Range image capturing device and range image capturing method

Abstract

To provide a distance image imaging device and a distance image imaging method with which, even when the dullness of a waveform of a square signal used in distance measurement becomes conspicuous, it is possible to calculate measurement distance with good accuracy.SOLUTION: A distance image imaging device comprises: a light receiving unit including a light source unit, a pixel having a photoelectric conversion element and three or more charge storage units and a pixel drive circuit for causing the charges to be stored separately in each of the charge storage units; and a distance image processing unit for determining measurement distance to a subject using the charge amount stored in each of the charge storage units. The distance image processing unit acquires waveform information that indicates the degree of waveform dullness of a square signal used in signal processing until measurement distance is determined, corrects the charge amount stored when the waveform of the square signal is free of dullness on the basis of the acquired waveform information, and determines measurement distance using the corrected charge amount.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, one technique for measuring the distance to an object is to measure the time of flight of a light pulse. This technique is called Time of Flight (TOF). Taking advantage of the fact that the speed of light is known, TOF irradiates an object with a light pulse in the near-infrared region. Then, it measures the time difference between the time when this light pulse is irradiated and the time when the light reflected by the object is received. The distance to the object is calculated based on this time difference. Ranging sensors that use a photodiode (photoelectric conversion element) to detect light for measuring distance have been put into practical use.

[0003] In recent years, distance measurement sensors have been put into practical use that can obtain not only the distance to an object but also depth information for each pixel in a two-dimensional image including the object, i.e., three-dimensional information about the object. Such distance measurement sensors are also called distance imaging devices. In distance imaging devices, multiple pixels each including a photodiode are arranged in a two-dimensional matrix on a silicon substrate, and the pixel surfaces receive light reflected from the object. In distance imaging devices, a photoelectric conversion signal based on the amount of light (electric charge) received by each pixel is output for one image, thereby obtaining a two-dimensional image including the object and distance information for each pixel constituting this image. For example, Patent Document 1 discloses a technology in which one pixel is provided with three charge accumulation units and the charges are allocated in order to calculate distance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 435729 Summary of the Invention [Problem to be solved by the invention]

[0005] These distance imaging devices employ two types of methods: a short-pulse method, which emits intermittent light pulses, and a continuous-wave (CW) method, which emits light continuously. In the short-pulse method, maintaining a rectangular waveform for the light pulses and reflected light while accumulating charge is crucial for maintaining the accuracy of distance measurements. That is, the timing signal of the driver controlling the laser diode that emits the light pulses and the gate signal that accumulates charge in the charge storage unit must be kept rectangular. However, signal delays within the circuit and charge transfer efficiency within the photoelectric conversion element cause delays in the rise and fall of the pulses, resulting in waveform distortion. In particular, narrowing the pulse width (pulse width) to improve processing speed can significantly reduce waveform distortion. This significant waveform distortion can significantly deviate from the actual accumulated charge amount, resulting in errors in the distance measurements. One solution to this problem is to correct the deviation (error) in the measured distance using polynomial approximation. However, this method imposes processing loads and has issues such as a deterioration in distance accuracy due to noise amplification in higher-order terms. Furthermore, when multiple time windows exist, the degree of deviation in the measured distance differs in each time window, so attempting to correct the distance using polynomial approximation in multiple time windows becomes complicated and makes calculations difficult.

[0006] The present invention has been made in light of the above-mentioned problems, and aims to provide a distance image capturing device and a distance image capturing method that can accurately calculate a measured distance even when the waveform of a rectangular signal used to measure distance is significantly rounded. [Means for solving the problem]

[0007] The distance image capturing device of the present invention comprises a light receiving unit having a light source unit that irradiates a measurement space in which a subject is present with a light pulse, pixels each having a photoelectric conversion element that generates charge in response to the incident light and a plurality of charge accumulation units that accumulate the charge, and a pixel drive circuit that allocates and accumulates the charge in each of the charge accumulation units in the pixel at a predetermined timing synchronized with the irradiation of the light pulse, and a distance image processing unit that determines a measurement distance to the subject using the amount of charge accumulated in each of the charge accumulation units, wherein the distance image processing unit acquires waveform information that indicates the degree of waveform rounding when a waveform corresponding to a rectangular signal used in signal processing to determine the measurement distance is rounded to form a footing waveform, and based on the acquired waveform information, corrects the amount of charge accumulated in each of the charge accumulation units to the amount of charge that would be accumulated if the footing waveform were not rounded, and determines the measurement distance using the corrected amount of charge. death, The waveform information is a tail ratio indicating the ratio of a second area to a first area derived by integrating the rectangular signal over time, the first area being an integral value obtained by integrating a first signal, which is the rectangular signal without the tail waveform rounding, from a rising edge start time to a falling edge start time, and the second area being an integral value obtained by subtracting a second signal, which is the rectangular signal with the tail waveform rounding, from the first signal, from a rising edge start time to a rising edge end time, and integrating the subtracted value, or an integral value obtained by integrating the second signal from a falling edge start time to a falling edge end time, The distance image processing unit calculates, for a first charge accumulation unit among the plurality of charge accumulation units that first accumulates an amount of charge corresponding to reflected light of the light pulse reflected by the subject, and a second charge accumulation unit that accumulates charge next to the first charge accumulation unit, a first distance calculation charge amount by subtracting an amount of charge corresponding to an external light component from a first charge amount accumulated in the first charge accumulation unit, and a second distance calculation charge amount by subtracting an amount of charge corresponding to the external light component from a second charge amount accumulated in the second charge accumulation unit, uses the waveform information to calculate a first correction charge amount that is not accumulated in the first charge accumulation unit but accumulated in the second charge accumulation unit due to rounding of the tail waveform, and corrects the first distance calculation charge amount and the second distance calculation charge amount using the first correction charge amount. do.

[0009] In the distance image capturing device of the present invention, the pixel has three of the charge accumulation sections, and the distance image processing unit controls the timing of accumulating charge in the charge accumulation section for accumulating external light, which is one of the three charge accumulation sections and is a charge accumulation section different from the first charge accumulation section and the second charge accumulation section, so that charge corresponding to the reflected light is not accumulated in the charge accumulation section for accumulating external light, and sets the amount of charge accumulated in the charge accumulation section for accumulating external light to an amount of charge corresponding to the external light component.

[0010] In the distance image pickup device of the present invention, the pixel includes three of the charge storage sections, and the waveform information is a tail ratio indicating a ratio of a second area to a first area derived by time-integrating the rectangular signal, and the first area is The skirt waveform the first signal is a rectangular signal without any distortion, and the second area is an integral value obtained by integrating the first signal from the rising edge start time to the falling edge start time, The skirt waveformthe distance image processing unit calculates, for a first charge accumulation unit that first accumulates an amount of charge corresponding to reflected light of the light pulse reflected by the subject, a second charge accumulation unit that accumulates charge next to the first charge accumulation unit, and a third charge accumulation unit that accumulates charge next to the second charge accumulation unit, a first distance calculation charge amount obtained by subtracting an amount of charge corresponding to the external light component from the first charge amount accumulated in the first charge accumulation unit, a second distance calculation charge amount obtained by subtracting an amount of charge corresponding to the external light component from the second charge amount accumulated in the second charge accumulation unit, and a third distance calculation charge amount obtained by subtracting an amount of charge corresponding to the external light component from the third charge amount accumulated in the third charge accumulation unit, and uses the waveform information to calculate hemline waveform a first correction charge amount that is not accumulated in the first charge accumulation unit but accumulated in the second charge accumulation unit due to the rounding of the waveform information; hemline waveform a second correction charge amount that is not accumulated in the second charge accumulation unit but accumulated in the third charge accumulation unit due to distortion of the charge amount; a correction charge amount for the first distance calculation is corrected using the first correction charge amount; and a correction charge amount for the second distance calculation is corrected using the first correction charge amount and the second correction charge amount.

[0011] In the distance image capturing device of the present invention, the pixel has four of the charge accumulation units, and the distance image processing unit controls the timing of accumulating charge in the charge accumulation unit for accumulating external light so that charge corresponding to the reflected light is not accumulated in a charge accumulation unit for accumulating external light that is different from the first charge accumulation unit, the second charge accumulation unit, and the third charge accumulation unit, and sets the amount of charge accumulated in the charge accumulation unit for accumulating external light to an amount of charge corresponding to the external light component.

[0012] The distance image capturing method of the present invention is a distance image capturing method using a distance image capturing device comprising: a light source unit that irradiates a measurement space in which a subject is present with a light pulse; pixels each having a photoelectric conversion element that generates charge in response to the incident light and a plurality of charge accumulation units that accumulate the charge; a pixel drive circuit that distributes and accumulates the charge in each of the charge accumulation units in the pixel at a predetermined timing synchronized with the irradiation of the light pulse; and a distance image processing unit that determines a measurement distance to the subject using the amount of charge accumulated in each of the charge accumulation units, wherein the distance image processing unit acquires waveform information that indicates the degree of waveform rounding when a waveform corresponding to a rectangular signal used in signal processing to determine the measurement distance is rounded to form a footing waveform, and based on the acquired waveform information, corrects the amount of charge accumulated in each of the charge accumulation units to the amount of charge that would be accumulated if the footing waveform were not rounded, and determines the measurement distance using the corrected amount of charge. the waveform information is a tail ratio indicating a ratio of a second area to a first area derived by integrating the rectangular signal over time, the first area being an integral value obtained by integrating a first signal, which is the rectangular signal without the tail waveform rounding, from a rising edge start time to a falling edge start time, and the second area being an integral value obtained by subtracting a second signal, which is the rectangular signal with the tail waveform rounding, from the first signal, from a rising edge start time to a rising edge end time, or an integral value obtained by integrating the second signal from a falling edge start time to a falling edge end time, and the distance image processing unit is configured to select one of the plurality of charge accumulation units that responds to light reflected by the subject when the light pulse is reflected therefrom. a first distance calculation charge amount obtained by subtracting an amount of charge corresponding to the external light component from a first charge amount accumulated in the first charge accumulation unit and a second distance calculation charge amount obtained by subtracting an amount of charge corresponding to the external light component from a second charge amount accumulated in the second charge accumulation unit, for a first charge accumulation unit in which an amount of charge accumulated after the first charge accumulation unit is accumulated first, and a second distance calculation charge amount obtained by subtracting an amount of charge corresponding to the external light component from a second charge amount accumulated in the second charge accumulation unit; do. [Effects of the Invention]

[0013] According to the present invention, even when the waveform of a rectangular signal used for measuring distance is significantly rounded, the measured distance can be calculated with high accuracy. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a schematic configuration of a distance image capturing device 1 according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing a schematic configuration of a range image sensor 32 according to the embodiment. [Figure 3] FIG. 3 is a circuit diagram showing an example of the configuration of a pixel 321 according to an embodiment. [Figure 4] 10 is a timing chart showing an example of timing for driving a pixel 321 according to an embodiment. [Figure 5] 10A and 10B are diagrams illustrating waveform rounding according to an embodiment of the present invention. [Figure 6] 10A and 10B are diagrams illustrating waveform rounding according to an embodiment of the present invention. [Figure 7] 10A and 10B are diagrams illustrating waveform rounding according to an embodiment of the present invention. [Figure 8] FIG. 4 is a diagram showing an example of the configuration of waveform information 440 according to the embodiment. [Figure 9] 10A to 10C are diagrams illustrating the process of correcting the amount of charge performed by distance image processing unit 4 of the embodiment. [Figure 10] 10 is a flowchart showing the flow of processing performed by a distance image processing unit 4 of the embodiment. [Figure 11] 10 is a timing chart showing an example of timing for driving a pixel 321 in a modified example of the embodiment. [Figure 12] 10A and 10B are diagrams illustrating a process in which distance image processing unit 4 corrects the amount of charge in a modified example of the embodiment. [Figure 13] 10A and 10B are diagrams illustrating the effects of the embodiment. [Figure 14] FIG. 10 is a diagram illustrating two time windows in a modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, a distance image capturing device according to an embodiment will be described with reference to the drawings.

[0016] <Embodiment> First, an embodiment will be described. Fig. 1 is a block diagram showing the schematic configuration of a distance image pickup device according to a first embodiment of the present invention. The distance image pickup device 1 shown in Fig. 1 comprises a light source unit 2, a light receiving unit 3, and a distance image processing unit 4. Fig. 1 also shows a subject OB, which is an object to which the distance is measured by the distance image pickup device 1.

[0017] The light source unit 2 irradiates a light pulse PO into a space to be photographed, in which a subject OB, the distance of which is to be measured by the distance image pickup device 1, is present, under the control of the distance image processor 4. The light source unit 2 is, for example, a surface-emitting semiconductor laser module such as a vertical cavity surface-emitting laser (VCSEL). The light source unit 2 includes a light source device 21 and a diffuser plate 22.

[0018] 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) that becomes the light pulses PO to be irradiated onto the subject OB. The light source device 21 is, for example, a semiconductor laser light-emitting element. The light source device 21 emits pulsed laser light in response to control from the timing control unit 41.

[0019] The diffusion plate 22 is an optical component that diffuses the laser light in the near-infrared wavelength band emitted by the light source device 21 to the extent of the surface that is irradiated onto 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 subject OB.

[0020] The light receiving unit 3 receives reflected light RL of the light pulse PO reflected by an object OB, the distance of which is to be measured in the range image pickup device 1, and outputs a pixel signal corresponding to the received reflected light RL. The light receiving unit 3 includes a lens 31 and a range image sensor 32.

[0021] The lens 31 is an optical lens that guides the incident reflected light RL to the range image sensor 32. The lens 31 outputs the incident reflected light RL to the range image sensor 32 side, and causes the light to be received (incident) by pixels provided in the light receiving region of the range image sensor 32.

[0022] The range image sensor 32 is an imaging element used in the range image capturing device 1. The range image sensor 32 has a plurality of pixels in a two-dimensional light receiving area. Each pixel of the range image sensor 32 is provided with one photoelectric conversion element, a plurality of charge accumulation units corresponding to this one photoelectric conversion element, and components that distribute charge to each of the charge accumulation units. In other words, the pixel is an imaging element with a distribution configuration in which charge is distributed and stored in a plurality of charge accumulation units.

[0023] The range image sensor 32 distributes the charges generated by the photoelectric conversion elements to the respective charge accumulation sections under the control of the timing control section 41. The range image sensor 32 also outputs pixel signals according to the amount of charge distributed to the charge accumulation sections. The range image sensor 32 has multiple pixels arranged in a two-dimensional matrix, and outputs pixel signals for one frame corresponding to each pixel.

[0024] 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 unit 4 includes a timing control unit 41, a distance calculation unit 42, a measurement control unit 43, and a memory unit 44. Note that some of the functional units of the distance image processing unit 4 (the timing control unit 41, the distance calculation unit 42, the measurement control unit 43, and the memory unit 44) may be incorporated into the distance image sensor 32.

[0025] The timing control unit 41 controls the timing of outputting various control signals required for measurement in accordance with the control of the measurement control unit 43. The various control signals here include, for example, a signal for controlling the irradiation of the light pulse PO, a signal for distributing and accumulating the reflected light RL among multiple charge accumulation units, a signal for controlling the number of distributions (number of accumulations) per frame, etc. The number of distributions is the number of times the process of distributing electric charges among the charge accumulation units CS (see FIG. 3) is repeated.

[0026] The distance calculation unit 42 calculates the distance to the object OB using the pixel signals output from the distance image sensor 32 and waveform information 440, which will be described later, and outputs the calculated distance information. The distance calculation unit 42 corrects the amount of charge accumulated in the multiple charge accumulation units obtained from the pixel signals output from the distance image sensor 32 using the waveform information 440, and calculates the distance to the object OB based on the corrected amount of charge. The waveform information 440 will be described in detail later. A method by which the distance calculation unit 42 determines the distance to the object OB using the waveform information 440 will also be described in detail later.

[0027] The measurement control unit 43 controls the timing control unit 41. For example, the measurement control unit 43 sets the number of allocations for one frame, the accumulation time Ta, etc., and controls the timing control unit 41 so that imaging is performed according to the set contents.

[0028] The storage unit 44 is configured by a storage medium, such as a hard disk drive (HDD), flash memory, electrically erasable programmable read-only memory (EEPROM), random access read / write memory (RAM), read-only memory (ROM), or any combination of these storage media. The storage unit 44 stores, for example, waveform information 440.

[0029] With this configuration, in the distance image capturing device 1, the light source unit 2 irradiates a light pulse PO in the near-infrared wavelength band onto the subject OB, and the light receiving unit 3 receives the reflected light RL reflected by the subject OB, and the distance image processing unit 4 outputs distance information measuring the distance to the subject OB.

[0030] Although FIG. 1 shows the distance image pickup device 1 having the distance image processing unit 4 built therein, the distance image processing unit 4 may be an element provided outside the distance image pickup device 1.

[0031] Next, there will be described the configuration of the distance image sensor 32 used as an imaging element in the distance image pickup device 1. Fig. 2 is a block diagram showing a schematic configuration of the imaging element (distance image sensor 32) used in the distance image pickup device 1 of the embodiment.

[0032] As shown in FIG. 2, 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 distribution operation, a horizontal scanning circuit 324, and a pixel signal processing circuit 325.

[0033] The light receiving area 320 is an area in which a plurality of pixels 321 are arranged, and FIG. 2 shows an example in which the pixels are arranged in a two-dimensional matrix of 8 rows and 8 columns. The pixels 321 accumulate electric charges according to the amount of light they receive. The control circuit 322 comprehensively controls the range image sensor 32. The control circuit 322 controls the operation of the components of the range image sensor 32 in accordance with instructions from, for example, the timing control unit 41 of the range image processing unit 4. Note that the components of the range image sensor 32 may be directly controlled by the timing control unit 41, in which case the control circuit 322 may be omitted.

[0034] The vertical scanning circuit 323 is a circuit that controls the pixels 321 arranged in the light receiving region 320 for each row in accordance with control from the control circuit 322. The vertical scanning circuit 323 outputs a voltage signal corresponding to the amount of charge accumulated in each charge accumulation unit CS of the pixels 321 to the pixel signal processing circuit 325. In this case, the vertical scanning circuit 323 distributes the charge converted by the photoelectric conversion element to each charge accumulation unit of the pixels 321. In other words, the vertical scanning circuit 323 is an example of a "pixel driving circuit."

[0035] The pixel signal processing circuit 325 is a circuit that performs predetermined signal processing (e.g., noise suppression processing, A / D conversion processing, etc.) on the voltage signals output from the pixels 321 in each column to the corresponding vertical signal lines in accordance with control from the control circuit 322.

[0036] Horizontal scanning circuit 324 is a circuit that sequentially outputs signals output from pixel signal processing circuit 325 to horizontal signal lines in accordance with control from control circuit 322. As a result, pixel signals corresponding to the amount of charge accumulated for one frame are sequentially output to distance image processing unit 4 via the horizontal signal lines.

[0037] In the following description, it is assumed that the pixel signal processing circuit 325 performs A / D conversion processing and the pixel signals are digital signals.

[0038] Here, the configuration of the pixel 321 arranged in the light receiving region 320 provided in the range image sensor 32 will be described. Fig. 3 is a circuit diagram showing an example of the configuration of the pixel 321 arranged in the light receiving region 320 of the range image sensor 32 of the embodiment. Fig. 3 shows an example of the configuration of one pixel 321 out of the multiple pixels 321 arranged in the light receiving region 320. In the example of this diagram, the pixel 321 is an example of a configuration including four pixel signal readout units.

[0039] 3, the pixel 321 includes one photoelectric conversion element PD, a drain gate transistor GD, and four pixel signal readout units RU (pixel signal readout units RU1 to RU4). Each pixel signal readout unit RU outputs a voltage signal from an output terminal O.

[0040] In the following description, the four pixel signal readout units RU are distinguished from one another by adding the numbers "1," "2," "3," or "4" after their reference numerals. Similarly, the components of the four pixel signal readout units RU are distinguished from one another by adding numbers after their reference numerals.

[0041] Each pixel signal readout unit RU includes a readout gate transistor G, a floating diffusion FD, a charge storage capacitance C, a reset gate transistor RT, a source follower gate transistor SF, and a select gate transistor SL. In each pixel signal readout unit RU, the floating diffusion FD and the charge storage capacitance C form a charge storage unit CS. Specifically, the pixel signal readout unit RU1 includes a readout gate transistor G1, a floating diffusion FD1, a charge storage capacitance C1, a reset gate transistor RT1, a source follower gate transistor SF1, and a select gate transistor SL1. In the pixel signal readout unit RU1, the floating diffusion FD1 and the charge storage capacitance C1 form a charge storage unit CS1. The pixel signal readout units RU2 to RU4 have a similar configuration.

[0042] The photoelectric conversion element PD is a buried photodiode that photoelectrically converts incident light to generate electric charges and accumulates the generated electric charges. The photoelectric conversion element PD may have any structure. For example, the photoelectric conversion element PD may be a PN photodiode having a structure in which a P-type semiconductor and an N-type semiconductor are joined together, or a PIN photodiode having a structure in which an I-type semiconductor is sandwiched between a P-type semiconductor and an N-type semiconductor. Furthermore, the photoelectric conversion element PD is not limited to a photodiode, and may be, for example, a photogate type photoelectric conversion element.

[0043] In pixel 321, the photoelectric conversion element PD photoelectrically converts incident light to generate electric charges, which are then distributed to each of the four charge accumulation units CS, and voltage signals corresponding to the amount of the distributed electric charges are output to the pixel signal processing circuit 325.

[0044] The configuration of the pixels arranged in the range image sensor 32 is not limited to the configuration including four pixel signal readout units RU as shown in Fig. 3, but may be any pixel configured to include multiple pixel signal readout units RU. In other words, the number of pixel signal readout units RU (charge accumulation units CS) provided in the pixels arranged in the range image sensor 32 may be two, three, five or more.

[0045] 3 shows an example in which the charge storage section CS is configured by a floating diffusion FD and a charge storage capacitance C. However, the charge storage section CS only needs to be configured by at least a floating diffusion FD, and the pixel 321 may not have a charge storage capacitance C.

[0046] 3 shows an example of a configuration including the drain gate transistor GD, but is not limited to this. For example, if there is no need to discard the charge remaining in the photoelectric conversion element PD without being stored in the charge storage unit CS, the pixel 321 may be configured without the drain gate transistor GD.

[0047] Next, the driving timing of the pixel 321 will be described with reference to Fig. 4. Fig. 4 is a timing chart showing the timing of driving the pixel 321 according to the embodiment.

[0048] In Figure 4, the time required for each charge accumulation unit CS to accumulate charge in one allocation process is represented as a "unit accumulation period." After the allocation process performed in the "unit accumulation period" is repeated the number of accumulations corresponding to one frame, a process is performed to read out the amount of charge accumulated during that time. The time during which this process of reading out the amount of accumulated charge is performed is represented as a "readout period."

[0049] In addition, in Figure 4, the timing at which the light pulse PO is irradiated is indicated by "L", the timing at which the reflected light RL is received is indicated by "R", the timing at which the readout gate transistor G1 is driven is indicated by "G1", the timing at which the readout gate transistor G2 is driven is indicated by "G2", the timing at which the readout gate transistor G3 is driven is indicated by "G3", the timing at which the readout gate transistor G4 is driven is indicated by "G4", and the timing of the drive signal RSTD is indicated by "GD".

[0050] The vertical scanning circuit 323 accumulates charges in the charge accumulation units CS1 to CS4 at timings synchronized with the irradiation of the light pulse PO. In the example of Fig. 4, charges are accumulated in the charge accumulation unit CS1 at the same timing as the irradiation of the light pulse PO, and after the charges are accumulated in the charge accumulation unit CS1, charges are sequentially accumulated in the charge accumulation units CS2 to CS4.

[0051] 4 shows a timing chart in which reflected light RL is received by the range image sensor 32 with a delay time Td from the time when the light pulse PO is emitted. According to the delay time Td, charge corresponding to reflected light RL is distributed and stored in charge accumulation units CS1 and CS2, or charge accumulation units CS2 and CS3. At the timing when charge accumulation unit CS4 accumulates charge, reflected light RL is not received, and charge corresponding to external light components such as background light is accumulated in the charge accumulation unit CS4.

[0052] Specifically, first, the vertical scanning circuit 323 irradiates an optical pulse PO. At the same timing as the irradiation, the vertical scanning circuit 323 turns off the drain gate transistor GD and turns on the readout gate transistor G1 for the accumulation time Ta. After turning on the readout gate transistor G1 for the accumulation time Ta, the vertical scanning circuit 323 turns off the readout gate transistor G1. As a result, charges photoelectrically converted by the photoelectric conversion element PD while the readout gate transistor G1 is controlled to be in the on state are accumulated in the charge accumulation unit CS1 via the readout gate transistor G1.

[0053] Next, at the timing when the read gate transistor G2 is turned off, the vertical scanning circuit 323 turns on the read gate transistor G2 for the accumulation time Ta. After turning on the read gate transistor G2 for the accumulation time Ta, the vertical scanning circuit 323 turns off the read gate transistor G2. As a result, the charge photoelectrically converted by the photoelectric conversion element PD while the read gate transistor G2 is controlled to be on is accumulated in the charge accumulation section CS2 via the read gate transistor G2.

[0054] Next, the vertical scanning circuit 323 turns on the readout gate transistor G3 for the accumulation time Ta at the same time as turning off the readout gate transistor G2. After turning on the readout gate transistor G3 for the accumulation time Ta, the vertical scanning circuit 323 turns off the readout gate transistor G3. As a result, 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 accumulation unit CS3 via the readout gate transistor G3.

[0055] Next, the vertical scanning circuit 323 turns on the read gate transistor G4 for the accumulation time Ta at the timing when the accumulation of charges in the charge accumulation unit CS3 is completed. After the read gate transistor G4 has been on for the accumulation time Ta, the vertical scanning circuit 323 turns off the read gate transistor G4. The vertical scanning circuit 323 turns on the drain gate transistor GD at the timing when the read gate transistor G4 is turned off. By turning on the drain gate transistor GD, the charges photoelectrically converted by the photoelectric conversion element PD during this time are discarded via the drain gate transistor GD without being accumulated in the charge accumulation unit CS.

[0056] The vertical scanning circuit 323 repeats the above-described driving a predetermined number of times throughout one frame. Thereafter, the vertical scanning circuit 323 outputs a voltage signal corresponding to the amount of charge accumulated in each charge accumulation unit CS. Specifically, the vertical scanning circuit 323 turns on the selection gate transistor SL1 for a predetermined period of time, thereby causing a voltage signal corresponding to the amount of charge accumulated in the charge accumulation unit CS1 to be output from the output terminal O1 via the pixel signal readout unit RU1. Similarly, the vertical scanning circuit 323 sequentially turns on the selection gate transistors SL2 to SL4, thereby causing voltage signals corresponding to the amount of charge accumulated in the charge accumulation units CS2 to CS4 to be output from the output terminals O2 to O4. As a result, an electrical signal corresponding to the amount of charge accumulated in each charge accumulation unit CS for one frame is output to the distance calculation unit 42.

[0057] In the above description, the read gate transistor G1 is turned on at the timing when the light pulse PO is irradiated. However, this is not limiting. It is sufficient that the light pulse PO is irradiated at a timing when at least the charge corresponding to the reflected light RL is distributed and accumulated in the charge accumulation units CS1 and CS2, or CS2 or CS3.

[0058] In FIG. 4, the amount of charge corresponding to the reflected light RL and the external light component is allocated and stored in the charge storage units CS1 and CS2 based on the relationship between the timing of irradiation of the light pulse PO and the timing of storing charge in each of the charge storage units CS. In this case, the charge storage unit CS1 is an example of a "first charge storage unit." The charge storage unit CS2 is an example of a "second charge storage unit." Furthermore, the charge storage unit CS4 stores an amount of charge corresponding to the external light component, such as background light. In this case, the charge storage unit CS4 is an example of a "charge storage unit for storing external light."

[0059] When reflected light RL from a relatively distant object OB is received, the delay time Td becomes large, and as a result, the amount of charge corresponding to the reflected light RL and the external light component is allocated and stored in the charge storage units CS2 and CS3. In this case, the charge storage unit CS2 is an example of a "first charge storage unit." The charge storage unit CS3 is an example of a "second charge storage unit."

[0060] The distribution (distribution ratio) of the charge amounts distributed to the charge storage units CS1 and CS2 is a ratio according to the delay time Td from when the light pulse PO is reflected by the object OB until it is incident on the range image pickup device 1.

[0061] Using this principle, the distance calculation unit 42 calculates the delay time Td using the following equation (1): In equation (1), To is the time interval during which the light pulse PO is irradiated, and R is the charge ratio indicating the distribution ratio of the reflected light RL.

[0062] Td = To × R … (1) However, R=Q2# / (Q1#+Q2#) Q1#=Q1-Qb Q2#=Q2-Qb Q4=Qb To is the time interval during which the light pulse PO is irradiated. R is the charge ratio calculated as follows: Q1# is the amount of charge stored in the charge storage section CS1 according to the reflected light RL. Q2# is the amount of charge stored in the charge storage section CS2 according to the reflected light RL Qb is the amount of charge stored in the charge storage section CS according to the external light component. Q1 is the amount of charge stored in the charge storage section CS1 Q2 is the amount of charge stored in the charge storage section CS2 Q4 is the amount of charge stored in the charge storage section CS4

[0063] In the short-distance light-receiving pixels, the distance calculation unit 42 calculates the round-trip distance to the subject OB by multiplying the delay time Td calculated by equation (1) by the speed of light (velocity).The distance calculation unit 42 then calculates the distance to the subject OB by dividing the calculated round-trip distance by 2.

[0064] Here, factors that cause an error in the distance (measured distance) calculated from the amount of accumulated charge will be described.

[0065] One possible cause of errors is waveform distortion in the rectangular signals used in various signal processing steps related to distance measurement. In actual circuits, high-frequency characteristics deteriorate during signal transmission due to factors such as wiring resistance and parasitic capacitance. Furthermore, delays occur during charge transfer due to the charge transfer efficiency of the photoelectric conversion element PD. Deterioration of high-frequency characteristics or a decrease in the charge transfer efficiency of the photoelectric conversion element PD causes delays when the signal amplitude changes sharply, such as at the rising or falling edges of the signal, resulting in waveform distortion. As a result, the rectangular shape collapses, resulting in a waveform with delayed rising and falling edges.

[0066] Any distortion in the rectangular signals used in various distance measurement processes can cause errors. For example, if the timing signal of the driver controlling the laser diode that emits the optical pulse is distorted, the specified light intensity will be reached slightly after the optical pulse is emitted, and the light intensity of the optical pulse PO will reach zero slightly after the emission is stopped. Because this waveform distortion affects the reflected light RL, the reflected light RL also appears as a tailing waveform and is received by the pixel 321. Furthermore, if the timing signal of the readout gate transistor G is distorted, the amount of charge that should be accumulated in the charge storage unit CS1 will be accumulated in the charge storage unit CS2, or the amount of charge that should be accumulated in the charge storage unit CS2 will be accumulated in the charge storage unit CS3. Thus, the delay time Td calculated from equation (1) using the amount of charge accumulated in a different charge storage unit CS than the one that should be accumulated will be different from the actual delay time Td and will contain errors.

[0067] To address this issue, in this embodiment, the amount of charge stored in each charge storage unit CS according to the reflected light RL is corrected to the amount of charge that would be stored if a rectangular signal with an unblurred waveform were used, using waveform information 440. The waveform information 440 is information that indicates the degree of waveform blunting. The corrected amount of charge is then used to calculate the delay time Td from equation (1). This makes it possible to reduce errors caused by the blunting of the rectangular signal.

[0068] Here, a method for correcting the amount of charge will be specifically described with reference to Figs. 5 to 9. Figs. 5 to 7 are diagrams illustrating waveform rounding in an embodiment. Fig. 8 is a diagram illustrating an example of the configuration of waveform information 440 in an embodiment. Fig. 9 is a diagram illustrating the process by which distance image processing unit 4 in an embodiment corrects the amount of charge.

[0069] A rectangular signal H1 (hereinafter also referred to as "rectangular signal H1") with no waveform distortion is shown in Fig. 5. As shown in Fig. 5, the signal amplitude of signal H1 changes from Lo to Hi at rising edge start time Trs, and changes from Hi to Lo at falling edge start time Tds.

[0070] 6 schematically shows a signal H2 with a rounded waveform and a trailing edge (hereinafter also referred to as "trailing edge signal H2"). As shown in FIG. 6, the signal amplitude of signal H2 gradually changes from Lo to Hi over time from the rising edge start time Trs to the rising edge end time Tre. Also, the signal amplitude of signal H2 gradually changes from Hi to Lo over time from the falling edge start time Tds to the falling edge end time Tde.

[0071] Fig. 7 is a diagram schematically illustrating the waveform of the footing signal H2 in Fig. 6 divided into a plurality of regions. In this embodiment, as shown in Fig. 7, the waveform of the footing signal H2 is divided into regions Sa to Sc, and the degree of rounding of the footing signal H2 is defined using the area of ​​each region.

[0072] The area Sa corresponds to the area caused by the decrease in amplitude due to the rising delay of the footing signal H2. The area of ​​the area Sa is the integral value obtained by integrating the subtraction value of the footing signal H2 from the rectangular signal H1 from the rising start time Trs to the rising end time Tre.

[0073] Region Sb corresponds to the rectangular area of ​​rectangular signal H1 minus region Sa. The area of ​​region Sb is the integral value of footing signal H2 from rising edge start time Trs to falling edge start time Tds. Alternatively, it is the area obtained by subtracting the area of ​​region Sa from the integral value (rectangular area) of rectangular signal H1 from rising edge start time Trs to falling edge start time Tds.

[0074] The region Sc corresponds to a trailing region caused by a delay in the trailing edge of the trailing edge signal H2. The area of ​​the region Sc is the integral of the trailing edge signal H2 from the trailing edge start time Tds to the trailing edge end time Tde.

[0075] In this embodiment, the ratio of the skirt area (area Sc) to the rectangular area (area Sa+Sb) is referred to as the skirt ratio Re, which is used as an index indicating the "degree of rounding" of the waveform. Note that the skirt ratio Re may be any value that indicates at least the "degree of rounding" of the waveform, and for example, the skirt ratio Re may be the ratio of the rectangular area (area Sa+Sb) to the skirt area (area Sc).

[0076] 8 shows an example of the configuration of waveform information 440. Waveform information 440 includes items such as a tailing ratio Re, a calculation formula, and remarks. The tailing ratio Re is an index indicating the degree of rounding in a waveform, and is the ratio of the tailing area (area Sc) to the rectangular area (area Sa+Sb). The calculation formula is a formula for calculating the tailing ratio Re.

[0077] In this embodiment, the distortions of various signal processes are aggregated in the reflected light RL, and correction is performed assuming that the reflected light RL with the distortion has been received. That is, it is assumed that the charge corresponding to the reflected light RL with the distortion is accumulated in the charge accumulation unit CS at the drive timing of the readout gate transistor G without the distortion. Then, the amount of charge accumulated in the charge accumulation unit CS is corrected based on the tailing ratio Re (degree of distortion) of the reflected light RL. The amount of charge after correction is the amount of charge that would be accumulated in the charge accumulation unit CS if the charge corresponding to the reflected light RL without the distortion were accumulated at the drive timing of the readout gate transistor G without the distortion.

[0078] Fig. 9 is a diagram illustrating the process of correcting the amount of charge performed by distance image processing unit 4. As shown in Fig. 9, this embodiment assumes that the reflected light RL with distortion is accumulated in charge accumulation unit CS at the drive timing of the readout gate transistor G without distortion.

[0079] 9, as in FIG. 4, it is assumed that the reflected light RL reaches the range image sensor 32 after a delay time Td, and an amount of charge corresponding to the reflected light RL is distributed and accumulated in the charge accumulation units CS1 and CS2. Also, in FIG. 9, it is assumed that the reflected light RL has a waveform that is rounded, and a charge corresponding to a portion of the reflected light RL caused by the rounding is accumulated in the charge accumulation unit CS3. In this case, the charge accumulation unit CS1 is an example of a "first charge accumulation unit." The charge accumulation unit CS2 is an example of a "second charge accumulation unit." The charge accumulation unit CS3 is an example of a "third charge accumulation unit."

[0080] Specifically, of the reflected light RL formed by the trailing signal H2 having a waveform with a rounded waveform, an amount of charge corresponding to a portion of the region Sb (region Sb1) is assumed to be accumulated in the charge accumulation unit CS1. Also, an amount of charge corresponding to the remaining portion of the region Sb (region Sb2) is assumed to be accumulated in the charge accumulation unit CS2. Also, an amount of charge corresponding to a portion of the region Sc (region Sc1) is assumed to be accumulated in the charge accumulation unit CS2. Also, an amount of charge corresponding to the remaining portion of the region Sc (region Sc2) is assumed to be accumulated in the charge accumulation unit CS3.

[0081] In correcting the amount of charge, this embodiment assumes that the irradiation time To for irradiating the light pulse PO and the accumulation time Ta for accumulating charge in the charge accumulation unit CS are the same time interval. Also, in this embodiment, the area of ​​region Sa and the area of ​​region Sc are calculated as being the same value.

[0082] Although the timing chart for "G4" is omitted in FIG. 9, the read gate transistor G4 is driven in the same manner as in FIG. 4, and an amount of charge corresponding to the external light component is stored in the charge storage section CS4.

[0083] The distance calculation unit 42 acquires an electrical signal corresponding to the amount of charge accumulated in each charge accumulation unit CS for one frame. The distance calculation unit 42 calculates the total amount of charge QSUM corresponding to the reflected light RL using the following equation (2). Here, the amount of charge Q1# is the amount of charge corresponding to the reflected light RL accumulated in the charge accumulation unit CS1 and is an example of the "first amount of charge for distance calculation." The amount of charge Q2# is the amount of charge corresponding to the reflected light RL accumulated in the charge accumulation unit CS2 and is an example of the "second amount of charge for distance calculation." The amount of charge Q3# is the amount of charge corresponding to the reflected light RL accumulated in the charge accumulation unit CS3 and is an example of the "third amount of charge for distance calculation."

[0084] QSUM=Q1#+Q2#+Q3# …(2) Q1#=Q1-Qb Q2#=Q2-Qb Q3#=Q3-Qb Q4=Qb However, Q1# is the amount of charge stored in the charge storage section CS1 according to the reflected light RL. Q2# is the amount of charge stored in the charge storage section CS2 according to the reflected light RL Q3# is the amount of charge stored in the charge storage section CS3 according to the reflected light RL. Qb is the amount of charge stored in the charge storage section CS according to the external light component. Q1 is the amount of charge stored in the charge storage section CS1 Q2 is the amount of charge stored in the charge storage section CS2 Q3 is the amount of charge stored in the charge storage section CS3 Q4 is the amount of charge stored in the charge storage section CS4

[0085] The distance calculation unit 42 uses the total amount of charge QSUM calculated by equation (2) and the tailing ratio Re stored in the waveform information 440 to calculate the amount of charge Qs of the tailing portion (the amount of charge corresponding to the region Sc in Figure 7) using the following equation (3).

[0086] Qs = QSUM × Re … (3) However, QSUM=Q1#+Q2#+Q3# Q1# is the amount of charge stored in the charge storage section CS1 according to the reflected light RL. Q2# is the amount of charge stored in the charge storage section CS2 according to the reflected light RL Q3# is the amount of charge stored in the charge storage section CS3 according to the reflected light RL. Re is the tailing ratio

[0087] The distance calculation unit 42 separates the charge amount Qs of the trailing portion calculated by equation (3) into the charge amount Q2s accumulated in the charge accumulation unit CS2 and the charge amount Q3# corresponding to the reflected light RL accumulated in the charge accumulation unit CS3 by equation (4).

[0088] Qs=Q2s+Q3# …(4) However, Q2s is the amount of charge corresponding to the tail portion of the reflected light RL accumulated in the charge accumulation section CS2. Q3# is the amount of charge stored in the charge storage section CS3 according to the reflected light RL.

[0089] The distance calculation unit 42 obtains the charge amount Q2s using equation (4). Since the charge amount Qs of the footing portion and the charge amount Q3# corresponding to the reflected light RL accumulated in the charge accumulation unit CS3 are known, the charge amount Q2s can be calculated using equation (5).

[0090] Q2s=Qs-Q3# …(5) However, Q2s is the amount of charge corresponding to the tail portion of the reflected light RL accumulated in the charge accumulation section CS2. Q3# is the amount of charge stored in the charge storage section CS3 according to the reflected light RL. Qs is the charge in the tail

[0091] Assuming that the area of ​​region Sa is the same as the area of ​​region Sc, distance calculation unit 42 corrects the amount of charge Q1# according to equation (6) to calculate the amount of charge Q1h after correction. Distance calculation unit 42 also corrects the amount of charge Q2# according to equation (7) to calculate the amount of charge Q2h after correction.

[0092] Q1h=Q1#+Q2s …(6) Q2h=Q2#-Q2s+Q3# …(7) However, Q1h is the amount of charge stored in the charge storage unit CS1 after correction according to the reflected light RL. Q1# is the amount of charge corresponding to the reflected light RL accumulated in the charge accumulation unit CS1 before correction. Q2s is the amount of charge stored in the charge storage section CS2 according to the tail of the reflected light RL. Q2h is the amount of charge stored in the charge storage unit CS2 after correction according to the reflected light RL Q2# is the amount of charge corresponding to the reflected light RL accumulated in the charge accumulation unit CS2 before correction. Q3# is the amount of charge stored in the charge storage section CS3 according to the reflected light RL.

[0093] 10 is a flowchart showing the flow of processing performed by distance image processing unit 4 according to the embodiment. Distance calculation unit 42 acquires the amounts of electric charges Q1 to Q4 accumulated in charge accumulation units CS1 to CS3 (step S10). Distance calculation unit 42 uses the acquired amount of electric charge Q4 to calculate the amount of electric charge Qb corresponding to the external light component (step S11).

[0094] The distance calculation unit 42 calculates the electric charge Qs corresponding to the tailing component using the electric charge amounts Q1 to Q3, the electric charge Qb, and the tailing ratio Re (step S12). The distance calculation unit 42 calculates the electric charge Qs by substituting the electric charge amounts Q1 to Q3, the electric charge Qb, and the tailing ratio Re into equations (2) and (3).

[0095] The distance calculation unit 42 calculates the amount of charge Q2s accumulated in the charge accumulation unit CS2 out of the amount of charge corresponding to the trailing component (step S13). The distance calculation unit 42 calculates the amount of charge Q2s using equations (4) and (5). The distance calculation unit 42 calculates a corrected amount of charge Q1h by correcting the amount of charge Q1#, and calculates a corrected amount of charge Q2h by correcting the amount of charge Q2# (step S14). The distance calculation unit 42 determines the measured distance using the corrected amounts of charge Q1h and Q2h (step S15). The distance calculation unit 42 calculates the delay time Td by substituting the corrected amount of charge Q1h for the amount of charge Q1# in equation (1) and substituting the corrected amount of charge Q2h for the amount of charge Q2# in equation (1). The distance calculation unit 42 calculates the measured distance by multiplying the calculated delay time Td by the speed of light (velocity) and dividing the result by 1 / 2.

[0096] In the above description, the pixel 321 of the distance image pickup device 1 has four charge storage units CS1 to CS4. However, this is not limiting. The pixel 321 of the distance image pickup device 1 may have five or more (for example, N, where N≧5) charge storage units CS.

[0097] If the pixel 321 of the range image pickup device 1 has N (N≧5) charge accumulation units CS, in step S10 the distance calculation unit 42 acquires the amounts of charge Q1 to QN accumulated in the charge accumulation units CS1 to CSN, respectively. In step S11, the distance calculation unit 42 calculates the amount of charge Qb corresponding to the external light component using the acquired amounts of charge Q1 to QN. The method by which the distance calculation unit 42 calculates the amount of charge Qb is the same as when the pixel 321 of the range image pickup device 1 has four charge accumulation units CS1 to CS4, by using the amount of charge accumulated in the charge accumulation unit CS that accumulates charge at a timing when reflected light RL is not received.

[0098] In step S12, the distance calculation unit 42 selects three charge accumulation units CS from the charge accumulation units CS1 to CSN in which charge corresponding to the reflected light RL (including the trailing portion) is distributed and accumulated. The distance calculation unit 42 selects the three charge accumulation units CS by, for example, selecting the three charge accumulation units CS in which the sum of the charge amounts accumulated in the charge accumulation units CS is the largest among the combinations of three charge accumulation units CS in which charge corresponding to the reflected light RL is distributed and accumulated. The distance calculation unit 42 calculates the charge amount Qs using the charge amount accumulated in each of the three charge accumulation units CS in which charge corresponding to the reflected light RL is distributed and accumulated, and the charge amount Qb corresponding to the external light component. The processes of steps S13 to S15 are the same as when the pixel 321 of the range image pickup device 1 has four charge accumulation units CS1 to CS4.

[0099] Alternatively, the pixel 321 of the range image pickup device 1 may be configured to include three charge accumulation units CS1 to CS3. In this case, the range image pickup device 1 performs two charge accumulation processes per measurement: a process (referred to as a first process) for accumulating only charges corresponding to the external light component, and a process (referred to as a second process) for accumulating charges including reflected light RL. For example, the range image pickup device 1 performs the first process in the first frame and the second process in the next frame. When performing the first process, the range image pickup device 1 accumulates charges in each of the charge accumulation units CS1 to CS3 without irradiating the light pulse PO. When performing the second process, the range image pickup device 1 irradiates the light pulse PO and accumulates charges in each of the charge accumulation units CS1 to CS3.

[0100] In this case, in step S10, the distance calculation unit 42 acquires the electric charges Q1ft to Q3ft accumulated in the charge accumulation units CS1 to CS3, respectively, in the first process. The distance calculation unit 42 also acquires the electric charges Q1sd to Q3sd accumulated in the charge accumulation units CS1 to CS3, respectively, in the second process. In step S11, the distance calculation unit 42 sets one of the acquired electric charges Q1ft to Q3ft, or a combination thereof, as the electric charge Qb corresponding to the external light component. In step S12, the distance calculation unit 42 calculates the electric charge Q2s using the acquired electric charges Q1sd to Q3sd and the electric charge Qb. The method by which the distance calculation unit 42 calculates the electric charge Q2s is the same as when the pixel 321 of the range image pickup device 1 has four electric charge accumulation units CS1 to CS4.

[0101] (Modification of the embodiment) Here, a modified example of the embodiment will be described. In this modified example, similar to the above-described embodiment, it is assumed that reflected light RL having a waveform with rounding is received, but it differs from the above-described embodiment in that charges corresponding to the trailing edge of the reflected light RL caused by the rounding are accumulated in the charge accumulation unit CS2.

[0102] Fig. 11 is a timing chart showing an example of timing for driving pixel 321 in a modified example of the embodiment. The "unit accumulation period" and "readout period" in Fig. 11 are the same as those in Fig. 4, and therefore their description will be omitted. Furthermore, "L", "R", "G1" to "G3", and "GD" in Fig. 11 are the same as those in Fig. 4, and therefore their description will be omitted.

[0103] 11, similarly to FIG. 4, a timing chart is shown for the case where reflected light RL is received by the range image sensor 32 with a delay time Td from the time when the light pulse PO is emitted. In FIG. 11, charge corresponding to reflected light RL is distributed and stored in charge accumulation units CS1 and CS2. At the timing when charge accumulation unit CS3 accumulates charge, reflected light RL is not received, and charge corresponding to external light components such as background light is accumulated in the charge accumulation unit CS3.

[0104] Fig. 12 is a diagram illustrating the process by which distance image processing unit 4 corrects the amount of charge in a modified embodiment. Similar to Fig. 11, Fig. 12 shows that reflected light RL reaches distance image sensor 32 with a delay of Td, and the amount of charge corresponding to reflected light RL is distributed and stored in charge accumulation units CS1 and CS2. In this case, charge accumulation unit CS1 is an example of a "first charge accumulation unit." Charge accumulation unit CS2 is an example of a "second charge accumulation unit."

[0105] Specifically, of the reflected light RL formed by the trailing signal H20 having a waveform with a rounded waveform, the amount of charge corresponding to a portion of the region Sb (region Sb1) is assumed to be accumulated in the charge accumulation unit CS1. Also, the amount of charge corresponding to the remaining portion of the region Sb (region Sb2) is assumed to be accumulated in the charge accumulation unit CS2. Also, the amount of charge corresponding to the region Sc is assumed to be accumulated in the charge accumulation unit CS2.

[0106] In correcting the amount of charge, this modification assumes, as in the above-described embodiment, that the irradiation time To for irradiating the light pulse PO and the accumulation time Ta for accumulating charge in the charge accumulation unit CS are the same time interval, and that the area of ​​the region Sa is the same as the area of ​​the region Sc.

[0107] Although the timing chart for "G3" is omitted in FIG. 12, the read gate transistor G3 is driven in the same manner as in FIG. 11, and an amount of charge corresponding to the external light component is stored in the charge storage section CS3.

[0108] The distance calculation unit 42 acquires an electrical signal corresponding to the amount of charge for one frame accumulated in each charge accumulation unit CS. The distance calculation unit 42 calculates the total amount QSUM of charge corresponding to the reflected light RL using the following equation (8).

[0109] QSUM=Q1#+Q2# …(8) Q1#=Q1-Qb Q2#=Q2-Qb Q3=Qb However, Q1# is the amount of charge stored in the charge storage section CS1 according to the reflected light RL. Q2# is the amount of charge stored in the charge storage section CS2 according to the reflected light RL Qb is the amount of charge stored in the charge storage section CS according to the external light component. Q1 is the amount of charge stored in the charge storage section CS1 Q2 is the amount of charge stored in the charge storage section CS2 Q3 is the amount of charge stored in the charge storage section CS3

[0110] The distance calculation unit 42 uses the total amount of charge QSUM calculated by equation (8) and the tailing ratio Re stored in the waveform information 440 to calculate the amount of charge Qs of the tailing portion (the amount of charge corresponding to the region Sc in Figure 12) using the following equation (9).

[0111] Qs = QSUM × Re … (9) However, QSUM=Q1#+Q2# Q1# is the amount of charge stored in the charge storage section CS1 according to the reflected light RL. Q2# is the amount of charge stored in the charge storage section CS2 according to the reflected light RL Re is the tailing ratio

[0112] The distance calculation unit 42 calculates the amount of charge Qs of the footing portion calculated by equation (9) as the amount of charge Q2s accumulated in the charge accumulation unit CS2 by equation (10).

[0113] Qs = Q2s …(10) However, Q2s is the amount of charge corresponding to the tail portion of the reflected light RL accumulated in the charge accumulation section CS2.

[0114] The distance calculation unit 42 obtains the amount of charge Q2s using equation (9). Since the amount of charge Qs in the footing portion is known, the amount of charge Q2s can be calculated using equation (10).

[0115] Q2s=Qs …(10) However, Q2s is the amount of charge corresponding to the tail portion of the reflected light RL accumulated in the charge accumulation section CS2. Qs is the charge in the tail

[0116] The distance calculation unit 42 calculates the area of ​​the region Sa as the same value as the area of ​​the region Sc, corrects the amount of electric charge Q1# according to equation (11), and calculates the amount of electric charge Q1h after correction.Furthermore, the distance calculation unit 42 corrects the amount of electric charge Q2# according to equation (12), and calculates the amount of electric charge Q2h after correction.

[0117] Q1h=Q1#+Q2s …(11) Q2h=Q2#-Q2s …(12) However, Q1h is the amount of charge stored in the charge storage unit CS1 after correction according to the reflected light RL. Q1# is the amount of charge corresponding to the reflected light RL accumulated in the charge accumulation unit CS1 before correction. Q2s is the amount of charge stored in the charge storage section CS2 according to the tail of the reflected light RL. Q2h is the amount of charge stored in the charge storage unit CS2 after correction according to the reflected light RL Q2# is the amount of charge corresponding to the reflected light RL accumulated in the charge accumulation unit CS2 before correction.

[0118] In the above description, the pixel 321 of the distance image pickup device 1 includes three charge accumulation units CS1 to CS3, and only charges corresponding to the external light component are accumulated in one of the charge accumulation units CS3. However, this is not limiting. The pixel 321 of the distance image pickup device 1 may include two charge accumulation units CS. In this case, the distance image pickup device 1 performs two charge accumulation processes for each measurement: a process (referred to as a first process) for accumulating only charges corresponding to the external light component, and a process (referred to as a second process) for accumulating charges including reflected light RL. For example, the distance image pickup device 1 performs the first process in the first frame and the second process in the next frame. When performing the first process, the distance image pickup device 1 accumulates charges in each of the charge accumulation units CS1 and CS2 without irradiating the light pulse PO. When performing the second process, the distance image pickup device 1 irradiates the light pulse PO and accumulates charges in each of the charge accumulation units CS1 and CS2.

[0119] In this case, in step S10, the distance calculation unit 42 acquires the electric charge amounts Q1ft and Q2ft accumulated in the charge accumulation units CS1 and CS2, respectively, in the first processing. The distance calculation unit 42 also acquires the electric charge amounts Q1sd and Q2sd accumulated in the charge accumulation units CS1 and CS2, respectively, in the second processing. In step S11, the distance calculation unit 42 sets one or both of the acquired electric charge amounts Q1ft and Q2ft as the electric charge amount Qb corresponding to the external light component. In step S12, the distance calculation unit 42 calculates the electric charge amount Q2s using the acquired electric charge amounts Q1sd, Q2sd, and electric charge amount Qb. The method by which the distance calculation unit 42 calculates the electric charge amount Q2s is the same as when the pixel 321 of the range image pickup device 1 includes the three electric charge accumulation units CS1 to CS3 in this modification.

[0120] As described above, the distance image capturing device 1 of this embodiment includes a light source unit 2, a light receiving unit 3, and a distance image processing unit 4. The light source unit 2 irradiates a measurement space containing an object OB with a light pulse PO. The light receiving unit 3 includes pixels 321 and a vertical scanning circuit 323 (an example of a drive circuit). Each pixel 321 includes a photoelectric conversion element PD and multiple charge accumulation units CS. The vertical scanning circuit 323 distributes and accumulates electric charge in each of the charge accumulation units CS in each pixel 321 at a predetermined timing synchronized with the irradiation of the light pulse PO. The distance image processing unit 4 determines the measured distance to the object OB using the amount of electric charge accumulated in each charge accumulation unit CS. The distance image processing unit 4 acquires waveform information 440. The waveform information 440 indicates the degree of waveform rounding in a rectangular signal used in signal processing to determine the measured distance. Based on the acquired waveform information 440, distance image processor 4 corrects the amount of charge (charges Q1#, Q2#) accumulated in each charge storage unit CS to the amount of charge (charges Q1h, Q2h) that would be accumulated if the rectangular signal waveform were not rounded. Distance image processor 4 determines the measured distance using the corrected amount of charge.

[0121] As a result, the distance image pickup device 1 of the embodiment can correct the charge amounts (charge amounts Q1#, Q2#) that include errors due to waveform rounding to charge amounts (charge amounts Q1h, Q2h) with reduced errors. Therefore, even when the waveform rounding in the rectangular signal is significant, it is possible to calculate the measured distance with high accuracy.

[0122] In the range image capturing device 1 according to the embodiment, the waveform information 440 is a tail ratio indicating the ratio of the second area (area of ​​region Sc) to the first area (area of ​​region Sa+Sb) derived by time integration of signals H1 and H2 (an example of a rectangular signal). The first area is the integral value obtained by integrating rectangular signal H1 (a rectangular signal with no waveform rounding, an example of a "first signal") from the rising edge start time Trs to the falling edge start time Tds. The second area is the integral value obtained by subtracting trailing signal H2 (a rectangular signal with a waveform rounding, an example of a "second signal") from rectangular signal H1, and integrating the result from the rising edge start time Trs to the rising edge end time Tre. Alternatively, the second area is the integral value obtained by integrating trailing signal H2 from the falling edge start time Tds to the falling edge end time Tde. The range image processing unit 4 calculates the electric charges Q1# and Q2#. The charge amount Q1# is the charge amount obtained by subtracting the charge amount Qb corresponding to the external light component from the charge amount Q1 (first charge amount) accumulated in the charge accumulation unit CS1 (first charge accumulation unit). The charge amount Q2# is the charge amount obtained by subtracting the charge amount Qb corresponding to the external light component from the charge amount Q2 (second charge amount) accumulated in the charge accumulation unit CS2 (second charge accumulation unit). The charge accumulation unit CS1 is the charge accumulation unit CS that first accumulates the charge amount corresponding to the reflected light RL. The charge accumulation unit CS2 is the charge accumulation unit CS that accumulates the charge amount corresponding to the reflected light RL next to the charge accumulation unit CS1. The distance image processing unit 4 calculates the charge amount Q2s (first corrected charge amount) using the waveform information 440. The charge amount Q2s is the charge amount that is not accumulated in the charge accumulation unit CS1 but accumulated in the charge accumulation unit CS2 due to the rounding of the rectangular signal, out of the charge amount Q2# corresponding to the reflected light RL accumulated in the charge accumulation unit CS2. Distance image processor 4 uses charge Q2s to calculate charge Q1h by correcting charge Q1#, for example, as in equations (6) and (11). Distance image processor 4 also uses charge Q2s to calculate charge Q2h by correcting charge Q2#, for example, as in equation (12).

[0123] As a result, the distance image pickup device 1 of the embodiment can calculate the amount of charge Q2s that was not accumulated in the charge accumulation unit CS1 but accumulated in the charge accumulation unit CS2 due to waveform dulling. Therefore, the amount of charge that would have originally accumulated in the charge accumulation unit CS1 can be corrected to return to the original amount, making it possible to calculate the measured distance with high accuracy.

[0124] Furthermore, in the range image pickup device 1 of the embodiment, the pixel 321 includes three charge accumulation units CS1 to CS3. The range image processor 4 controls the timing of charge accumulation so that charge corresponding to reflected light RL is not accumulated in one of the three charge accumulation units CS (charge accumulation unit CS3, an example of an "external light accumulation unit") other than charge accumulation units CS1 and CS2. The range image processor 4 sets the amount of charge accumulated in charge accumulation unit CS3 to charge amount Qb corresponding to the external light component. This makes it possible for the range image pickup device 1 of the embodiment to calculate the amounts of charge Q1, Q2, and Qb accumulated by dividing the reflected light RL within one frame. This makes it possible to shorten the processing time compared to determining the measured distance by performing accumulation and readout processes in two frames related to the first and second processes.

[0125] Furthermore, in the range image pickup device 1 of the embodiment, the pixel 321 includes three charge storage units CS1 to CS3. The waveform information 440 is a tail ratio indicating the ratio of a second area (area of ​​region Sc) to a first area (area of ​​region Sa+Sb) derived by time integration of signals H1 and H2 (an example of a rectangular signal). The first area is an integral value obtained by integrating rectangular signal H1 (a rectangular signal with no waveform rounding, an example of a "first signal") from the rising edge start time Trs to the falling edge start time Tds. The second area is an integral value obtained by subtracting a tail signal H2 (a rectangular signal with a waveform rounding, an example of a "second signal") from rectangular signal H1, and integrating the result from the rising edge start time Trs to the rising edge end time Tre. Alternatively, the second area is an integral value obtained by integrating tail signal H2 from the falling edge start time Tds to the falling edge end time Tde. The distance image processing unit 4 calculates electric charges Q1#, Q2#, and Q3#. The electric charge Q1# is obtained by subtracting the electric charge Qb corresponding to the external light component from the electric charge Q1 (first electric charge) accumulated in the charge accumulation unit CS1 (first charge accumulation unit). The electric charge Q2# is obtained by subtracting the electric charge Qb corresponding to the external light component from the electric charge Q2 (second electric charge) accumulated in the charge accumulation unit CS2 (second charge accumulation unit). The electric charge Q3# is obtained by subtracting the electric charge Qb corresponding to the external light component from the electric charge Q3 (third electric charge) accumulated in the charge accumulation unit CS3 (third charge accumulation unit). The electric charge accumulation unit CS1 is the charge accumulation unit CS in which the electric charge corresponding to the reflected light RL is accumulated first. The electric charge accumulation unit CS2 is the charge accumulation unit CS in which the electric charge corresponding to the reflected light RL is accumulated next after the electric charge accumulation unit CS1. Charge accumulation unit CS3 is the charge accumulation unit CS in which the amount of charge corresponding to reflected light RL is accumulated next after charge accumulation unit CS2. Distance image processing unit 4 calculates charge amount Q2s (first corrected charge amount) using waveform information 440. Distance image processing unit 4 calculates charge amount Q3# (second corrected charge amount) using waveform information 440. Charge amount Q2s is the amount of charge Q2# corresponding to reflected light RL accumulated in charge accumulation unit CS2 that was not accumulated in charge accumulation unit CS1 due to the distortion of the rectangular signal, but was accumulated in charge accumulation unit CS2. Charge amount Q3# is the amount of charge that was not accumulated in charge accumulation unit CS2 due to the distortion of the rectangular signal, but was accumulated in charge accumulation unit CS3.Distance image processor 4 uses charge Q2s to calculate charge Q1h by correcting charge Q1#, for example, as in equations (6) and (11). Distance image processor 4 also uses charge Q2s and Q3# to calculate charge Q2h by correcting charge Q2#, for example, as in equation (7).

[0126] As a result, the range image pickup device 1 of the embodiment can calculate the amount of charge Q3# that has accumulated in the charge accumulation unit CS3 even if charge corresponding to the reflected light RL is accumulated in the charge accumulation unit CS3, where charge corresponding to the reflected light RL is not expected to be accumulated due to waveform dulling. Therefore, the amount of charge that would have originally accumulated in the charge accumulation unit CS2 can be corrected to return to the original amount, making it possible to calculate the measured distance with high accuracy.

[0127] Furthermore, in the range image pickup device 1 of the embodiment, the pixel 321 has four charge accumulation units CS1 to CS4. The range image processor 4 controls the timing of charge accumulation so that charge corresponding to reflected light RL is not accumulated in one of the four charge accumulation units CS1 to CS4 (charge accumulation unit CS4, an example of an "external light accumulation unit") other than charge accumulation units CS1 to CS3. The range image processor 4 sets the amount of charge accumulated in charge accumulation unit CS4 to charge amount Qb corresponding to the external light component. This makes it possible for the range image pickup device 1 of the embodiment to calculate the amounts of charge Q1, Q2, Q3, and Qb accumulated by dividing the reflected light RL within one frame. Therefore, the processing time can be shortened compared to when the measured distance is determined by performing accumulation and readout processes in two frames related to the first and second processes.

[0128] (Effects of the embodiment) Here, the effect of the range image pickup device 1 of the embodiment will be described with reference to FIG. 13. FIG. 13 is a diagram illustrating the effect of the embodiment. FIG. 13 shows the relationship between the actual distance (real distance) and the measured distance. The horizontal axis of FIG. 13 represents the actual distance, and the vertical axis represents the measured distance. The distance here is the distance to the object OB. In FIG. 13, the measured distance without correction, indicated by the black circles, is the distance calculated, for example, by substituting the electric charge amounts Q1 to Q3 into equation (1). The measured distance with correction, indicated by the black triangles, is the distance calculated using the electric charge amounts Q1h and Q2h corrected using waveform information 440, for example, as in equations (6) and (7). As shown in this figure, the measured distance with correction matches the actual distance. On the other hand, the measured distance without correction does not match the actual distance and is a value that includes an error. That is, in the range image pickup device 1 of the embodiment, by determining the measured distance using the waveform information 440, it is possible to calculate a value closer to the actual distance.

[0129] (Modification of the embodiment) FIG. 14 is a diagram illustrating the characteristics of two time windows in a modified example of the embodiment. The characteristics here indicate the correspondence between the actual distance and the measured distance. The horizontal axis of FIG. 14 indicates the actual distance, and the vertical axis indicates the measured distance. Characteristic L0 indicates the ideal relationship between the actual distance and the measured distance. Characteristic L1 indicates the relationship between the actual distance and the measured distance in the first time window. Characteristic L2 indicates the relationship between the actual distance and the measured distance in the second time window. As shown in the example of this figure, the correspondence between the actual distance and the measured distance in one time window often differs from that in another time window. For this reason, when waveform information 440 that can be used to perform accurate correction in one time window is used to correct the distance in another time window, accurate correction is not necessarily possible.

[0130] To address this issue, in this modification, waveform information 440 for each time window is created in advance and stored in the storage unit 44. This makes it possible to use the waveform information 440 corresponding to the time window even if the degree of deviation (error) between the measured distance and the actual distance differs for each time window, and to calculate the distance easily and accurately.

[0131] The range image capture device 1 and range image processing unit 4 in the above-described embodiment may be implemented in whole or in part by a computer. In this case, a program for implementing these functions may be recorded on a computer-readable recording medium and then loaded and executed by a computer system. Note that the term "computer system" as used herein includes hardware such as an OS and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into a computer system. Furthermore, the term "computer-readable recording medium" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within a computer system acting as a server or client. The program may also be designed to implement some of the above-described functions, or may be capable of implementing the above-described functions in combination with a program already stored in the computer system, or may be implemented using a programmable logic device such as an FPGA.

[0132] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Explanation of symbols]

[0133] 1...Distance image capturing device 2...Light source section 3...Light receiving section 32...Distance image sensor 321...pixels 323...Vertical scanning circuit 4...Distance image processing section 41...Timing control section 42...Distance calculation section 43...Measurement control section 44...Storage section 440…Waveform information CS…Charge storage section PO...light pulse

Claims

1. a light source unit that irradiates a measurement space in which a subject is present with a light pulse; a light receiving unit including pixels each including a photoelectric conversion element that generates an electric charge according to incident light and a plurality of charge accumulation units that accumulate the electric charge, and a pixel drive circuit that distributes and accumulates the electric charge in each of the charge accumulation units in the pixel at a predetermined timing synchronized with the irradiation of the light pulse; a distance image processing unit that determines a measured distance to the subject using the amount of charge accumulated in each of the charge accumulation units; Equipped with the distance image processing unit acquires waveform information indicating the degree of waveform rounding when a waveform corresponding to a rectangular signal used in signal processing until the measurement distance is determined is rounded to form a trailing waveform, corrects the amount of charge accumulated in each of the charge accumulation units based on the acquired waveform information to the amount of charge that would be accumulated if the trailing waveform were not rounded, and determines the measurement distance using the corrected amount of charge; The waveform information is a tail ratio indicating the ratio of a second area to a first area derived by integrating the rectangular signal over time, the first area being an integral value obtained by integrating a first signal, which is the rectangular signal without the tail waveform rounding, from a rising edge start time to a falling edge start time, and the second area being an integral value obtained by subtracting a second signal, which is the rectangular signal with the tail waveform rounding, from the first signal, from a rising edge start time to a rising edge end time, and integrating the subtracted value, or an integral value obtained by integrating the second signal from a falling edge start time to a falling edge end time, the distance image processing unit calculates, for a first charge accumulation unit among the plurality of charge accumulation units that first accumulates an amount of charge corresponding to the reflected light of the light pulse reflected by the subject, and a second charge accumulation unit that accumulates charge next to the first charge accumulation unit, a first distance calculation charge amount by subtracting an amount of charge corresponding to the external light component from the first charge amount accumulated in the first charge accumulation unit, and a second distance calculation charge amount by subtracting an amount of charge corresponding to the external light component from the second charge amount accumulated in the second charge accumulation unit; calculates, using the waveform information, a first correction charge amount that is not accumulated in the first charge accumulation unit but accumulated in the second charge accumulation unit due to rounding of the footing waveform, of the second distance calculation charge amount, and corrects the first distance calculation charge amount and the second distance calculation charge amount using the first correction charge amount; Range imaging device.

2. The pixel includes three of the charge storage units, the distance image processing unit controls the timing of accumulating charges in the charge accumulation unit for accumulating external light, which is a charge accumulation unit different from the first charge accumulation unit and the second charge accumulation unit, among the three charge accumulation units, so that charges corresponding to the reflected light are not accumulated in the charge accumulation unit for accumulating external light, and sets the amount of charge accumulated in the charge accumulation unit for accumulating external light to an amount of charge corresponding to the external light component.

2. The distance imaging device according to claim 1.

3. The pixel includes three of the charge storage units, The waveform information is a tail ratio indicating the ratio of a second area to a first area derived by integrating the rectangular signal over time, the first area being an integral value obtained by integrating a first signal, which is the rectangular signal without a tail waveform, from a rising edge start time to a falling edge start time, and the second area being an integral value obtained by subtracting a second signal, which is the rectangular signal with a tail waveform, from the first signal, from a rising edge start time to a rising edge end time, and integrating the subtracted value, or an integral value obtained by integrating the second signal from a falling edge start time to a falling edge end time, The distance image processing unit calculates a first distance calculation charge amount obtained by subtracting an amount of charge corresponding to an external light component from a first charge amount accumulated in the first charge accumulation unit, a second distance calculation charge amount obtained by subtracting an amount of charge corresponding to an external light component from a second charge amount accumulated in the second charge accumulation unit, and a third distance calculation charge amount obtained by subtracting an amount of charge corresponding to an external light component from a third charge amount accumulated in the third charge accumulation unit, for a first charge accumulation unit that first accumulates an amount of charge corresponding to light reflected from the object when the light pulse is reflected by the object, a second charge accumulation unit that accumulates an amount of charge corresponding to an external light component from a first charge amount accumulated in the first charge accumulation unit, and a third distance calculation charge amount obtained by subtracting an amount of charge corresponding to an external light component from a second charge amount accumulated in the third charge accumulation unit. calculates a third distance calculation charge amount by subtracting the electric charge amount from the first electric charge amount, calculates a first correction electric charge amount, which is a part of the second distance calculation charge amount that has not been accumulated in the first charge accumulation unit but has been accumulated in the second charge accumulation unit due to the rounding of the footing waveform, using the waveform information; calculates a second correction electric charge amount, which is a part of the third distance calculation charge amount that has not been accumulated in the second charge accumulation unit but has been accumulated in the third charge accumulation unit due to the rounding of the footing waveform, corrects the first distance calculation charge amount using the first correction electric charge amount; and corrects the second distance calculation charge amount using the first correction electric charge amount and the second correction electric charge amount.

2. The distance imaging device according to claim 1.

4. The pixel includes four of the charge storage units, the distance image processing unit controls the timing at which charges are accumulated in the charge accumulation unit for accumulating external light so that charges corresponding to the reflected light are not accumulated in a charge accumulation unit for accumulating external light that is different from the first charge accumulation unit, the second charge accumulation unit, and the third charge accumulation unit, and sets the amount of charge accumulated in the charge accumulation unit for accumulating external light to an amount of charge corresponding to the external light component.

4. The distance imaging device according to claim 3.

5. a light receiving unit having a light source unit that irradiates a measurement space in which a subject exists with a light pulse, pixels each having a photoelectric conversion element that generates an electric charge according to the incident light and a plurality of charge accumulation units that accumulate the electric charge, and a pixel drive circuit that distributes and accumulates the electric charge in each of the charge accumulation units in the pixel at a predetermined timing synchronized with the irradiation of the light pulse, and a distance image processing unit that determines a measurement distance to the subject using the amount of electric charge accumulated in each of the charge accumulation units, the distance image processing unit acquires waveform information indicating the degree of waveform rounding when a waveform corresponding to a rectangular signal used in signal processing until the measurement distance is determined is rounded to form a trailing waveform, corrects the amount of charge accumulated in each of the charge accumulation units based on the acquired waveform information to the amount of charge that would be accumulated if the trailing waveform were not rounded, and determines the measurement distance using the corrected amount of charge; The waveform information is a tail ratio indicating the ratio of a second area to a first area derived by integrating the rectangular signal over time, the first area being an integral value obtained by integrating a first signal, which is the rectangular signal without the tail waveform rounding, from a rising edge start time to a falling edge start time, and the second area being an integral value obtained by subtracting a second signal, which is the rectangular signal with the tail waveform rounding, from the first signal, from a rising edge start time to a rising edge end time, and integrating the subtracted value, or an integral value obtained by integrating the second signal from a falling edge start time to a falling edge end time, the distance image processing unit calculates, for a first charge accumulation unit among the plurality of charge accumulation units that first accumulates an amount of charge corresponding to the reflected light of the light pulse reflected by the subject, and a second charge accumulation unit that accumulates charge next to the first charge accumulation unit, a first distance calculation charge amount by subtracting an amount of charge corresponding to the external light component from the first charge amount accumulated in the first charge accumulation unit, and a second distance calculation charge amount by subtracting an amount of charge corresponding to the external light component from the second charge amount accumulated in the second charge accumulation unit; calculates, using the waveform information, a first correction charge amount that is not accumulated in the first charge accumulation unit but accumulated in the second charge accumulation unit due to rounding of the footing waveform, of the second distance calculation charge amount, and corrects the first distance calculation charge amount and the second distance calculation charge amount using the first correction charge amount; Range imaging method.

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