if one or more of the light reception count values ​​for each bin exceed a predetermined threshold, it can be determined that reflected light 14 is present, and if not, it can be determined that reflected light 14 is absent. In this case, the threshold may be a fixed value, or a value obtained by adding a fixed value to the average value of the light reception count values ​​for each bin. Furthermore, since the S / N ratio improves as the number of pixels to be binned increases, if the binning processing unit 60 is configured to be able to change the number of pixels to be binned, the threshold may be changed depending on the number of pixels to be binned.

[0030] The distance calculation unit 50 has a role of calculating the distance to the object 110 for each pixel (light receiving element 42) based on signals from the light receiving unit 40, the time count unit 20, and the reflected light determination unit 74. When the distance calculation unit 50 receives a pulse signal from the light receiving element 42, it acquires the time count value at that time from the time count unit 20 and receives the determination result of the reflected light 14 corresponding to the pulse signal from the low-resolution histogram processing unit 70. Next, the distance calculation unit 50 determines whether or not the light receiving element 42 is likely to have received the reflected light 14 based on the output from the light receiving element 42 and the output from the low-resolution histogram processing unit 70. The determination of whether or not the reflected light 14 is likely to have been received can be made using the output from the light receiving element 42 and the output from the low-resolution histogram processing unit 70, as shown in Table 1, for example. [Table 1]

[0031] However, if both the output from the light receiving unit 40 and the output from the low-resolution histogram processing unit 70 are 1, it is highly likely that the light is reflected at that coordinate, but it may also be ambient light. Therefore, the distance calculation unit 50 calculates the distance from the time count value corresponding to the pulse signal received from the light receiving element 42, and sets it as a candidate for the high-resolution distance at the coordinate of the light receiving element 42. Next, from among the distance candidates calculated in this way, one that is highly likely to be the reflected light 14 at that coordinate is selected and stored in the data storage unit 52. If the reflected light determination unit 54 determines that the high-resolution distance at that coordinate is highly likely to be the correct distance, it outputs that distance as the distance at that coordinate; otherwise, it outputs a message indicating that there is no object whose distance can be measured at that coordinate.

[0032] Although the above description shows an example in which distance information is output at a resolution corresponding to the light receiving element 42, the distance calculation unit 50 may be configured to output distance information at a resolution different from the resolution corresponding to the light receiving element 42. In this case, a conversion unit (not shown) that converts the resolution (spatial resolution) of the light receiving unit 40 to the resolution of the distance calculation unit 50 may be inserted between the light receiving unit 40 and the distance calculation unit 50. This conversion unit may be configured to convert the resolution of the signal output from the light receiving unit 40 to a resolution higher than the resolution of the low-resolution histogram processing unit 70 but lower than the resolution of the signal output from the light receiving unit 40.

[0033] For example, the conversion unit can be configured to convert a plurality of signals output from a plurality of pixels into a plurality of signals corresponding to a plurality of unit areas, each of which includes at least one pixel. The binning processing unit 60 can then convert the plurality of signals output from the plurality of unit areas into a plurality of signals corresponding to a plurality of pixel blocks, each of which includes at least two unit areas. In this case, each of the plurality of unit areas can include a first number of pixels, which is two or more, and each of the pixel blocks can include a second number of pixels, which is greater than the first number.

[0034] The binning processing unit 60 can also be said to have a function of converting multiple first signals output from multiple pixels into multiple second signals having a spatial resolution lower than that of the multiple first signals. In this case, the data accumulation unit 72 accumulates, for each of multiple first unit areas corresponding to the multiple second signals, information indicating the relationship between a class determined according to the time until pulsed light is detected and a frequency indicating the number of times pulsed light is detected, based on the multiple second signals. The reflected light determination unit 74 extracts from the information a class candidate including a signal due to reflected light from the object 110 for each of multiple second unit areas corresponding to multiple signals having a spatial resolution higher than that of the multiple second signals. The distance calculation unit 50 calculates the distance to the object 110 corresponding to each of the multiple second unit areas based on the candidate. Note that the multiple signals having a spatial resolution higher than that of the multiple second signals may be multiple first signals, and the multiple second unit areas may be multiple pixels. Alternatively, the multiple signals having a spatial resolution higher than that of the multiple second signals may be multiple third signals having a spatial resolution higher than that of the multiple second signals and different from the multiple first signals.

[0035] The output unit 80 serves to output the distance measurement information received from the distance calculation unit 50 to the outside.

[0036] FIG. 2 is a timing diagram showing the basic operation of a typical LiDAR system. During a ranging period of a typical LiDAR system, a plurality of frame periods FP of a predetermined length are sequentially executed. FIG. 2 assumes that N frame periods FP, including a first frame period FP1, a second frame period FP2, ..., an Nth frame period FPN, are executed during the ranging period. During each frame period FP, a plurality of shot periods SP and a peak determination period PP are executed. FIG. 2 assumes that M shot periods SP, including a first shot period SP1, a second shot period SP2, ..., an Mth shot period SPM, and a peak determination period PP are executed during one frame period FP. Each shot period SP is divided into a plurality of bins separated based on a time count.

[0037] One frame period FP corresponds to the period for acquiring one distance image. During one shot period SP, a pulse of light is emitted from the light-emitting unit 10 once. That is, each shot period SP starts when the light-emitting unit 10 emits a pulse of light, and the length of each shot period SP is determined by the interval at which the pulse of light is emitted. During each shot period SP, a counting operation is performed to count the pulse signals output from the light-receiving unit 40 for each bin separated based on the time count. In this way, by acquiring the light-receiving count value for each bin during each shot period SP, data including histogram information (histogram information) such as that shown in FIG. 3 can be acquired.

[0038] Figure 3(a) shows an example of a histogram acquired in the first shot period SP1, Figure 3(b) shows an example of a histogram acquired in the second shot period SP2, and Figure 3(c) shows an example of a histogram acquired in the third shot period SP3. Figure 3(d) shows a histogram obtained by integrating the histograms in Figures 3(a) to 3(c).

[0039] As shown in FIG. 3(a), in the histogram acquired in the first shot period SP1, the light reception count value in bin 5 reaches its peak. As shown in FIG. 3(b), in the histogram acquired in the second shot period SP2, the light reception count value in bins 2 and 4 reaches its peak. As shown in FIG. 3(c), in the histogram acquired in the third shot period SP3, the light reception count value in bin 5 reaches its peak. On the other hand, in the histogram obtained by accumulating these counts, the light reception count value in bin 5 reaches its peak, as shown in FIG. 3(d). In this way, by accumulating information from multiple shot periods SP, it is possible to determine the bin that is more likely to contain reflected light from the object being measured.

[0040] During the peak determination period PP, the distance to the object 110 is calculated based on the time information of the bin where the light reception count value reaches its peak. The distance D [m] to the object 110 can be calculated by the following formula (1). Here, t is the time count value (unit: seconds) obtained from the time count unit 20 at the timing when the pulse signal is received from the light receiving unit 40, and c is the speed of light (2.998×10 8 [m / sec]). D = c × t / 2 [m] … (1)

[0041] For example, if the bins are set at 10 nanosecond intervals, bin 5, where the light reception count value peaks, corresponds to the class that counts pulse signals detected between 50 nanoseconds and 60 nanoseconds after light emission from the light-emitting unit 10. Therefore, the distance D to the target object 110 can be calculated from equation (1) to be 7.5 [m] to 9.0 [m].

[0042] In this embodiment, the processing for each shot period SP in a typical LiDAR system described above corresponds to the processing performed by the data storage unit 72 and reflected light determination unit 74 of the low-resolution histogram processing unit 70. However, the low-resolution histogram processing unit 70 does not perform processing for the peak determination period PP. Instead, the reflected light determination unit 74 determines the presence or absence of reflected light for each coordinate when it is in a state where it can determine reflected light and outputs the result. The state where it is possible to determine reflected light will be described later. The distance calculation unit 50 receives output from the reflected light determination unit 74 and operates for each shot period SP. After the last shot period SPM of one frame period FP, the reflected light determination unit 54 determines whether it can output distance information instead of the reflected light determination unit 74. If it determines that it can output distance information, the reflected light determination unit 54 calculates the distance and outputs the distance information from the output unit 80.

[0043] Next, the operation of the distance measuring device according to this embodiment will be described in more detail with reference to FIGS.

[0044] When ranging begins, as described with reference to FIG. 2, multiple frame periods FP are executed sequentially starting with the first frame period FP1. When the frame period FP begins, first, in step S101, initialization processing of the data storage unit 52 of the distance calculation unit 50 is performed. The data storage unit 52 can store any number of entries corresponding to each pixel, as shown in FIG. 8, for example. Each entry includes a data area for holding a bin and a frequency corresponding to the bin. Here, for example, as shown in FIG. 8, a description will be given assuming that the number of entries for each pixel in the data storage unit 52 is four, but the number of entries can be set arbitrarily. The four entries are numbered 0, 1, 2, and 3 as entry indexes. In the initialization processing of step S101 in this embodiment, as shown in step S201 in FIG. 5, the frequency of each entry for each pixel in the data storage unit 52 is initialized to 0.

[0045] In the following step S102, a shot period SP is started. The shot period SP is started by emitting pulsed light from the light emitting unit 10 under the control of the control unit 30 and starting time counting in the time counting unit 20 in synchronization with this. The time counting in the time counting unit 20 starts from 0. The time counting can be performed, for example, by a method of counting a clock signal. For example, when a clock signal with a 1 nanosecond period is used, an increase in the time count value from 0 to 10 indicates that 10 nanoseconds have elapsed.

[0046] In the following step S103, it is determined whether or not the light receiving unit 40 has detected light. If the result of the determination is that at least one of the multiple light receiving elements 42 that make up the light receiving unit 40 has detected light ("YES" in step S103), the process proceeds to step S104. If the result of the determination is that the light receiving unit 40 has not detected light ("NO" in step S103), the process proceeds to step S111.

[0047] In step S104, the binning processing unit 60 performs binning processing on signals detected by the multiple light-receiving elements 42 that make up the light-receiving unit 40. Specifically, the binning processing unit 60 performs a calculation of (floor(X / 4), floor(Y / 4)) for the coordinates (X, Y) of each light-receiving element 42 to calculate the coordinates (Xi, Yi) for each light-receiving element 42. Then, the output signals of each light-receiving element 42 with the same coordinates (Xi, Yi) are combined (logical ORed) to generate an output signal for each coordinate (Xi, Yi). The floor(x) function returns the largest integer less than or equal to x. By performing a calculation of (floor(X / 4), floor(Y / 4)) for the coordinates (X, Y), 4×4 pixel binning processing can be performed. The binning processing unit 60 outputs the binned signals to the low-resolution histogram processing unit 70 as output signals for each of the low-resolution pixel coordinates (XL, YL).

[0048] In the following step S105, the reflected light determination unit 74 of the low-resolution histogram processing unit 70 determines whether or not the reflected light 14 can be determined for each of the signals received from the binning processing unit 60. If the determination result shows that the reflected light can be determined ("YES" in step S105), the process proceeds to step S108. If the determination result shows that the reflected light cannot be determined ("NO" in step S105), the process proceeds to step S106. Note that in this specification, a period in which the reflected light cannot be determined may be referred to as a first period, and a period in which the reflected light can be determined may be referred to as a second period.

[0049] In step S106, the data storage unit 72 of the low-resolution histogram processing unit 70 calculates the bins of the light reception times in the low-resolution histogram based on the time count values ​​acquired from the time count unit 20. The data storage unit 72 has a three-dimensional array of storage areas, and can store the light reception count values ​​for each combination of the low-resolution coordinates (XL, YL) and the bins.

[0050] In the following step S107, the data accumulation unit 72 increments the light reception count value of the bin at the light reception time in the low-resolution histogram calculated in step S106 by 1. After the processing of step S107, the process proceeds to step S111.

[0051] In step S108, the reflected light determination unit 74 determines whether the signal at the low-resolution coordinates (XL, YL) is due to reflected light. If it is determined to be reflected light (YES in step S108), the process proceeds to step S109. If it is determined not to be reflected light (NO in step S108), the process proceeds to step S111.

[0052] In step S109, the data storage unit 52 of the distance calculation unit 50 calculates the bin of the light reception time based on the time count value acquired from the time count unit 20 in correspondence with each signal from the pixel at coordinates (X, Y).

[0053] In the next step S110, the data accumulation unit 52 performs a state update process to update the state of the distance that is likely to be reflected light for the bin of the light reception time acquired in step S109. The state update process will be described in detail later. After the state update process, the process proceeds to step S111.

[0054] In step S111, it is determined whether the time count value has reached the final value corresponding to the end of the shot period SP. If the determination result shows that the time count value has not reached the final value ("NO" in step S111), the process returns to step S103, and the shot period SP continues. If the determination result shows that the time count value has reached the final value ("YES" in step S111), the process proceeds to step S112.

[0055] In step S112, it is determined whether the shot period SP is the last shot period SPM in the frame period FP. If the result of the determination is that the shot period SP is not the last shot period SPM in the frame period FP ("NO" in step S112), the process returns to step S102, and the next shot period SP in the frame period FP is started. If the result of the determination is that the shot period SP is the last shot period SPM in the frame period FP ("YES" in step S112), the process proceeds to step S113.

[0056] In step S113, the reflected light determination unit 54 performs a distance output determination process to determine whether or not to output distance information. Specifically, it determines whether or not the signals at each coordinate (Xi, Yi) after the binning process contain reflected light. If the result of the determination shows that reflected light is included, the distance calculation unit 50 calculates the distance from the bin and outputs it to the output unit 80. If the result of the determination shows that reflected light is not included, information indicating that there is no object whose distance can be measured is output to the output unit 80.

[0057] The state update process of step S110 can be performed, for example, in accordance with steps S301 to S304 of the flowchart shown in Fig. 6. Step S110 is executed in data storage unit 52 of distance calculation unit 50 in response to each signal of coordinates (X, Y).

[0058] First, in step S301, it is determined whether or not there is a bin in each entry of data storage unit 52 shown in Fig. 8 that is the same as the bin for the light reception time calculated in step S109. If the determination result shows that there is a bin that is the same as the bin for the light reception time calculated in step S109 ("YES" in step S301), the process proceeds to step S304. If there is no bin that is the same as the bin for the light reception time calculated in step S109 ("NO" in step S301), the process proceeds to step S302.

[0059] In step S302, an entry with a low frequency among all entries is selected as the entry to be replaced. The entry to be replaced may be the entry with the lowest frequency, or may be selected using a random number with a setting that the lower the frequency, the higher the probability of replacement. If there are multiple entries to be replaced under the same conditions, they may be selected randomly, or a cyclic counter that increments the entry number by 1 each time replacement is performed may be used to prevent bias in the entries to be replaced, and an entry with a value close to the count value may be selected as the entry to be replaced.

[0060] In the following step S303, the bin of the entry to be replaced selected in step S302 is set to the bin of the light reception time calculated in step S109, and the frequency of that entry is set to 1, and the state update process ends.

[0061] In step S304, the frequency of entries in the bin that is the same as the bin for the light reception time calculated in step S109 is incremented by 1, and the state update process ends.

[0062] By repeating the state update process in this manner, the more times a bin is determined to possibly contain a signal due to reflected light from an object, the greater the frequency value of that bin.

[0063] The distance output determination process in step S113 may be performed, for example, in accordance with steps S401 to S403 in the flowchart shown in Fig. 7. Step S113 is executed by reflected light determination unit 54 of distance calculation unit 50 for each signal at coordinates (Xi, Yi).

[0064] First, in step S401, the entry with the highest frequency is extracted from the entries in data storage unit 52 shown in Fig. 8, and it is determined whether the frequency is equal to or greater than a predetermined threshold. If the determination result shows that the frequency is equal to or greater than the threshold ("YES" in step S401), the process proceeds to step S402. If the frequency is less than the threshold ("NO" in step S401), the process proceeds to step S403. The threshold used for the determination can be set, for example, based on the maximum or average value of the frequency of entries not determined to be reflected light in the low brightness histogram.

[0065] In step S402, it is determined that the most frequently occurring entry in the data storage unit 52 corresponds to reflected light, and the bin of that entry is converted to a distance and output, thereby completing the distance output determination process and the series of processes for that frame.

[0066] In step S403, it is determined that there is no entry corresponding to the reflected light among the entries in data storage unit 52, and an output is made indicating that there is no object whose distance can be measured. This ends the distance output determination process, and the series of processes for that frame is completed.

[0067] In this way, when it is determined that the light is reflected at the coordinates (XL, YL) of the low-resolution pixel by the state update process shown in Fig. 6, the frequency of the bin for the coordinates (X, Y) where the light was received increases. Then, when the frequency of the bin with the highest frequency is equal to or greater than a predetermined threshold, it is determined to be reflected light, and the bin is converted into a distance and output.

[0068] By performing processing in this manner, it is possible to reduce the required memory capacity. The reason for this will be explained below using an example in which the number of bins is 1000 (for example, distance measurement is possible up to 100 m with a distance resolution of 10 cm) and the number of shot periods SP per frame period FP is 10,000. Note that the number of pixels (number of light receiving elements 42) of the light receiving section 40 is assumed to be 256 pixels (16 vertical × 16 horizontal), as in the above example.

[0069] The memory capacity required to store histogram information is the number of pixels x the number of bins x ceil(log2(number of shots)) bits, which in the above example is (16 x 16 x 1000 x 14 = 3584000) bits. Here, the ceil(x) function returns the smallest integer greater than or equal to x.

[0070] In contrast, in this embodiment, the memory capacity required to hold low-resolution histogram information is (number of pixels / (number of bins in X direction) / (number of bins in Y direction)×number of bins×ceil(log2(number of shots))). In the above example, it is (16×16 / 4 / 4×1000×14=224000) bits. The memory capacity required for each pixel is (4 entries×(ceil(log2(number of bins))+ceil(log2(number of shots)))) bits, and for all pixels it is (16×16×4×(10+14)=24576) bits. In total, it is 248576 bits, which is significantly smaller than the usual 3584000 bits.

[0071] As described above, according to this embodiment, it is possible to reduce the required memory capacity while maintaining the distance measurement accuracy and resolution.

[0072] [Second embodiment] A distance measuring device and distance measuring method according to a second embodiment of the present invention will be described with reference to FIGS. 9 to 18. Components similar to those in the distance measuring device according to the first embodiment are given the same reference numerals, and their description will be omitted or simplified. FIGS. 9 to 11 are flowcharts showing the operation of the distance measuring device according to this embodiment. FIG. 12 is a diagram showing an example of the configuration of entries held in the data storage unit of the distance calculation unit in the distance measuring device according to this embodiment. FIG. 13 is a diagram explaining the positional relationship between a pixel of interest and surrounding pixels. FIGS. 14, 16, 17, and 18 are diagrams showing an example of the operation of the distance measuring device according to this embodiment. FIG. 15 is a diagram showing an example of a low-resolution histogram acquired in a first period and an example of a low-resolution histogram of ambient light acquired in a second period.

[0073] The distance measuring device according to this embodiment is the same as the distance measuring device according to the first embodiment except for the processing performed by the distance calculation unit 50. In this embodiment, the differences from the distance measuring device according to the first embodiment will be mainly described, and the description of the similarities between the distance measuring device according to the first embodiment will be omitted as appropriate.

[0074] Generally, there is a spatial correlation between the data of a pixel and the data of its neighboring pixels. In this embodiment, this property is utilized to reduce the memory capacity of the data storage unit 52. In this embodiment, when updating the data of a pixel, the data storage unit 52 refers to the data of the neighboring pixels of that pixel. Furthermore, when the reflected light determination unit 54 determines the reflected light of a pixel, it also refers to the data of the neighboring pixels of that pixel.

[0075] For simplicity's sake, in this embodiment, the data storage unit 52 includes one entry for each pixel, as shown in FIG. 12 . Each entry includes a data area for storing a bin and a frequency corresponding to the bin. Since there is one entry for each pixel, the entry is assigned an entry index number of 0. The data storage unit 52 of the distance calculation unit 50 weights and sums the frequency of the pixel of interest and the frequencies of the entries for the light-receiving time bins of the eight surrounding pixels ranging from −1 to +1, and calculates the update probability based on the total frequency. The number of entries, the number of surrounding pixels, the range of the light-receiving time bins for which the frequencies are summed, and the update probability are all arbitrary and can be changed as appropriate depending on the usage situation. In this embodiment, the bin range is from 0 to 999, with bin 999 representing the absence of any object reflecting light.

[0076] In this embodiment, in the initialization process of step S101, as shown in step S211 of FIG. 9, for example, the bin value of each pixel entry is initialized to 999, and the frequency value is initialized to 0 (not registered).

[0077] The state update process in step S110 can be performed, for example, in accordance with steps S311 to S316 in the flowchart shown in Fig. 10. Step S110 is executed in data storage unit 52 of distance calculation unit 50 for each signal of coordinates (X, Y).

[0078] First, in step S311, it is determined whether or not there is a bin that is the same as the bin calculated in step S109 for each entry in data accumulation unit 52 shown in Fig. 12. If the determination result shows that there is a bin that is the same as the bin calculated in step S109 ("YES" in step S311), the process proceeds to step S316. If there is no bin that is the same as the bin calculated in step S109 ("NO" in step S311), the process proceeds to step S312.

[0079] In step S312, the frequency of the pixel of interest is added to the frequencies of the surrounding pixels weighted according to the bin value. For example, for surrounding pixels with the same bin value as the pixel of interest, the value of (frequency x 1 / 4) is added to the frequency of the pixel of interest. For surrounding pixels with bin values ​​that are ±1 of the bin value of the pixel of interest, the value of (frequency x 1 / 16) is added to the frequency of the pixel of interest.

[0080] For example, as shown in FIG. 13, a total of nine light receiving elements 42 are arranged two-dimensionally from coordinates (x-1, y-1) to coordinates (x+1, y+1), and the pixel of interest is the light receiving element 42 at coordinates (x, y). In this case, the surrounding pixels may be the other eight pixels (light receiving elements 42) among the nine pixels excluding the pixel at coordinates (x, y) of interest. A large value obtained by adding up the frequencies of these pixels indicates that the distance between the object in the detection range of the pixel of interest and the object in the detection range of the surrounding pixels is short, and it is considered that the bin in question is likely to represent the correct distance to the object.

[0081] In the next step S313, the update probability for the frequency is calculated. As described above, the larger the value obtained by adding up the pixel frequencies, the more likely it is that the correct distance to the object is represented. Therefore, when calculating the update probability for the frequency, it is advisable to reduce the update probability when the added value is large and increase the update probability when the added value is small. For example, when the added value is 1 or less, the update probability is set to 1 / 2; when the added value is greater than 1 and less than 4, the update probability is set to 1 / 4; when the added value is greater than 4 and less than 16, the update probability is set to 1 / 16; and when the added value is greater than 16 and less than 32, the update probability is set to 1 / 32. In this embodiment, because the number of entries corresponding to each pixel is small, bin updates are performed probabilistically.

[0082] In the following step S314, it is determined whether the update probability calculated in step S313 is equal to or less than a random number value (here, in the range of 0 to 1). If the result of the determination is that the random number value is equal to or greater than the update probability ("YES" in step S314), the entry is not updated and the state update process is terminated. If the random number value is less than the update probability ("NO" in step S314), the process proceeds to step S315.

[0083] In step S315, the bin is set to the bin at the time of light reception, the frequency is set to 1, and the state update process is terminated.

[0084] In step S316, the frequency of entries in which the bin at the light reception time calculated in step S109 is the same as the bin is incremented by 1, and the state update process ends.

[0085] The distance output determination process in step S113 may be performed, for example, in accordance with steps S411 to S413 in the flowchart shown in Fig. 11. Step S113 is executed by reflected light determination unit 54 of distance calculation unit 50 for each signal at coordinates (Xi, Yi).

[0086] First, in step S411, it is determined whether the frequency value in the entry of data accumulation unit 52 shown in Fig. 12 is equal to or greater than a predetermined threshold. If the result of the determination is that the frequency value is equal to or greater than the threshold ("YES" in step S411), the process proceeds to step S412. If the frequency value is less than the threshold ("NO" in step S411), the process proceeds to step S413. Note that when determining the frequency, the frequency of the pixel of interest may be added with the frequency of surrounding pixels weighted by a predetermined weight, using a method similar to that in step S312.

[0087] In step S412, it is determined that the entry corresponds to reflected light, and the bin of the entry is converted to distance and output, thereby completing the distance output determination process and the series of processes for the frame.

[0088] In step S413, it is determined that the entry does not correspond to reflected light, and an output is made indicating that there is no object whose distance can be measured. This ends the distance output determination process, and the series of processes for that frame is completed.

[0089] In this way, when it is determined that the light is reflected at the coordinates (XL, YL) of the low-resolution pixel by the state update process shown in Fig. 10, the frequency of the bin for the coordinates (X, Y) where the light was received increases. Then, when the frequency is equal to or greater than a predetermined threshold, it is determined to be reflected light, and the bin is converted to a distance and output.

[0090] Next, a specific example of the operation in step S110 will be described with reference to Figures 14 to 18. For simplicity of explanation, it is assumed that the bins in the low-resolution histogram and the bins of the light reception time in the distance calculation unit 50 are the same.

[0091] 14 shows the distances to objects detected at pixels (light receiving elements 42) from coordinates (0,0) to coordinates (4,4) as bin values ​​at the light receiving times in the distance calculation unit 50. Of these pixels, 16 pixels from coordinates (0,0) to coordinates (3,3) (pixels surrounded by thick lines in FIG. 14) are included in one low-resolution pixel (coordinates (XL,YL)=(0,0)).

[0092] FIG. 15(a) is a low-resolution histogram of a low-resolution pixel (coordinates (XL, YL) = (0, 0)), showing an example of the frequency distribution of light (the sum of reflected light and ambient light) received by the pixel in a certain frame until it becomes possible to determine reflected light. In this example, the frequency is above the threshold in the bins corresponding to time count values ​​of 30, 40, 100, 110, and 120. Therefore, in the low-resolution histogram, the bins corresponding to time count values ​​30, 40, 100, and 120 are determined to be reflected light, and the distance calculation unit 50 corresponding to the coordinates (X, Y) of the pixel that received the light operates.

[0093] Figure 15(b) is a low-resolution histogram for a low-resolution pixel (coordinates (XL, YL) = (0, 0)), showing an example of the frequency distribution of ambient light when it is determined that reflected light is present and output after it becomes possible to determine reflected light in a certain frame. In this example, ambient light is detected as reflected light in the bins corresponding to time count values ​​of 30, 40, 100, 110, and 120.

[0094] FIG. 16 shows the bins and frequencies at a certain point in time for pixels (photodetectors 42) from coordinates (0,0) to coordinates (4,4). The two numerical values ​​written at each coordinate indicate the bin value on the top row and the frequency value on the bottom row. In addition, bins that are different from the bins in FIG. 14 due to ambient light are marked with a triangle to the right of the bin value.

[0095] At this point, assume that light is detected at the pixel at coordinates (1, 2), and the bin for the light reception time in the distance calculation unit 50 is 30. In step S311, a determination is made as to whether there is an entry for the same bin as the bin for the light reception time. Since the bin for the entry for the pixel at coordinates (1, 2) is 120, processing proceeds to step S312. In step S312, a weighted sum of the frequencies of surrounding pixels with similar bin values ​​is performed on the frequency value of the pixel at coordinates (1, 2) of interest. In this example, there are two surrounding pixels with the same bin value and a frequency of 1, and no pixels with a bin value of -1 or +1. Therefore, for example, according to the above-mentioned rule, a calculation of 1 + (1 + 1) × 1 / 4 + 0 × 1 / 8 is performed, resulting in a frequency value of 1.5. In step S313, the update probability for the frequency is calculated as 1 / 4. In step S314, the update probability 1 / 4 is compared with a random value greater than or equal to 0 and less than 1. Since the random value is 0.81, which is greater than the state update probability, the state update is terminated without changing the bin and frequency.

[0096] FIG. 17 shows the bins and frequencies at a later point in time for pixels (photosensitive elements 42) from coordinates (0,0) to coordinates (4,4).

[0097] At this point, assume that light is detected at the pixel at coordinates (1, 2), and the bin for the light reception time in the distance calculation unit 50 is 30. In step S311, a determination is made as to whether there is an entry for the same bin as the bin for the light reception time. Since the bin for the entry for the pixel at coordinates (1, 2) is 120, processing proceeds to step S312. In step S312, a weighted sum of the frequencies of surrounding pixels with similar bin values ​​is performed on the frequency value of the pixel at coordinates (1, 2) of interest. In this example, among the surrounding pixels, there is one pixel with the same bin value and a frequency of 1, two pixels with a frequency of 2, and no pixels with a bin value of -1 or +1. Therefore, for example, according to the above-mentioned rule, 1 + (2 + 2 + 1) × 1 / 4 + 0 × 1 / 8 is calculated, resulting in a frequency value of 2.25. In step S313, the update probability for the frequency is calculated as 1 / 4. In step S314, the update probability 1 / 4 is compared with a random value greater than or equal to 0 and less than 1. Since the random number value is 0.12, which is smaller than the state update probability, the process proceeds to step S315, where the bin is set to 30, which is the bin for the light reception time, the frequency is set to 1, and the state update is completed.

[0098] 18 shows the bins and frequencies after the state update for the pixels (light receiving elements 42) from coordinates (0,0) to coordinates (4,4). It can be seen that the value of the bin at coordinates (1,2) is the same as the value in FIG.

[0099] By performing processing in this manner, it is possible to reduce the required memory capacity. The reason for this will be explained below using an example in which the number of bins is 1000 (for example, distance measurement is possible up to 100 m with a distance resolution of 10 cm) and the number of shot periods SP per frame period FP is 10,000. Note that the number of pixels (number of light receiving elements 42) of the light receiving section 40 is assumed to be 256 pixels (16 vertical × 16 horizontal), as in the above example.

[0100] In this embodiment, the memory capacity required to hold low-resolution histogram information is 224,000 bits, the same as in the first embodiment. The memory capacity required per pixel is (ceil(log2(number of bins)) + ceil(log2(number of shots))) bits, and for all pixels it is ((16 × 16 × (10 + 14)) = 6,144) bits. In total, this is 230,144 bits, which is significantly smaller than the usual 3,584,000 bits.

[0101] As described above, according to this embodiment, it is possible to reduce the required memory capacity while maintaining the distance measurement accuracy and resolution.

[0102] [Third embodiment] A distance measuring device and a distance measuring method according to a third embodiment of the present invention will be described. Components similar to those of the distance measuring device according to the first or second embodiment will be given the same reference numerals, and their description will be omitted or simplified.

[0103] The distance measuring device according to this embodiment is the same as the distance measuring device according to the first embodiment except for the processing performed by the reflected light determination unit 74 of the low-resolution histogram processing unit 70. In this embodiment, the differences from the distance measuring device according to the first embodiment will be mainly described, and descriptions of the similarities between the distance measuring device according to the first embodiment will be omitted as appropriate.

[0104] In the first and second embodiments, the reflected light determination unit 74 determines reflected light based on low-resolution histogram information generated by the data storage unit 72 of the low-resolution histogram processing unit 70. However, depending on the measurement environment, it may not always be possible to ensure a sufficient difference between ambient light and reflected light, and reflected light may not be determined. In this embodiment, an example of how to deal with such a case will be described.

[0105] As described above, pixel binning reduces resolution but increases the probability of receiving reflected light. From this perspective, in this embodiment, when it is difficult to determine reflected light using histogram information based on data generated by the binning processing unit 60, the reflected light determination unit 74 generates histogram information with lower resolution. Then, using this lower-resolution histogram information, the reflected light is determined using, for example, a method similar to that of the first embodiment. In this way, it is possible to more easily distinguish between reflected light and ambient light. For example, the lower-resolution histogram information can be generated based on multiple signals corresponding to multiple pixel block groups, each of which includes at least two pixel blocks used to generate the low-resolution histogram.

[0106] As described above, according to this embodiment, it is possible to reduce the required memory capacity while maintaining the distance measurement accuracy and resolution.

[0107] [Fourth embodiment] A distance measuring device and distance measuring method according to a fourth embodiment of the present invention will be described with reference to Fig. 19. Components similar to those of the distance measuring device according to the first or second embodiment will be given the same reference numerals, and their description will be omitted or simplified. Fig. 19 is a diagram showing an example of the configuration of the data area of ​​the data storage unit in the distance measuring device according to this embodiment.

[0108] The distance measuring device according to this embodiment is similar to the distance measuring device according to the first embodiment, except that the data storage unit 72 of the low-resolution histogram processing unit 70 and the data storage unit 52 of the distance calculation unit 50 share a memory device. In this embodiment, differences from the distance measuring device according to the first embodiment will be mainly described, and descriptions of similarities to the distance measuring device according to the first embodiment will be omitted as appropriate. Note that, although this embodiment describes an embodiment in which the data storage unit 52 of the distance calculation unit 50 uses the memory unit of the data storage unit 72 of the low-resolution histogram processing unit 70, another functional block may also be provided with a memory device.

[0109] For ease of explanation, in this embodiment, the number of shot periods SP per frame period FP is set to 10,000 (maximum frequency value=10,000), and the number of bins per shot period SP is set to 1,000. In addition, the number of pixels to be binned by the binning processing unit 60 is set to 16 (4 pixels horizontally × 4 pixels vertically), and the number of entries in the data accumulation unit 52 is set to 4. However, these can be changed as desired.

[0110] 19 , the data held by the distance measuring device during distance measurement processing includes frequency data 92 of the low-resolution histogram, data 94 of entries in the coordinate range to be binned, and data 96 of bins in the low-resolution histogram for reflected light determination. In the first embodiment, of these, the frequency data 92 of the low-resolution histogram is held in the data storage unit 72 of the low-resolution histogram processing unit 70. In addition, the data 94 of entries in the coordinate range to be binned and data 96 of bins in the low-resolution histogram for reflected light determination are held in the data storage unit 52 of the distance calculation unit 50.

[0111] In contrast, in this embodiment, these data are stored in the data storage unit 72 of the low-resolution histogram processing unit 70. The data area for storing the frequency data 92 of the low-resolution histogram and the data area for storing the entry data 94 of the coordinate range to be binned are shared, thereby reducing memory capacity. In other words, the data area for storing the frequency data 92 of the low-resolution histogram and the data area for storing the entry data 94 of the coordinate range to be binned at least partially overlap. With this configuration, only one of the frequency data 92 of the low-resolution histogram and the entry data 94 of the coordinate range to be binned can be stored in the data storage unit 72, and therefore, in this embodiment, the following processing is performed.

[0112] When the reflected light determination unit 74 of the low-resolution histogram processing unit 70 is not in a state where reflected light determination is possible, the low-resolution histogram processing unit 70 updates the low-resolution histogram using the low-resolution histogram frequency data 92 stored in the data accumulation unit 72. When the low-resolution histogram processing unit 70 updates the frequency data of the low-resolution histogram, in step S107, it accumulates the light reception count values ​​as frequencies for the bins of the low-resolution histogram calculated in step S106. Because the frequency data of the low-resolution histogram has 1,000 bins, it can store 1,000 frequencies, from the frequency of bin 0 to the frequency of bin 999. At this time, the distance calculation unit 50 is in a stopped state, and the distance calculation unit 50 does not use the data 94 of the entry of the coordinate range to be binned. In other words, the data accumulation unit 72 of the low-resolution histogram processing unit 70 can be used to store the frequency data 92 of the low-resolution histogram.

[0113] When the reflected light determination unit 74 transitions from a state in which reflected light determination is not possible to a state in which reflected light determination is possible, it converts the data held by the data accumulation unit 72 from low-resolution histogram frequency data 92 to bin data 96 of a low-resolution histogram for reflected light determination. The generated bin data 96 of the low-resolution histogram for reflected light determination is held in the data accumulation unit 72. In this conversion process, the values ​​of the kth most frequent bins whose frequencies are equal to or greater than a threshold are extracted from the low-resolution histogram frequency data 92 as bins for the low-resolution histogram for reflected light determination. In the example of FIG. 19, the value of k is set to 16 (the number of pixels to be binned). As long as the bin data 96 of the low-resolution histogram for reflected light determination is available, the reflected light determination unit 74 can perform reflected light determination even if the frequency data 92 of the low-resolution histogram is not yet available.

[0114] When reflected light determination is possible, data 94 of the entry of the coordinate range to be binned and data 96 of the bin of the low-resolution histogram for reflected light determination are valid. The reflected light determination unit 74 performs reflected light determination using data 96 of the bin of the low-resolution histogram for reflected light determination. In step S109, the distance calculation unit 50 calculates the bin of the light reception time using data 94 of the entry of the coordinate range to be binned, and performs a state update process in step S110.

[0115] When the number of pixels to be binned is 16 (4 pixels horizontally by 4 pixels vertically), the data stored in the data storage unit 72 as entry data 94 of the coordinate range to be binned includes data for 16 pixels from coordinates (0,0) to coordinates (3,3). The data for each pixel includes four entries. One entry consists of a bin and a frequency. In other words, the data storage unit 52 stores 128 pieces of data as entry data for the coordinate range to be binned.

[0116] In the above example, one piece of data in the entry of the coordinate range to be binned corresponds to one piece of data in the frequency data of the low-resolution histogram. Also, the number of pieces of data in the entry of the coordinate range to be binned is smaller than the number of pieces of data in the frequency data of the low-resolution histogram. Therefore, in this example, the data area corresponding to the frequency of bin 128 to the frequency of bin 999 in the frequency data of the low-resolution histogram is not used as the data area of ​​the entry of the coordinate range to be binned.

[0117] As described above, according to this embodiment, it is possible to reduce the required memory capacity while maintaining the distance measurement accuracy and resolution.

[0118] [Fifth embodiment] A moving body according to a fifth embodiment of the present invention will be described with reference to Fig. 20. Fig. 20 is a diagram showing an example of the configuration of a moving body according to this embodiment.

[0119] 20(a) shows an example of the configuration of a device mounted on a vehicle as an on-board camera. The device 300 has a distance measurement unit 303 that measures the distance to an object, and a collision determination unit 304 that determines whether or not there is a possibility of a collision based on the distance measured by the distance measurement unit 303. The distance measurement unit 303 is configured by the distance measuring device 100 described in any of the first to fourth embodiments. Here, the distance measurement unit 303 is an example of a distance information acquisition means that acquires distance information to the object. In other words, the distance information is information related to the distance to the object, etc.

[0120] The device 300 is connected to a vehicle information acquisition device 310 and can acquire vehicle information such as vehicle speed, yaw rate, and steering angle. The device 300 is also connected to a control ECU 320, which is a control device that outputs a control signal to generate a braking force for the vehicle based on the determination result of the collision determination unit 304. The device 300 is also connected to an alarm device 330 that issues an alarm to the driver based on the determination result of the collision determination unit 304. For example, if the collision determination unit 304 determines that a collision is highly likely, the control ECU 320 performs vehicle control to avoid a collision and mitigate damage by applying the brakes, releasing the accelerator, suppressing engine output, etc. The alarm device 330 warns the user by sounding an alarm, displaying alarm information on a screen of a car navigation system, etc., or vibrating a seat belt or steering wheel. These devices of the device 300 function as a mobile object control unit that controls the operation of controlling the vehicle as described above.

[0121] In this embodiment, the device 300 measures the distance around the vehicle, for example, the front or rear. Fig. 20(b) shows the device when measuring the distance in front of the vehicle (distance measurement range 350). The vehicle information acquisition device 310, which serves as a distance measurement control means, sends an instruction to the device 300 or the distance measurement unit 303 to perform a distance measurement operation. This configuration can further improve the accuracy of distance measurement.

[0122] Although the above describes an example of control to prevent collision with other vehicles, the present invention can also be applied to control of automatic driving by following other vehicles, control of automatic driving to prevent deviation from a lane, etc. Furthermore, the present invention is not limited to vehicles such as automobiles, but can be applied to moving objects (moving devices) such as ships, aircraft, artificial satellites, industrial robots, and consumer robots. In addition, the present invention can be applied to a wide range of devices that use object recognition or biometric recognition, such as intelligent transport systems (ITS) and surveillance systems, without being limited to moving objects.

[0123] [Modified embodiment] The present invention is not limited to the above-described embodiment, and various modifications are possible.

[0124] For example, an example in which part of the configuration of any one of the embodiments is added to another embodiment, or an example in which part of the configuration of another embodiment is substituted therefor, is also an embodiment of the present invention.

[0125] Furthermore, in the above embodiment, the light-emitting unit 10 and the light-receiving unit 40 are described as parts of the components of the distance measuring device 100, but at least one of the light-emitting unit 10 and the light-receiving unit 40 does not necessarily have to be part of the configuration of the distance measuring device 100.

[0126] Furthermore, although the above embodiment has been described with respect to a distance measuring device, the algorithms described in the above embodiment can also be applied to an information processing device for processing signals output from the light receiving unit 40. In this case, the information processing device can be configured with an input unit to which signals are input, a distance calculation unit 50, a binning processing unit 60, a low-resolution histogram processing unit 70, and an output unit 80. The information processing device can be a device such as a personal computer including a processor (e.g., a CPU or MPU). Alternatively, the information processing device can be a circuit such as an ASIC that realizes the functions of the input unit to which signals are input, the distance calculation unit 50, the binning processing unit 60, the low-resolution histogram processing unit 70, and the output unit 80.

[0127] 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.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0128] It should be noted that the above-described embodiments are merely examples of specific embodiments for carrying out the present invention, and the technical scope of the present invention should not be construed as being limited by these embodiments. In other words, the present invention can be carried out in various forms without departing from its technical concept or main features.

[0129] The disclosure of the above embodiment includes the following configurations and methods. (Configuration 1) a light receiving unit having a plurality of pixels for detecting pulsed light emitted from the light emitting unit and reflected by an object in the measurement target area; a binning processing unit that converts a plurality of signals output from a plurality of unit areas, each of which includes at least one pixel, into a plurality of signals corresponding to a plurality of pixel blocks, each of which includes at least two unit areas; a data storage unit that stores, for each pixel block, information indicating a relationship between a class determined according to a time from when the pulsed light is emitted until when the pulsed light is detected by the light receiving unit and a frequency indicating the number of times the pulsed light is detected, based on the plurality of signals output from the binning processing unit; a reflected light determination unit that extracts, for each of the plurality of unit regions, class candidates including signals due to reflected light from the object from the information; a distance calculation unit that calculates a distance to the object corresponding to each of the plurality of unit areas based on the candidate; A distance measuring device comprising: (Configuration 2) the data storage unit generates the information by counting, for each class, pulse signals output from the binning processing unit a plurality of times in response to a plurality of emissions of the pulsed light during a first period of one frame period; The reflected light determination unit extracts the candidate based on pulse signals output from the plurality of unit areas a plurality of times in response to emission of the pulsed light a plurality of times during a second period subsequent to the first period of the one frame period. 2. The distance measuring device according to configuration 1, (Configuration 3) The reflected light determination unit a first determination unit that, when at least one unit area among the plurality of unit areas detects light, determines whether or not an output signal of a pixel block including the one unit area is likely to include a signal due to reflected light from the object; a second determination unit that determines whether or not there is a possibility that the output signal of the one unit area includes a signal due to reflected light from the object; When it is determined by both the first determination unit and the second determination unit that there is a possibility that a signal due to reflected light from the object is included, a class corresponding to a timing at which the one unit area detects light is extracted as the candidate corresponding to the one unit area. 3. The distance measuring device according to configuration 1 or 2. (Configuration 4) The first determination unit and the second determination unit determine that the output signal may include a signal due to reflected light from the object when a class corresponding to the timing at which the one unit area detected light corresponds to a class having a frequency equal to or greater than a predetermined threshold among the classes constituting the information. 4. The distance measuring device according to configuration 3. (Configuration 5) The distance calculation unit Counting the number of times that the second determination unit has determined that the candidate may contain a signal due to reflected light from the object; If the count value of the class with the highest number of times among the candidates exceeds a predetermined threshold, the distance corresponding to the class with the highest number of times is calculated as the distance to the object in the one unit area. 5. The distance measuring device according to configuration 3 or 4. (Configuration 6) When the candidate does not include a class corresponding to the timing at which the one unit area detected light, the distance calculation unit adds the class corresponding to the timing at which the one unit area detected light to the candidate. 6. The distance measuring device according to configuration 5. (Configuration 7) When the candidate does not include a class corresponding to the timing at which the one unit area detected light, the distance calculation unit selects, as the candidate, a class corresponding to the timing at which the one unit area detected light, with an update probability according to the count values ​​of the one unit area and its surrounding unit areas. 6. The distance measuring device according to configuration 5. (Configuration 8) The data storage unit stores the information for each pixel block group based on a plurality of signals output from the plurality of pixel blocks corresponding to a plurality of pixel block groups each including at least two pixel blocks. 8. The distance measuring device according to any one of configurations 1 to 7. (Configuration 9) The data storage unit includes a first data area for storing the information corresponding to each of the plurality of unit areas, and a second data area for storing the candidates and their frequencies in each of the unit areas constituting the pixel block including the unit area, and the first data area and the second data area at least partially overlap each other. 9. The distance measuring device according to any one of configurations 1 to 8. (Configuration 10) Each of the plurality of unit areas includes one pixel. 10. The distance measuring device according to any one of configurations 1 to 9. (Configuration 11) a conversion unit that converts the spatial resolution of the signal output from the light receiving unit, The conversion unit converts the signals output from the pixels into the signals corresponding to the unit regions. 10. A distance measuring device according to claim 1, wherein the distance measuring device is a distance measuring device having a first distance and a second distance. (Configuration 12) each of the plurality of unit areas includes a first number of the pixels that is two or more; Each of the pixel blocks includes a second number of the pixels that is greater than the first number. 12. The distance measuring device according to claim 11, (Configuration 13) a light receiving unit having a plurality of pixels for detecting pulsed light emitted from the light emitting unit and reflected by an object in the measurement target area; a binning processing unit that converts a plurality of first signals output from the plurality of pixels into a plurality of second signals having a spatial resolution lower than that of the plurality of first signals; a data storage unit that stores, based on the plurality of second signals output from the binning processing unit, information indicating a relationship between a class determined according to a time from when the pulsed light is emitted to when it is detected by the light receiving unit and a frequency indicating the number of times the pulsed light is detected, for each of a plurality of first unit areas corresponding to the plurality of second signals; a reflected light determination unit that extracts, from the information, candidates for a class including a signal due to reflected light from the object for each of a plurality of second unit areas corresponding to a plurality of signals having a higher spatial resolution than the plurality of second signals; a distance calculation unit that calculates a distance to the object corresponding to each of the plurality of second unit areas based on the candidate; A distance measuring device comprising: (Configuration 14) the plurality of signals having a higher spatial resolution than the plurality of second signals are the plurality of first signals; The plurality of second unit areas are the plurality of pixels. 14. The distance measuring device according to configuration 13. (Configuration 15) The plurality of signals having a higher spatial resolution than the plurality of second signals are a plurality of third signals having a higher spatial resolution than the plurality of second signals and different from the plurality of first signals. 14. The distance measuring device according to configuration 13. (Configuration 16) an input unit to which signals output from a plurality of pixels that detect pulsed light emitted from the light emitting unit and reflected by an object in a measurement target area are input; a binning processing unit that converts a plurality of signals output from a plurality of unit areas, each of which includes at least one pixel, into a plurality of signals corresponding to a plurality of pixel blocks, each of which includes at least two unit areas; a data storage unit that stores, for each pixel block, information indicating a relationship between a class determined according to a time from when the pulsed light is emitted until when the pulsed light is detected, and a frequency indicating the number of times the pulsed light is detected, based on the plurality of signals output from the binning processing unit; a reflected light determination unit that extracts, for each of the plurality of unit regions, class candidates including signals due to reflected light from the object from the information; a distance calculation unit that calculates a distance to the object corresponding to each of the plurality of unit areas based on the candidate; An information processing device comprising: (Configuration 17) A mobile object, a distance information acquisition device according to any one of configurations 1 to 15; a control means for controlling the moving object based on the distance information acquired by the distance information acquisition device; A moving object characterized by having: (Method 1) A distance measuring method comprising: detecting pulsed light emitted from a light emitting unit and reflected by an object in a measurement target area using a plurality of pixels; and calculating a distance to the object based on signals detected by the plurality of pixels, converting a plurality of signals output from a plurality of unit areas each including at least one of the pixels into a plurality of signals corresponding to a plurality of pixel blocks each including at least two unit areas; storing, for each pixel block, information representing a relationship between a class determined according to a time from when the pulsed light is emitted until when the pulsed light is detected by a light receiving unit and a frequency indicating the number of times the pulsed light is detected, based on the plurality of signals corresponding to the pixel block; extracting, for each of the plurality of unit regions, class candidates including signals due to reflected light from the object from the information; Calculating a distance to the object corresponding to each of the plurality of unit areas based on the candidate. A distance measuring method characterized by: [Explanation of symbols]

[0130] 10...Light emitting part 20...Time counter 30...Control unit 40...Light receiving section 42...Photodetector 50...Distance calculation unit 52, 72...Data storage section 54,74...Reflected light determination section 60...Binning processing unit 70...Low-resolution histogram processing unit 80...Output section 100…Distance measuring device

Claims

1. a light receiving section having a plurality of pixels for detecting pulsed light emitted from the light emitting section and reflected by an object in a measurement target area; a binning processing unit that converts a plurality of signals output from a plurality of unit areas each including at least one of the pixels into a plurality of signals corresponding to a plurality of pixel blocks each including at least two unit areas; a data storage unit that stores, for each pixel block, information indicating a relationship between a class determined according to a time from when the pulsed light is emitted until when the pulsed light is detected by the light receiving unit, and a frequency indicating a number of times the pulsed light is detected, based on the plurality of signals output from the binning processing unit; a reflected light determination unit that extracts, for each of the plurality of unit regions, a candidate class including a signal due to reflected light from the object from the information; a distance calculation unit that calculates a distance to the object corresponding to each of the plurality of unit regions based on the candidates; A distance measuring device comprising:

2. the data storage unit generates the information by counting, for each class, a pulse signal output from the binning processing unit a plurality of times in response to a plurality of emissions of the pulsed light during a first period of one frame period; The reflected light determination unit extracts the candidates based on pulse signals outputted multiple times from the multiple unit areas in response to multiple emissions of the pulsed light during a second period subsequent to the first period of the one frame period.

2. The distance measuring device according to claim 1.

3. The reflected light determination unit a first determination unit that, when at least one unit area among the plurality of unit areas detects light, determines whether or not an output signal of a pixel block including the one unit area is likely to include a signal due to reflected light from the object; a second determination unit that determines whether or not there is a possibility that the output signal of the one unit area includes a signal due to reflected light from the object, When it is determined in both the first determination unit and the second determination unit that there is a possibility that a signal due to reflected light from the object is included, a class corresponding to a timing at which the one unit area detects light is extracted as the candidate corresponding to the one unit area.

3. A distance measuring device according to claim 1 or 2.

4. The first determination unit and the second determination unit determine that the output signal may include a signal due to reflected light from the object when a class corresponding to a timing at which the one unit area detects light corresponds to a class having a frequency equal to or greater than a predetermined threshold among the classes constituting the information.

4. The distance measuring device according to claim 3.

5. The distance calculation unit Counting the number of times that the second determination unit has determined that the candidate may include a signal due to reflected light from the object, and When the count value of the class with the highest number of occurrences among the candidates exceeds a predetermined threshold, the distance corresponding to the class with the highest number of occurrences is calculated as the distance to the object in the one unit area.

4. The distance measuring device according to claim 3.

6. When a class corresponding to the timing at which the one unit area detects light is not included in the candidates, the distance calculation unit adds a class corresponding to the timing at which the one unit area detects light to the candidates.

6. The distance measuring device according to claim 5.

7. When the candidate does not include a class corresponding to the timing at which the one unit area detects light, the distance calculation unit selects, as the candidate, a class corresponding to the timing at which the one unit area detects light with an update probability according to the count values ​​of the one unit area and its surrounding unit areas.

6. The distance measuring device according to claim 5.

8. The data storage unit stores the information for each pixel block group based on a plurality of signals output from the plurality of pixel blocks, the plurality of pixel block groups each including at least two pixel blocks.

3. A distance measuring device according to claim 1 or 2.

9. The data storage unit includes a first data area for storing the information corresponding to each of the plurality of unit areas, and a second data area for storing the candidates and their frequencies in each unit area constituting the pixel block including the unit area, and the first data area and the second data area are at least partially overlapped with each other.

3. A distance measuring device according to claim 1 or 2.

10. Each of the plurality of unit areas includes one pixel.

3. A distance measuring device according to claim 1 or 2.

11. A conversion unit that converts a spatial resolution of a signal output from the light receiving unit, The conversion unit converts the signals output from the pixels into the signals corresponding to the unit regions.

2. The distance measuring device according to claim 1.

12. Each of the plurality of unit areas includes a first number of the pixels that is two or more; Each of the pixel blocks includes a second number of the pixels that is greater than the first number.

12. The distance measuring device according to claim 11.

13. a light receiving section having a plurality of pixels for detecting pulsed light emitted from the light emitting section and reflected by an object in a measurement target area; a binning processing unit that converts a plurality of first signals output from the plurality of pixels into a plurality of second signals having a spatial resolution lower than that of the plurality of first signals; a data storage unit that stores, based on the plurality of second signals output from the binning processing unit, information indicating a relationship between a class determined according to a time from when the pulsed light is emitted to when the pulsed light is detected by the light receiving unit and a frequency indicating a number of times the pulsed light is detected for each of a plurality of first unit areas corresponding to the plurality of second signals; a reflected light determination unit that extracts, from the information, candidates for a class including a signal due to reflected light from the object for each of a plurality of second unit areas corresponding to a plurality of signals having a spatial resolution higher than that of the plurality of second signals; a distance calculation unit that calculates a distance to the object corresponding to each of the plurality of second unit regions based on the candidate; A distance measuring device comprising:

14. the plurality of signals having a higher spatial resolution than the plurality of second signals are the plurality of first signals; The plurality of second unit regions are the plurality of pixels.

14. The distance measuring device according to claim 13.

15. The plurality of signals having a higher spatial resolution than the plurality of second signals are a plurality of third signals having a higher spatial resolution than the plurality of second signals and different from the plurality of first signals.

14. The distance measuring device according to claim 13.

16. an input section to which signals output from a plurality of pixels that detect pulsed light emitted from the light emitting section and reflected by an object in a measurement target area are input; a binning processing unit that converts a plurality of signals output from a plurality of unit areas each including at least one of the pixels into a plurality of signals corresponding to a plurality of pixel blocks each including at least two unit areas; a data storage unit that stores, for each pixel block, information indicating a relationship between a class determined according to a time from when the pulsed light is emitted until when the pulsed light is detected, and a frequency indicating a number of times the pulsed light is detected, based on the plurality of signals output from the binning processing unit; a reflected light determination unit that extracts, for each of the plurality of unit regions, a candidate class including a signal due to reflected light from the object from the information; a distance calculation unit that calculates a distance to the object corresponding to each of the plurality of unit regions based on the candidates; 13. An information processing device comprising:

17. A mobile object, A distance information acquisition device according to claim 1 or 2, a control means for controlling the moving object based on the distance information acquired by the distance information acquisition device; A moving object comprising:

18. A distance measuring method comprising: detecting pulsed light emitted from a light emitting unit and reflected by an object in a measurement target area using a plurality of pixels; and calculating a distance to the object based on signals detected by the plurality of pixels, converting a plurality of signals output from a plurality of unit areas each including at least one of the pixels into a plurality of signals corresponding to a plurality of pixel blocks each including at least two unit areas; storing, for each pixel block, information indicating a relationship between a class determined according to a time from when the pulsed light is emitted until when the pulsed light is detected by a light receiving unit and a frequency indicating a number of times the pulsed light is detected, based on the plurality of signals corresponding to the pixel block; extracting, from the information, class candidates including a signal due to reflected light from the object for each of the plurality of unit regions; Calculating a distance to the object corresponding to each of the plurality of unit regions based on the candidates. A distance measuring method comprising:

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