Imaging device, imaging method, and computer program

Abstract

The present invention provides an imaging device capable of improving image quality when there are changes in brightness within a single frame. [Solution] The imaging device includes a counter for counting photons for each pixel, a first determination means for determining whether the count value of the counter has reached a predetermined value within a predetermined determination period from the start of exposure, a second determination means for determining whether there is a change in brightness during the exposure period based on the determination result of the first determination means and the count value of the counter, a determination means for determining the determination period based on the maximum value of the count value, and a correction means for correcting the count value when the second determination means determines that there is a change in brightness.

Description

Technical Field

[0007] ,

[0001] The present invention relates to an imaging device, an imaging method, a computer program, and the like.

Background Art

[0002] In recent years, an imaging device has been proposed that digitally counts the number of photons arriving at an avalanche photodiode (APD) and performs photoelectric conversion by outputting the count value from each pixel.

[0003] Patent Document 1 describes an imaging device including an APD, a detection unit that detects an avalanche current, and a switch disposed between the APD and the detection unit. Further, Patent Document 1 describes a reset unit that applies a predetermined potential to an input unit of the switch to reset a node between the switch and the detection unit.

[0004] In Patent Document 1, by resetting the reset unit with a clock pulse at a constant period, it is possible to suppress the power consumption of the imaging device even when photons are incident on the APD at a high frequency. Furthermore, it is possible to obtain accurate signal information in which the linearity between the number of photons incident on the APD and the count value of the photons detected by the imaging device is maintained.

[0005] Also, when the count values corresponding to each exposure time reach a predetermined threshold at a plurality of exposure times shorter than the maximum exposure time, the operating voltage of the APD is changed. Thereby, the counting of the number of photons is paused, and the estimated value of the count is calculated and substituted to reduce the power consumption.

[0006] Here, the estimated value of the count is a count value that is expected to be obtained when the APD is exposed for the length of the maximum exposure time, based on the count value when the count is paused at an exposure time shorter than the maximum exposure time.

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Japanese Patent Publication No. 2021-019281 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, in the prior art disclosed in Patent Document 1 mentioned above, if the threshold is reached during an exposure time shorter than the maximum exposure time, the count is paused in the middle of the frame and an estimated count value is calculated. Therefore, if there is an increase in brightness in the middle of the frame, the estimated count value may become smaller than the count value at maximum exposure.

[0009] In other words, bright subjects may be underestimated in terms of brightness. In particular, when photographing light sources whose brightness changes rapidly and periodically, flicker may occur, causing the light source area of ​​the captured image to repeatedly flicker unintentionally, resulting in poor image visibility.

[0010] One of the objectives of the present invention is to provide an imaging device capable of improving image quality when there is a change in brightness within a single frame, in order to solve the above-mentioned problems. [Means for solving the problem]

[0011] To solve the above problems, the imaging apparatus of the embodiment of the present invention is A counter that counts photons for each pixel, A first determination means for determining whether the count value of the counter has reached a predetermined value within a predetermined determination period from the start of exposure, A second determination means determines whether or not there is a change in brightness during the exposure period based on the determination result by the first determination means and the count value of the counter, A determination means for determining the determination period based on the maximum value of the count value, A correction means for correcting the count value when the second determination means determines that there is a change in brightness, It is characterized by having the following features. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an imaging device that can improve image quality when there is a change in brightness within a single frame. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows an example configuration of a photoelectric conversion element according to Embodiment 1 of the present invention. [Figure 2] This figure shows an example configuration of the sensor substrate 11 according to Embodiment 1 of the present invention. [Figure 3] This figure shows an example configuration of a circuit board 21 according to Embodiment 1 of the present invention. [Figure 4] Figures 2 and 3 show examples of equivalent circuits for the photoelectric conversion unit 102 and the signal processing circuit 103 corresponding to the photoelectric conversion unit 102. [Figure 5] This figure schematically illustrates an example of the relationship between the operation of the APD201 and the output signal according to Embodiment 1 of the present invention. [Figure 6] This is a timing chart illustrating an example of the operation of the signal processing circuit 103 according to Embodiment 1 of the present invention. [Figure 7] This figure shows an example of the relationship between the exposure time for each pixel 101 included in the photoelectric conversion element 100 according to Embodiment 1 of the present invention and the count value of the counter circuit 211. [Figure 8] This figure shows an example of the relationship between the exposure time for each pixel 101 and the count value of the counter circuit 211 according to Embodiment 1 of the present invention. [Figure 9] This is a functional block diagram showing an example configuration of the imaging device 900 according to Embodiment 1. [Figure 10] This flowchart shows an example of brightness increase detection and correction processing in Embodiment 1. [Figure 11] (A) and (B) are diagrams illustrating examples of the relationship between exposure time and count distribution within one frame, used to explain the processing flow of the flowchart in Figure 10. [Figure 12](A) and (B) are diagrams showing other examples of the relationship between the exposure time and the count distribution within one frame for explaining the processing flow of the flowchart in FIG. 10. [Figure 13] It is a flowchart showing an example of luminance increase detection and correction processing in Embodiment 2. [Figure 14] (A) and (B) are diagrams showing an example of the relationship between the exposure time and the count distribution within one frame for explaining the processing flow of the flowchart in FIG. 13. [Figure 15] It is a flowchart showing an example of luminance increase detection and correction processing in Embodiment 2. [Figure 16] It is a diagram showing an example of the relationship between the exposure time and the count distribution within one frame for explaining the processing flow of step S1501 of the flowchart in FIG. 15

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments. In each figure, the same members or elements are given the same reference numerals, and duplicate explanations are omitted or simplified.

[0015] <Embodiment 1> FIG. 1 is a diagram showing a configuration example of a photoelectric conversion element according to Embodiment 1 of the present invention. In the present embodiment, the photoelectric conversion element 100 will be described by taking, as an example, an imaging device in which two substrates, a sensor substrate 11 and a circuit substrate 21, are laminated and the substrates are electrically connected to each other, and the photoelectric conversion unit has a so-called laminated structure. The circuit substrate 21 includes a circuit region 22 that processes signals detected in the pixel region 12.

[0016] FIG. 2 is a diagram showing a configuration example of the sensor substrate 11 according to Embodiment 1 of the present invention. The pixel region 12 of the sensor substrate 11 includes pixels 101 arranged two-dimensionally in a plurality of rows and columns.

[0017] Each pixel 101 includes a photoelectric conversion unit 102 containing an avalanche photodiode (hereinafter referred to as APD). The number of rows and columns of the pixel array forming the pixel region 12 is not particularly limited.

[0018] Figure 3 shows an example of the configuration of a circuit board 21 according to Embodiment 1 of the present invention. The circuit board 21 includes a signal processing circuit 103, a vertical scanning circuit section 110, a horizontal scanning circuit section 111, a readout circuit 112, a signal line 113, an output circuit 114, and a control section 115.

[0019] The signal processing circuit 103 acquires and processes the electrical signals output from the photoelectric conversion unit 102 of each pixel. The signal processing circuit 103 includes a counter and memory associated with each pixel.

[0020] The signal processing circuit 103 stores the count value obtained by counting the number of photons in memory. Based on the control pulse received from the vertical scanning circuit unit 110, the signal processing circuit 103 outputs the counted value.

[0021] The vertical scanning circuit unit 110 receives control pulses supplied from the control unit 115 and supplies control pulses to the signal processing circuit 103 of each pixel.

[0022] The horizontal scanning circuit unit 111 receives control pulses supplied from the control unit 115 and supplies control pulses to each pixel column in order to sequentially select each column via the readout circuit 112 and the signal processing circuit 103. The control pulses of the horizontal scanning circuit unit 111 are pulses for reading out the pixel signal, which includes the count value of each pixel, held in the memory of the signal processing circuit 103.

[0023] The readout circuit 112 reads out pixel signals, including the count value which is the output of the signal processing circuit 103, column by column via the signal line 113, based on the control pulse generated by the vertical scanning circuit unit 110.

[0024] The readout circuit 112 has a shift register and an address decoder that connect multiple rows as a single unit. Therefore, the readout circuit 112 achieves high-speed readout by reading out the pixel signals of multiple rows at once.

[0025] In particular, in imaging devices that digitally count the number of photons incident on the APD and output the count value from the pixel as a photoelectrically converted digital signal, the operation of the counter circuit that digitally counts the number of photons takes time.

[0026] Therefore, high-speed pixel signal reading is achieved by simultaneously reading pixel signals from multiple rows. In this embodiment, the reading circuit 112 reads, for example, the pixel signals from pixels in the first row and the pixel signals from pixels in the second row simultaneously, column by column.

[0027] The signal line 113 outputs pixel signals, including count values, from the signal processing circuit 103 of the pixels where the column selected by the horizontal scanning circuit unit 111 and one or more rows selected by the vertical scanning circuit unit 110 intersect. The pixel signals output to the signal line 113 are output to the outside of the photoelectric conversion element 100 via the readout circuit 112 and the output circuit 114.

[0028] The control unit 115 controls the photoelectric conversion element 200. Specifically, the control unit 115 supplies control pulses to the vertical scanning circuit unit 110 and the horizontal scanning circuit unit 111 in order to selectively read out pixel signals from each pixel.

[0029] The control unit 115 sets threshold information (count threshold) that serves as the judgment criterion and exposure time information that indicates the timing for performing the judgment to the count judgment circuit described later. The exposure time information may also be information related to the timing of the control pulses mentioned above.

[0030] As shown in Figures 2 and 3, multiple signal processing circuits 103 are arranged in the area that overlaps with the pixel area 12 in a plan view. Then, the vertical scanning circuit section 110, the horizontal scanning circuit section 111, the readout circuit 112, the output circuit 114, and the control unit 115 are arranged so as to overlap with the peripheral area (non-pixel area) between the edge of the sensor substrate 11 and the edge of the pixel area 12 in a plan view.

[0031] The vertical scanning circuit 110 receives control pulses supplied from the control unit 115 and supplies control pulses to each pixel. The vertical scanning circuit 110 is composed of a shift register and an address decoder that connect multiple rows as a single unit, and high-speed reading is achieved by reading multiple rows at once.

[0032] In other words, the vertical scanning circuit section 110, which functions as a readout circuit for reading pixel signals from pixels, simultaneously reads out pixel signals from pixels in the first row and pixel signals from pixels in the second row.

[0033] Note that the arrangement of the signal line 113, the read circuit 112, and the output circuit 114 is not limited to Figure 3. For example, the signal line 113 may be arranged so as not to extend in the row direction, and the read circuit 112 may be placed at the end of the signal line 113.

[0034] Furthermore, the signal processing circuit 103 does not necessarily need to be provided in one unit for each photoelectric conversion unit; a single signal processing unit may be shared by multiple photoelectric conversion units, and sequential signal processing may be performed.

[0035] Figure 4 shows an example of the equivalent circuits of the photoelectric conversion unit 102 and the signal processing circuit 103 corresponding to the photoelectric conversion unit 102, as seen in Figures 2 and 3.

[0036] The APD201 generates charge pairs corresponding to incident light through photoelectric conversion. One of the two nodes of the APD201 is connected to a power line that supplies the drive voltage VL (first voltage).

[0037] Furthermore, the other of the two nodes of the APD201 is connected to a power line supplied with a drive voltage VH (second voltage) higher than voltage VL via a quench element 202. In Figure 4, one node of the APD201 is the anode, and the other node of the APD is the cathode.

[0038] A reverse bias voltage is supplied to the anode and cathode of the APD201, causing it to perform avalanche multiplication. This voltage supply causes the charge generated by the incident light to undergo avalanche multiplication, resulting in the generation of an avalanche current.

[0039] Furthermore, the APD201's operating mode is classified into two types depending on the value of the reverse bias voltage used to operate it. The two modes are Geiger mode, in which the Anode and cathode voltage difference is greater than the breakdown voltage, and Linear mode, in which the Anode and cathode voltage difference is near or below the breakdown voltage.

[0040] An APD that operates in Geiger mode is called a SPAD (Single Photon Avalanche Diode). In the case of a SPAD, for example, the voltage VL (first voltage) is -30V and the voltage VH (second voltage) is 1V.

[0041] The quench element 202 is connected to the power line to which the drive voltage VH is supplied and to one of the nodes, either the anode or cathode, of the APD201. The quench element 202 functions as a load circuit (quench circuit) during signal multiplication by avalanche multiplication, suppressing the voltage supplied to the APD201 and thereby suppressing avalanche multiplication (quench operation).

[0042] Furthermore, the quench element 202 has the function of returning the voltage supplied to the APD201 to the drive voltage VH by supplying current to compensate for the voltage drop caused by the quench operation (recharge operation).

[0043] In this embodiment, the quench element 202 is composed of a MOS transistor, and the on / off state of the quench element 202 is controlled by a control pulse CLK connected to the gate of the quench element. The control pulse CLK is controlled by a signal generation unit in the control unit 115.

[0044] The waveform shaping unit 210 shapes the voltage change at the cathode of the APD201 that occurs when the APD201 detects a photon, and outputs a pulse signal. For example, an inverter circuit can be used as the waveform shaping unit 210.

[0045] Figure 4 shows an example where one inverter is used as the waveform shaping unit 210, but a circuit with multiple inverters connected in series may also be used, or other circuits that have a waveform shaping effect may be used.

[0046] The counter circuit 211 is a counter that performs a count step to count photons for each pixel, and it counts the pulse signal output from the waveform shaping unit 210 and holds the count value.

[0047] Furthermore, when the counter circuit 211 receives a control pulse STOP from the count determination circuit 212 via the drive line 217, it stops counting and continues to hold the count value at that time. In addition, when the control pulse RES is supplied from the vertical scanning circuit unit 110 via the drive line 214, the count value held in the counter circuit 211 is reset.

[0048] The count determination circuit 212 is supplied with the count value held by the counter circuit 211 via the drive line 216. In addition, the count determination circuit 212 is supplied with a control pulse φt from the control unit 115 via the drive line 218.

[0049] The count determination circuit 212, upon receiving the control pulse φt, compares the count value with a predetermined threshold. If the count value exceeds the threshold, it supplies a control pulse STOP to the counter circuit 211 via the drive line 217.

[0050] Furthermore, the count determination circuit 212 functions as a first determination means that performs a first determination step of determining whether the counter's count value has reached a specified value (threshold) within a predetermined determination period from the start of exposure.

[0051] Furthermore, exposure time information (exposure time when the count threshold is exceeded) and the count value at the timing of the control pulse φt are output to the selection circuit 213 via the drive line 219. The timing chart of the control pulse φt will be described later using Figure 6.

[0052] The selection circuit 213 receives a control pulse SEL from the vertical scanning circuit section 110 in Figure 3 via the drive line 215 (not shown in Figure 3) in Figure 4, which switches the electrical connection between the count determination circuit 212 and the signal line 113. The selection circuit 213 includes, for example, a buffer circuit for outputting a signal, and outputs the output signal from the count determination circuit 212 to the signal line 113.

[0053] Furthermore, switches such as transistors may be placed between the quench element 202 and the APD201, or between the photoelectric conversion unit 102 and the signal processing circuit 103, to switch the electrical connections. Similarly, the supply of voltage VH or voltage VL to the photoelectric conversion unit 102 may be electrically switched using switches such as transistors.

[0054] Figure 5 schematically shows an example of the relationship between the operation of the APD201 and the output signal according to Embodiment 1 of the present invention. Figure 4 schematically shows the relationship between the control pulse CLK to the quench element 202, the voltage at node A, the voltage at node B, and the count value of the counter circuit 211 in the photoelectric conversion element.

[0055] When the control pulse CLK is at a high level, the drive voltage VH is less likely to be supplied to the APD201, and when the control pulse CLK is at a low level, the drive voltage VH is supplied to the APD201.

[0056] A high level control pulse CLK is, for example, 1V, and a low level control pulse CLK is, for example, 0V. When the control pulse CLK is high level, the quench element 202 is turned off, and when the control pulse CLK is low level, the quench element 202 is turned on.

[0057] The resistance of the quench element 202 when the control pulse CLK is at a high level is higher than the resistance of the quench element 202 when the control pulse CLK is at a low level.

[0058] When the control pulse CLK is at a high level, even if avalanche multiplication occurs in the APD201, recharge operation is less likely to occur, and the voltage supplied to the APD201 becomes below the breakdown voltage of the APD201. Therefore, the avalanche multiplication operation in the APD201 stops.

[0059] At time t1, the control pulse CLK changes from a high level to a low level, the quench element 202 turns on, and the recharge operation of APD201 begins. As a result, the cathode voltage of APD201 transitions to a high level.

[0060] Then, the difference in voltage applied to the anode and cathode of the APD201 puts the APD201 into an avalanche multiplication state. The cathode voltage is the same as the voltage of node A. Subsequently, when the cathode voltage transitions from a low level to a high level, the voltage of node A becomes greater than or equal to the threshold at time t2.

[0061] When the voltage at node A exceeds the threshold, the pulse signal output from node B of the waveform shaping unit 210 is inverted, changing from a high level to a low level.

[0062] Once recharging is complete, a voltage of (drive voltage VH - drive voltage VL) is applied to APD201. Then, between time t2 and time t3, the control pulse CLK becomes high, and the quench element 202 turns off.

[0063] Next, at time t3, when a photon is incident on APD201, avalanche multiplication occurs in APD201, an avalanche multiplication current flows through the quench element 202, and the cathode voltage, i.e., the voltage at node A, drops.

[0064] If the voltage at nodeA falls below the threshold during its voltage drop, the voltage at nodeB changes from a low level to a high level. In other words, the portion of the output waveform at nodeA that exceeds the threshold is reshaped by the waveform shaping unit 210 and output as a low-level signal at nodeB.

[0065] Then, the rising edge of nodeB from low level to high level is counted by the counter circuit 211, and the count value of the counter signal output from the counter circuit 211 increases by 1 LSB.

[0066] Although photons are incident on APD201 between time t3 and time t4, the quench element 202 is in the off state, and the voltage applied to APD201 is not a voltage difference that allows for avalanche multiplication, so the voltage level of node A does not exceed the judgment threshold.

[0067] At time t4, the control pulse CLK changes from a high level to a low level, and the quench element 202 turns on. Consequently, a current flows through node A to compensate for the voltage drop from the drive voltage VL, and the voltage at node A returns to its original voltage level. At this time, at time t5, the voltage at node A exceeds the threshold, so the pulse signal at node B inverts, changing from a high level to a low level.

[0068] Subsequently, at time t6, the control pulse CLK changes from a low level to a high level, and node A settles back to its original voltage level. In principle, the period during which the control pulse CLK is low only needs to be set to be longer than the period during which node A transitions from low to high level.

[0069] In Figure 5, the period during which the control pulse CLK is at a low level is set to be the same as the period during which nodeA transitions from a low level to a high level. This allows the frequency of the control pulse CLK to be set higher, thereby reducing the effect of the "nonlinear relationship between the number of output signals and the number of input signals," which will be discussed later.

[0070] Subsequently, as explained in the sections from time t1 to t6, the voltages of each node and signal line change in response to the control pulse CLK and the incidence of photons. However, when the APD recharge frequency is controlled by the control pulse CLK, the relationship between the number of input signals and the number of output signals is not linear. The number of input signals refers to the number of photons incident on the APD, and the number of output signals refers to the photon count value detected by the imaging device.

[0071] In SPADs, when avalanche breakdown occurs, secondary photons are emitted, causing emission crosstalk with adjacent pixels. However, if we ignore the effects of emission crosstalk, the relationship between the number of output signals and the number of input signals can be theoretically derived as follows.

[0072] Specifically, when the number of input signals is Nph, the number of output signals is Nct, the frequency of the control pulse CLK (number of CLK pulses per unit time) is f, and the exposure time is T, the following equation 1 holds true.

number

[0073] Figure 6 is a timing chart illustrating an example of the operation of the signal processing circuit 103 according to Embodiment 1 of the present invention. In this embodiment, the exposure time of each pixel is set by the control unit 115 to a predetermined exposure time represented by T / (n to the power of (m-1)).

[0074] T is the maximum exposure time within one frame, and m is any integer such that m ≥ 1. Figure 6 shows the timing chart when 1 ≤ m ≤ 4. Therefore, the drive line 218 in Figure 4 is supplied with a control pulse φt that becomes high only at the moment the exposure time determined by t = T / (n to the power of (m-1)) is reached.

[0075] Furthermore, if the count value of the counter circuit 211 exceeds a predetermined count threshold at the moment of exposure time T / (n^(m-1)) for four exposure times when m=1, 2, 3, and 4, the photoelectric conversion element 100 is switched from Geiger mode to linear mode and the APD201 is put into standby mode.

[0076] Once paused, the pulse signal from the waveform shaping unit 210 is not output, and the count of the counter circuit 211 remains unchanged. The count determination circuit 212 then outputs T / (n to the power of (m-1)), which represents the exposure time corresponding to the control pulse φt, and the count value to the selection circuit 213.

[0077] Figure 7 shows an example of the relationship between the exposure time for each pixel 101 included in the photoelectric conversion element 100 according to Embodiment 1 of the present invention and the count value of the counter circuit 211. In Figure 7, as in Figure 6, the control unit 115 sets a predetermined exposure time T / (n to the power of (m-1)), (where 1 ≤ m ≤ 4).

[0078] When the upper limit of the count of the counter circuit 211 is set to Cmax, the count threshold is set to Cmax / n for reasons described later. In Figure 7, it is assumed that the count value of a certain pixel increases in proportion to time.

[0079] As shown in Figure 6, the count determination circuit 212 determines whether the count value exceeds the count threshold at the moment T / (n^(m-1)) in order of shortest exposure time. As shown in Figure 7, when the count value increases, it is determined that the count threshold Cmax / n was not exceeded at T / n^3 and T / n^2, but was exceeded at T / n. Note that n^3 means n to the power of 3, and n^2 means n to the power of 2.

[0080] At this point, when T / n occurs, a control pulse STOP is supplied from the count determination circuit 212 to the counter circuit 211 via the drive line 217, stopping the counter circuit 211 from counting. The count value Cout at T / n and the exposure time T / n are then output from the count determination circuit 212 to the selection circuit 213.

[0081] Table 1 below shows an example of the relationship between the exposure time when the count threshold is exceeded in Embodiment 1 and the exposure time information (Tcode) corresponding to each exposure time. [Table 1]

[0082] Furthermore, while the count determination circuit 212 may output the exposure time T / n directly as time information to the selection circuit 213, as shown in Table 1, it is also possible to determine and output exposure time information (Tcode) corresponding to the exposure time when the count threshold is exceeded. Note that the Tcode shown in Table 1 is just one example of the data format output from the count determination circuit 212, and is not limited to this.

[0083] Furthermore, the count estimate (Cest) shown in Figure 7 is calculated using the formula Cest = Cout × n, assuming that the count increases at the same rate during the exposure time from 0 to T / n and the non-exposure time from T / n to T.

[0084] As mentioned earlier, the above count estimation method assumes that the count increases at the same rate during the exposure time from 0 to T / n and the non-exposure time from T / n to T. Therefore, if the upper limit of the count, Cmax, is reached before the exposure time T / n is reached, the rate of increase during the exposure time from 0 to T / n cannot be estimated correctly, and the accuracy of the count estimation decreases.

[0085] Therefore, in this embodiment, a threshold determination is performed before the upper count limit Cmax is reached in order to maintain the accuracy of the count estimation. Also, when the recharge frequency of the APD is controlled by the control pulse CLK, the relationship between the number of output signals and the number of input signals is not linear, so in this embodiment, linearity correction is performed before the count estimation.

[0086] Figure 8 shows an example of the relationship between the exposure time for each pixel 101 and the count value of the counter circuit 211 according to Embodiment 1 of the present invention. Figure 8 shows how the count increases when the count value becomes equal to the count threshold or the upper count limit at the moment of each exposure time for which threshold determination is performed.

[0087] As described above, in this embodiment, in order to maintain the accuracy of the count estimation, a threshold determination is made before the upper limit of the count, Cmax, is reached. Therefore, the timing of the threshold determination when the count increases at a rate that reaches Cmax at the moment of the maximum exposure time T is defined as t1. Also, the timing of the threshold determination when the count increases at a rate that reaches Cmax at the moment of t1 is defined as t2.

[0088] Here, if the count threshold is Cmax / n, the time it takes to reach Cmax / n when the count increases at a rate that reaches Cmax at the moment of maximum exposure time T is calculated as T × (1 / n), so t1 = T / n.

[0089] Similarly, t2 is calculated as t1 × (1 / n) = T / n^2. In this way, each exposure time used for threshold determination is calculated as T / (n^(m-1)).

[0090] Furthermore, as shown in Figure 4, when the APD recharge frequency is controlled by the control pulse CLK, the relationship between the number of output signals and the number of input signals is not linear, as shown in Equation 1. Therefore, in this embodiment, linearity correction is performed based on the estimated count value calculated by the signal processing circuit 103.

[0091] Here, linearity correction refers to determining the number of input signals Nph from the number of output signals Nct per exposure time using Equation 2 below, where f is the frequency of the control pulse CLK (number of CLK pulses per unit time) and T is the length of the exposure time.

number

[0092] In this embodiment, the input signal number Nph derived by Equation 2 is the number of photons per exposure time for threshold determination. Therefore, the number of photons in one frame exposure time is calculated as Nph × (n to the power of (m-1)).

[0093] Figure 9 is a functional block diagram showing an example configuration of the imaging device 900 according to Embodiment 1. Note that some of the functional blocks shown in Figure 9 are realized by having the CPU 909, which acts as a computer included in the imaging device 900, execute a computer program stored in the memory 910, which acts as a storage medium.

[0094] However, some or all of these may be implemented in hardware. Hardware options include dedicated circuits (ASICs) and processors (reconfigurable processors, DSPs). Furthermore, each functional block shown in Figure 9 does not necessarily have to be housed in the same enclosure; they may be composed of separate devices connected to each other via signal paths.

[0095] In Figure 9, the imaging device 900 includes an optical imaging system 901, a photoelectric conversion element 100, a signal processing unit 902, a parameter setting unit 903, a brightness increase detection unit 904, a correction processing unit 905, a control unit 906, a storage unit 907, and an I / F unit 908. The photoelectric conversion element 100 has the configuration described in Figures 1 to 8.

[0096] The optical imaging system 901 consists of a zoom lens, a focus lens, an aperture, a shutter, an optical low-pass filter, an IR cut filter, and the like. The signal processing unit 902 calculates an estimated count value based on the count value output from each pixel 101 of the photoelectric conversion element 100, exposure time information, and the timing signal output from the parameter setting unit 903.

[0097] Furthermore, the signal processing unit 902 performs linearity correction processing using the aforementioned equation 2 based on the above-mentioned count estimate value, and also performs development processing. The parameter setting unit 903 outputs various timing signals to the photoelectric conversion element 100 and the signal processing unit 902. The brightness increase detection unit 904 determines whether or not there has been a brightness increase in the frame based on the output count value, and transmits the count value and the determination result to the correction processing unit 905.

[0098] The correction processing unit 905 performs a correction process on the count value if it determines that there has been an increase in brightness, based on the brightness increase detection result output from the brightness increase detection unit 904. The control unit 906 outputs a timing signal to the parameter setting unit 903 based on the image signal output from the signal processing unit 902 and the correction processing unit 905.

[0099] Furthermore, the control unit 906 controls each part of the imaging device 900 by causing the CPU 909, which acts as a computer, to execute a computer program stored in the memory 910, which acts as a storage medium.

[0100] The memory unit 907 records exposure time information and a corrective LUT (Lookup table) used for linearity correction. The memory unit 907 can also store image signals. The I / F unit 908 outputs video to display devices and terminal devices connected to the outside of the imaging device 900.

[0101] Furthermore, video output will be in formats such as SDI (Serial Digital Interface) and HDMI (High Definition Multimedia Interface).

[0102] Figure 10 is a flowchart showing an example of brightness increase detection and correction processing in Embodiment 1. The CPU 909, acting as a computer within the control unit 906, executes a computer program stored in the memory 910, thereby sequentially performing each step of the flowchart in Figure 10. The processing flow of the flowchart in Figure 10 is executed periodically (for example, every frame period).

[0103] In step S1001, image data is acquired. Specifically, the control unit 906 acquires the image data generated via the optical imaging system 901, photoelectric conversion element 100, signal processing unit 902, etc., of the imaging device 900.

[0104] In step S1002, the control unit 906 calculates the exposure time information for the photoelectric conversion element 100 based on the image data acquired in step S1001, and transmits the calculated exposure time to the parameter setting unit 903.

[0105] At that time, the aforementioned determination period is determined based on the maximum value of the counter. Step S1002 functions as a determination step (determination means) that determines the determination period based on the maximum value of the counter. The determination means determines the determination period such that it is a larger factor than the ratio of the specified value (threshold) to the maximum value of the counter.

[0106] In step S1003, the control unit 906 calculates a count threshold to be used in the count determination circuit 212 within the photoelectric conversion element 100, based on the exposure time calculated in step S1002. The control unit 906 transmits the calculated count threshold to the parameter setting unit 903.

[0107] In step S1004, the two imaging parameters, exposure time and count threshold, received by the parameter setting unit 903 in steps S1002 and S1003, are set and transmitted to the photoelectric conversion element 100.

[0108] Furthermore, the processing in steps S1002 to S1004 may be carried out in parallel with the processing in steps S1005 to S1008.

[0109] In step S1005, the image data acquired by the signal processing unit 902 in step S1001 is input to the brightness increase detection unit 904 to determine whether or not there is a brightness increase within the frame. If a brightness increase is detected, the process proceeds to step S1006. If it is determined that there is no brightness increase, the process shown in the flowchart of Figure 10 is terminated.

[0110] Here, step S1005 functions as a second determination step (second determination means) that determines whether or not there is a change in brightness during the exposure period based on the determination result in the first determination step and the count value of the counter.

[0111] In step S1006, the correction processing unit 905 performs image data correction processing (e.g., gain-up processing) based on the image data and the brightness increase detection result detected by the brightness increase detection unit 904. Here, step S1006 functions as a correction step (correction means) that corrects the count value when the second determination means determines that there is a change in brightness.

[0112] Furthermore, if the second determination means determines that there has been a change in brightness during the determination period and the count value has reached the upper limit, the correction means may correct the pixel value of the pixel in which the brightness change was determined to be present to the maximum pixel value within one frame.

[0113] In step S1007, it is determined whether or not the correction process is functioning. That is, the correction processing unit 905 determines whether or not the correction process is functioning based on the image data corrected with the correction parameters that were initially set or calculated in step S1008. If it is determined that the correction process is not functioning, the process proceeds to step S1008. If it is determined that the correction process is functioning, the process shown in the flowchart of Figure 10 is terminated.

[0114] In step S1008, the correction processing unit 905 calculates the correction parameters based on the captured image data. After that, the process shown in the flowchart in Figure 10 is completed.

[0115] Figures 11(A) and (B) illustrate an example of the relationship between exposure time and count distribution within a frame, illustrating the processing flow of the flowchart in Figure 10. The count distribution 1100 in Figure 11(A) shows an example of the distribution of count values ​​for each pixel within a frame.

[0116] As mentioned above, the exposure time is set by T / (n to the power of (m-1)). In Embodiment 1, m ≤ 4. The maximum value of m is not limited to this value and can be changed, but in this embodiment, when calculating the exposure time, m is fixed and the value of n is changed.

[0117] Furthermore, in this embodiment, the value of n is calculated based on the brightness distribution in the imaging area of ​​the imaging device 900. If a threshold determination can be made before the count upper limit Cmax of the counter circuit 211 in the photoelectric conversion element 100 is reached, the count value can be estimated with high accuracy, assuming that the count increase rate is proportional.

[0118] Under the condition n=2, the minimum exposure time is T / 8. However, in the count distribution 1100 shown in Figure 11(A), the count value does not reach Cmax at the instant of T / 8, thus meeting the conditions for accurately estimating the count value.

[0119] Furthermore, since the threshold value exceeds Cmax / 2 (the first count value) when a threshold judgment is performed at an exposure time T / 8, it can be said that n=2 is the maximum exposure time setting that can maintain the accuracy of the count estimation.

[0120] Here, the first count value refers to Cmax / n as described in the count estimation method. In this embodiment, n is set such that the count upper limit Cmax is not reached at the minimum exposure time, and n exceeds the first count value. This allows for maintaining a dynamic range that appropriately represents the brightness of the subject within the imaging area. In other words, the maximum exposure time can be optimized, and a decrease in the signal-to-noise ratio can be suppressed.

[0121] Furthermore, in Embodiment 1, an example will be described in which the second count value shown in Figure 11(B) is used as the count threshold instead of the first count value. The method for determining the second count threshold and its effects will be described using Figure 11(B).

[0122] The count increase graphs 1101 and 1102 in Figure 11(B) are graphs that show examples of the change in the count value of a certain pixel over time within one frame.

[0123] Count increase graph 1101 is a count increase graph when the count value at exposure time T becomes the upper limit of the count, assuming that the count threshold is the first count value Cmax / 2 and the count increase rate is constant.

[0124] In this case, the count increase graph 1101 passes through P1(T / 2, Cmax / 2), so it can be seen that the count range at exposure time T is 0 ≤ Cout ≤ Cmax.

[0125] On the other hand, the count increase graph 1102 is the count increase graph when the count value at exposure time T is the maximum value, 2 × Cth, assuming that the count threshold is the second count value Cth and the count increase rate is constant.

[0126] The second count value Cth is set to a value smaller than the first count value Cmax / 2. In this case, the count increase graph 1102 passes through P2(T / 2,Cth), so it can be seen that the count value Cout at exposure time T is 0 ≤ Cout ≤ 2 × Cth.

[0127] In other words, if the count threshold is set to the second count value Cth, then the count value such that 2 × Cth ≤ Cout is a value that can only be obtained if there is no increase in brightness during the exposure time period T / 2 to T.

[0128] For the reasons stated above, by setting the count threshold to a second count value Cth that is smaller than the first count value Cmax / 2, it becomes possible to detect increases in brightness within a single frame. While the above explanation described a case where brightness increases within the exposure time period T / 2 to T, similar processing can be used to detect brightness increases within the exposure time ranges T / 8 to T / 4 and T / 4 to T / 2 for the same reasons mentioned above.

[0129] Furthermore, the determination method may involve first determining a predetermined value from the frequency of occurrence and count value of the judgment value corresponding to the shortest judgment period among multiple judgment periods, and then determining multiple judgment periods based on the determined predetermined value.

[0130] Figures 12(A) and (B) illustrate other examples of the relationship between exposure time and count distribution within a single frame, illustrating the processing flow of the flowchart in Figure 10.

[0131] The count increase graph 1200 shown in Figure 12(A) is another example of the variation in the count value over time within a single frame for a given pixel. The count increase graph 1200 shows an example where, as a result of a brightness change at P3, the count increased to the upper limit Cmax before the exposure time T was reached, as shown at P4.

[0132] In this case, even though the second count value Cth has not been exceeded at exposure time T / 2, the upper limit count value Cmax, which is the count value at exposure time T, is output as the count value. For the reasons mentioned above, the upper limit count value Cmax is a value that cannot be obtained unless there is an increase in brightness within one frame, and it is possible to detect that there was an increase in brightness during the period from exposure time T / 2 to T.

[0133] In other words, if the second count value Cth is less than the second count value Cmax at exposure time T / 2, and the count value at exposure time T reaches the upper limit of the count Cmax, then there was a rapid increase in brightness during the period from exposure time T / 2 to T.

[0134] Therefore, in such cases, it is assumed that bright subjects such as flicker light sources are included. Accordingly, in this embodiment, correction is performed by performing the same count estimation process as when the count upper limit Cmax is reached at T / 8, which is the maximum value that the photoelectric conversion element 100 can output.

[0135] Furthermore, the correction method is not limited to the methods described above. For example, the correction may be made so that the pixel has the same count value as the brightest subject in a single frame, or so that the image is corrected to the upper limit of the count range that does not result in overexposure in the output image after image processing. In addition, it is also possible to allow the user to select from multiple correction methods during image capture.

[0136] The count increase graph 1201 shown in Figure 12(B) is another example of the change in the count value of a pixel over time within one frame. The count increase graph 1201 shows an example where the second count threshold is not exceeded at time T / 2, a change in brightness occurs at P6, and the brightness increases by more than 2 × Cth when the exposure time T is reached, as shown in P7.

[0137] For the reasons mentioned above, a count value exceeding 2 × Cth at exposure time T is a value that cannot be obtained unless there is an increase in brightness within one frame, and the brightness increase detection unit 904 detects that there was an increase in brightness during the period from exposure time T / 2 to T.

[0138] If the subject exhibits a rapid increase in brightness from P6 to P7, it is assumed that the subject is bright enough to exceed the threshold before the exposure time T. Therefore, in this embodiment, if the correction processing unit 905 can obtain the count value at P5, it performs a count value estimation process from the slopes of P5 and P7.

[0139] Furthermore, in this embodiment, if the P5 count value cannot be obtained by the correction processing unit 905, multiple correction intensities (e.g., gain-up levels) are set, and correction is performed by dynamically changing the correction intensity before or during shooting. The weakest correction intensity is used when the count threshold is not reached at T / 2 for P2, and when the slope of P7 is used to estimate the count value.

[0140] Furthermore, the strongest correction strength occurs when the same count estimation process is performed as when the count upper limit Cmax is reached at T / 8, which is the maximum value that the photoelectric conversion element 100 can output. The method for changing the correction strength may be to automatically determine the accuracy of the correction using image recognition, or the user may perform a calibration process for the correction strength in advance.

[0141] Alternatively, the correction strength of the correction means may be determined from the count value in the next shortest judgment period after the judgment period in which the specified value is reached, the count value in the judgment period in which the specified value is reached, and the judgment period in which the specified value is reached. Furthermore, the lower limit of the correction strength of the correction means may be determined from the specified value and the judgment period.

[0142] This correction method can improve the phenomenon of underestimating the brightness of a subject by correcting the count value based on the increase in brightness.

[0143] As described above, the imaging method of Embodiment 1 detects an increase in the brightness of a subject within a single frame and corrects the count value based on the increase in brightness, thereby improving the phenomenon of underestimating the brightness of a subject that is actually bright, and thus improving the visibility of the image.

[0144] <Embodiment 2> Figure 13 is a flowchart showing an example of brightness increase detection and correction processing in Embodiment 2. The CPU 909, acting as a computer within the control unit 906, executes a computer program stored in the memory 910, thereby sequentially performing each step of the flowchart in Figure 13. The processing flow of the flowchart in Figure 13 is executed periodically (for example, every frame period).

[0145] The configuration of the imaging device used in the description of Embodiment 2 is the same as the configuration shown in Figure 9. Note that in the flowchart of Embodiment 2 shown in Figure 13, the processing order of steps S1002 and S1003 is replaced with steps S1301 and S1302, compared to the flowchart of Embodiment 1 shown in Figure 10. The processing other than steps S1301 and S1302 is the same as in Embodiment 1.

[0146] In step S1301 of Figure 13, the control unit 906 calculates a count threshold to be used in the count determination circuit 212 within the photoelectric conversion element 100 from the image data acquired in step S1001, and transmits the calculated count threshold to the parameter setting unit 903.

[0147] In step S1302, the control unit 906 calculates the exposure time of the photoelectric conversion element 100 based on the count threshold calculated in step S1302, transmits the calculated exposure time to the parameter setting unit 903, and proceeds to step S1004.

[0148] Figures 14(A) and (B) illustrate an example of the relationship between exposure time and count distribution within a frame, illustrating the processing flow of the flowchart in Figure 13. Count distribution 1400 shows an example of the distribution of count values ​​for each pixel within a frame.

[0149] As described above, the count threshold is set to Cmax / n and the exposure time to T / (n to the power of (m-1)). In Embodiment 2, m ≤ 4. The value of n is calculated based on the brightness distribution in the imaging area of ​​the imaging device 900.

[0150] Since the luminance distribution is the same as in Embodiment 1, n is set to 2, as in Embodiment 1. In this case, in Embodiment 2, in step S1301, the count threshold is set before the exposure time, so the count threshold is set to Cmax / 2.

[0151] In Embodiment 2, in step S1302, the exposure time set for the photoelectric conversion element 100 is the second exposure time shown in Figure 14(B), rather than the first exposure time. The method for determining the second exposure time and its effects will be explained using Figure 14(B).

[0152] Count increase graph 1401 and count increase graph 1402 are both graphs that show examples of the change in the count value of a certain pixel over time within one frame.

[0153] Count increase graph 1401 is a count increase graph when a first exposure time is set as the exposure time and the count increase rate is assumed to be constant, showing the case where the count value is maximum at exposure time T. At this time, since it passes through P1(T / 2, Cmax / 2), it can be seen that the count range at exposure time T is 0 ≤ Cout ≤ Cmax.

[0154] Count increase graph 1402 is a count increase graph when a second exposure time is set as the exposure time and the count increase rate is assumed to be constant, and it is the count increase graph when the count value at exposure time T is maximum.

[0155] The second exposure time is set to T / ((2 - α)^(m - 1)) using a real number α satisfying 0 < α ≤ 2 so that it is longer than the first exposure time. At this time, since the count increase graph 1402 passes through P8(T / (2 - α), Cmax / 2), it can be read that the count value Cout at the exposure time T satisfies 0 ≤ Cout ≤ ((2 - α) / 2) × Cmax.

[0156] That is, when the exposure time is set to the second exposure time, the count value where ((2 - α) / 2) × Cmax < Cout cannot be a value where there is no luminance increase during the period from the exposure time T / 2 to T.

[0157] For the above reasons, by setting the exposure time to a second exposure time longer than the first exposure time, it becomes possible to detect the luminance increase within one frame. In FIG. 14(B), a case where there is a luminance increase during the period from the exposure time T / 2 to T is shown, but for any range within the exposure times T / 8 to T / 4 and T / 4 to T / 2, the luminance increase can be detected by the same processing for the above reasons. Note that the correction processing when the luminance increase is detected is the same as that in Embodiment 1.

[0158] In this way, the determination means may determine the prescribed value based on the determined determination period after determining the plurality of determination periods from the appearance frequency of the determination value corresponding to the shortest determination period among the plurality of determination periods and the count value.

[0159] As described above, in the method according to Embodiment 2, by detecting the luminance increase of the subject within one frame and correcting the count value in consideration of the luminance increase, it is possible to improve the phenomenon of underestimating a subject that is originally bright and to improve the visibility of the video.

[0160] <Embodiment 3> Figure 15 is a flowchart showing an example of brightness increase detection and correction processing in Embodiment 2. The CPU 909, acting as a computer within the control unit 906, executes a computer program stored in the memory 910, thereby sequentially performing each step of the flowchart in Figure 15. The processing flow of the flowchart in Figure 15 is executed periodically (for example, every frame period).

[0161] The configuration of the imaging device used in the description of Embodiment 3 is the same as the configuration shown in Figure 9. Note that in the flowchart of Embodiment 3 shown in Figure 15, the process of step S1008 is replaced by step S1501 compared to the flowchart of Embodiment 1 shown in Figure 10. The processes other than step S1501 are the same as in Embodiment 1.

[0162] In step S1501, the count threshold and correction parameters are calculated. Specifically, based on the image data after correction processing acquired in step S1006, the control unit 906 calculates the count threshold to be used in the count determination circuit 212 within the photoelectric conversion element 100. The calculated count threshold is then transmitted to the parameter setting unit 903. After that, the processing shown in the flowchart of Figure 15 is completed.

[0163] Figure 16 is a diagram illustrating an example of the relationship between exposure time and count distribution within one frame, illustrating the processing flow of step S1501 in the flowchart of Figure 15.

[0164] Count increase graph 1601 is a count increase graph assuming that the count threshold is Cth1 and the count increase rate is constant. In this case, since it passes through P9(T / 2,Cth1), it can be seen that the count range at exposure time T is 0≦Cout≦2×Cth1.

[0165] The count increase graph 1602 is a count increase graph when it is assumed that the count threshold is Cth2 and the count increase rate is constant. At this time, since it passes through P10(T / 2, Cth2), it can be read that the count range at the exposure time T is 0≦Cout≦2×Cth2.

[0166] As described in Embodiment 1, when the count threshold is Cth1, 2×Cth1<Cout, and when the count threshold is Cth2, 2×Cth2<Cout. In the case of Cout where the luminance increase within one frame can be detected.

[0167] That is, the smaller the count threshold is within the range less than Cmax / 2, the wider the count range for detecting the luminance increase becomes. The wider the count range for detecting the luminance increase, the easier it is to discriminate the amount of luminance increase, so the rate of luminance increase is easy to calculate. If the rate of luminance change is easy to calculate, it is easy to discriminate whether the factor of luminance change is a flicker light source.

[0168] Conversely, the larger the count threshold is within the range less than Cmax / 2, the more difficult it becomes to discriminate whether the factor of luminance change is a flicker light source. On the other hand, when photographing a subject with the same luminance, a longer exposure time can be ensured.

[0169] For example, when photographing a subject with luminance within the count range of Cth1 to Cth2 at the time of exposure time T / 2, when the count threshold is set to Cth2, the exposure is stopped, but when the count threshold is set to Cth1, the exposure continues. Therefore, when it is desired to ensure the exposure time and suppress the decrease in S / N, it is desirable to increase the count threshold.

[0170] For example, in a state where the luminance of a subject of the same pixel such as fixed-point photography does not frequently change, when it is estimated that the factor of luminance change is a flicker light source, it is desirable to set a large count threshold. On the other hand, in a situation where it is difficult to discriminate whether the factor of luminance change is a flicker light source, it is desirable to lower the count threshold and make it easier to specify by detecting the rate of luminance change.

[0171] Furthermore, if the count threshold is to be changed automatically, it should be changed automatically based on the detection frequency of brightness increase, comparison of count values ​​with surrounding pixels, and shooting scene determination. Alternatively, the user may manually adjust the count threshold while viewing the video. In addition, the determination means may be determined by multipliers of multiple determination periods and the difference between a predetermined value and the maximum count value, based on the occurrence frequency and count value of the second determination means.

[0172] As described above, in Embodiment 3, by adjusting the count threshold, it becomes easier to determine whether the increase in brightness is due to a flicker light source or an error in the brightness change within a single frame.

[0173] Furthermore, in cases where the brightness of a flicker light source increases, correcting the count value to account for the brightness increase can improve the phenomenon of underestimating the brightness of a subject that is actually bright, thereby improving the visibility of the image.

[0174] Although the present invention has been described in detail above based on its preferred embodiments, the present invention is not limited to the above embodiments, and various modifications and combinations of the above embodiments are possible in accordance with the spirit of the present invention, and these are not excluded from the scope of the present invention. Furthermore, some of the above embodiments may be combined as appropriate.

[0175] Furthermore, the present invention includes, for example, a system that realizes the functions of the above embodiment using at least one processor such as a CPU, memory, and circuitry (e.g., an ASIC). Alternatively, multiple processors may be used for distributed processing.

[0176] Furthermore, in order to implement some or all of the control in the above embodiment, a computer program that implements the functions of the above embodiment may be supplied to the imaging device, etc., via a network or various storage media.

[0177] The computer (or CPU or MPU, etc.) in the imaging device may read and execute the program. In that case, the program and the storage medium storing the program constitute the present invention. The present invention includes the following combinations.

[0178] (Configuration 1) An imaging apparatus characterized by comprising: a counter for counting photons for each pixel; a first determination means for determining whether the count value of the counter has reached a predetermined value within a predetermined determination period from the start of exposure; a second determination means for determining whether or not there is a change in brightness during the exposure period based on the determination result of the first determination means and the count value of the counter; a determination means for determining the determination period based on the maximum value of the count value; and a correction means for correcting the count value when the second determination means determines that there is a change in brightness.

[0179] (Configuration 2) The imaging apparatus according to Configuration 1, characterized in that the determination means determines the determination period such that the ratio is greater than the ratio of the specified value to the maximum value of the count value.

[0180] (Configuration 3) The imaging apparatus according to Configuration 1 or 2, characterized in that when the second determination means determines that there has been a change in brightness during the determination period and the count value has reached the upper limit, the correction means corrects the pixel value of the pixel in which the change in brightness was determined to have occurred to the maximum pixel value in one frame.

[0181] (Configuration 4) An imaging device according to any one of Configurations 1 to 3, characterized in that the correction strength of the correction means is determined from the count value in the next shortest determination period after the determination period in which the specified value is reached, the count value in the determination period in which the specified value is reached, and the determination period in which the specified value is reached.

[0182] (Configuration 5) The imaging apparatus according to any one of Configurations 1 to 4, characterized in that the lower limit of the correction intensity in the correction means is determined from the specified value and the determination period.

[0183] (Configuration 6) The imaging apparatus according to any one of Configurations 1 to 5, characterized in that the determination means determines a plurality of determination periods from the frequency of occurrence of the determination value corresponding to the shortest determination period among the plurality of determination periods and the count value, and then determines the predetermined value based on the determined determination period.

[0184] (Configuration 7) The imaging apparatus according to any one of Configurations 1 to 8, characterized in that the determination means determines a predetermined value from the frequency of occurrence of the determination value corresponding to the shortest determination period among the plurality of determination periods and the count value, and then determines a plurality of determination periods based on the determined predetermined value.

[0185] (Configuration 8) The imaging apparatus according to Configuration 2, characterized in that the determination means determines the difference between the magnification of a plurality of determination periods and the specified value with respect to the maximum value of the count value from the occurrence frequency of the second determination means and the count value.

[0186] (Method) An imaging method characterized by comprising: a count step of counting photons for each pixel; a first determination step of determining whether the count value of the count step has reached a predetermined value within a predetermined determination period from the start of exposure; a second determination step of determining whether or not there is a change in brightness during the exposure period based on the determination result of the first determination step and the count value; a determination step of determining the determination period based on the maximum value of the count value; and a correction step of correcting the count value if it is determined in the second determination step that there is a change in brightness.

[0187] (Program) A computer program for controlling each means of the imaging device described in any one of configurations 1 to 8 by computer. [Explanation of symbols]

[0188] 100: Photoelectric conversion element 11: Sensor board 12: Pixel area 21: Circuit board 22: Circuit area 101: Pixels 102: Photoelectric conversion unit 103: Signal Processing Circuit 110: Vertical scanning circuit 111: Horizontal scanning circuit 112: Readout circuit 113: Signal line 114: Output Circuit 115: Control pulse generation unit 201: Avalanche photodiode 202: Quench element 210: Waveform shaping section 211: Counter circuit 213: Selection Circuit 214: Drive line 215: Drive line 216: Drive line 217: Drive line 218: Drive line 900: Imaging device 901: Optical imaging system 902: Signal Processing Unit 903: Timing generation unit 904: Brightness increase detection unit 905: Correction Processing Unit 906: Control Unit 907: Storage section 908:I / F section

Claims

1. A counter that counts photons for each pixel, A first determination means for determining whether the count value of the counter reaches a specified value within a predetermined determination period from the start of exposure, A second determination means determines whether or not there is a change in brightness during the exposure period based on the determination result by the first determination means and the count value of the counter, A determination means for determining the determination period based on the maximum value of the count value, A correction means for correcting the count value when the second determination means determines that there is a change in brightness, An imaging device characterized by having the following features.

2. The imaging apparatus according to claim 1, characterized in that the determination means determines the determination period such that the ratio is greater than the ratio of the specified value to the maximum value of the count value.

3. The imaging apparatus according to claim 1, characterized in that, if the second determination means determines that there has been a change in brightness during the determination period and the count value has reached the upper limit, the correction means corrects the pixel value of the pixel in which the change in brightness was determined to have occurred to the maximum pixel value in one frame.

4. The imaging apparatus according to claim 1, characterized in that the correction intensity of the correction means is determined from the count value in the next shortest determination period after the determination period in which the specified value is reached, the count value in the determination period in which the specified value is reached, and the determination period in which the specified value is reached.

5. The imaging apparatus according to claim 1, characterized in that the lower limit of the correction intensity in the correction means is determined from the specified value and the determination period.

6. The imaging apparatus according to claim 1, wherein the determination means determines a plurality of determination periods from the frequency of occurrence of the determination value corresponding to the shortest determination period among the plurality of determination periods and the count value, and then determines the predetermined value based on the determined determination period.

7. The imaging apparatus according to claim 1, wherein the determination means determines a predetermined value from the frequency of occurrence of the determination value corresponding to the shortest determination period among the plurality of determination periods and the count value, and then determines a plurality of determination periods based on the determined predetermined value.

8. The imaging apparatus according to claim 2, characterized in that the determination means determines the difference between the magnification of a plurality of determination periods and the specified value with respect to the maximum value of the count value from the occurrence frequency of the second determination means and the count value.

9. A counting step that counts photons for each pixel, A first determination step to determine whether the count value of the count step reaches a specified value within a predetermined determination period from the start of exposure, A second determination step determines whether or not there is a change in brightness during the exposure period based on the determination result in the first determination step and the count value, A decision step in which the determination period is determined based on the maximum value of the count value, If the second determination step determines that there is a change in brightness, a correction step is performed to correct the count value, An imaging method characterized by having the following features.

10. A computer program for controlling each means of an imaging apparatus according to any one of claims 1 to 8 by computer.

Images