Photon counting device, photon counting method, and program

Abstract

An apparatus is an apparatus that converts a digital value output from an image sensor into the number of photons. The image sensor includes: a plurality of pixels including a photoelectric conversion element that converts input light into charge and an amplifier that amplifies and converts the charge converted by the photoelectric conversion element into voltage; and an A / D converter that converts the voltage output from the amplifiers of the plurality of pixels into a digital value. The apparatus includes: a conversion unit that converts the digital value into the number of photons based on corresponding reference data for distinguishing the number of photons; and a data processing unit that generates a two-dimensional image representing the number of photons of each of the plurality of pixels based on the number of photons converted by the conversion unit.

Description

[0001] This application is a divisional application of a patent application with an application date of June 18, 2018 , application number 201880075244.2 , and invention title Photon counter Device and method for photon counting . Technical Field

[0002] The present disclosure relates to a photon counting device and a photon counting method. Background Art

[0003] For example, Non-Patent Document 1 describes a technique of photon counting using a CMOS image sensor. In this technique, by increasing the frame rate of the image sensor, shooting is performed under the condition that only one photon is incident on one pixel in one frame.

[0004] Prior Art Documents

[0005] Non-Patent Documents

[0006] Non-Patent Document 1: B Saleh Masoodian, Jiaju Ma, Dakota Starkey, Yuichiro Yamashita, and Eric R. Fossum, “A1Mjot 1040fps 0.22e-rms Stacked BSI QuantaImage Sensor with Cluster-Parallel Readout”, preprint of the 2017 International Image Sensor Workshop (IISW), May 30 - June 2, 2017, P230 - 233 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] For example, when it is desired to perform photon counting using a CMOS image sensor, it is considered to determine the number of photons based on the digital value output from the A / D converter. However, in a CMOS image sensor, each pixel constituting the sensor has readout noise. In addition, the gain and offset values of multiple pixels have deviations within a certain range. Therefore, for example, there is a case where the digital value when one photon is incident represents the same value as the digital value when two photons are incident, and there is a concern that the photon counting accuracy may decrease.

[0009] An object of one aspect of the present disclosure is to provide a photon counting device and a photon counting method capable of suppressing a decrease in photon counting accuracy.

[0010] Technical Solutions for Solving the Problems

[0011] A photon counting device according to one aspect includes: a plurality of pixels each including a photoelectric conversion element that converts input light into charge and an amplifier that amplifies the charge converted by the photoelectric conversion element and converts it into a voltage; an A / D converter that converts the voltage output from the amplifiers of the plurality of pixels into a digital value; and a conversion unit that converts the digital value output from the A / D converter into the number of photons for each of the plurality of pixels with reference to reference data, the reference data being created based on the gain and offset values for each of the plurality of pixels.

[0012] In such a photon counting device, a voltage corresponding to the photons input to the photoelectric conversion element is output from the amplifier. The output voltage is converted into a digital value by the A / D converter. Then, the digital value is converted into the number of photons by the conversion unit. In the conversion unit, the digital value is converted into the number of photons with reference to the reference data. The reference data is created based on the respective gain and offset values in the plurality of pixels. Therefore, even if there are deviations in the gain and offset values between the pixels, the conversion unit can suppress the influence of the deviations and convert the digital value into the number of photons. Thus, a decrease in the counting accuracy of photons can be suppressed.

[0013] Further, the reference data has a plurality of threshold data created based on the gain and offset values for each of the plurality of pixels, and the conversion unit can convert the digital value for each of the plurality of pixels into the number of photons based on the plurality of threshold data. In this configuration, even if there are deviations in the gain and offset values of each pixel, the number of photons can be derived using thresholds corresponding to the deviations.

[0014] Further, the reference data includes preset parameters common to the plurality of pixels corresponding to the gain and offset values, and the conversion unit can correct the digital value for each of the plurality of pixels based on the deviation between the gain and offset values and the parameters, and convert the corrected digital value into the number of photons. In this configuration, the digital value can be corrected according to the deviation of the gain and offset values. Therefore, for example, the digital value can be converted into the number of photons using the same threshold for all pixels.

[0015] Further, the readout noise of the amplifier can be 0.2 [e-rms] or less. In this case, for example, the false detection rate can be suppressed to 1% or less. Further, the readout noise of the amplifier can be 0.15 [e-rms] or less. In this case, for example, the false detection rate can be suppressed to 0.1% or less.

[0016] Further, the gain can be 10 [DN / e] or more. By increasing the gain, the analog value output from the amplifier can be reproduced with higher accuracy.

[0017] In addition, a photon counting method according to one aspect includes: a step of converting light input to each photoelectric conversion element constituting a plurality of pixels into charge; a step of amplifying the converted charge by amplifiers constituting the plurality of pixels and converting it into voltage; a step of converting the voltage output from each amplifier into a digital value by an A / D converter and outputting the digital value; and a step of converting the digital value of each of the plurality of pixels output from the A / D converter into the number of photons based on the respective gain and offset values in the plurality of pixels.

[0018] In such a photon counting method, the voltage output from the amplifier according to the input photons is converted into a digital value by the A / D converter. Then, the digital value is converted into the number of photons based on the respective gain and offset values in the plurality of pixels. Therefore, even if there are deviations in the gain and offset values between pixels, the influence of the deviations can be suppressed and the digital value can be converted into the number of photons. Thus, a decrease in the counting accuracy of photons can be suppressed.

[0019] In addition, in the step of converting the digital value into the number of photons, threshold data created for each of the plurality of pixels based on the respective gain and offset values in the plurality of pixels may be used to convert the digital value into the number of photons. In this configuration, even if there are deviations in the gain and offset values of each pixel, the number of photons can be derived using thresholds corresponding to the deviations.

[0020] In addition, in the step of converting the digital value into the number of photons, the digital value of each of the plurality of pixels is corrected based on the deviation of the gain and offset values from a parameter, and the corrected digital value is converted into the number of photons. The parameter corresponds to the gain and offset values and may be preset in a manner common to the plurality of pixels. In such a configuration, the digital value can be corrected according to the deviation of the gain and offset values. Therefore, for example, the digital value can be converted into the number of photons using the same threshold for all pixels.

[0021] Advantages of the Invention

[0022] According to a photon counting device and a photon counting method according to one aspect, a decrease in the counting accuracy of photons can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a diagram showing the configuration of a photon counting device according to an embodiment.

[0024] Figure 2 is a graph showing the relationship between the number of electrons and the probability density.

[0025] Figure 3 is a graph showing the relationship between the readout noise and the false detection rate.

[0026] Figure 4 (a) is a graph showing the relationship between the number of electrons and the probability density. Figure 4(b) is a graph showing the results of the simulation based on Figure 4 (a).

[0027] Figure 5 (a) is a graph showing the relationship between the number of electrons and the probability density. Figure 5 (b) is a graph obtained by converting the results of the simulation based on Figure 5 (a) into numerical values.

[0028] Figure 6 (a) is a graph showing the relationship between the number of electrons and the probability density. Figure 6 (b) is a graph obtained by converting the results of the simulation based on Figure 6 (a) into numerical values.

[0029] Figure 7 (a) is a graph showing the relationship between the number of electrons and the probability density. Figure 7 (b) is a graph obtained by converting the results of the simulation based on Figure 7 (a) into numerical values.

[0030] Figure 8 is a diagram schematically showing the process of converting the measured numerical value into the number of photons.

[0031] Figure 9 is a diagram schematically showing the process of converting the measured numerical value into the number of photons.

[0032] Figure 10 is a diagram schematically showing the process of deriving the offset value.

[0033] Figure 11 is a diagram schematically showing the process of deriving the gain.

[0034] Figure 12 is a graph showing the correspondence between the gain and the offset value and the threshold.

[0035] Figure 13 is a diagram schematically showing the process of converting the measured numerical value into the number of photons.

[0036] Figure 14 is a flowchart showing the operation of a photon counting device according to an embodiment.

[0037] Figure 15 is a graph showing the correspondence between the measured numerical value and the corrected numerical value.

[0038] Figure 16 is a flowchart showing the operation of a photon counting device according to another embodiment. Detailed implementation mode

[0039] Hereinafter, embodiments will be specifically described with reference to the drawings. For convenience, substantially the same elements are denoted by the same reference numerals and their description is omitted. In addition, photon counting in the embodiments includes both counting the number of photoelectrons generated by each pixel of the image sensor and counting the number of photons considering the quantum efficiency (QE) of the image sensor.

[0040] [First Embodiment]

[0041] Figure 1 is a diagram showing the configuration of a photon counting device. As Figure 1 shown, the photon counting device 1 includes a CMOS image sensor 10 and a computer 20 connected to the CMOS image sensor 10. The CMOS image sensor 10 includes: a plurality of pixels 11; and an A / D converter 15. The plurality of pixels 11 are arranged in a two-dimensional shape, arranged in the row direction and the column direction. Each pixel 11 has a photodiode (photoelectric conversion element) 12 and an amplifier 13. The photodiode 12 stores the electrons (photoelectrons) generated by the input of photons as charges. The amplifier 13 converts the charges stored in the photodiode 12 into a voltage and amplifies it. The amplified voltage is transmitted to the vertical signal line 16 row by row (each row) through the switching of the selection switch 14 of each pixel 11. A CDS (correlated double sampling) circuit 17 is arranged on each vertical signal line 16. The CDS circuit 17 removes the noise with deviations between pixels and temporarily stores the transmitted voltage.

[0042] The A / D converter 15 converts the voltage output from each amplifier 13 among the plurality of pixels 11 into a digital value. In the present embodiment, the A / D converter 15 converts the voltage stored in the CDS circuit 17 into a digital value. The converted digital values are respectively output to the computer 20. For example, the digital values can also be transmitted to a horizontal signal line (not shown) through the switching of column selection and then output to the computer 20. In this way, in the CMOS image sensor 10, when photons are input to each pixel 11, digital values corresponding to the number of input photons are output to the computer 20. In addition, the A / D converter 15 can also be provided in each pixel 11.

[0043] When reading the voltage amplified by the amplifier 13, read noise, which is random noise, is generated in the amplifier 13. Figure 2 is a graph showing the probability distribution of electrons, with the horizontal axis being the number of electrons and the vertical axis being the probability density. As Figure 2 shown, the number of electrons generated by the input photons follows a Poisson distribution. In Figure 2In [the figure], the probability distribution of electrons is shown for the case where 2 photons are input on average per pixel, for each readout noise. As examples of readout noise, 0.12, 0.15, 0.25, 0.35, 0.40, 0.45, and 1.0 [e-rms] can be cited. As Figure 2 shown, the smaller the readout noise, the more intense the peak of the waveform of the probability distribution becomes, and the distinction between the distributions of each number of electrons becomes obvious. On the other hand, when the readout noise becomes large, the distributions repeat each other between adjacent numbers of electrons, and it becomes difficult to distinguish the distribution of each number of electrons. For example, when the readout noise is 0.40 [e-rms] or less, the peak of each number of electrons can be recognized. In contrast, when the readout noise is 0.45 [e-rms] or more, it is difficult to recognize the peak of each number of electrons. In the present embodiment, the magnitude of the readout noise capable of distinguishing the number of electrons is obtained based on whether the peak can be recognized. Thus, in the CMOS image sensor 10 of the present embodiment, the readout noise is 0.4 [e-rms] or less. In addition, the magnitude of the readout noise capable of distinguishing the number of electrons can also be obtained by detecting the inflection point by performing a second-order differential on the probability distribution.

[0044] In addition, when a threshold value for distinguishing between adjacent numbers of electrons is set, the false detection rate of the detected number of electrons varies according to the readout noise. Figure 3 is a graph showing the relationship between the readout noise and the false detection rate when, for example, a value intermediate between the numbers of electrons such as 0.5e, 1.5e, 2.5e... is used as the threshold value. In addition, the false detection rate is the ratio detected as the wrong number of electrons, and is caused by the spread of the probability distribution of electrons. As Figure 3 shown, when it is desired to make the false detection rate 1% or less, it is necessary to make the readout noise 0.2 [e-rms] or less. In addition, when it is desired to make the false detection rate 0.1% or less, it is necessary to make the readout noise 0.15 [e-rms] or less.

[0045] Figure 4 (a) is a graph showing the relationship between the number of electrons and the probability density. Figure 4 (b) is a graph showing the result of a simulation experiment based on Figure 4 (a). In Figure 4 (a), the probability distribution of electrons when 2 photons are input on average per pixel is shown for a readout noise of 0.15 [e-rms]. In addition, in Figure 4 (b), the distribution of the number of electrons for each measurement number is shown by simulation values. In the A / D converter 15, the Figure 4 simulation values shown in (b) are converted into digital values and output. The digital values output from each pixel 11 are represented by the following formula.

[0046] Digital value [DN] = Gain [DN / e] × Number of electrons [e] + Offset value [DN]

[0047] Figure 5 (b), Figure 6 (b) and Figure 7 (b) are respectively graphs when converting the analog value of Figure 4 (b) into a digital value. In Figure 5 (a), Figure 6 (a) and Figure 7 (a), the probability distribution of electrons when the readout noise is 0.15 [e-rms] and the average number of photons input per pixel is 2 is shown in the same way as Figure 4 (a). In Figures 5 to 7 , values intermediate between the numbers of electrons, such as 0.5e, 1.5e, 2.5e..., are used as a reference to set thresholds for distinguishing between the numbers of electrons. In the drawings, the thresholds are represented by dashed lines. In Figure 5 (b), the gain is 2 [DN / e] and the offset value is 100 [DN]. As shown in Figure 5 (b), when the gain is 2 [DN / e], it is difficult to reflect the deviation of the measured values observed through the analog value in the graph. In addition, the proportion of digital values representing the same value as the threshold becomes higher.

[0048] In Figure 6 (b), the gain is 10 [DN / e] and the offset value is 100 [DN]. As shown in Figure 6 (b), when the gain is 10 [DN / e], the distribution of digital values is approximated to the distribution of analog values. On the other hand, since the gain is an even number, as shown in the drawings, there are also cases where digital values corresponding to the thresholds are taken. In Figure 7 (b), the gain is 11 [DN / e] and the offset value is 100 [DN]. As shown in Figure 7 (b), when the gain is 11 [DN / e], the distribution of digital values is even more approximated to the distribution of analog values. Further, since the gain is an odd number, the cases of taking digital values corresponding to the thresholds can be suppressed. In this way, by increasing the value of the gain, the output digital value can be approximated to the analog value. In this embodiment, the CMOS image sensor 10 may also have a gain of, for example, 10 [DN / e] or more.

[0049] Refer again to Figure 1。The computer 20 physically includes storage devices such as RAM (Random Access Memory) and ROM (Read Only Memory), a processor (arithmetic circuit) such as a CPU, a communication interface, etc. As such a computer 20, for example, a personal computer, a cloud server, a smart device (such as a smart phone, a tablet terminal, etc.), a microcomputer, an FPGA (Field-Programmable Gate Array), etc. can be cited. The computer 20 functions as a storage unit 21, a conversion unit 22, a data processing unit 23, and a control unit 24 by executing a program stored in the storage device by the CPU of the computer system. The computer 20 can be configured either inside the camera including the CMOS image sensor 10 or outside the camera. The computer 20 can be connected to a display device 25 and an input device 26. The display device 25 is, for example, a display capable of displaying the photon counting result obtained by the computer 20. The input device 26 is a keyboard, a mouse, etc. for the user to input measurement conditions. In addition, a common touch screen can also be used as the display device 25 and the input device 26.

[0050] The storage unit 21 stores a table (reference data) for converting the digital value output from the CMOS image sensor 10 into the number of photons. The table is, for example, a look-up table. The table is created based on the gain and offset values of each of the plurality of pixels 11. In the present embodiment, the threshold data corresponding to each pixel 11 is stored as the table.

[0051] The conversion unit 22 converts the digital value of each of the plurality of pixels 11 output from the A / D converter 15 into the number of photons with reference to the table stored in the storage unit 21. The data processing unit 23 creates a two-dimensional image representing the number of photons of each pixel 11 based on the number of photons output from the conversion unit 22. In addition, the data processing unit 23 can also create a histogram, etc. which is a layout (plot) of the number of pixels with respect to the number of photons. The created two-dimensional image, etc. can be output to the display device 25. The control unit 24 can uniformly control each function of the computer 20 or the CMOS image sensor 10.

[0052] Next, the details of the photon counting device 1 will be described centering on the processing of the conversion unit 22. Hereinafter, for the sake of simplicity of explanation, the CMOS image sensor 10 of the photon counting device will be described as a CMOS image sensor having pixels 11 arranged in 3 rows × 3 columns.

[0053] First, a method for converting a digital value into the number of photons assuming no deviation in the gain and offset values will be described. Figure 8 Schematically shows the process of converting the measured digital value into the number of electrons. In Figure 8In the example, it is assumed that in each pixel, the offset value is 100 [DN] and the gain is 11 [DN / e]. In addition, it is assumed that the readout noise is 0.15 [e-rms].

[0054] As Figure 8 shown, in such a CMOS image sensor 10, when photons are input to each pixel 11, charges are stored in each pixel 11 according to the number of photons. In the example shown, a case where 5 electrons are stored in all pixels 11 is shown. The stored charges are converted into voltage by an amplifier 13 and into digital values by an A / D converter 15. In Figure 8 it, the digital values of each pixel are shown inside the pixel. Then, the converted digital values are converted into the number of electrons. In this case, for example, the digital values are converted into the number of electrons using a threshold range. In Figure 8 the example, as described above, it is assumed that there is no deviation in the gain and offset values. Therefore, when the upper and lower limits of the threshold range are the intermediate values of the number of electrons, the threshold range corresponding to 5 electrons is 4.5e or more and less than 5.5e. When represented by digital values, this threshold range is 150 - 160 [DN]. When referring to this threshold range and converting the digital values exemplified in Figure 8 into the number of electrons, the digital values are all converted into 5 electrons in all pixels 11. As described above, the number of electrons generated by the input photons follows a Poisson distribution. Therefore, by dividing the average number of electrons by the quantum efficiency for each pixel, the average number of photons can be obtained. When the quantum efficiency is 100%, the number of electrons is the same as the number of photons.

[0055] Next, consider the case of converting digital values into the number of electrons using the same threshold range in a state where the gain and offset values have deviations. Figure 9 represents the digital values in the case where the gain and offset values have deviations. In this example, the average gain is 11 [DN / e], and the deviation σ of the gain is 10%. That is, the gain ±σ can take values from 9.9 to 12.1. In addition, the average offset value is 100 [DN], and the deviation σ of the offset value is 3%. That is, the offset value ±σ can take values from 97 to 103. Figure 9 The example of Figure 8 is also a model in which 5 electrons are stored in all pixels. When using the same threshold as in the example of Figure 8 , it is 4 electrons in the case of 139 - 149, 5 electrons in the case of 150 - 160, and 6 electrons in the case of 161 - 171. Thus, in a state where the gain and offset values have deviations, there is a case where it is difficult to convert digital values into the correct number of electrons.

[0056] Thus, the conversion unit 22 of the present embodiment refers to the table stored in the storage unit 21 and converts the digital value of each of the multiple pixels output from the A / D converter 15 into the number of electrons respectively. The table has threshold data created based on the respective offset values and gains of the multiple pixels 11. Figure 10 It is a schematic diagram showing the process of obtaining the offset value. As described above, the digital value is represented by the following formula. Therefore, the offset value is represented as the digital value output in the state without input light. Thus, in the present embodiment, as Figure 10 shown, in the state without input light, a plurality of digital values are obtained from the plurality of dark images acquired by the CMOS image sensor 10. The offset value can be obtained by averaging the acquired digital values for each pixel.

[0057] Digital value [DN] = gain [DN / e] × number of electrons [e] + offset value [DN]

[0058] Figure 11 It is a schematic diagram showing the process of obtaining the gain. When obtaining the gain of each pixel, a plurality of frame images are acquired by the CMOS image sensor 10 with sufficient light amount. Then, the average light signal value S [DN] and the standard deviation N [DN] of the digital values of each pixel are obtained. The gain can be expressed as N 2 / S, so the gain can be derived from the average light signal value S and the standard deviation N.

[0059] The storage unit 21 of the present embodiment holds, as a table, the threshold data for each pixel derived based on the gain and the offset value. When taking the intermediate value of the number of electrons as the threshold, the threshold representing the lower limit of each number of electrons and the threshold representing the upper limit are respectively represented by the following formulas, and the ranges of these lower limit thresholds and upper limit thresholds are the threshold ranges corresponding to the number of electrons.

[0060] Threshold (lower limit) = (number of electrons - 0.5) × gain + offset value

[0061] Threshold (upper limit) = (number of electrons + 0.5) × gain + offset value

[0062] Thus, for example, the threshold in the case where the number of electrons is 5 electrons can be derived as Figure 12 shown. Figure 12 It is a diagram showing the correspondence between the gain, the offset value, and the threshold. In Figure 12The acquired gain and offset values are shown for each pixel. In addition, the threshold value in the case where the number of electrons is judged to be 5 electrons is shown for each pixel. For example, when the gain is 10.9 [DN / e] and the offset value is 97.7 [DN], the lower threshold value is 146.8 [DN], and the upper threshold value is 157.7 [DN]. In the storage unit 21, as a table, threshold data corresponding to each number of electrons is provided for each pixel. Figure 13 is a diagram schematically showing the process of converting the digital value of each measured pixel into the number of electrons. In the conversion unit 22, by referring to the table stored in the storage unit 21, the correct number of electrons can be derived from the digital value. For example, in Figure 9 the example of, when the digital value is 162 [DN], it is judged as 6 electrons, and in Figure 13 the example of, it is judged as 5 electrons. The conversion unit 22 can obtain the average number of photons by dividing the average number of electrons by the quantum efficiency for each pixel.

[0063] Next, the operation of the photon counting device 1 will be described. Figure 14 is a flowchart showing the operation of the photon counting device. In the present embodiment, when the measurement starts in the state where the photon counting device 1 is operating, first, photons incident on the pixel 11 of the CMOS image sensor 10 are converted into charges by the photodiode 12 (step S11). Then, the converted charges are converted into voltages by the amplifier 13 (step S12). This voltage is converted into a digital value by the A / D converter 15 and output to the computer 20 (step S13). The conversion unit 22 of the computer 20 compares the digital value with the threshold value set for each pixel 11 (step S14), and converts the digital value into the number of photons based on the comparison result (step S15). Thus, the number of photons input to each pixel can be measured. The measurement result can also be displayed on the display device 25 as image data or the like, for example.

[0064] As described above, in the photon counting device 1, the digital value is converted into the number of photons by the conversion unit 22. In the conversion unit 22, by referring to the table stored in the storage unit 21, the digital value is converted into the number of electrons using the threshold value set for each pixel. The table is created in consideration of the gain and offset values of each of the plurality of pixels 11. Therefore, even when there are deviations in the gain and offset values between the pixels 11, the conversion unit 22 can suppress the influence of the deviations and convert the digital value into the number of electrons. Thus, a decrease in the counting accuracy of photons can be suppressed.

[0065] The table has a plurality of threshold data corresponding to the plurality of pixels 11 respectively. In this configuration, appropriate threshold data is created for each pixel 11 according to the deviation of the gain and offset values, so that the number of electrons can be judged with high accuracy. In addition, for example, there is no need to correct the digital value without considering the deviation.

[0066] The readout noise of amplifier 13 can be 0.2 [e-rms] or less. In this case, for example, the false detection rate can be suppressed to 1% or less. Further, the readout noise of amplifier 13 can be 0.15 [e-rms] or less. In this case, for example, the false detection rate can be suppressed to 0.1% or less.

[0067] The gain can be 10 [DN / e] or more. By having a relatively high gain in the CMOS image sensor 10, the analog value output from amplifier 13 can be reproduced as a digital value with relatively high accuracy.

[0068] [Second Embodiment]

[0069] The photon counting device of the present embodiment is different from the photon counting device of the first embodiment in terms of the configuration of the storage unit 21 and the conversion unit 22. Hereinafter, the points different from the first embodiment will be mainly described. In addition, in the device configuration, since it is the same as that of the Figure 1 first embodiment shown, it is omitted.

[0070] The storage unit 21 stores a table (reference data) for converting the digital value output from the CMOS image sensor 10 into the number of electrons. The table is created based on the gain and offset values of each of the plurality of pixels 11. The storage unit 21 in the present embodiment stores the gain and offset values of each pixel 11 as a table. In addition, the storage unit stores the threshold data for each number of electrons common to all the pixels 11 as a table.

[0071] The conversion unit 22 may also correct the digital value of each of the plurality of pixels 11 based on the gain and offset values of each of the plurality of pixels 11 in such a way as to suppress the influence of the deviation of the gain and offset values among the plurality of pixels 11, and convert the corrected digital value into the number of photons. In the present embodiment, by correcting the digital value of each pixel 11 by the conversion unit 22, the apparent gain and offset values (parameters) of each pixel 11 become the same. The corrected digital value can be derived based on the deviation of the gain and offset values of each pixel from the apparent gain and apparent offset values common to all the pixels. In this case, the corrected digital value can be derived using the following correction formula. In addition, the apparent gain and apparent offset values are set in advance and may be stored in the storage unit 21 or the conversion unit 22.

[0072] Corrected digital value = ((digital value - offset value) / gain) × apparent gain + apparent offset value

[0073] Figure 15 is a diagram showing the correspondence between the measured digital value and the corrected digital value. In Figure 15In the example, an example of correcting the digital value measured by the CMOS image sensor ( Figure 9 refer to) 10 in the first embodiment by the above-described correction formula is shown. In this example, the conversion unit 22 corrects the digital value so that the apparent gain in all pixels becomes 11 [DN / e] and the apparent offset value becomes 100 [DN]. That is, the corrected digital value is derived from the following correction formula.

[0074] Corrected digital value = ((digital value - offset value) / gain) × 11 + 100

[0075] In the conversion unit 22, the threshold data common to each pixel is used for the corrected digital value to obtain the number of electrons. For example, the storage unit 21 may hold the threshold range derived by the following formula as a table. The conversion unit 22 can refer to the threshold data held in the table and convert the corrected digital value into the number of electrons. In addition, in Figure 15 the example, since the apparent gain is 11 [DN / e] and the apparent offset value is 100 [DN], when the corrected digital value is 150 to 160, it is determined as 5 electrons. The conversion unit 22 can obtain the average number of photons by dividing the average number of electrons by the quantum efficiency for each pixel.

[0076] Threshold (lower limit) = (number of electrons - 0.5) × apparent gain + apparent offset value

[0077] Threshold (upper limit) = (number of electrons + 0.5) × apparent gain + apparent offset value

[0078] Figure 16 is a flowchart showing the operation of the photon counting device. In the present embodiment, when the measurement is started in the state where the photon counting device 1 is operating, first, the light incident on the pixels of the CMOS image sensor 10 is converted into charge by the photodiode 12 (step S21). Then, the converted charge is converted into voltage by the amplifier 13 (step S22). This voltage is converted into a digital value by the A / D converter 15 and output to the computer 20 (step S23). The digital value is corrected for each pixel by the conversion unit 22 of the computer 20 (step S24). The corrected digital value is compared with the set threshold data (step S25), and based on the comparison result, the corrected digital value is converted into the number of photons (step S26). Thus, the number of photons input to each pixel can be measured.

[0079] In the present embodiment, according to the deviation of the gain and the offset value, the digital value is corrected in a manner that suppresses the influence of the deviation. Therefore, as described above, the corrected digital value can be converted into the number of electrons using the same threshold data for all pixels.

[0080] As described above, the embodiments have been described in detail with reference to the drawings, but the specific configuration is not limited to this embodiment.

[0081] For example, in the conversion unit, the number of electrons per pixel can also be obtained by dividing the value obtained by subtracting the offset value from the measured digital value by the gain, as shown in the following formula. In this case, for the obtained number of electrons, a common threshold range corresponding to all pixels can be used. For example, the upper and lower limits of the threshold range can be set as the intermediate value of the number of electrons as described above, and a common threshold range can be set. In this case, the threshold range corresponding to 5 electrons is 4.5e or more and less than 5.5e.

[0082] Number of electrons = ((Digital value - Offset value) / Gain)

[0083] In addition, in the CMOS image sensor 10 of the present embodiment, an example in which the readout noise of each pixel is 0.4 [e-rms] or less is shown. However, even if the readout noise in the sensor mode is 0.4 [e-rms], there are cases where the noise of some pixels is larger than 0.4 [e-rms]. In such a case, pixels with a readout noise of 0.4 [e-rms] or less can be grasped in advance by measurement or the like, and photon counting can be performed only using pixels with a readout noise of 0.4 [e-rms] or less.

[0084] Symbol description

[0085] 1... Photon counting device, 11... Pixel, 12... Photodiode (photoelectric conversion element), 13... Amplifier, 15... A / D converter, 21... Storage unit, 22... Conversion unit.

Claims

1. A device, characterized in that, it is a device that converts a digital value output from an image sensor into the number of photons. The image sensor includes: a plurality of pixels, which include a photoelectric conversion element that converts input light into charge and an amplifier that amplifies and converts the charge converted by the photoelectric conversion element into voltage; and an A / D converter that converts the voltage output from the amplifier of the plurality of pixels into the digital value, the device includes: a conversion unit that converts the digital value into the number of photons based on corresponding reference data for differentiating the number of photons; and a data processing unit that generates a two-dimensional image representing the number of photons of each of the plurality of pixels based on the number of photons converted by the conversion unit, further includes: a correction unit that corrects the digital value by correcting the deviation of the gain and offset value of each of the amplifiers constituting the plurality of pixels, the conversion unit converts the digital value corrected by the correction unit into the number of photons based on the corresponding reference data for differentiating the number of photons.

2. The device according to claim 1, characterized in that, the reference data is data representing a threshold range, and the threshold range includes an upper limit value and a lower limit value of the digital value set for each number of photons.

3. The device according to claim 1, characterized in that, the A / D converter is provided in each of the plurality of pixels.

4. The device according to claim 2, characterized in that, the A / D converter is provided in each of the plurality of pixels.

5. The device according to any one of claims 1 to 4, characterized in that, the readout noise of the amplifier is 0.2 [e-rms] or less.

6. The device according to any one of claims 1 to 4, characterized in that, the readout noise of the amplifier is 0.15 [e-rms] or less.

7. The device according to any one of claims 1 to 4, characterized in that, the gain is 10 [DN / e] or more.

8. The device according to any one of claims 1 to 4, characterized in that, the number of photons is the number of photons considering the quantum efficiency of the image sensor.

9. The device according to any one of claims 1 to 4, characterized in that, the number of photons is the number of photo-electrons.

10. A device, characterized in that, it is a device that converts a digital value output from an image sensor into the number of photons. The image sensor includes: a plurality of pixels, which include a photoelectric conversion element that converts input light into charge and an amplifier that amplifies and converts the charge converted by the photoelectric conversion element into voltage; and an A / D converter that converts the voltage output from the amplifier of the plurality of pixels into the digital value, the device includes: a conversion unit that converts the digital value into the number of photons based on corresponding reference data for differentiating the number of photons; and a data processing unit that generates a two-dimensional image representing the number of photons of each of the plurality of pixels based on the number of photons converted by the conversion unit, the reference data is data representing a threshold range, and the threshold range includes an upper limit value and a lower limit value of the digital value set for each number of photons.

11. The device according to claim 10, characterized in that, the A / D converter is provided for each of the plurality of pixels.

12. The device according to claim 10, characterized in that, the readout noise of the amplifier is 0.2 [e-rms] or less.

13. The device according to claim 11, characterized in that, the readout noise of the amplifier is 0.2 [e-rms] or less.

14. The device according to claim 10, characterized in that, the readout noise of the amplifier is 0.15 [e-rms] or less.

15. The device according to claim 11, characterized in that, the readout noise of the amplifier is 0.15 [e-rms] or less.

16. The device according to any one of claims 10 to 15, characterized in that, the number of photons is the number of photons taking into account the quantum efficiency of the image sensor.

17. The device according to any one of claims 10 to 15, characterized in that, the number of photons is the number of photo-electrons.

18. A method, characterized in that, it is a method for converting a digital value output from an image sensor into the number of photons, the image sensor including: a plurality of pixels, which include a photoelectric conversion element that converts input light into charge and an amplifier that amplifies and converts the charge converted by the photoelectric conversion element into voltage; and an A / D converter that converts the voltage output from the amplifier of the plurality of pixels into the digital value, the method includes: a conversion step of converting the digital value into the number of photons based on corresponding reference data for distinguishing the number of photons; and a data processing step of generating two-dimensional image data representing the number of photons of each of the plurality of pixels based on the number of photons converted by the conversion unit, further includes: a correction step of correcting the digital value by correcting the deviation of the gain and offset value of each of the amplifiers constituting the plurality of pixels, the conversion step converts the digital value corrected by the correction step into the number of photons based on the corresponding reference data for distinguishing the number of photons.

19. The method according to claim 18, characterized in that, further includes: a step of generating a histogram as the layout of the number of pixels with respect to the number of photons based on the converted number of photons.

20. The method according to claim 18, characterized in that, the reference data is data representing a threshold range, and the threshold range includes an upper limit value and a lower limit value of the digital value set for each number of photons.

21. The method according to claim 19, characterized in that, the reference data is data representing a threshold range, and the threshold range includes an upper limit value and a lower limit value of the digital value set for each number of photons.

22. The method according to any one of claims 18 to 21, characterized in that, the readout noise of the amplifier is 0.2 [e-rms] or less.

23. The method according to any one of claims 18 to 21, characterized in that, the readout noise of the amplifier is 0.15 [e-rms] or less.

24. The method according to any one of claims 18 to 21, characterized in that, The gain is 10 [DN / e] or more.

25. The method according to any one of claims 18 to 21, wherein, the number of photons is the number of photons taking into account the quantum efficiency of the image sensor.

26. The method according to any one of claims 18 to 21, wherein, the number of photons is the number of photo-electrons.

27. The method according to any one of claims 18 to 21, wherein, the A / D converter is provided for each of the plurality of pixels.

28. A method, wherein, is a method for converting a digital value output from an image sensor into the number of photons, the image sensor including: a plurality of pixels including a photoelectric conversion element that converts input light into charge and an amplifier that amplifies and converts the charge converted by the photoelectric conversion element into voltage; and an A / D converter that converts the voltage output from the amplifier of the plurality of pixels into the digital value, the method includes: a conversion step of converting the digital value into the number of photons based on corresponding reference data for distinguishing the number of photons; and a data processing step of generating two-dimensional image data representing the number of photons of each of the plurality of pixels based on the number of photons converted by the conversion unit, further includes: a step of generating a histogram as a layout of the number of pixels with respect to the number of photons based on the converted number of photons.

29. The method according to claim 28, wherein, the reference data is data representing a threshold range including an upper limit value and a lower limit value of a digital value set for each number of photons.

30. The method according to claim 28, wherein, the readout noise of the amplifier is 0.2 [e-rms] or less.

31. The method according to claim 29, wherein, the readout noise of the amplifier is 0.2 [e-rms] or less.

32. The method according to claim 28, wherein, the readout noise of the amplifier is 0.15 [e-rms] or less.

33. The method according to claim 29, wherein, the readout noise of the amplifier is 0.15 [e-rms] or less.

34. The method according to any one of claims 28 to 33, wherein, the number of photons is the number of photons taking into account the quantum efficiency of the image sensor.

35. The method according to any one of claims 28 to 33, wherein, the number of photons is the number of photo-electrons.

36. The method according to any one of claims 28 to 33, wherein, the A / D converter is provided for each of the plurality of pixels.

37. A method, wherein, is a method for converting a digital value output from an image sensor into the number of photons, the image sensor including: a plurality of pixels including a photoelectric conversion element that converts input light into charge and an amplifier that amplifies and converts the charge converted by the photoelectric conversion element into voltage; and an A / D converter that converts the voltage output from the amplifier of the plurality of pixels into the digital value, the method includes: A conversion step of converting the digital value into the number of photons based on corresponding reference data for differentiating the number of photons; and A data processing step of generating two-dimensional image data representing the number of photons of each of the plurality of pixels based on the number of photons converted by the conversion unit, The reference data is data representing a threshold range, and the threshold range includes an upper limit value and a lower limit value of the digital value set for each number of photons.

38. The method according to claim 37, wherein, the readout noise of the amplifier is 0.2 [e-rms] or less.

39. The method according to claim 37, wherein, the readout noise of the amplifier is 0.15 [e-rms] or less.

40. The method according to any one of claims 37 to 39, wherein, the number of photons is the number of photons considering the quantum efficiency of the image sensor.

41. The method according to any one of claims 37 to 39, wherein, the number of photons is the number of photo-electrons.

42. The method according to any one of claims 37 to 39, wherein, the A / D converter is provided for each of the plurality of pixels.

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