WO2022158603A1 - 距離画像撮像装置、及び距離画像撮像方法 - Google Patents
距離画像撮像装置、及び距離画像撮像方法 Download PDFInfo
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- G—PHYSICS
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/88—Lidar systems specially adapted for specific applications
- G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
- G01S17/894—3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C3/00—Measuring distances in line of sight; Optical rangefinders
- G01C3/02—Details
- G01C3/06—Use of electric means to obtain final indication
- G01C3/08—Use of electric radiation detectors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
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- G—PHYSICS
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Definitions
- the present invention relates to a range image capturing device and a range image capturing method.
- TOF Time of Flight
- the distance to an object is calculated using the fact that the speed of light is known.
- a depth image capturing apparatus for obtaining depth information for each pixel in a two-dimensional image including an object, that is, three-dimensional information for the object has been put into practical use.
- pixels including photodiodes (PD) are arranged in a two-dimensional matrix on a silicon substrate, and light pulses reflected by an object on the pixel surface are received.
- a depth image pickup device outputs a photoelectric conversion signal for one image based on the amount of light (amount of charge) received by each pixel, thereby obtaining a two-dimensional image including an object and each pixel constituting the image.
- Get distance information for each For example, Patent Literature 1 discloses a technique of calculating a distance by sequentially distributing and accumulating electric charges corresponding to received light in three charge accumulating portions provided in one pixel.
- an arithmetic expression for calculating the distance is defined on the assumption that the pixels receive a direct wave (single path) that directly reciprocates between the light source of the light pulse and the object.
- a direct wave single path
- the light pulse is multiple-reflected at a corner portion of the object, a portion where the surface of the object has an uneven structure, or the like, and multipaths in which direct waves and indirect waves are mixed are received.
- multipath light is received, if the distance is calculated assuming that the light is received as a single path, there is a problem that an error occurs in the measured distance.
- the present invention has been made based on the above problems, and provides a range image capturing apparatus and a range image capturing method that can determine whether a pixel has received single-path light or multi-path light. for the purpose. Further, calculating the distance to one reflector if it is determined that the pixel received single-pass light, and calculating the distance to each of a plurality of reflectors if it is determined that the pixel received multi-path light. intended to
- the distance image pickup device of the present invention comprises a light source unit that irradiates a light pulse into a measurement space, which is a space to be measured, a photoelectric conversion element that generates charges according to the incident light, and three or more that store the charges.
- a light-receiving portion having a pixel having a charge storage portion; and a pixel drive circuit that distributes and accumulates the charge in each of the charge storage portions of the pixel at a timing synchronized with the irradiation of the light pulse; and the light pulse. and the accumulation timing of distributing and accumulating the charge in each of the charge accumulation units, and based on the amount of charge accumulated in each of the charge accumulation units, up to the object existing in the measurement space.
- the distance image processing unit performs a plurality of measurements with different relative timing relationships between the irradiation timing and the accumulation timing, and extracts a feature amount based on the amount of charge accumulated in each of the plurality of measurements. and determining whether the reflected light of the light pulse is received by the pixel through a single pass or whether the reflected light of the light pulse is received by the pixel through multiple passes, based on the tendency of the extracted feature quantity. and calculating the distance to the subject existing in the measurement space according to the result of the determination.
- the distance image processing unit performs lookup in which the relative timing relationship and the feature amount are associated with each other when the reflected light is received by the pixels in a single pass. using a table, based on the degree of similarity between the tendency of the lookup table and the tendency of the feature amount of each of the plurality of measurements, whether the reflected light was received by the pixel in a single pass, or whether the light It may be determined whether the reflected light of the pulse is received by the pixel in multiple paths.
- the lookup table defines at least one measurement condition among the shape of the light pulse, the irradiation time of the light pulse, and the accumulation time for accumulating charges in each of the charge accumulation units.
- the distance image processing unit uses the lookup table corresponding to the measurement conditions to determine whether the reflected light was received by the pixel in a single pass or whether the reflected light was received in multiple passes. It may be determined whether light is received by the pixel.
- the feature amount is stored in the charge storage unit that stores at least the charge corresponding to the reflected light among the charges stored in each of the three or more charge storage units. It may be a value calculated using the charge amount obtained.
- the pixels are provided with a first charge storage section, a second charge storage section, and a third charge storage section
- the range image processing section comprises the first charge storage section
- the feature amount has a real part as a first variable that is a difference between a first charge amount accumulated in the first charge accumulation unit and a second charge amount accumulated in the second charge accumulation unit, and Even if there is a value represented by a complex number whose imaginary part is the second variable that is the difference between the second charge amount accumulated in the second charge accumulation unit and the third charge amount accumulated in the third charge accumulation unit good.
- the plurality of measurements may be controlled such that delay times for delaying the irradiation timing relative to the accumulation timing are different from each other.
- the distance image processing unit performs lookup in which the relative timing relationship and the feature amount are associated with each other when the reflected light is received by the pixels in a single pass.
- an index value indicating a degree of similarity between the tendency of the lookup table and the tendency of each of the feature amounts of the plurality of measurements is calculated, and if the index value does not exceed a threshold, the reflected light is received by the pixel in a single pass, and if the index value exceeds the threshold value, it is determined that the reflected light is received by the pixel in multiple passes, and the index value is determined by the plurality of measurements
- the difference between the first feature amount that is the feature amount calculated from each of the and the second feature amount that is the feature amount that corresponds to each of the plurality of measurements in the lookup table is calculated as the second feature amount may be an addition value obtained by adding the normalized difference values of each of the plurality of measurements to the normalized difference values normalized by the absolute value of .
- the distance image processing unit determines that the reflected light is received by the pixel through multipaths
- the distance corresponding to each light path included in the multipaths is minimized. It may be calculated by using the square method.
- the distance image pickup device of the present invention may further include a charge discharging section for discharging charges generated by the photoelectric conversion elements.
- the distance image processing unit repeats a unit accumulation process a plurality of times in which charges are distributed to and accumulated in the respective charge accumulation units of the pixels at timing synchronized with the irradiation of the light pulse, Charges are accumulated in each of the charge accumulation units, and in a time interval different from a time interval in which charges are accumulated in each of the charge accumulation units in the unit accumulation process, charges generated by the photoelectric conversion element are discharged from the charge discharge. You may control so that it may be discharged by the department.
- the distance image processing unit calculates the provisional distance to the subject based on the first measurement among the plurality of measurements, and calculates the provisional distance to the subject based on the provisional distance.
- a delay time used for the remaining measurements may be determined, and the delay time may be a time for delaying the irradiation timing relative to the accumulation timing.
- the distance image processing unit may determine the delay time based on the time required for the light pulse to travel the provisional distance and the tendency of the feature amount.
- the distance image processing unit compares a case where the provisional distance is a short distance not exceeding the threshold with the plurality of The number of times of accumulation may be determined so that the number of times of accumulation for distributing and accumulating the electric charge in each of the charge accumulating units in the remaining measurements among the measurements of (1) increases.
- the distance image processing unit when the distance image processing unit determines that the reflected light is received by the pixels in a single pass, calculates the provisional distance to the subject based on the measurements at the plurality of measurement timings. may be calculated, and a representative value of each of the calculated provisional distances may be determined as the distance to the subject. Further, in the distance image capturing device, when the distance image processing unit determines that the reflected light is received by the pixels in a single pass, the distance image processing unit calculates a provisional distance to the subject based on measurements at the plurality of measurement timings. Determine each based on the least squares method. When determining that the reflected light is received by the pixel through multipath, the distance image processing unit determines the distance of each of the objects based on the least squares method based on the measurements at the plurality of measurement timings. may
- the depth image capturing method of the present invention comprises a light source unit that irradiates a light pulse into a measurement space, which is a space to be measured, a photoelectric conversion element that generates charges according to the incident light, and three or more that store charges.
- a light-receiving portion having a pixel having a charge storage portion; and a pixel drive circuit that distributes and accumulates the charge in each of the charge storage portions of the pixel at a timing synchronized with the irradiation of the light pulse; and the light pulse. and the accumulation timing of distributing and accumulating the charge in each of the charge accumulation units, and based on the amount of charge accumulated in each of the charge accumulation units, up to the object existing in the measurement space.
- a distance image capturing method performed by a distance image capturing device comprising: performing a plurality of different measurements, extracting a feature quantity based on the amount of charge accumulated in each of the plurality of measurements, and measuring the reflected light of the light pulse in a single pass based on the tendency of the extracted feature quantity It is determined whether the light is received by the pixel or whether the reflected light of the light pulse is received by the pixel by multipath, and the distance to the subject existing in the measurement space is calculated according to the determination result.
- the present invention it is possible to determine whether a pixel receives single-pass light or multi-pass light. Further, when it is determined that the pixel has received single-path light, the distance to one reflector is calculated, and when it is determined that the pixel has received multi-path light, the distance to each of a plurality of reflectors is calculated. can be done.
- FIG. 1 is a block diagram showing a schematic configuration of a distance image capturing device according to one embodiment
- FIG. 1 is a block diagram showing a schematic configuration of a distance image sensor of one embodiment
- FIG. 2 is a circuit diagram showing an example of the configuration of a pixel according to one embodiment
- FIG. 4 is a timing chart showing timings for driving pixels of one embodiment. It is a figure explaining the multipath of one embodiment.
- FIG. 4 illustrates an example of a complex function CP( ⁇ ) of one embodiment
- FIG. 4 illustrates an example of a complex function CP( ⁇ ) of one embodiment
- 4 is a timing chart showing timings for driving pixels of one embodiment. It is a figure explaining the process which the distance image processing part of one embodiment performs.
- a distance image pickup device according to one embodiment will be described below with reference to the drawings.
- FIG. 1 is a block diagram showing a schematic configuration of a distance image pickup device according to one embodiment of the present invention.
- a distance image pickup device 1 configured as shown in FIG. FIG. 1 also shows an object OB, which is an object whose distance is to be measured in the distance image pickup device 1 .
- the light source unit 2 irradiates the space of the object of measurement in which the object OB whose distance is to be measured in the distance image capturing device 1 exists, with a light pulse PO.
- the light source unit 2 is, for example, a surface emitting semiconductor laser module such as a vertical cavity surface emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser).
- the light source unit 2 includes a light source device 21 and a diffuser plate 22 .
- the light source device 21 is a light source that emits laser light in a near-infrared wavelength band (for example, a wavelength band of 850 nm to 940 nm) as a light pulse PO to irradiate the subject OB.
- the light source device 21 is, for example, a semiconductor laser light emitting device.
- the light source device 21 emits pulsed laser light under the control of the timing control section 41 .
- the diffuser plate 22 is an optical component that diffuses the laser light in the near-infrared wavelength band emitted by the light source device 21 over the area of the surface that irradiates the subject OB.
- the pulsed laser light diffused by the diffusion plate 22 is emitted as a light pulse PO, and is irradiated onto the object OB.
- the light receiving unit 3 receives the reflected light RL of the light pulse PO reflected by the object OB whose distance is to be measured in the distance image pickup device 1, and outputs a pixel signal corresponding to the received reflected light RL.
- the light receiving section 3 includes a lens 31 and a distance image sensor 32 .
- the lens 31 is an optical lens that guides the incident reflected light RL to the range image sensor 32 .
- the lens 31 emits the incident reflected light RL to the distance image sensor 32 side, and causes pixels provided in the light receiving area of the distance image sensor 32 to receive the light (incident).
- the distance image sensor 32 is an image pickup device used in the distance image pickup device 1 .
- the distance image sensor 32 has a plurality of pixels in a two-dimensional light receiving area.
- Each pixel of the distance image sensor 32 is provided with one photoelectric conversion element, a plurality of charge storage units corresponding to this one photoelectric conversion element, and a component for distributing the charge to each charge storage unit.
- the pixel is an imaging device having a distribution structure in which charges are distributed and accumulated in a plurality of charge accumulation units.
- the distance image sensor 32 distributes the charges generated by the photoelectric conversion elements to the respective charge storage units according to control from the timing control unit 41 . Also, the distance image sensor 32 outputs a pixel signal corresponding to the amount of charge distributed to the charge storage section. A plurality of pixels are arranged in a two-dimensional matrix in the range image sensor 32, and pixel signals for one frame (one frame period) corresponding to each pixel are output.
- the distance image processing unit 4 controls the distance image capturing device 1 and calculates the distance to the subject OB.
- the distance image processing section 4 includes a timing control section 41 , a distance calculation section 42 and a measurement control section 43 .
- the timing control section 41 controls the timing of outputting various control signals required for measurement according to the control of the measurement control section 43 .
- the various control signals here include, for example, a signal for controlling the irradiation of the light pulse PO, a signal for distributing the reflected light RL to a plurality of charge accumulation units, a signal for controlling the number of times of distribution (number of times of accumulation) per frame, and the like. is.
- the distribution count (accumulation count) is the number of repetitions of the process of distributing the charge to the charge storage section CS (see FIG. 3).
- the exposure time is the product of the number of distribution times and the time (accumulation time Ta, which will be described later) for accumulating charges in each charge accumulation unit per charge distribution process.
- the distance calculation unit 42 outputs distance information obtained by calculating the distance to the object OB based on the pixel signal output from the distance image sensor 32 .
- the distance calculation unit 42 calculates the delay time Td (see FIG. 4) from the irradiation of the light pulse PO to the reception of the reflected light RL based on the charge amounts accumulated in the plurality of charge accumulation units.
- the distance calculator 42 calculates the distance to the subject OB according to the calculated delay time Td.
- the measurement control section 43 controls the timing control section 41 .
- the measurement control unit 43 sets the number of allocation times for one frame and the accumulation time Ta (see FIG. 4), and controls the timing control unit 41 so that imaging is performed according to the set contents.
- the light receiving unit 3 receives the reflected light RL that is reflected by the object OB from the light pulse PO in the near-infrared wavelength band that the light source unit 2 irradiates the object OB.
- a distance image processing unit 4 outputs distance information obtained by measuring the distance to the subject OB.
- FIG. 1 shows the distance image pickup device 1 having a configuration in which the distance image processing unit 4 is provided inside, the distance image processing unit 4 is a component provided outside the distance image pickup device 1.
- FIG. 2 is a block diagram showing a schematic configuration of an imaging device (distance image sensor 32) used in the distance image pickup device 1 according to one embodiment of the present invention.
- the distance image sensor 32 includes, for example, a light receiving area 320 in which a plurality of pixels 321 are arranged, a control circuit 322, a vertical scanning circuit 323 having a sorting operation, a horizontal scanning circuit 324, and a pixel signal processing circuit 325 .
- the light-receiving region 320 is a region in which a plurality of pixels 321 are arranged, and FIG. 2 shows an example in which they are arranged in a two-dimensional matrix of 8 rows and 8 columns.
- the pixel 321 accumulates electric charge corresponding to the amount of light received.
- a control circuit 322 controls the distance image sensor 32 in an integrated manner.
- the control circuit 322 controls the operation of the components of the range image sensor 32 according to instructions from the timing control section 41 of the range image processing section 4, for example. It should be noted that the components provided in the distance image sensor 32 may be controlled directly by the timing control section 41, in which case the control circuit 322 may be omitted.
- the vertical scanning circuit 323 is a circuit that controls the pixels 321 arranged in the light receiving area 320 for each row according to control from the control circuit 322 .
- the vertical scanning circuit 323 causes the pixel signal processing circuit 325 to output a voltage signal corresponding to the amount of charge accumulated in each charge accumulation portion CS of the pixel 321 .
- the vertical scanning circuit 323 distributes the charges converted by the photoelectric conversion elements to the respective charge accumulating portions of the pixels 321 . That is, the vertical scanning circuit 323 is an example of a "pixel driving circuit".
- the pixel signal processing circuit 325 performs predetermined signal processing (for example, noise suppression processing) on the voltage signals output to the corresponding vertical signal lines from the pixels 321 in each column under the control of the control circuit 322 . , A/D conversion processing, etc.).
- predetermined signal processing for example, noise suppression processing
- the horizontal scanning circuit 324 is a circuit that sequentially outputs signals output from the pixel signal processing circuit 325 to horizontal signal lines in accordance with control from the control circuit 322 . As a result, pixel signals corresponding to the amount of charge accumulated for one frame are sequentially output to the distance image processing section 4 via the horizontal signal line.
- the pixel signal processing circuit 325 performs A/D conversion processing and the pixel signal is a digital signal.
- FIG. 3 is a circuit diagram showing an example of the configuration of the pixels 321 arranged within the light receiving area 320 of the range image sensor 32 of one embodiment.
- FIG. 3 shows an example of the configuration of one pixel 321 among the plurality of pixels 321 arranged in the light receiving region 320.
- the pixel 321 is an example of a configuration including three pixel signal readout units.
- the pixel 321 includes one photoelectric conversion element PD, a drain gate transistor GD, and three pixel signal readout units RU for outputting voltage signals from corresponding output terminals OUT.
- Each pixel signal readout unit RU includes a readout gate transistor G, a floating diffusion FD, a charge storage capacitor C, a reset gate transistor RT, a source follower gate transistor SF, and a selection gate transistor SL.
- the floating diffusion FD and the charge storage capacitor C constitute a charge storage unit CS.
- three pixel signal readout units RU are distinguished by adding numerals "1", “2” or “3” after the symbol "RU" of the three pixel signal readout units RU. do.
- each component provided in the three pixel signal readout units RU is also indicated by a numeral representing each pixel signal readout unit RU after the symbol, so that each component corresponds to the pixel signal readout unit. RUs are distinguished.
- the pixel signal readout unit RU1 that outputs a voltage signal from the output terminal OUT1 includes a readout gate transistor G1, a floating diffusion FD1, a charge storage capacitor C1, a reset gate transistor RT1, and a source follower. It includes a gate transistor SF1 and a selection gate transistor SL1.
- the charge storage unit CS1 is composed of the floating diffusion FD1 and the charge storage capacitor C1.
- the pixel signal readout unit RU2 and the pixel signal readout unit RU3 also have the same configuration.
- the charge storage section CS1 is an example of a "first charge storage section".
- the charge storage section CS2 is an example of a "second charge storage section”.
- the charge storage section CS3 is an example of a "third charge storage section”.
- the photoelectric conversion element PD is an embedded photodiode that photoelectrically converts incident light to generate charges and accumulate the generated charges.
- the structure of the photoelectric conversion element PD may be arbitrary.
- the photoelectric conversion element PD may be, for example, a PN photodiode having a structure in which a P-type semiconductor and an N-type semiconductor are joined together, or a structure in which an I-type semiconductor is sandwiched between a P-type semiconductor and an N-type semiconductor. It may be a PIN photodiode.
- the photoelectric conversion element PD is not limited to a photodiode, and may be, for example, a photogate type photoelectric conversion element.
- the charge generated by photoelectrically converting the light incident on the photoelectric conversion element PD is distributed to each of the three charge storage units CS, and each voltage signal corresponding to the charge amount of the distributed charge is output to the pixel. Output to the signal processing circuit 325 .
- the configuration of the pixels arranged in the distance image sensor 32 is not limited to the configuration provided with three pixel signal readout units RU as shown in FIG. If it is That is, the number of pixel signal readout units RU (charge storage units CS) provided for the pixels arranged in the distance image sensor 32 may be four or more.
- the charge storage section CS may be composed of at least the floating diffusion FD, and the pixel 321 may be configured without the charge storage capacitor C.
- an example of the configuration including the drain gate transistor GD is shown. may be configured without the drain gate transistor GD.
- FIG. 4 is a timing chart showing timings for driving the pixels 321 of one embodiment.
- FIG. 4 shows a timing chart of pixels receiving reflected light after the delay time Td has elapsed since the light pulse PO was applied.
- the timing of emitting the light pulse PO is “L”
- the timing of receiving the reflected light is “R”
- the timing of the driving signal TX1 is “G1”
- the timing of the driving signal TX2 is “G2”
- the driving signal The timing of TX3 and the timing of the drive signal RSTD are indicated by item names of "G3" and "GD,” respectively.
- the drive signal TX1 is a signal for driving the readout gate transistor G1. The same applies to the drive signals TX2 and TX3.
- the vertical scanning circuit 323 accumulates charges in the order of the charge accumulation units CS1, CS2, and CS3 in synchronization with the irradiation of the light pulse PO.
- the unit accumulation time UT represents the time from the irradiation of the light pulse PO to the accumulation of charges in the charge accumulation units CS in order.
- the vertical scanning circuit 323 turns off the drain gate transistor GD and turns on the readout gate transistor G1 in synchronization with the timing of irradiating the light pulse PO.
- the vertical scanning circuit 323 turns off the readout gate transistor G1 after the accumulation time Ta has elapsed since turning on the readout gate transistor G1.
- the charge photoelectrically converted by the photoelectric conversion element PD while the readout gate transistor G1 is controlled to be on is accumulated in the charge storage unit CS1 via the readout gate transistor G1.
- the vertical scanning circuit 323 turns on the readout gate transistor G2 for the accumulation time Ta at the timing when the readout gate transistor G1 is turned off.
- the charge photoelectrically converted by the photoelectric conversion element PD while the readout gate transistor G2 is controlled to be on is accumulated in the charge storage unit CS2 via the readout gate transistor G2.
- the vertical scanning circuit 323 turns on the readout gate transistor G3 at the timing when the charge accumulation in the charge accumulation unit CS2 is completed, and turns off the readout gate transistor G3 after the accumulation time Ta has elapsed. do.
- the charge photoelectrically converted by the photoelectric conversion element PD while the readout gate transistor G3 is controlled to be on is accumulated in the charge storage unit CS3 via the readout gate transistor G3.
- the vertical scanning circuit 323 turns on the drain gate transistor GD at the timing when the charge storage in the charge storage section CS3 is completed to discharge the charge. As a result, charges photoelectrically converted by the photoelectric conversion element PD are discarded via the drain gate transistor GD.
- control is performed so that photoelectrically converted charges are not accumulated at a timing other than the time period during which charges are accumulated in the charge accumulation section CS during the unit accumulation time UT.
- the present embodiment employs a so-called short pulse method (hereinafter referred to as an SP method) in which the optical pulse PO is intermittently emitted.
- the SP method the drain gate transistor GD is turned on during a unit storage time UT during which the reflected light RL is not supposed to be received, and the charge is discharged. This avoids the continuous accumulation of electric charges corresponding to the external light component in the time interval in which the reflected light RL of the light pulse PO is not supposed to be received.
- the CW method in which the light pulse PO is continuously irradiated, it is impossible to discharge the charge each time the charge is accumulated in the charge accumulation portion CS during the unit accumulation time UT. do not have. This is because, in the CW system, since the reflected light RL is always received, there is no time interval in which the reflected light RL is not supposed to be received.
- a charge discharging unit such as a reset gate transistor connected to the photoelectric conversion element PD is controlled to be in an off state, No charge discharge.
- the charge discharging unit such as the reset gate transistor is controlled to be in an ON state, and the charge is discharged.
- the mechanism in which the charge discharging unit is connected to the photoelectric conversion element PD is described as an example, but the present invention is not limited to this.
- a mechanism using a reset gate transistor in which a charge discharging portion is not present in the photoelectric conversion element PD and the charge discharging portion is connected to the floating diffusion FD may be used.
- charges photoelectrically converted in a time interval different from the time interval for accumulating charges in the charge accumulation portion CS in the unit accumulation time UT are discharged by the drain gate transistor GD (an example of the “charge discharge portion”). control so that As a result, even if there is an error in the amount of charge accumulated in the charge accumulation unit CS due to a delay in charge transfer or the like, it is compared to the case where charges are not discharged every unit accumulation time UT as in the CW method. By doing so, it is possible to reduce the error.
- the pixel 321 of the range image pickup device 1 has the drain gate transistor GD.
- the SN ratio of the amount of charges ratio of errors to signal components
- the accuracy of the charge amount accumulated in the charge accumulation section CS can be maintained, and the feature amount can be calculated with high accuracy.
- the vertical scanning circuit 323 repeats the above-described driving a predetermined number of times over one frame. After that, the vertical scanning circuit 323 outputs a voltage signal corresponding to the amount of charge distributed to each charge storage section CS. Specifically, the vertical scanning circuit 323 outputs a voltage signal corresponding to the amount of charge accumulated in the charge storage unit CS1 via the pixel signal readout unit RU1 by turning on the selection gate transistor SL1 for a predetermined time. Output from OUT1. Similarly, the vertical scanning circuit 323 sequentially turns on the selection gate transistors SL2 and SL3 to output voltage signals corresponding to the amounts of charge accumulated in the charge accumulation units CS2 and CS3 from the output terminals OUT2 and OUT3. Let Then, an electric signal corresponding to the amount of charge for one frame accumulated in each of the charge accumulation units CS is output to the distance calculation unit 42 via the pixel signal processing circuit 325 and the horizontal scanning circuit 324 .
- the case where the light source unit 2 irradiates the light pulse PO at the timing when the readout gate transistor G1 is turned on has been described as an example. However, it is not limited to this.
- the light pulse PO may be emitted at a timing such that at least the reflected light RL from the object to be measured is received across any two of the three charge storage units CS1 to CS3.
- the light pulse PO may be applied after the readout gate transistor G1 is turned on.
- the case where the irradiation time To for irradiating the light pulse PO is the same length as the accumulation time Ta has been described as an example. However, it is not limited to this.
- the irradiation time To and the accumulation time Ta may be different time intervals.
- the relationship between the timing of irradiating the light pulse PO and the timing of accumulating the charge in each of the charge accumulating portions CS causes the reflected light RL and the amount of charge corresponding to the external light component is distributed and held.
- the charge storage section CS3 holds a charge amount corresponding to an external light component such as background light.
- the distribution (distribution ratio) of the amount of charge distributed to the charge accumulating units CS1 and CS2 is a ratio corresponding to the delay time Td until the light pulse PO is reflected by the object OB and is incident on the range image pickup device 1 .
- the distance calculation unit 42 calculates the delay time Td in the conventional short-distance light-receiving pixel using the following formula (1).
- the formula (1) assumes that the charge amount corresponding to the external light component among the charge amounts accumulated in the charge storage units CS1 and CS2 is the same as the charge amount accumulated in the charge storage unit CS3.
- Td To ⁇ (Q2 ⁇ Q3)/(Q1+Q2 ⁇ 2 ⁇ Q3) Equation (1)
- Q1 is the amount of charge accumulated in the charge storage section CS1
- Q2 is the amount of charge accumulated in the charge storage section CS2
- Q3 is the amount of charge accumulated in the charge storage section CS3.
- the distance calculation unit 42 multiplies the delay time Td obtained by Equation (1) by the speed of light (velocity) in the short-distance light-receiving pixel, thereby calculating the round-trip distance to the object OB. Then, the distance calculation unit 42 obtains the distance to the object OB by halving the round trip distance calculated above.
- FIG. 5 is a diagram illustrating multipath according to one embodiment.
- the distance image pickup device 1 uses a light source with a wider irradiation range than Lider (Light Detection and Ranging). For this reason, while it has the advantage of being able to measure a space having a certain range at once, it has the disadvantage of being susceptible to the occurrence of multipaths.
- the range imaging device 1 irradiates the measurement space E with a light pulse PO and receives a plurality of reflected waves (multipaths) of the direct wave W1 and the indirect wave W2.
- a multipath is composed of two reflected waves
- the present invention is not limited to this, and a multipath may be composed of three or more reflected waves. Even when the multipath is composed of three or more reflected waves, it is possible to apply the method described below.
- the shape (time-series change) of the reflected light received by the range imaging device 1 when receiving multipath light differs from the shape of the reflected light when only a single path is received.
- the reflected light (direct wave W1) having the same shape as the light pulse is received by the distance imaging device 1 with a delay time Td.
- the reflected light (indirect wave W2) having the same shape as the optical pulse is received with a delay time Td+ ⁇ .
- ⁇ is the time by which the indirect wave W2 is delayed with respect to the direct wave W1. That is, in the case of multipath, the distance image pickup device 1 receives reflected light in a state in which a plurality of light beams having the same shape as the light pulse are added while having a time difference.
- the formula (1) above is a formula based on the premise that the delay time is the time required for the light pulse to directly go back and forth between the light source and the object. That is, the formula (1) assumes that the range image pickup device 1 receives single-pass light. Therefore, if the distance is calculated using the formula (1) even though the distance image capturing device 1 receives multipath light, the calculated distance is an unphysical distance that does not correspond to the position of any reflector. distance. For this reason, for example, the difference between the calculated distance (measured distance) and the actual distance diverges, causing an error.
- the distance image capturing device 1 it is determined whether the distance image capturing device 1 has received single-path light or multi-path light, and the distance is calculated according to the determination result. For example, when the distance imaging device 1 receives a single-pass light, the distance is calculated using a relational expression assuming a single reflector, such as Expression (1). When the distance imaging device 1 receives multipath light, the distance is calculated by other means without using the equation (1). As a result, the calculated distance can always be the distance corresponding to the position where the reflector exists, or it can be a physically reasonable distance corresponding to a plurality of positions, and the error occurring in the measured distance can be reduced. can be reduced.
- the distance image pickup device 1 extracts the feature amount based on the amount of charge accumulated in each of the three charge accumulation units CS included in the pixel 321 . Then, it is determined whether the pixel 321 has received single-path light or multi-path light according to the tendency of the extracted feature amount.
- the distance image processing unit 4 calculates a complex variable CP represented by the following equation (2) based on the amount of charge accumulated in each charge accumulation unit CS.
- the complex variable CP is an example of a "feature amount”.
- CP (Q1-Q2)+j(Q2-Q3) Equation (2)
- j is an imaginary unit
- Q1 is the accumulated charge amount (first charge amount) accumulated in the charge accumulating section CS1
- Q2 is the accumulated charge amount (second charge amount) accumulated in the charge accumulation unit CS2
- Q3 is the accumulated charge amount (third charge amount) accumulated in the charge accumulation unit CS3;
- the distance image processing unit 4 expresses the complex variable CP shown in Equation (2) as a function GF of the phase (2 ⁇ f ⁇ A ) using Equation (3).
- Equation (3) assumes that only reflected light from object OB A at distance LA is received, that is, a single pass is received.
- the function GF is an example of a "feature amount".
- Equation (3) if the values of the function GF corresponding to phases 0 (zero) to 2 ⁇ can be obtained, all single paths that can be received by the range image pickup device 1 can be defined. Therefore, the distance image processing unit 4 defines the complex function CP( ⁇ ) of the phase ⁇ for the complex variable CP shown in Equation (3), and expresses it as Equation (4).
- ⁇ is the amount of phase change when the phase of the complex variable CP in Equation (3) is set to 0 (zero).
- FIG. 6 and 7 are diagrams illustrating examples of the complex function CP( ⁇ ) of one embodiment.
- the horizontal axis of FIG. 6 is the phase x, and the vertical axis is the value of the function GF(x).
- the solid line indicates the real part of the complex function CP( ⁇ )
- the dotted line indicates the imaginary part of the complex function CP( ⁇ ). That is, the feature amount has the real part as the first variable that is the difference between the first charge amount and the second charge amount, and the imaginary part as the second variable that is the difference between the second charge amount and the third charge amount.
- a value represented by a complex number A value represented by a complex number.
- FIG. 7 shows an example of the function GF(x) of FIG. 6 in the complex plane.
- the horizontal axis in FIG. 7 indicates the real axis, and the vertical axis indicates the imaginary axis.
- the complex function CP( ⁇ ) is obtained by multiplying the function GF(x) in FIGS. 6 and 7 by a constant (D A ) corresponding to the intensity of the signal.
- a change in the complex function CP( ⁇ ) is determined according to the shape (time series change) of the optical pulse PO.
- FIG. 6 shows, for example, a trajectory associated with phase changes in the complex function CP( ⁇ ) when the optical pulse PO is a rectangular wave.
- max is a signal value corresponding to the amount of charge corresponding to the total reflected light.
- the distance image processing unit 4 determines that the pixel 321 has received a single pass when the tendency of change in the complex function CP( ⁇ ) calculated by the measurement matches the tendency of change in the function GF(x) in the single pass. do.
- range image processing unit 4 determines that pixel 321 received multipath light. I judge.
- the distance image processing unit 4 changes the measurement environment and performs measurements a plurality of times (M times in the example of this figure).
- M is any natural number of 2 or more.
- the irradiation timing for irradiating the light pulse PO and the accumulation timing for accumulating charges in each of the charge accumulating units CS are set to be the same timing. More specifically, as in FIG. 4, the charge storage section CS1 is turned on at the same time as the irradiation of the light pulse PO is started, and thereafter, the charge storage sections CS2 and CS3 are turned on in order, and the charge storage sections CS1 to CS3 are turned on. Accumulate charge.
- the reflected light reflected by the object OB existing in the measurement space is received by the pixel 321 with a delay time Td after the irradiation timing, as in FIG.
- the distance image processing unit 4 calculates the complex function CP(0) in the first measurement.
- the irradiation timing is delayed from the accumulation timing by an irradiation delay time Dtm2. More specifically, in the second measurement, the start of irradiation of the light pulse PO is delayed by the irradiation delay time Dtm2 while fixing the timing of turning on the charge storage units CS1 to CS3. The position of the object OB existing in the measurement space is unchanged from the first measurement. Therefore, as in the first measurement, the reflected light reflected by the object OB is received by the pixel 321 with a delay time Td after the irradiation timing.
- the reflected light is apparently received by the pixel 321 with a delay (delay time Td+irradiation delay time Dtm2) from the irradiation timing. be done.
- the distance image processing unit 4 calculates the complex function CP( ⁇ 1) based on the second measurement.
- the phase ⁇ 1 is a phase (2 ⁇ f ⁇ Dtm2) corresponding to the irradiation delay time Dtm2.
- f is the irradiation frequency (frequency) of the light pulse PO.
- the irradiation timing is delayed from the accumulation timing by the irradiation delay time Dtm3. More specifically, in the (M ⁇ 1)th measurement, the start of irradiation of the light pulse PO is delayed by the irradiation delay time Dtm3 while the timing of turning on the charge storage units CS1 to CS3 is fixed. As a result, the reflected light is apparently received by the pixel 321 with a delay of (delay time Td+irradiation delay time Dtm3) from the irradiation timing.
- the distance image processing unit 4 calculates a complex function CP( ⁇ 2) based on the (M ⁇ 1)th measurement.
- the phase ⁇ 2 is a phase (2 ⁇ f ⁇ Dtm3) corresponding to the irradiation delay time Dtm3.
- the irradiation timing is delayed by an irradiation delay time Dtm4 with respect to the accumulation timing. More specifically, the start of irradiation of the light pulse PO is delayed by the irradiation delay time Dtm4 while fixing the timing of turning on the charge storage units CS1 to CS3. As a result, the reflected light is received by the pixel 321 apparently with a delay of (delay time Td+irradiation delay time Dtm4) from the irradiation timing.
- the distance image processing unit 4 calculates a complex function CP( ⁇ 3) based on the Mth measurement.
- the phase ⁇ 3 is a phase (2 ⁇ f ⁇ Dtm4) corresponding to the irradiation delay time Dtm4.
- the distance image processing unit 4 performs a plurality of measurements while changing the measurement timing in this way, and calculates the complex function CP for each measurement.
- the distance image processing unit 4 performs the measurement with the irradiation delay time Dtm2 in the second measurement, and calculates the complex function CP( ⁇ 1).
- the distance image processing unit 4 performs measurement with the irradiation delay time Dtm3 in the (M ⁇ 1)th measurement, and calculates the complex function CP( ⁇ 2).
- the distance image processing unit 4 performs measurement with the irradiation delay time Dtm4 in the Mth measurement, and calculates the complex function CP( ⁇ 3).
- FIGS. 9 to 12 show a complex plane in which the horizontal axis is the real axis and the vertical axis is the imaginary axis.
- the distance image processing unit 4 plots the lookup table LUT and the measured points P1 to P3 on the complex plane.
- the lookup table LUT is information that associates the function GF(x) with its phase x when the pixel 321 receives single-pass light.
- the lookup table LUT is, for example, measured in advance and stored in a storage unit (not shown).
- the measured points P1 to P3 are the values of the complex function CP( ⁇ ) calculated by measurement.
- the distance image processing unit 4 determines that the pixel 321 has received a single pass in the measurement when the change tendency of the lookup table LUT matches the change tendency of the actual measurement points P1 to P3. judge.
- the distance image processing unit 4 plots the lookup table LUT and the measured points P1# to P3# on the complex plane, as shown in FIG.
- the lookup table LUT is similar to the lookup table LUT in FIG.
- the measured points P1# to P3# are values of the complex function CP( ⁇ ) calculated by measurement in a measurement space different from that in FIG.
- the distance image processing unit 4 determines that when the trend of change in the lookup table LUT does not match the trend of change in the actual measurement points P1# to P3#, the pixel 321 receives multipath light during measurement. It is determined that
- the distance image processing unit 4 determines whether or not the tendency of the lookup table LUT matches the tendency of the measured points P1 to P3 (coincidence determination).
- a method for the distance image processing unit 4 to perform match determination using scale adjustment and an SD index will be described.
- Scale adjustment is a process of adjusting the scale (absolute value of complex number) of the lookup table LUT and the scale (absolute value of complex number) of the measurement point P so that they have the same value.
- the complex function CP( ⁇ ) is the function GF(x) multiplied by the constant DA .
- the constant DA is a constant value determined according to the amount of reflected light received. That is, the constant DA is a value determined for each measurement according to the irradiation time of the optical pulse PO, the irradiation intensity, the number of allocations per frame, and the like. Therefore, the measured point P has coordinates enlarged (or reduced) by a constant DA with respect to the origin as compared with the corresponding points in the lookup table LUT.
- the distance image processing unit 4 adjusts the scale in order to easily determine whether the change tendency of the lookup table LUT and the change tendency of the measured points P1 to P3 match.
- the distance image processing unit 4 extracts a specific measured point P (for example, measured point P1) from among the measured points P1 to P3.
- the distance image processing unit 4 scales the extracted actual measurement point so that the actual measurement point Ps (for example, actual measurement point P1s) after scale adjustment, which is obtained by multiplying the extracted actual measurement point by a constant D with the origin as a reference, becomes a point on the lookup table LUT. make adjustments.
- the distance image processing unit 4 also multiplies the remaining measured points P (for example, the measured points P2 and P3) by the same multiplication value (constant D), and converts the scale-adjusted measured points Ps (for example, the measured points Ps points P2s and P3s).
- the distance image processing unit 4 does not need scale adjustment when a specific measured point P (for example, measured point P1) is a point on the lookup table LUT without scale adjustment. In this case, the distance image processing unit 4 can omit the scale adjustment.
- FIG. 12 shows a lookup table LUT showing the function GF(x) when the pixel 321 receives single-pass light, and points G(x0), G(x0+ ⁇ ), and G(x0+2 ⁇ ) on the lookup table LUT. It is shown.
- FIG. 12 also shows complex functions CP(0), CP(1), and CP(2) as actual measurement points.
- the distance image processing unit 4 first creates (defines) a function GG(n) whose starting point matches the complex function CP(n) obtained by measurement.
- the function GG(x) is a function obtained by shifting the phase of the function GF(x) so as to coincide with the starting point of the complex function CP(n) obtained by measurement.
- x0 is the initial phase
- n is the measurement number
- ⁇ is the phase shift amount for each measurement.
- the distance image processing unit 4 creates (defines) the complex function CP(n), the function GG(x), and the function SD(n) representing the difference, as shown in Equation (6).
- n in Formula (6) indicates a measurement number.
- the distance image processing unit 4 uses the function SD(n) to use the SD index (index value).
- n indicates the measurement number
- NN indicates the number of measurements.
- the SD index defined here is an example.
- the SD index replaces the complex function CP(n) and the degree of dissociation on the complex plane in the function GG(n) with a single real number, and the function Of course, the shape is adjustable.
- the SD index may be arbitrarily defined as long as it indicates at least the degree of dissociation of the complex function CP(n) and the function GG(n) on the complex plane.
- the distance image processing unit 4 compares the calculated SD index with a predetermined threshold. The distance image processing unit 4 determines that the pixel 321 has received a single pass when the SD index does not exceed a predetermined threshold. On the other hand, when the SD index exceeds a predetermined threshold, the distance image processing unit 4 determines that the pixel 321 has received multipath light.
- the SD index is the difference between the first feature amount, which is the feature amount calculated from each of the plurality of measurements, and the second feature amount, which is the feature amount corresponding to each of the plurality of measurements in the lookup table LUT. It is an added value obtained by adding the respective normalized differential values of a plurality of measurements to the normalized differential values normalized by the absolute values of the two feature quantities.
- the judgment result here is the result of judging whether the single-path light was received or the multi-path light was received.
- the distance image processing unit 4 calculates the measured distance using Equation (8).
- n is the measurement number
- x0 is the initial phase
- n is the measurement number
- ⁇ is the phase shift amount for each measurement.
- the internal distance in Expression (8) may be arbitrarily set according to the structure of the pixel 321 or the like. If the internal distance is not particularly considered, the internal distance is set to 0.
- the delay time Td is calculated based on the equation (1), and the measured distance is calculated using the calculated delay time Td.
- the distance image processing unit 4 converts the complex function CP obtained by the measurement as the sum of the reflected light arriving from a plurality of (here, two) paths as shown in equation (9). show.
- D A in Equation (9) is the intensity of the reflected light from the object OB A at the distance LA .
- xA is the phase required for light to make a round trip to object OBA at distance LA .
- n is the measurement number.
- ⁇ indicates the amount of phase shift for each measurement.
- D B is the intensity of the reflected light from the object OB B at the distance L B.
- xB is the phase required for light to make a round trip to an object OBB at a distance LB.
- the distance image processing unit 4 determines a combination of ⁇ phases x A , x B and intensities D A , D B ⁇ that minimizes the difference J shown in Equation (10).
- the difference J corresponds to the sum of the squares of the absolute values of the differences between the complex function CP(n) and the function G in Equation (9).
- the distance image processing unit 4 determines a combination of ⁇ phases x A , x B and intensities D A , D B ⁇ by applying, for example, the method of least squares.
- the lookup table LUT is used as an example to determine whether single-path light is received or multi-path light is received.
- the distance image processing unit 4 may use a formula representing the function GF(x) instead of the lookup table LUT.
- the formula representing the function GF(x) is, for example, a formula defined according to the phase range.
- the function GF(x) is defined as a linear function with a slope ( ⁇ 1/2) and an intercept (max/2) in the range (0 ⁇ x ⁇ 2/ ⁇ ) for the phase x. .
- the function GF(x) is defined as a linear function with slope (-2) and intercept (-max).
- lookup table LUT may be created based on actual measurement results performed in an environment where only a single path is received, or may be created based on calculation results by simulation or the like.
- the complex variable CP may be a variable calculated using at least the amount of charge accumulated in the charge accumulation unit CS that accumulates the amount of charge corresponding to the reflected light RL.
- the timing (accumulation timing) for turning on the charge accumulation section CS is fixed, and the irradiation timing for irradiating the light pulse PO is delayed.
- the accumulation timing and the irradiation timing should at least change relatively.
- the irradiation timing may be fixed and the accumulation timing may be advanced.
- the function SD(n) is defined by Equation (6) has been described as an example. However, it is not limited to this.
- the function SD(n) may be arbitrarily defined as long as it is a function representing at least the difference between the complex function CP(n) and the function GG(n) on the complex plane.
- FIG. 13 is a flow chart showing the flow of processing performed by the distance image capturing device 1 of one embodiment.
- NN ⁇ 2 measurements are performed.
- Dtm the irradiation delay time Dtm for each of the NN measurements is determined in advance.
- Step S10 The distance image processing unit 4 sets the irradiation delay time Dtm and performs measurement.
- the distance image processing unit 4 sets the irradiation delay time Dtm, performs charge accumulation for the number of distribution times corresponding to one frame at the set measurement timing, and causes each of the charge accumulation units CS to accumulate charges.
- Step S11 The distance image processing unit 4 calculates a complex function CP(n) based on the amount of charge accumulated in each charge accumulation unit CS obtained by measurement. n is the measurement number.
- Step S12 The distance image processing unit 4 determines whether or not NN measurements have been completed. If NN measurements have been completed, the process proceeds to step S13.
- the distance image processing unit 4 calculates the SD index.
- the distance image processing unit 4 adjusts the scale of the complex function CP(n) obtained from the measurement as necessary.
- the distance image processing unit 4 uses the scale-adjusted complex function CP(n) to create a function GG(n) with the same starting point.
- the distance image processing unit 4 uses the created function GG(n) and the scale-adjusted complex function CP(n) to create a difference function SD(n).
- the distance image processing unit 4 uses the created function SD(n) and function GG(n) to calculate the SD index.
- Step S14 The distance image processing unit 4 compares the SD index with a predetermined threshold. If the SD index does not exceed the threshold, the distance image processing unit 4 proceeds to step S15. On the other hand, if the SD index does not exceed the threshold, the distance image processing unit 4 proceeds to step S16.
- Step S15 The distance image processing unit 4 determines that the pixel 321 has received the single pass, and calculates the distance corresponding to the round trip route of the single pass as the measured distance.
- Step S16 The distance image processing unit 4 determines that the pixel 321 has received the multipath, and calculates the distance corresponding to each path of the multipath as the measurement distance using, for example, the least squares method.
- the distance image capturing device 1 of one embodiment includes the light source unit 2, the light receiving unit 3, and the distance image processing unit 4.
- the light source unit 2 irradiates the measurement space E with a light pulse PO.
- the light-receiving unit 3 includes a pixel having a photoelectric conversion element PD that generates charges according to incident light, a plurality of charge storage units CS that store the charges, and a predetermined accumulation synchronized with the irradiation of the light pulse PO. and a vertical scanning circuit 323 (pixel driving circuit) that performs a unit accumulation process of distributing and accumulating electric charges in each of the charge accumulating portions CS at timing.
- the distance image processing unit 4 controls the irradiation timing of irradiating the light pulse PO and the accumulation timing of distributing and accumulating the charge in each of the charge accumulating units CS.
- the distance image processing unit 4 calculates the distance to the object OB existing in the measurement space E based on the amount of charge accumulated in each of the charge accumulation units CS.
- the distance image processing unit 4 performs a plurality of measurements. In the plurality of measurements, measurements with different relative timing relationships between the irradiation timing and the accumulation timing are performed.
- the distance image processing unit 4 calculates a complex function CP(n) from each of the multiple measurements. n is the measurement number.
- the distance image processing unit 4 determines whether the reflected light RL is received by the pixel 321 in a single pass or whether the reflected light RL is received by the pixel 321 in multiple passes. The distance image processing unit 4 calculates the distance to the subject OB existing in the measurement space E according to the determination result.
- the distance image capturing device 1 of one embodiment can determine whether the pixel 321 has received single-path light or multi-path light.
- the complex variable CP, complex function ( ⁇ ), complex function CP(n), function GF(x), and function GG(n) are examples of "feature amounts based on the amount of charge accumulated in each of a plurality of measurements.” be.
- the SD index is an example of the "tendency of feature amount”.
- determination may be made using a lookup table LUT.
- the lookup table LUT is a table in which phases (relative timing relationships) and functions GF(x) (feature amounts) are associated with each other when the reflected light RL is received by the pixels 321 in a single pass.
- the distance image processing unit 4 determines that the reflected light RL has been received by the pixel 321 in a single pass when the measured point P can be plotted as a point on the lookup table LUT.
- the distance image capturing device 1 of the embodiment can make a determination by a simple method of comparing the tendency with the lookup table LUT.
- the lookup table LUT includes: It is created according to at least one measurement condition.
- the distance image processing unit 4 uses a lookup table LUT corresponding to the measurement conditions to determine whether the reflected light RL is received by the pixel 321 in a single pass or whether the reflected light RL is received by the pixel 321 in multiple passes. judge.
- the distance image capturing device 1 of the embodiment can select an appropriate lookup table LUT according to the measurement conditions, and can perform determination with high accuracy.
- the feature amount is the charge storage unit in which at least the charge corresponding to the reflected light RL is stored among the charges stored in each of the three or more charge storage units CS. This value is calculated using the amount of charge accumulated in CS.
- the reflected light RL is received by the pixels 321 in a single pass, or the reflected light RL is received in the pixels 321 in multiple passes, depending on how the reflected light RL is received. It becomes possible to determine whether the light is received by 321 .
- the feature amount is the complex variable CP. Accordingly, in the range image pickup device 1 of one embodiment, by observing the behavior of the complex variable CP regarding the delay time Td as a phase delay, it is possible to determine whether the reflected light RL is received by the pixels 321 in a single pass. It is possible to determine whether the reflected light RL is received by the pixel 321 through multipath.
- the distance image processing unit 4 determines the distance image of the object OB based on the measurements at a plurality of measurement timings. Each distance may be determined based on the least squares method. In this case as well, the most probable route can be determined for each single path, and the distance corresponding to each single path can be calculated. Further, when the distance image processing unit 4 determines that the reflected light RL is received by the pixel 321 through multipaths, the distance corresponding to each light path included in the multipaths is obtained by applying the least squares method to calculate. As a result, the range image capturing apparatus 1 of the embodiment can determine the most probable route for each route of the multipaths, and can calculate the distance corresponding to each multipath.
- FIG. 14 is a flow chart showing the flow of processing performed by the distance imaging device 1 according to the modification of one embodiment.
- the processing shown in steps S23 to S30 in the flow chart of FIG. 14 is the same as the processing shown in steps S10 to S17 in the flow chart of FIG. 13, so description thereof will be omitted.
- Step S20 The distance image processing unit 4 performs the first measurement at a predetermined irradiation delay time Dtim1.
- the irradiation delay time Dtim1 is a predetermined value, such as 0 (zero).
- Step S21 The distance image processing unit 4 calculates the provisional distance ZK based on the amount of charge accumulated in each of the charge accumulation units CS in the first measurement.
- the distance image processing unit 4 calculates the provisional distance ZK assuming that the pixel 321 received the single-pass light in the first measurement.
- the distance image processing unit 4 calculates the provisional distance ZK using the same method as when it is determined that the pixel 321 has received a single pass.
- the distance image processing unit 4 uses the provisional distance ZK to determine irradiation delay times Dtim2 to DtimNN to be applied to the remaining measurements.
- the distance image processing unit 4 for example, determines the irradiation delay times Dtim2 to DtimNN so that distances in the vicinity of the provisional distance ZK can be calculated with high accuracy.
- the distance image processing unit 4 considers a case where the phase corresponding to the provisional distance ZK is near ⁇ /4.
- the distance image processing unit 4 considers a case where the phase corresponding to the provisional distance ZK is near ( ⁇ 3/4).
- the distance image processing unit 4 considers a case where the phase corresponding to the provisional distance ZK is near ⁇ /2.
- the phase x is (0 ⁇ x ⁇ /2) or ( ⁇ /2 ⁇
- the irradiation delay time Dtim corresponds to one of x ⁇ )
- the range image processing unit 4 sets the irradiation delay times Dtim2 to DtimNN applied to the remaining measurements to either the range of (0 ⁇ x ⁇ /2) or ( ⁇ /2 ⁇ x ⁇ ). decide to be
- the distance image processing unit 4 may determine not only the irradiation delay time Dtim, but also the number of distributions in the remaining measurements. For example, when the provisional distance ZK is a long distance larger than a predetermined distance, the distance image processing unit 4 increases the number of allocations compared to when the provisional distance ZK is a short distance smaller than the predetermined distance. In general, when reflected light arrives from an object OB existing at a long distance, the light amount of the reflected light RL reaching the range imaging device 1 decreases. Therefore, by increasing the number of distributions in the case of a long distance, the amount of charge accumulated in one measurement is increased. By doing so, it is possible to accurately calculate the measured distance even in the case of a long distance.
- the distance image processing unit 4 calculates the provisional distance ZK to the object OB based on the first measurement among multiple measurements. Based on the provisional distance ZK, the distance image processing unit 4 determines the irradiation delay time Dtim (an example of the “delay time”) used for the remaining measurements among the plurality of measurements.
- the irradiation delay time Dtim can be determined according to the situation of the object OB existing in the measurement space E, and single-pass or multi-pass can be determined. It is possible to make an accurate determination.
- the distance image processing unit 4 determines the time (phase) required for the light pulse PO to travel the provisional distance ZK and the trend of the function GF(x). Based on this, the irradiation delay time Dtim may be determined.
- the irradiation delay time Dtim can be determined. Therefore, it is possible to accurately determine whether it is a single pass or a multipass.
- the distance image processing unit 4 performs the following when the provisional distance ZK is a long distance exceeding the threshold and when the provisional distance ZK is a short distance not exceeding the threshold: , the allocation count (an example of the “accumulation count”) is increased in the remaining measurements among the plurality of measurements.
- the distance imaging device 1 according to the modified example of the embodiment can accurately calculate the distance even when the subject exists at a long distance.
- the representative value of the measured distances calculated from a plurality of measurements is You may make it determine as a calculation result. This makes it possible to determine the measured distance with high accuracy compared with the measured distance calculated from one measurement.
- the distance image processing unit 4 when calculating the respective distances of the multipaths using the least squares method, determines the range for finding the optimal solution combination based on the provisional distance ZK. You can also narrow it down. For example, the distance image processing unit 4 considers that the reflected light reflected from the object OB existing in the range of the provisional distance ZK ⁇ with the provisional distance ZK as the center is received as multipath, and finds the combination of the optimum solutions within that range. Do the math to find out. This makes it possible to calculate the error of the combination of solutions within a limited range compared to the case of calculating the error of all possible combinations of solutions, thereby reducing the computational load.
- the pixel 321 includes the three charge storage units CS1 to CS3 has been exemplified and explained. However, it is not limited to this. It can also be applied when the pixel 321 has four or more charge storage units CS.
- the pixel 321 has four charge storage units CS, as an example, it is possible to define the complex variable CP as shown in Equations (11) and (12) below. Further, the formulas are not limited to the formulas (11) and (12), and the first charge amount, the second charge amount, the third charge amount, and the It is possible to define a complex variable CP whose real part or imaginary part is a value calculated by adding or subtracting the four electric charges.
- CP (Q1-Q3)+j(Q2-Q4) Equation (11)
- CP ⁇ (Q1+Q2)-(Q3+Q4) ⁇ +j ⁇ (Q2+Q3)-(Q4+Q1) ⁇
- j an imaginary unit
- Q1 is the accumulated charge amount (first charge amount) accumulated in the charge accumulating section CS1
- Q2 is the accumulated charge amount (second charge amount) accumulated in the charge accumulation unit CS2
- Q3 is the accumulated charge amount (third charge amount) accumulated in the charge accumulation unit CS3
- Q4 is the accumulated charge amount (fourth charge amount) accumulated in the charge accumulation unit CS4;
- the feature amount is the real part of the first variable, which is the difference between the first charge amount accumulated in the first charge accumulation unit and the third charge amount accumulated in the third charge accumulation unit.
- All or part of the distance image capturing device 1 and the distance image processing unit 4 in the above-described embodiment may be realized by a computer.
- a program for realizing this function may be recorded in a computer-readable recording medium, and the program recorded in this recording medium may be read into a computer system and executed.
- the "computer system” referred to here is a system including hardware such as an OS and peripheral devices.
- the term "computer-readable recording medium” refers to portable media such as flexible discs, magneto-optical discs, ROMs and CD-ROMs, and storage devices such as hard discs incorporated in computer systems.
- “computer-readable recording medium” refers to a program that dynamically retains programs for a short period of time, like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line.
- a medium such as a volatile memory inside a computer system that is a server or a client in that case, may also include a medium that retains the program for a certain period of time.
- the program may be a program for realizing part of the functions described above, or may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system. It may be a program implemented using a programmable logic device such as FPGA.
- the present invention it is possible to determine whether a pixel receives single-pass light or multi-pass light. Further, when it is determined that the pixel has received single-path light, the distance to one reflector is calculated, and when it is determined that the pixel has received multi-path light, the distance to each of a plurality of reflectors is calculated. can be done.
Abstract
Description
本願は、2021年1月25日に日本に出願された特願2021-009673号について優先権を主張し、その内容をここに援用する。
また、距離画像撮像装置では、前記距離画像処理部は、前記反射光がシングルパスで前記画素に受光されたと判定した場合、前記複数の測定タイミングでの測定に基づいて前記被写体までの暫定距離を最小二乗法に基づいてそれぞれ決定する。前記距離画像処理部は、前記反射光がマルチパスで前記画素に受光されたと判定した場合、前記複数の測定タイミングでの測定に基づいて前記被写体の各々の距離を最小二乗法に基づいて決定してもよい。
まず、一実施形態について説明する。図1は、本発明の一実施形態の距離画像撮像装置の概略構成を示したブロック図である。図1に示した構成の距離画像撮像装置1は、光源部2と、受光部3と、距離画像処理部4とを備える。図1には、距離画像撮像装置1において距離を測定する対象物である被写体OBも併せて示している。
画素信号読み出し部RUのそれぞれは、読み出しゲートトランジスタGと、フローティングディフュージョンFDと、電荷蓄積容量Cと、リセットゲートトランジスタRTと、ソースフォロアゲートトランジスタSFと、選択ゲートトランジスタSLとを備える。それぞれの画素信号読み出し部RUでは、フローティングディフュージョンFDと電荷蓄積容量Cとによって電荷蓄積部CSが構成されている。
ただし、Toは光パルスPOが照射された期間
Q1は電荷蓄積部CS1に蓄積された電荷量
Q2は電荷蓄積部CS2に蓄積された電荷量
Q3は電荷蓄積部CS3に蓄積された電荷量
ただし、jは虚数単位
Q1は電荷蓄積部CS1に蓄積された蓄積電荷量(第1電荷量)
Q2は電荷蓄積部CS2に蓄積された蓄積電荷量(第2電荷量)
Q3は電荷蓄積部CS3に蓄積された蓄積電荷量(第3電荷量)
ただし、DAは距離LAにある被写体OBAからの反射光の強度(定数)
τAは距離LAにある被写体OBAまで光が往復するのに要する時間
τA=2LA/c
cは光速
そこで、距離画像処理部4は、式(3)に示す複素変数CPについて位相φの複素関数CP(φ)を定義し、式(4)のように表す。φは、式(3)における複素変数CPの位相を0(ゼロ)とした場合の位相変化量である。
ただし、DAは距離LAにある被写体OBAからの反射光の強度
τAは距離LAにある被写体OBAまで光が往復するのに要する時間
τA=2LA/c
cは光速
φは位相
すなわち、特徴量は、第1電荷量と第2電荷量との差分である第1変数を実部とし、第2電荷量と第3電荷量との差分である第2変数を虚部とする複素数で現される値である。
図7には、図6の関数GF(x)を複素平面に示した例が示されている。図7の横軸は実軸、縦軸は虚軸を示している。図6、及び図7の関数GF(x)に、信号の強度に相当する定数(DA)を乗じた値が複素関数CP(φ)となる。
次に、距離画像処理部4は、複素関数CP(0)に対応する測定環境において位相φだけ変化させた測定環境にて測定を行い、複素関数CP(φ)を算出する。
ここで、距離画像処理部4は、必要に応じてスケール調整を行う。スケール調整とは、ルックアップテーブルLUTのスケール(複素数の絶対値)と、実測点Pのスケール(複素数の絶対値)とが同じ値となるように調整する処理である。式(4)に示すように、複素関数CP(φ)は、関数GF(x)に定数DAを乗算した値である。定数DAは、受光する反射光の光量に応じて決定される一定値である。すなわち、定数DAは、光パルスPOの照射時間、照射強度、及び1フレームあたりの振り分け回数などに応じて、測定毎に決定される値となる。このため、実測点Pは、ルックアップテーブルLUTの対応点と比較して、原点を基準として定数DAだけ拡大(或いは縮小)された座標となる。
ここで、図12を用いて、SD指標を用いた一致判定について説明する。図12の上側には複素平面を示しており、横軸が実軸、縦軸が虚軸を示している。図12には、画素321がシングルパスを受光した場合における関数GF(x)を示すルックアップテーブルLUT、及びルックアップテーブルLUT上の点G(x0)、G(x0+Δφ)、G(x0+2Δφ)が示されている。また、図12には、実測点として複素関数CP(0)、CP(1)、CP(2)が示されている。
SD指標は、複数の測定のそれぞれから算出される特徴量である第1特徴量と、ルックアップテーブルLUTにおいて複数の測定のそれぞれに対応する特徴量である第2特徴量との差分を、第2特徴量の絶対値で正規化した差分正規化値について、複数の測定のそれぞれの差分正規化値を加算した加算値である。
図7の例であれば、位相xについて(0≦x≦2/π)の範囲において関数GF(x)は傾き(-1/2)、切片(max/2)の一次関数として定義される。また(2/π0<x≦π)の範囲において関数GF(x)は傾き(-2)、切片(-max)の一次関数として定義される。
図13は一実施形態の距離画像撮像装置1が行う処理の流れを示すフローチャートである。
このフローチャートの例では、NN(≧2)回の測定を行うことを前提とする。また、NN回の測定のそれぞれにおける照射遅延時間Dtmが予め決定されていることを前提とする。
距離画像処理部4は、照射遅延時間Dtmを設定し測定を行う。距離画像処理部4は、照射遅延時間Dtmを設定し、設定した測定タイミングにて1フレームに相当する振り分け回数の電荷蓄積を行い、電荷蓄積部CSのそれぞれに電荷を蓄積させる。
(ステップS11)
距離画像処理部4は、測定により得られた電荷蓄積部CSのそれぞれに蓄積された電荷量に基づき複素関数CP(n)を算出する。nは測定番号である。
(ステップS12)
距離画像処理部4は、NN回の測定が終了したか否かを判定する。NN回の測定が終了した場合にはステップS13に進み、NN回の測定が終了していない場合には、測定回数をインクリメントし(ステップS17)、ステップS10に戻り測定を繰り返す。
(ステップS13)
距離画像処理部4は、SD指標を算出する。距離画像処理部4は、測定から得られた複素関数CP(n)について、必要に応じてスケール調整を行う。距離画像処理部4は、スケール調整後の複素関数CP(n)を用いて、始点を一致させた関数GG(n)を作成する。距離画像処理部4は、作成した関数GG(n)とスケール調整後の複素関数CP(n)を用いて、差分の関数SD(n)を作成する。距離画像処理部4は、作成した関数SD(n)と関数GG(n)とを用いて、SD指標を算出する。
(ステップS14)
距離画像処理部4は、SD指標と所定の閾値とを比較する。距離画像処理部4は、SD指標が閾値を超えていない場合、ステップS15に進む。一方、距離画像処理部4は、SD指標が閾値を超えていない場合、ステップS16に進む。
(ステップS15)
距離画像処理部4は、画素321がシングルパスを受光したと判定し、そのシングルパスが往復した経路に相当する距離を測定距離として算出する。
(ステップS16)
距離画像処理部4は、画素321がマルチパスを受光したと判定し、そのマルチパスのそれぞれの経路に相当する距離を測定距離として、例えば最小二乗法を用いて算出する。
ここで、一実施形態の変形例について説明する。本変形例では、複数の測定のうちの最初の測定の結果に応じて、残りの測定における照射遅延時間Dtimを決定する点において、上述した一実施形態と相違する。
距離画像処理部4は、所定の照射遅延時間Dtim1にて最初の測定を行う。照射遅延時間Dtim1は、予め決定された値であり、例えば0(ゼロ)である。
(ステップS21)
距離画像処理部4は、最初の測定にて電荷蓄積部CSのそれぞれに蓄積された電荷量に基づいて暫定距離ZKを算出する。距離画像処理部4は、最初の測定において画素321がシングルパスを受光したとみなして、暫定距離ZKを算出する。距離画像処理部4は、画素321がシングルパスを受光したと判定した場合と同様な方法を用いて、暫定距離ZKを算出する。
(ステップS22)
距離画像処理部4は、暫定距離ZKを用いて、残りの測定に適用する照射遅延時間Dtim2~DtimNNを決定する。距離画像処理部4は、例えば、暫定距離ZKの近傍の距離が精度よく算出できるように、照射遅延時間Dtim2~DtimNNを決定する。
CP={(Q1+Q2)-(Q3+Q4)}
+j{(Q2+Q3)-(Q4+Q1)} …式(12)
ただし、jは虚数単位
Q1は電荷蓄積部CS1に蓄積された蓄積電荷量(第1電荷量)
Q2は電荷蓄積部CS2に蓄積された蓄積電荷量(第2電荷量)
Q3は電荷蓄積部CS3に蓄積された蓄積電荷量(第3電荷量)
Q4は電荷蓄積部CS4に蓄積された蓄積電荷量(第4電荷量)
上記式(11)において、特徴量は、第1電荷蓄積部に蓄積された第1電荷量と第3電荷蓄積部に蓄積された第3電荷量との差分である第1変数を実部とし、第2電荷蓄積部に蓄積された第2電荷量と第4電荷蓄積部に蓄積された第4電荷量との差分である第2変数を虚部とする複素数で表される値である。
2…光源部
3…受光部
32…距離画像センサ
321…画素
323…垂直走査回路
4…距離画像処理部
41…タイミング制御部
42…距離演算部
43…測定制御部
CS…電荷蓄積部
PO…光パルス
Claims (18)
- 測定対象の空間である測定空間に光パルスを照射する光源部と、
入射した光に応じた電荷を発生する光電変換素子、及び電荷を蓄積する三つ以上の電荷蓄積部を具備する画素と、前記光パルスの照射に同期させたタイミングで前記画素における前記電荷蓄積部のそれぞれに電荷を振り分けて蓄積させる画素駆動回路と、を有する受光部と、
前記光パルスを照射する照射タイミングと前記電荷蓄積部のそれぞれに電荷を振り分けて蓄積させる蓄積タイミングとを制御し、前記電荷蓄積部のそれぞれに蓄積された電荷量に基づいて、前記測定空間に存在する被写体までの距離を算出する距離画像処理部と、
を備え、
前記距離画像処理部は、前記照射タイミングと前記蓄積タイミングとの相対的なタイミング関係が互いに異なる複数の測定を行い、前記複数の測定のそれぞれにて蓄積された電荷量に基づく特徴量を抽出し、前記抽出した特徴量の傾向に基づいて、前記光パルスの反射光がシングルパスにて前記画素に受光されたか、前記光パルスの反射光がマルチパスにて前記画素に受光されたかを判定し、前記判定した結果に応じて前記測定空間に存在する被写体までの距離を算出する、
距離画像撮像装置。 - 前記距離画像処理部は、前記反射光がシングルパスで前記画素に受光された場合における、前記相対的なタイミング関係と前記特徴量とが対応付けられたルックアップテーブルを用いて、前記ルックアップテーブルの傾向と、前記複数の測定のそれぞれの前記特徴量の傾向との類似度合いに基づいて、前記反射光がシングルパスにて前記画素に受光されたか、前記光パルスの前記反射光がマルチパスにて前記画素に受光されたかを判定する、
請求項1に記載の距離画像撮像装置。 - 前記ルックアップテーブルは、前記光パルスの形状、前記光パルスの照射時間、前記電荷蓄積部のそれぞれに電荷を蓄積させる蓄積時間のうち、少なくともいずれかの測定条件に応じて作成され、
前記距離画像処理部は、前記測定条件に対応する前記ルックアップテーブルを用いて、前記反射光がシングルパスにて前記画素に受光されたか、前記反射光がマルチパスにて前記画素に受光されたかを判定する、
請求項2に記載の距離画像撮像装置。 - 前記特徴量は、前記三つ以上の電荷蓄積部のそれぞれに蓄積された電荷のうち、少なくとも前記反射光に応じた電荷が蓄積される電荷蓄積部に蓄積された電荷量を用いて算出される値である、
請求項1から請求項3のいずれか一項に記載の距離画像撮像装置。 - 前記画素には、第1電荷蓄積部、第2電荷蓄積部、及び第3電荷蓄積部が設けられ、
前記距離画像処理部は、前記第1電荷蓄積部、前記第2電荷蓄積部、又は前記第3電荷蓄積部の少なくともいずれかに前記反射光に応じた電荷が蓄積されるタイミングにて、前記第1電荷蓄積部、前記第2電荷蓄積部、前記第3電荷蓄積部の順に電荷を蓄積させ、
前記特徴量は、前記第1電荷蓄積部、前記第2電荷蓄積部、及び前記第3電荷蓄積部のそれぞれの蓄積電荷量を変数とする複素数である、
請求項1から請求項4のいずれか一項に記載の距離画像撮像装置。 - 前記特徴量は、前記第1電荷蓄積部に蓄積された第1電荷量と前記第2電荷蓄積部に蓄積された第2電荷量との差分である第1変数を実部とし、前記第2電荷蓄積部に蓄積された第2電荷量と前記第3電荷蓄積部に蓄積された第3電荷量との差分である第2変数を虚部とする複素数で表される値である、
請求項5に記載の距離画像撮像装置。
- 前記画素には、第1電荷蓄積部、第2電荷蓄積部、第3電荷蓄積部、及び第4電荷蓄積部が設けられ、
前記距離画像処理部は、前記第1電荷蓄積部、前記第2電荷蓄積部、前記第3電荷蓄積部、又は前記第4電荷蓄積部の少なくともいずれかに前記反射光に応じた電荷が蓄積されるタイミングにて、前記第1電荷蓄積部、前記第2電荷蓄積部、前記第3電荷蓄積部、前記第4電荷蓄積部の順に電荷を蓄積させ、
前記特徴量は、前記第1電荷蓄積部、前記第2電荷蓄積部、前記第3電荷蓄積部、及び前記第4電荷蓄積部のそれぞれの蓄積電荷量を変数とする複素数である、
請求項1から請求項4のいずれか一項に記載の距離画像撮像装置。 - 前記特徴量は、前記第1電荷蓄積部に蓄積された第1電荷量と前記第3電荷蓄積部に蓄積された第3電荷量との差分である第1変数を実部とし、前記第2電荷蓄積部に蓄積された第2電荷量と前記第4電荷蓄積部に蓄積された第4電荷量との差分である第2変数を虚部とする複素数で表される値である、
請求項7に記載の距離画像撮像装置。 - 前記複数の測定では、前記蓄積タイミングに対して前記照射タイミングを相対的に遅らせる遅延時間が互いに異なる時間となるように制御される、
請求項1から請求項8のいずれか一項に記載の距離画像撮像装置。 - 前記距離画像処理部は、前記反射光がシングルパスで前記画素に受光された場合における、前記相対的なタイミング関係と前記特徴量とが対応付けられたルックアップテーブルを用いて、前記ルックアップテーブルの傾向と、前記複数の測定のそれぞれの前記特徴量の傾向との類似度合いを示す指標値を算出し、前記指標値が閾値を超えない場合に前記反射光がシングルパスにて前記画素に受光されたと判定し、前記指標値が前記閾値を超える場合に前記反射光がマルチパスにて前記画素に受光されたと判定し、
前記指標値は、前記複数の測定のそれぞれから算出される前記特徴量である第1特徴量と、前記ルックアップテーブルにおいて前記複数の測定のそれぞれに対応する前記特徴量である第2特徴量との差分を、前記第2特徴量の絶対値で正規化した差分正規化値について、前記複数の測定のそれぞれの前記差分正規化値を加算した加算値である、
請求項1から請求項9のいずれか一項に記載の距離画像撮像装置。 - 前記距離画像処理部は、前記反射光がマルチパスで前記画素に受光されたと判定した場合、マルチパスに含まれる光の経路のそれぞれに対応する距離を、最小二乗法を用いることにより算出する、
請求項1から請求項10のいずれか一項に記載の距離画像撮像装置。 - 前記光電変換素子によって発生された電荷を排出する電荷排出部を更に備え、
前記距離画像処理部は、1フレーム期間において、前記光パルスの照射に同期させたタイミングで前記画素における前記電荷蓄積部のそれぞれに電荷を振り分けて蓄積させる単位蓄積処理を、複数回繰り返すことによって、前記電荷蓄積部のそれぞれに電荷を蓄積させ、前記単位蓄積処理において前記電荷蓄積部のそれぞれに電荷を蓄積させる時間区間とは異なる時間区間では、前記光電変換素子によって発生された電荷が前記電荷排出部によって排出されるように制御する、
請求項1から請求項11のいずれか一項に記載の距離画像撮像装置。 - 前記距離画像処理部は、前記複数の測定のうち最初の測定に基づいて前記被写体までの暫定距離を算出し、前記暫定距離に基づいて前記複数の測定のうち残りの測定に用いる遅延時間を決定し、
前記遅延時間は、前記蓄積タイミングに対して前記照射タイミングを相対的に遅らせる時間である、
請求項1から請求項12のいずれか一項に記載の距離画像撮像装置。 - 前記距離画像処理部は、前記暫定距離を前記光パルスが進むのに要する時間、及び前記特徴量の傾向に基づいて、前記遅延時間を決定する、
請求項13に記載の距離画像撮像装置。 - 前記距離画像処理部は、前記暫定距離が閾値を超える遠距離である場合、前記暫定距離が前記閾値を超えない短距離である場合と比較して、前記複数の測定のうち残りの測定における前記電荷蓄積部のそれぞれに電荷を振り分けて蓄積させる蓄積回数を増加させる、
請求項13又は請求項14に記載の距離画像撮像装置。 - 前記距離画像処理部は、前記反射光がシングルパスで前記画素に受光されたと判定した場合、前記複数の測定タイミングでの測定に基づいて前記被写体までの暫定距離をそれぞれ算出し、算出した暫定距離のそれぞれの代表値を、前記被写体までの距離と決定する、
請求項1から請求項15のいずれか一項に記載の距離画像撮像装置。 - 前記距離画像処理部は、前記反射光がシングルパスで前記画素に受光されたと判定した場合、前記複数の測定タイミングでの測定に基づいて前記被写体までの暫定距離を最小二乗法に基づいてそれぞれ決定し、
前記距離画像処理部は、前記反射光がマルチパスで前記画素に受光されたと判定した場合、前記複数の測定タイミングでの測定に基づいて前記被写体の各々の距離を最小二乗法に基づいて決定する、
請求項1から請求項15のいずれか一項に記載の距離画像撮像装置。 - 測定対象の空間である測定空間に光パルスを照射する光源部と、入射した光に応じた電荷を発生する光電変換素子、及び電荷を蓄積する三つ以上の電荷蓄積部を具備する画素と、前記光パルスの照射に同期させたタイミングで前記画素における前記電荷蓄積部のそれぞれに電荷を振り分けて蓄積させる画素駆動回路と、を有する受光部と、前記光パルスを照射する照射タイミングと前記電荷蓄積部のそれぞれに電荷を振り分けて蓄積させる蓄積タイミングとを制御し、前記電荷蓄積部のそれぞれに蓄積された電荷量に基づいて、前記測定空間に存在する被写体までの距離を算出する距離画像処理部と、を備える距離画像撮像装置が行う距離画像撮像方法であって、
前記距離画像処理部は、
前記照射タイミングと前記蓄積タイミングとの相対的なタイミング関係が互いに異なる複数の測定を行い、
前記複数の測定のそれぞれにて蓄積された電荷量に基づく特徴量を抽出し、
前記抽出した特徴量の傾向に基づいて、前記光パルスの反射光がシングルパスにて前記画素に受光されたか、前記光パルスの反射光がマルチパスにて前記画素に受光されたかを判定し、
前記判定した結果に応じて前記測定空間に存在する被写体までの距離を算出する、
距離画像撮像方法。
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