JP7698202B2 - Measurement device, measurement method, and program - Google Patents

Description

The present invention relates to a measurement device, a measurement method, and a program for measuring changes in a speckle pattern, for example.

When coherent light such as laser light is irradiated onto an object with minute irregularities on its reflective surface or an object that causes internal scattering, scattered light is generated from the object in response to the coherent light, and a pattern resulting from the interference of the scattered light can be observed. This pattern is called a speckle pattern, and at each point in the speckle pattern, light and dark appear due to the strengthening and weakening caused by the overlapping of multiple scattered lights.

When the phase difference of the scattered light changes with the deformation or movement of an object, the speckle pattern also changes. Therefore, by measuring the change in the speckle pattern over time, it is possible to estimate the change in the minute shape of the object over time, the change in the amount of movement over time, and so on. Measurement methods that use speckle patterns are used for various purposes, such as material measurement, medical sensors such as blood flow meters, and speed meters for machine control. For example, in a laser Doppler blood flow meter, a laser light is irradiated from above the skin, and a light receiving element detects a received light intensity signal from the speckle pattern light generated by the interference between the light scattered by red blood cells moving in the blood vessels and the light scattered by stationary biological tissue. The speed of the red blood cells passing through the blood vessels is calculated from the frequency of the detected received light intensity signal, and the blood flow rate and pulse rate are estimated from the calculated red blood cell speed.

Speckle patterns can be observed in two dimensions by capturing images using an image sensor such as a CCD (Charge Coupled Device). However, when capturing images of scattering bodies that produce extremely high frequencies of received light intensity signals, such as the blood flow speckle pattern described above, an image sensor with a high frame rate corresponding to the high frequency is required. In general, the higher the frame rate and the higher the resolution of an image sensor, the higher its price becomes. Image sensors with high frame rates and high resolutions have the problem of being strongly affected by noise due to insufficient light.

For example, the technology disclosed in Non-Patent Document 1, i.e., a blood flow meter using a laser speckle blood flow imaging method, uses a speckle pattern measurement method using an image sensor with a general frame rate, thereby solving the problems related to the cost and noise of the image sensor as described above. In a blood flow meter using a laser speckle blood flow imaging method, the image data obtained by the image sensor indicates the result of integrating the light receiving intensity signal within the exposure time for each pixel. The faster the blood flow speed, the higher the frequency of the light receiving intensity signal in real time, so there is a tendency for the variation in the integrated value to be smaller. A blood flow meter using a laser speckle blood flow imaging method makes use of this tendency, acquiring and comparing image data multiple times, and making it possible to determine the blood flow rate from the amount of variation between the image data based on the comparison results.

OMEGAWAVE, INC., "2D laser blood flow imaging device, OMEGAZONE 2D Laser Blood Flow Imager, measurement principle", [online], [searched on August 18, 2021], Internet <http://www.omegawave.co.jp/products/oz/principle.shtml>

However, when measuring a speckle pattern using an image sensor with a general frame rate, as in the technology disclosed in Non-Patent Document 1, if the object being measured is an object with a high frequency of the received light intensity signal, such as the blood flow described above, multiple continuous measurements are required. This poses the problem that it is difficult to perform measurements under conditions where there are restrictions on the time interval of measurements, such as so-called real-time measurements. When using an image sensor with a general frame rate, multiple continuous measurements are required, which poses the problem that it is difficult to perform accurate measurements if the ratio of changes occurring in the object being measured is not a constant ratio.

In view of the above, the present invention aims to provide a technology that can estimate changes in an object that does not change constantly based on a speckle pattern under conditions where the measurement time interval is restricted.

One aspect of the present invention is a measurement device that includes an irradiation unit that generates coherent light, a measurement unit that receives light of a speckle pattern generated by interference of scattered light caused by a scatterer receiving the coherent light with a plurality of pixels, detects pixels having a predetermined amount of luminance change to be detected, and generates event data including a position of the detected pixel, a code value indicating a direction of change in the amount of luminance change of the pixel, and a detection time indicating the time of detection, and a calculation processing unit that calculates a physical quantity indicating a change in the scatterer based on the event data.

One aspect of the present invention is a measurement method that generates coherent light, receives light of a speckle pattern generated by interference of scattered light caused by a scatterer receiving the coherent light with a plurality of pixels, detects pixels having a predetermined amount of luminance change to be detected, and generates event data including a position of the detected pixel, a code value indicating a direction of change in the amount of luminance change of the pixel, and a detection time indicating the time of detection, and calculates a physical quantity indicating a change in the scatterer based on the generated event data.

One aspect of the present invention is a program for causing a computer to execute a measurement step of receiving light of a speckle pattern generated by interference of scattered light caused by a scatterer receiving coherent light with a plurality of pixels, detecting pixels having a predetermined amount of luminance change to be detected, in which a luminance change amount indicating a change in luminance value detected by each of the pixels receiving the light of the speckle pattern is a predetermined amount of luminance change to be detected, and generating event data including a position of the detected pixel, a code value indicating a direction of change in the amount of luminance change of the pixel, and a detection time indicating the time of detection, and a calculation processing step of calculating a physical quantity indicating a change in the scatterer based on the event data.

The present invention makes it possible to estimate changes in objects that do not change constantly based on speckle patterns under conditions where the measurement time interval is restricted.

2 is a block diagram showing the internal configuration of a measuring device and a scatterer according to the first embodiment; FIG. 11 is a flowchart showing a flow of processing of a first technique performed by a calculation processing unit of the first embodiment. 10 is a flowchart showing a flow of processing of a second technique performed by a calculation processing unit according to the first embodiment. 11 is a graph showing an example of a change in an integrated value calculated by the calculation processing unit in a second technique performed by the calculation processing unit of the first embodiment. 13 is a graph for explaining the relationship between the magnitude of a detection threshold set in the event detection unit and the position of a peak detected by the event detection unit in the third technique performed by the calculation processing unit of the first embodiment. 13 is a flowchart showing a flow of processing of a third technique performed by a calculation processing unit of the first embodiment. 13 is a flowchart showing a flow of processing of a fourth technique performed by a calculation processing unit according to the first embodiment. FIG. 13 is a block diagram showing an internal configuration of a measuring device and a scatterer according to a second embodiment. 13A and 13B are diagrams illustrating an example of an optical system applied to a light branching unit and a light converging unit of the second embodiment. 10 is a flowchart showing a flow of processing by a calculation processing unit according to the second embodiment.

First Embodiment
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing a measurement device 1 in a first embodiment and a scattering medium 30 that is a measurement target of the measurement device 1. The scattering medium 30 includes a moving scattering medium 31 that moves in part, and may be any object that receives coherent light and generates scattered light. For example, the scattering medium 30 is a human body, and the moving scattering medium 31 is blood flowing through the blood vessels of the human body.

The measurement device 1 includes an irradiation unit 11, a measurement unit 12, and a calculation processing unit 13. The irradiation unit 11 includes a light source that generates laser light, which is coherent light, and generates the laser light with a constant light intensity using the light source. The irradiation unit 11 diffuses the generated laser light into a planar shape using an optical element provided therein, and irradiates the diffused laser light 40 onto the scattering body 30. Here, the optical element provided inside the irradiation unit 11 may be any optical element that diffuses laser light, and is, for example, a convex lens arranged in a position that diffuses the laser light generated by the light source.

In FIG. 1, scattered light 50 indicates scattered light generated when the parts of the scatterer 30 other than the moving scatterer 31, i.e., the stationary parts, receive the laser light 40, and scattered light 51 indicates scattered light generated when the moving scatterer 31 receives the laser light 40. When the moving scatterer 31 is not moving, the scattered light 51 is included in the scattered light 50, and in this case, a speckle pattern is generated due to interference of the scattered light 50. In contrast, when the moving scatterer 31 is moving, scattered light 51 is generated, and interference between the scattered light 50 and the scattered light 51 causes a change in the speckle pattern.

The measurement unit 12 is, for example, an event camera equipped with an event-based vision sensor, and includes a light receiving unit 21 and an event detection unit 23. The light receiving unit 21 is arranged at a position where it can receive light of a speckle pattern generated by the interference of scattered light 50, 51. The light receiving unit 21 includes, for example, a plurality of pixels 22-1 to 22-n arranged in a rectangular shape to form the light receiving surface of the light receiving unit 21. Here, n may be any integer value of 2 or more, and in the case of a general event camera, n is a value of tens of thousands to hundreds of thousands. Note that FIG. 1 shows an example of n=54, that is, an example in which the light receiving unit 21 includes 54 pixels 22-1 to 22-54 of 6 rows and 9 columns, and the first and last pixels therein are indicated by the symbols "22-1" and "22-n", respectively. When each of the pixels 22-1 to 22-n receives light of a speckle pattern generated by the interference of the scattered lights 50 and 51, it outputs a luminance value indicating the intensity of the light of the speckle pattern measured at each position. Hereinafter, when referring to any one of the pixels 22-1 to 22-n, it will be referred to as pixel 22 without indicating the subnumber of the reference symbol.

The event detection unit 23 asynchronously detects the amount of luminance change indicating the change in the luminance value output by each of the pixels 22-1 to 22-n. When the event detection unit 23 detects a pixel 22 whose detected amount of luminance change has a predetermined amount of luminance change to be detected, the event detection unit 23 generates event data including the position of the detected pixel 22, a code value indicating the direction of change in the amount of luminance change, and a detection time indicating the time of detection. Here, the position of the pixel 22 is, for example, a position indicated by coordinate data represented by the row and column positions with the position of the pixel 22-1 as the origin, i.e. (0,0), and the position of the pixel one row below the pixel 22-1 in the same column is indicated as coordinate data (1,0), and the position of the pixel one column to the right of the pixel 22-1 in the same row is indicated as coordinate data (0,1). The code value indicating the direction of change in the amount of luminance change is, for example, "+1" when the luminance value is changing from a small value to a large value, and "-1" when the luminance value is changing from a large value to a small value.

Here, the relationship between the amount of luminance change detected by the event detection unit 23 and the received light intensity signal that causes a change in the speckle pattern will be described. The received light intensity signal is a signal in which the light intensity values of the speckle pattern measured at a certain position are arranged in time series. There is a relationship in which the frequency of the received light intensity signal increases as the change in the speckle pattern increases. The luminance values detected by each of the pixels 22-1 to 22-n indicate the intensity of the light of the speckle pattern measured at each position, and the received light intensity signals of the speckle pattern measured at each of the pixels 22-1 to 22-n are obtained by arranging the luminance values detected by each of them in time series. Here, the received light intensity signal measured at a certain pixel 22 is I(t) (where, in I(t), t is time, and I(t) is the luminance value detected by the pixel 22 at time t). For example, if the luminance value detected by pixel 22 at time _t1 is I( _t1 ), and the luminance value detected by pixel 22 at time t2, which is the detection time immediately after time _t1 , is I( _t2 ), then event detection unit 23 detects the amount of luminance change at time _t2 , log(I( _t2 ))-log(I( _t1 )), which is expressed as the difference in logarithmic values. Here, the base _of log(.) is "e", and hereinafter, when "logarithm" is mentioned, it is assumed that it is the natural logarithm with a base of "e". Event detection unit 23 detects the sign of the result of the calculation of log(I( _t2 ))-log(I( _t1 )) as the sign of the code value. Hereinafter, the equation for luminance change amount log(I(t ₂ ))-log(I(t ₁ )) will be generalized to express the luminance change amount at time t as Δ(log(I(t)).

The calculation processing unit 13 calculates a physical quantity indicating a change in the scatterer 30 based on the event data output by the event detection unit 23. Below, four methods for calculating the moving speed of the moving scatterer 31 included in the scatterer 30 as a physical quantity indicating a change in the scatterer 30 are described.

(First Method Using the Measurement Apparatus of the First Embodiment)
A first method by the measurement device 1 in the first embodiment will be described with reference to Fig. 2. Fig. 2 is a flowchart showing the flow of the first method by the calculation processing unit 13. As a prerequisite for starting the processing of the flowchart in Fig. 2, it is assumed that the following has been performed. The irradiation unit 11 is installed at a fixed position and direction, and irradiates a measurement region with laser light 40. Here, the measurement region is, for example, a region of the scattering body 30 in which the moving scattering body 31 exists. The light receiving unit 21 of the measurement unit 12 receives light of a speckle pattern generated by interference of the scattered light 50, 51 by the pixels 22-1 to 22-n.

The event detection unit 23 asynchronously detects the amount of luminance change indicating a change in the luminance value output by each of the pixels 22-1 to 22-n. The event detection unit 23 pre-stores a predetermined detection threshold in an internal storage area, and when it detects an amount of luminance change, it refers to the internal storage area and determines whether the detected amount of luminance change is equal to or greater than the detection threshold. When the event detection unit 23 determines that the detected amount of luminance change is equal to or greater than the predetermined detection threshold, it detects the pixel 22 corresponding to the amount of luminance change as a pixel having a predetermined amount of luminance change to be detected. The event detection unit 23 generates event data for the detected pixel 22, that is, event data including the position of the pixel 22, a code value indicating the direction of change in the amount of luminance change, and the detection time, and outputs the generated event data to the calculation processing unit 13.

As described above, when the moving scatterer 31 included in the scatterer 30 is not moving, all of the scatterers 30 are stationary. In this case, the scattered light 51 is included in the scattered light 50, so only the scattered light 50 is generated. The irradiation unit 11 irradiates the laser light 40 with a constant light intensity in a constant direction as described above. That is, the laser light 40 irradiated by the irradiation unit 11 does not change over time. Therefore, the speckle pattern generated by the interference of the scattered light 50 also does not change over time. In this case, the luminance value output by each of the pixels 22-1 to 22-n upon receiving the light of the speckle pattern does not change, so the event detection unit 23 detects a luminance change of "0" from each of the pixels 22-1 to 22-n. However, in reality, due to the presence of noise, the luminance change detected by the event detection unit 23 may not be "0", but it will not be equal to or greater than the detection threshold. Therefore, in this case, the event detection unit 23 does not output event data.

In contrast, when the moving scatterer 31 included in the scatterer 30 is moving, the speckle pattern changes due to interference between the scattered light 50 generated when the stationary parts of the scatterer 30 other than the moving scatterer 31 receive the laser light 40, and the scattered light 51 generated when the moving scatterer 31 receives the laser light 40. When the speckle pattern changes, the luminance values detected by the pixels 22-1 to 22-n corresponding to the positions where the speckle pattern change occurs change. When the event detection unit 23 detects the amount of luminance change from the luminance values output by the pixels 22-1 to 22-n and determines that the detected amount of luminance change is equal to or greater than a predetermined detection threshold, it generates and outputs event data related to the pixel 22 corresponding to the amount of luminance change.

The process flow will be explained below according to the flowchart in FIG. 2. The calculation processing unit 13 takes in the event data output asynchronously by the event detection unit 23 (step Sa1). The calculation processing unit 13 counts the number of event data per unit time for each of the pixels 22-1 to 22-n based on the position of the pixel 22 and the detection time included in each piece of event data (step Sa2).

As the moving speed of the moving scatterer 31 increases, the change in the speckle pattern becomes greater. As the change in the speckle pattern becomes greater, the frequency of the received light intensity signal becomes higher. As the frequency of the received light intensity signal becomes higher, the number of event data per unit time also increases. Therefore, a large number of event data per unit time indicates that the moving speed of the moving scatterer 31 is fast, and the number of event data can indicate the relative moving speed of the moving scatterer 31.

The position of each of the pixels 22-1 to 22-n can be associated with any position of the scatterer 30. The calculation processing unit 13 outputs the number of event data per unit time for each of the pixels 22-1 to 22-n as a value indicating the relative moving speed of the moving scatterer 31 at the position of the scatterer 30 corresponding to each of the pixels 22-1 to 22-n (step Sa3).

(Second Method Using the Measurement Apparatus of the First Embodiment)
The second technique by the measuring device 1 in the first embodiment will be described with reference to Figures 3 and 4. When the second technique is performed, a detection threshold value that is the same as the detection threshold value stored in the internal storage area of the event detection unit 23 is stored in advance in the internal storage area of the calculation processing unit 13.

Figure 3 is a flowchart showing the flow of the second method by the calculation processing unit 13. Note that the premise for starting the process of the flowchart in Figure 3 is the same as the premise for the first method described above. The calculation processing unit 13 takes in event data output asynchronously by the event detection unit 23 (step Sb1). The calculation processing unit 13 multiplies the code value included in the taken-in event data by a detection threshold stored in an internal storage area to calculate a multiplication value for each event data (step Sb2). For each detection time of each of the pixels 22-1 to 22-n, the calculation processing unit 13 integrates the multiplication values corresponding to the detection times before the detection time, and calculates an integration value for each detection time (step Sb3).

For example, the calculation processing unit 13 calculates an integrated value for each detection time of each of the pixels 22-1 to 22-n as follows. An integration start time is determined in advance in the calculation processing unit 13. The calculation processing unit 13 sequentially acquires event data of a certain pixel 22, the detection time of which is after the integration start time. Here, the detection times included in the multiple event data of the pixel 22 that are sequentially acquired by the calculation processing unit 13 are assumed to be t ₁ , t ₂ , ... in order from the earliest time. However, t ₁ , t ₂ , ... are times after the integration start time.

When the calculation processing unit 13 receives the event data of the detection time _t1 of the pixel 22, the calculation processing unit 13 calculates a multiplication value corresponding to the detection time _t1 by the process of step Sb2. Since there is no multiplication value corresponding to a detection time before the detection time _t1 and after the integration start time, the calculation processing unit 13 sets the calculated multiplication value corresponding to the detection time _t1 as the integrated value of the detection time _t1 of the pixel 22. Next, when the calculation processing unit 13 receives the event data of the detection time _t2 of the pixel 22, the calculation processing unit 13 calculates a multiplication value corresponding to the detection time _t2 by the process of step Sb2. The calculation processing unit 13 adds the calculated multiplication value corresponding to the detection time _t2 to the integrated value of the detection time _t1 of the pixel ₂₂ , and sets the added value as the integrated value of the detection time t2 of the pixel 22. In this way, the calculation processing unit 13 repeatedly adds the multiplication value corresponding to the detection time included in the received event data to the integrated value of the previous detection time every time the calculation processing unit 13 receives the event data of the pixel 22, thereby calculating the integrated value for each detection time of the pixel 22. The calculation processing unit 13 performs the same calculation for all the pixels 22-1 to 22-n, and calculates an integrated value for each detection time of the pixels 22-1 to 22-n.

Figure 4 is a bar graph showing an example of an integrated value for each detection time of a certain pixel 22 calculated by the calculation processing unit 13. In the bar graph shown in Figure 4, the horizontal axis is the detection time, and the vertical axis is the integrated value calculated by the calculation processing unit 13. Since the event data output by the event detection unit 23 is asynchronous, the interval between detection times in the bar graph is not a constant interval. The integrated value is a quantized value with the magnitude of the detection threshold as the step width because the value obtained by multiplying the code value "-1" or "+1" by the detection threshold is added. In this case, the change in the bar graph shown in Figure 4 includes an error due to quantization by the magnitude of the detection threshold, but it can be considered as a temporal change when the brightness change amount Δ(log(I(t)) at the pixel 22 is integrated in the time direction, that is, log(I(t)) measured at the position of the pixel 22.

The calculation processing unit 13 calculates each received light intensity signal I(t) from log(I(t)) for each of the pixels 22-1 to 22-n. From the frequency of the received light intensity signal I(t) calculated for each of the pixels 22-1 to 22-n, the calculation processing unit 13 calculates the moving speed of the moving scatterer 31 at the position of the scatterer 30 corresponding to each of the pixels 22-1 to 22-n, for example, by a method using a laser Doppler blood flow meter shown in Reference 1 below (step Sb4).

[Reference 1: Kokyo Co., Ltd., Optimedia, "38-7 Laser Speckle Blood Flow Imaging Method", [online], [searched on August 18, 2021], Internet <https://optipedia.info/laser/handbook/laser-handbook-9th-section/38-7/>]

That is, the calculation processing unit 13 of the second method multiplies a code value indicating the direction of change in the amount of change in luminance contained in the event data by a detection threshold value to calculate a multiplied value. For each detection time of each of the pixels 22-1 to 22-n, the calculation processing unit 13 calculates an integrated value for each detection time by integrating the multiplied values corresponding to detection times prior to the detection time. The calculation processing unit 13 performs processing to calculate the moving speed of the moving scatterer 31 at the position of the scatterer 30 corresponding to each of the pixels 22-1 to 22-n based on the integrated value calculated for each detection time of each of the pixels 22-1 to 22-n.

The moving speed calculated by the calculation processing unit 13 using the second method is a relative moving speed, as in the first method. However, in the case of the first method, if there is variation in the amount of event data generated at each detection time due to external factors such as noise, detection delay depending on the amount of light of the laser light 40, and insufficient bandwidth in the light receiving unit 21 and the event detection unit 23 when a large amount of event data is generated at once, the calculated moving speed will also vary. In contrast, in the second method, the code value is multiplied by the detection threshold and the multiplied value is integrated in the time direction to calculate the received light intensity signal I(t) corresponding to each of the pixels 22-1 to 22-n. Therefore, in the second method, it is possible to calculate a relative moving speed with reduced influence from the external factors.

The calculation processing unit 13 may generate a curve indicated by the reference symbol 100 by performing a filtering process on the bar graph of the integrated value for each detection time of pixel 22 shown in FIG. 4, and may regard the change in the generated curve as log(I(t)) measured at the position of pixel 22. This reduces the error due to quantization and makes it possible to calculate the moving speed of the moving scatterer 31 at the position of the scatterer 30 corresponding to each of pixels 22-1 to 22-n.

(Third Method Using the Measurement Apparatus of the First Embodiment)
A third technique by the measurement device 1 in the first embodiment will be described with reference to Fig. 5 and Fig. 6. When the third technique is performed, the detection threshold value stored in advance in the internal storage area of the event detection unit 23 is preset to the following value. The event detection unit 23 detects in advance a maximum value and a minimum value from among the luminance values detected by each of the pixels 22-1 to 22-n of the light receiving unit 21 upon receiving light of the speckle pattern. The event detection unit 23 calculates the absolute value of the difference between the maximum value and the minimum value of the luminance values detected in advance, and stores the calculated absolute value of the difference in an internal storage area in advance as a detection threshold value.

Figure 5 is a graph showing an example of a change in luminance value detected by a pixel 22 upon receiving light of a speckle pattern, with the horizontal axis representing time and the vertical axis representing luminance value. The magnitude of the detection threshold is the length from the maximum luminance value to the minimum luminance value indicated by reference numeral 110. In this case, the event detection unit 23 generates event data for pixel 22 because the amount of change in luminance detected from pixel 22 is equal to or greater than the detection threshold at the time of peak 121, where the luminance value changes from the maximum value to the minimum value, and at the time of peak 122, where the luminance value changes from the minimum value to the maximum value.

The peak of reference number 121 indicates the state where the interference between the scattered lights 50, 51 is the weakest, and the peak of reference number 122 indicates the state where the interference between the scattered lights 50, 51 is the strongest. Therefore, the occurrence interval between the peaks of reference number 121 and 122 indicates the frequency of the received light intensity signal I(t) measured at the position of pixel 22. Note that the graph in FIG. 5 is an example shown to explain the cases in which event data occurs when the absolute value of the difference between the maximum and minimum luminance values is set as the detection threshold, and an actual speckle pattern light graph is a graph in which light and dark patterns appear periodically.

Figure 6 is a flowchart showing the flow of the third method by the calculation processing unit 13. The premise for starting the processing of the flowchart in Figure 6 is the same as the premise for the first method described above. The calculation processing unit 13 takes in event data output asynchronously by the event detection unit 23 (step Sc1). The calculation processing unit 13 measures the occurrence interval of the event data for each of the pixels 22-1 to 22-n from the detection time of the taken-in event data (step Sc2). The calculation processing unit 13 calculates the frequency of the light receiving intensity signal I(t) corresponding to each of the pixels 22-1 to 22-n based on the measured occurrence interval of the event data for each of the pixels 22-1 to 22-n (step Sc3). The calculation processing unit 13 calculates and outputs the moving speed of the moving scatterer 31 at the position of the scatterer 30 corresponding to each of the pixels 22-1 to 22-n from the frequency of the received light intensity signal I(t) corresponding to each of the pixels 22-1 to 22-n, for example, by using the method using the laser Doppler blood flow meter shown in the above-mentioned Reference 1 (step Sc4).

That is, the calculation processing unit 13 of the third method calculates the occurrence interval of the event data for each of the pixels 22-1 to 22-n based on the detection time included in the event data. The calculation processing unit 13 calculates the moving speed of the moving scatterer 31 at the position of the scatterer 30 corresponding to each of the pixels 22-1 to 22-n based on the calculated occurrence interval of the event data for each of the pixels 22-1 to 22-n.

In the third method, as described above, event data occurs only at the time when the received light intensity signal I(t) peaks. Therefore, the frequency of the received light intensity signal I(t) can be directly calculated from the occurrence interval of the event data. Therefore, it is not necessary to count the number of event data as in the first method, or to calculate an integrated value as in the second method, and it is possible to calculate the moving speed of the moving scatterer 31 at the position of the scatterer 30 corresponding to each of the pixels 22-1 to 22-n with less calculations than the first and second methods. In the third method, since the frequency of the received light intensity signal I(t) measured at each of the positions of the pixels 22-1 to 22-n is calculated, it is possible to calculate the absolute moving speed of the moving scatterer 31 at the position of the scatterer 30 corresponding to each of the pixels 22-1 to 22-n, rather than calculating the relative moving speed as in the first and second methods.

In the third method described above, it is assumed that there is no variation in the maximum and minimum luminance values detected by each of the pixels 22-1 to 22-n, and the absolute value of the difference between the maximum and minimum luminance values detected by each of the pixels 22-1 to 22-n upon receiving the light of the speckle pattern is set as a common detection threshold for all of the pixels 22-1 to 22-n. In contrast, if there is variation in the maximum and minimum luminance values detected by each of the pixels 22-1 to 22-n, the event detection unit 23 may detect the maximum and minimum luminance values for each of the pixels 22-1 to 22-n in advance, and set the absolute value of the difference between the maximum and minimum luminance values corresponding to each of the pixels 22-1 to 22-n as an individual detection threshold for each of the pixels 22-1 to 22-n.

(Fourth Method Using the Measurement Apparatus of the First Embodiment)
A fourth method by the measuring device 1 in the first embodiment will be described with reference to FIG. 7. The fourth method is assumed to be applied when the area of the moving scatterer 31 included in the scatterer 30 is sufficiently large. When the area of the moving scatterer 31 included in the scatterer 30 is sufficiently large, the light of the speckle pattern in the part where the pattern is changed due to the interference of the scattered light 50, 51 can be received by many pixels 22-1 to 22-n of the light receiving unit 21. In this case, an image showing the degree of intensity of the light of the speckle pattern measured at the light receiving surface of the light receiving unit 21, i.e., the positions of the pixels 22-1 to 22-n, is generated for each detection time from the event data detected by the event detection unit 23, and the images at two different detection times are compared, whereby a temporal change in the speckle pattern can be detected.

Figure 7 is a flowchart showing the flow of the fourth method by the calculation processing unit 13. The premise for starting the process of the flowchart in Figure 7 is the same as the premise for the first method described above. The calculation processing unit 13 takes in event data output asynchronously by the event detection unit 23 (step Sd1). For each detection time, the calculation processing unit 13 integrates the code values corresponding to the detection times before the detection time for each of the pixels 22-1 to 22-n, and calculates the integrated value for each detection time (step Sd2). Note that in the fourth method, the procedure by which the calculation processing unit 13 integrates the code values is the same as the procedure for integrating the multiplied values in the second method, except that the target of integration is changed from the multiplied values to the code values.

The calculation processing unit 13 regards the calculated integrated value for each detection time for each of the pixels 22-1 to 22-n as the pixel value, and generates image data for each detection time (step Sd3). In the second method, the integrated value is a value obtained by multiplying the code value by the detection threshold value, and the change in the integrated value for each detection time for each of the pixels 22-1 to 22-n is regarded as log(I(t)) obtained by integrating Δlog(I(t)) for each of the pixels 22-1 to 22-n. In contrast, the integrated value for each detection time for each of the pixels 22-1 to 22-n calculated by the fourth method indicates the degree of intensity of the light of the speckle pattern. Therefore, in step Sd3, the image represented by the image data for the detection time t generated by the calculation processing unit 13 is an image that indicates the degree of intensity of the light of the speckle pattern at the detection time t.

The calculation processing unit 13 calculates the cross-correlation of the image data at two different detection times that are arbitrarily selected (step Sd4). If a peak occurs in the cross-correlation calculated by the calculation processing unit 13, the position at which the peak occurs indicates the amount of movement of the speckle pattern between the two different detection times. The calculation processing unit 13 divides the position of the peak obtained by the cross-correlation, i.e., the amount of movement of the speckle pattern, by the time difference between the two different detection times to calculate the speed of the speckle pattern, i.e., the overall speed of the moving scatterer 31 (step Sd5).

That is, the calculation processing unit 13 of the fourth technique calculates, for each detection time of each of the pixels 22-1 to 22-n, an integrated value of the code values included in the event data corresponding to the detection times before the detection time, as the pixel value of the pixels 22-1 to 22-n for each detection time. The calculation processing unit 13 generates image data for each detection time from the calculated pixel values, and calculates the moving speed of the moving scatterer 31 based on the generated image data for two different detection times.

In the fourth method described above, the amount of movement of the speckle pattern is calculated by calculating the cross-correlation between image data at two different detection times, but the amount of movement of the speckle pattern may be calculated by a method other than cross-correlation, such as pattern matching.

In the fourth method described above, in step Sd2, the calculation processing unit 13 accumulates the code values corresponding to the detection times before each detection time for each of the pixels 22-1 to 22-n, and calculates an accumulated value for each detection time. Alternatively, the calculation processing unit 13 may generate image data in which the pixel value is the code value of the event data corresponding to each of the pixels 22-1 to 22-n for each detection time. In this case, the calculation processing unit 13 generates image data by setting the pixel values of the pixels 22-1 to 22-n for which no event data exists corresponding to the detection time for which image data is to be generated to "0". Therefore, the pixel values of the image data generated by the calculation processing unit 13 will be either "-1", "0", or "+1".

The image represented by the image data generated by the calculation processing unit 13 does not undergo integration as in the fourth method described above, and therefore the difference in intensity is not as clear as in the image data generated by the fourth method, but it is an image that shows the degree of intensity of the light of the speckle pattern at the detection time. Therefore, the calculation processing unit 13 can calculate the amount of movement of the speckle pattern by comparing image data at two different detection times. Note that the method for comparing image data at two different detection times may be the cross-correlation used in the fourth method described above, or a method other than cross-correlation, such as pattern matching. The calculation processing unit 13 can calculate the speed of the speckle pattern, i.e., the overall speed of the moving scatterer 31, by dividing the calculated amount of movement by the time difference between the two different detection times.

In the measurement device 1 of the first embodiment described above, the irradiation unit 11 generates coherent light. The measurement unit 12 receives light of a speckle pattern generated by the interference of scattered light 50, 51 generated when the scatterer 30 receives the coherent light, using a plurality of pixels 22-1 to 22-n, detects pixels 22-1 to 22-n having a detection target luminance change amount in which the luminance change amount indicating the change in luminance value detected by each of the pixels 22-1 to 22-n receiving the light of the speckle pattern is predetermined, and generates event data including the position of the detected pixel 22-1 to 22-n, a code value indicating the change direction of the luminance change amount of the pixel 22-1 to 22-n, and a detection time indicating the time of detection. The calculation processing unit 13 calculates the speed of movement of the position of the moving scatterer 31 corresponding to each of the pixels 22-1 to 22-n, or the moving speed of the moving scatterer 31, based on the event data generated by the measurement unit 12.

A frame camera equipped with a typical image sensor outputs the brightness value accumulated for each pixel for each frame. In a frame camera, the accumulation time, i.e. the exposure time and the dynamic range of the signal, are the same for all pixels. Therefore, when there are very bright pixels and very dark pixels, whiteout, blackout, quantization errors, etc. will occur. When the brightness of a scene changes drastically due to the influence of lighting, etc., it may not be possible to adjust the exposure time, resulting in whiteout and blackout.

In contrast, as described above, an event camera asynchronously outputs event data each time the amount of change in luminance of each pixel exceeds the detection threshold. Therefore, problems such as blown-out highlights, crushed shadows, and quantization errors do not occur. Because the event data output by an event camera is output asynchronously, it is very sparse data compared to the image data output by a frame camera. Therefore, less memory capacity is required to store the event data, and less transmission capacity is required when transmitting the event data. Because the event data is very sparse data, an event camera can keep costs such as the amount of calculations and power consumption required for shooting and data processing much lower than a frame camera.

For example, if one tries to achieve a temporal resolution in event data equivalent to that of image data output by a frame camera, it is possible to achieve this with event data of a much smaller volume than the volume of image data output by a frame camera. In other words, if event data of a volume equivalent to that of image data output by a frame camera is collected, a very high temporal resolution can be obtained. For these reasons, the use of an event camera makes it possible to perform measurements stably, at low cost, and with a very high temporal resolution in environments with low light levels or where the lighting changes drastically.

In the measurement device 1 of the first embodiment, an event camera, which has the above-mentioned advantages over a frame camera, is applied to the measurement unit 12. Therefore, unlike a frame camera, there is no need to perform multiple continuous measurements, and the measurement device 1 can measure changes in an object whose changes are not constant based on the speckle pattern under conditions where there are restrictions on the time interval of measurements, such as so-called real-time measurement.

In the first embodiment, the irradiation unit 11 irradiates the scattering body 30 with planar laser light 40, which is a diffused laser light. Alternatively, the position of an optical element such as a convex lens provided inside the irradiation unit 11 may be adjusted so that the irradiation unit 11 irradiates a specific location of the scattering body 30 with spot laser light, i.e., non-diffused laser light. For example, a cylindrical lens may be used as the optical element provided inside the irradiation unit 11, so that the irradiation unit 11 irradiates the scattering body 30 with line-shaped laser light. A projector equipped with a light source that generates laser light may be used as the irradiation unit 11, so that laser light of any pattern may be irradiated at any timing.

Depending on the performance of the event camera applied to the measurement unit 12, if a change in luminance value occurs in a large number of pixels 22-1 to 22-n at once, the bandwidth of the light receiving unit 21 and the event detection unit 23 may be insufficient, and all event data may not be output to the calculation processing unit 13. In such cases, the lack of bandwidth in the light receiving unit 21 and the event detection unit 23 can be eliminated by making the laser light 40 irradiated by the irradiation unit 11 the spot laser light, line-shaped laser light, or laser light of an arbitrary pattern as described above, narrowing the range to which the laser light 40 is irradiated, or irradiating different parts of the scatterer 30 with the laser light 40 at different times.

The laser light 40 emitted by the irradiation unit 11 is a spot laser light, which is irradiated only in a small range of the scatterer 30, for example, the range of the light receiving surface of one pixel 22, and adjusted so that the light of the speckle pattern is measured only by one pixel 22. In this case, by performing triangulation based on the irradiation position of the irradiation unit 11 and the position of the pixel 22, it is possible to calculate the position in three-dimensional space where the laser light 40 is irradiated on the scatterer 30. Therefore, by measuring while shifting the irradiation position of the laser light 40, it is possible to calculate the position in three-dimensional space of the scatterer 30 corresponding to each of the pixels 22-1 to 22-n, and the moving speed of the moving scatterer 31 when it is moving at a constant speed.

The irradiation unit 11 may be a device that irradiates a raster-scan type laser, such as a MEMS (Micro Electro Mechanical Systems) laser projector. In this case, the irradiation unit 11 irradiates a point on the scattering medium 30 with the laser light 40, and changes the irradiation destination of the laser light 40 point by point so as to raster-scan the scattering medium 30 with the laser light 40. The event detection unit 23 of the measurement unit 12 generates event data only when constructive interference occurs due to the interference between the scattered lights 50 and 51. Specifically, the event detection unit 23 sets the absolute value of the difference between the minimum and maximum luminance values as a detection threshold, and generates event data only when the luminance value changes from the minimum to the maximum and detects a luminance change amount equal to or greater than the detection threshold. This allows the calculation processing unit 13 to detect the interval during which constructive interference occurs from the occurrence interval of the event data in each of the pixels 22-1 to 22-n. The calculation processing unit 13 can calculate the frequency of the received light intensity signal measured at each position of the pixels 22-1 to 22-n from the detected interval, and can calculate the moving speed of the moving scatterer 31 at the position of the scatterer 30 corresponding to each of the pixels 22-1 to 22-n. In this case, the laser light 40 is irradiated to only one point at a time on the scatterer 30, so the range of the pixels 22-1 to 22-n where the luminance value changes is also limited, and a large amount of event data is not generated at once, making it possible to avoid processing lags due to the generation of a large amount of event data that may occur when the laser light 40 is irradiated to a wide area at once. In addition, it is possible to measure a large area with a low-power laser compared to the case where the laser light 40 is irradiated to a wide area at once.
In addition, by using a raster scan type laser irradiation device that can arbitrarily control the scan speed, it is possible to arbitrarily control the timing of moving from one irradiation position to the next irradiation position, and to match the timing of the sleep of the event sensor with the timing of the movement of the irradiation position, and to detect only events caused by changes in speckles without detecting events caused by the movement of the irradiation position. In a general event sensor, after detecting an event in each pixel, a certain sleep period is passed before the next event is detected, so that events caused by brightness changes that occur during the sleep period are not detected. The sleep period and the timing of the movement of the irradiation position may be set in advance, or may be dynamically controlled using a synchronization device. Alternatively, for a similar laser irradiation device, the calculation processing unit 13 may perform a process of classifying events caused by changes in the irradiation position and events caused by changes in the speckles. For example, when the irradiation position is changed every T seconds, events occurring at a period T can be determined to be caused by changes in the irradiation position. Alternatively, for a series of events occurring during the irradiation period for each pixel, events for a certain period at the beginning and end can be determined to be caused by changes in the irradiation position.

Second Embodiment
8 is a block diagram showing a measuring device 1a in the second embodiment and a scatterer 32 that is a measurement target of the measuring device 1a. In the second embodiment, the same components as those in the first embodiment are given the same reference numerals, and different components will be described below. The scatterer 32 in the second embodiment may be any object, as long as the object changes shape over time and receives coherent light to generate scattered light.

The measurement device 1a includes an irradiation unit 11a, a measurement unit 12, a calculation processing unit 13a, a light branching unit 14, and a light focusing unit 15. The irradiation unit 11a adjusts the position of the optical element provided inside the irradiation unit 11 of the first embodiment from a position where the laser light is diffused to a position where the laser light travels straight, and generates and irradiates the straight-traveling laser light 41 as coherent light with a constant light intensity. The light branching unit 14 branches the optical path from the irradiation point of the laser light 41 of the irradiation unit 11a to the light receiving surface of the light receiving unit 21 of the measurement unit 12 into two optical paths so that an optical path difference is generated. FIG. 8 shows, as an example, a configuration in which the light branching unit 14 branches the laser light 41 irradiated by the irradiation unit 11a so that an optical path difference is generated, and two laser lights 42 and 43 are irradiated to the scattering body 32.

When the scatterer 32 receives the laser light 42, the scattered light 52 is irradiated in the direction of the light receiving surface of the light receiving unit 21, and when the scatterer 32 receives the laser light 43, the scattered light 53 is irradiated in the direction of the light receiving surface of the light receiving unit 21. The light focusing unit 15 focuses the two light paths branched by the light branching unit 14, i.e., focuses the scattered light 52 and the scattered light 53, and forms a speckle pattern generated by the interference of the focused scattered light 52, 53 on the light receiving surface of the light receiving unit 21. For example, a convex lens is used as the light focusing unit 15, but an optical element other than a convex lens may be used as long as it can form an image of the speckle pattern on the light receiving surface of the light receiving unit 21.

Figure 9 shows four different optical system configurations as examples of optical systems that can be applied to the optical branching unit 14 and the optical focusing unit 15. The diagrams of the four optical systems shown in Figures 31 and 34 of Reference 2 below are quoted, and symbols are added to explain the optical system configurations. For ease of explanation, the order of the figures is reversed compared to Figures 31 and 34 of Reference 2.

[Reference 2: Kokyo Co., Ltd., Optimedia, "31.3 Speckle", [online], [searched on August 18, 2021], Internet <https://optipedia.info/laser/handbook/laser-handbook-7th-section/31-3/>]

(Configuration of the optical branching section using the two-beam method)
Fig. 9(a) is an example of the light branching unit 14 that branches one laser beam 41 shown in Fig. 8 into two laser beams 42 and 43, and is an optical system called a two-beam method. In Fig. 9(a), a half mirror 61, mirrors 62 and 64, and convex lenses 63 and 65 are optical elements included in the light branching unit 14. Fig. 9(a) shows an example of the light focusing unit 15 that includes a convex lens 15a, and Figs. 9(b) to (d) also show similar examples. In Fig. 9(a), the scatterer 32 before its shape is deformed is shown as a scatterer 32-1, and the scatterer 32 after its shape is deformed is shown as a scatterer 32-2.

The positional relationship of the convex lenses 63, 65, and 15a and the mirrors 62 and 64 is as follows. The angle between the optical axis 66 of the convex lens 15a and the optical axis 67, which is the optical axis of the convex lens 63 in the direction in which the laser light is reflected by the mirror 62, and the angle between the optical axis 66 and the optical axis 68, which is the optical axis of the convex lens 65 in the direction in which the laser light is reflected by the mirror 64, coincide with each other, and the optical axes 66, 67, and 68 intersect on the surface of the scatterer 32-1 before deformation. The angle between the optical axis 67 and the optical axis 68 is set to be larger than the aperture angle of the convex lens 15a. The convex lens 15a is arranged so that its optical axis is perpendicular to the light receiving surface of the light receiving unit 21 of the measurement unit 12, between the scatterers 32-1 and 32-2 and the light receiving unit 21, and at a position where the speckle pattern is imaged on the light receiving surface of the light receiving unit 21.

The half mirror 61 and the mirrors 62 and 64 are arranged so that the laser light 41 emitted by the irradiation unit 11a is reflected by the half mirror 61 and reaches the mirror 62, and the laser light 41 passes through the half mirror 61 and reaches the mirror 64. The half mirror 61 and the mirrors 62 and 64 are arranged so that an optical path difference occurs in the optical path from the irradiation point of the irradiation unit 11a to the light receiving surface of the light receiving unit 21.

By arranging as described above, the laser light 41 irradiated by the irradiation unit 11a is split into a laser light reflected by the half mirror 61 and reaching the mirror 62, and a laser light transmitted through the half mirror 61 and reaching the mirror 64. The mirror 62 reflects the received laser light in the direction of the optical axis 67, and the reflected laser light is diffused by the convex lens 63 and irradiated to the scatterers 32-1 and 32-2. The mirror 64 reflects the received laser light in the direction of the optical axis 68, and the reflected laser light is diffused by the convex lens 65 and irradiated to the scatterers 32-1 and 32-2. For example, the laser light 42 irradiated by the light branching unit 14 in FIG. 8 corresponds to the laser light diffused by the convex lens 63, and the laser light 43 corresponds to the laser light diffused by the convex lens 65. Hereinafter, the laser light diffused by the convex lens 63 is referred to as the laser light 42, and the laser light diffused by the convex lens 65 is referred to as the laser light 43.

The scattered light generated when the scatterer 32-1 before deformation receives the laser light 42 is referred to as scattered light 52-1, and the scattered light generated when the scatterer 32-2 after deformation receives the laser light 42 is referred to as scattered light 52-2. Similarly, the scattered light generated when the scatterer 32-1 before deformation receives the laser light 43 is referred to as scattered light 53-1, and the scattered light generated when the scatterer 32-2 after deformation receives the laser light 43 is referred to as scattered light 53-2. The scattered light 52-1, 52-2, 53-1, 53-2 is focused by the convex lens 15a and reaches the light receiving surface of the light receiving unit 21.

The scattered lights 52-1, 53-1 generated from the scatterer 32-1 before deformation are generated by laser light irradiated from two directions with an optical path difference, and a speckle pattern reflecting the phase difference generated by the optical path difference due to interference between the scattered lights 52-1, 53-1 is imaged on the light receiving surface of the light receiving unit 21. Here, it is assumed that the surface to be measured of the scatterer 32-1, i.e. the surface irradiated with the laser light 42, 43, is deformed so as to move in the direction indicated by the arrow 39a, becoming the scatterer 32-2. Hereinafter, the displacement due to such deformation is referred to as an in-plane displacement, which is a displacement parallel to the surface to be measured. The scattered light 52-2, 53-2 from the deformed scatterer 32-2 is also generated by laser light irradiated from two directions with an optical path difference, and the scattered light 52-2, 53-2 interfere with each other, resulting in a speckle pattern that reflects the optical path difference and the phase difference caused by the amount of displacement when the scatterer 32-1 is transformed into the scatterer 32-2, and is imaged on the light receiving surface of the light receiving unit 21.

(Configuration of the optical branching section using the reference light method)
The optical system shown in FIG. 9B is an optical system called a reference light method. In FIG. 9B, the scatterer 32 before its shape is deformed is shown as a scatterer 32-1, and the scatterer 32 after its shape is deformed is shown as a scatterer 32-2. In the reference light method, the scattered light generated by the scatterer 32-1 receiving the laser light is also referred to as the scattered light 52-1, and the scattered light generated by the scatterer 32-2 receiving the laser light is also referred to as the scattered light 52-2. In the reference light method, unlike the above-mentioned two-beam method, two laser lights are not irradiated onto the scatterers 32-1 and 32-2, but one of the laser lights is irradiated onto the scatterers 32-1 and 32-2, and the other laser light is irradiated onto the light receiving surface of the light receiving unit 21 as a reference light.

In FIG. 9(b), a convex lens 71, a half mirror 72, and a mirror 73 are optical elements included in the light branching unit 14. The mirror 73 is arranged so that the reflecting surface of the mirror 73 is perpendicular to the direction in which the laser light 41 irradiated by the irradiation unit 11a travels straight. The half mirror 72 is arranged at a position tilted at 45 degrees to the direction in which the laser light 41 irradiated by the irradiation unit 11a travels straight. The convex lens 71 is arranged so that its optical axis coincides with the direction in which the laser light 41 travels straight. The convex lens 15a, which is an example of the light focusing unit 15, is arranged so that its optical axis is perpendicular to the light receiving surface of the light receiving unit 21 of the measurement unit 12. The convex lens 15a is arranged at a position where the scattered light 52-1 and 52-2 that arrive after passing through the half mirror 72 are focused to form a speckle pattern on the light receiving surface of the light receiving unit 21.

By arranging as described above, the laser light 41 emitted by the irradiation unit 11a is diffused by the convex lens 71, and the diffused laser light 41 is split into a laser light reflected by the half mirror 72 and traveling in the direction of the scatterers 32-1 and 32-2, and a laser light that passes through the half mirror 72 and reaches the mirror 73. Hereinafter, the laser light that passes through the half mirror 72 and reaches the mirror 73 is referred to as the reference light. The scattered light 52-1 and 52-2 generated when the scatterers 32-1 and 32-2 receive the laser light travels in the direction of the half mirror 72, passes through the half mirror 72, and is collected by the convex lens 15a to reach the light receiving surface of the light receiving unit 21. On the other hand, the reference light is reflected by the mirror 73 in the direction of the half mirror 72, is further reflected by the half mirror 72 and travels in the direction of the convex lens 15a, is collected by the convex lens 15a and reaches the light receiving surface of the light receiving unit 21.

When the scattered light 52-1 and the reference light reach the light receiving surface of the light receiving unit 21, the scattered light 52-1 and the reference light interfere with each other, and a speckle pattern reflecting the phase difference caused by the optical path difference between the scattered light 52-1 and the reference light is imaged on the light receiving surface of the light receiving unit 21. Now, assume that the scatterer 32-1 is deformed so that it moves in the direction indicated by the arrow 39b, and becomes the scatterer 32-2. Hereinafter, the displacement caused by such deformation is referred to as out-of-plane displacement, which is a displacement that is not parallel to the surface of the scatterer 32-1 to be measured, i.e., the surface onto which the laser light reflected by the half mirror 72 is irradiated. After the scatterer 32-1 transforms into the scatterer 32-2, the scattered light 52-2 and the reference light reach the light receiving surface of the light receiving unit 21. As a result of interference between the scattered light 52-2 and the reference light, a speckle pattern reflecting the optical path difference between the scattered light 52-2 and the reference light and the phase difference caused by the amount of displacement when the scatterer 32-1 transforms into the scatterer 32-2 is formed on the light receiving surface of the light receiving unit 21.

(Configuration of optical branching section using two-aperture method)
The optical system shown in FIG. 9(c) is an optical system called a two-aperture method. In FIG. 9(c), the scatterer 32 before its shape is deformed is shown as a scatterer 32-1, and the scatterer 32 after its shape is deformed is shown as a scatterer 32-2. In the two-aperture method, the scattered light generated by the scatterer 32-1 receiving the laser light is also referred to as the scattered light 52-1, and the scattered light generated by the scatterer 32-2 receiving the laser light is also referred to as the scattered light 52-2. In the two-aperture method, a double-aperture plate 82 having slits in two places is disposed on the optical path from the irradiation point of the laser light 41 of the irradiation unit 11a to the light receiving surface of the light receiving unit 21 of the measurement unit 12, thereby generating two optical paths with an optical path difference.

The convex lens 81 and the double aperture plate 82 are optical elements included in the light branching unit 14. The convex lens 81 is arranged so that its optical axis coincides with the direction in which the laser light 41 irradiated by the irradiation unit 11a travels straight ahead. The convex lens 15a, which is an example of the light focusing unit 15, is arranged so that its optical axis 83 is perpendicular to the light receiving surface of the light receiving unit 21 of the measurement unit 12 and the surface of the flat portion of the double aperture plate 82. The convex lens 15a is arranged at a position where the scattered light 52-1, 52-2 that arrives after passing through the double aperture plate 82 is collected and a speckle pattern is formed on the light receiving surface of the light receiving unit 21. The double aperture plate 82 is arranged so that the surface of the flat portion is parallel to the light receiving surface of the light receiving unit 21, and further arranged so that the distance from the position where it intersects with the optical axis 83 to each of the two slits is equal.

By arranging as described above, the laser light 41 emitted by the irradiating unit 11a is diffused by the convex lens 81, and the diffused laser light 41 is irradiated to the scatterers 32-1 and 32-2. The scattered light 52-1 and 52-2 generated when the scatterers 32-1 and 32-2 receive the diffused laser light 41 is diffracted and an optical path difference occurs when passing through the two slits in the double aperture plate 82. The scattered light 52-1 and 52-2 that passed through the two slits in the double aperture plate 82 is focused by the convex lens 15a and reaches the light receiving surface of the light receiving unit 21.

When the scattered light 52-1 reaches the light receiving surface of the light receiving unit 21 through two optical paths with an optical path difference caused by the double aperture plate 82, a speckle pattern reflecting the phase difference caused by the optical path difference is formed on the light receiving surface of the light receiving unit 21. Here, it is assumed that the surface to be measured of the scatterer 32-1, that is, the surface irradiated with the laser light diffused by the convex lens 81, is deformed so as to move in the direction indicated by the arrow of symbol 39c and becomes the scatterer 32-2. In other words, it is assumed that the same in-plane displacement as that of the two-beam method shown in FIG. 9(a) occurs in the scatterer 32-1. In this case, when the scattered light 52-2 reaches the light receiving surface of the light receiving unit 21 through two optical paths with an optical path difference caused by the double aperture plate 82, a speckle pattern reflecting the optical path difference and the phase difference caused by the amount of displacement when the scatterer 32-1 is deformed to the scatterer 32-2 is formed on the light receiving surface of the light receiving unit 21.

(Configuration of optical branching section using the lateral shift method)
The optical system shown in FIG. 9(d) is an optical system called a lateral shift method. In the lateral shift method, a biprism 92 is disposed in the middle of the optical path from the irradiation point of the laser light 41 of the irradiation unit 11a to the light receiving surface of the light receiving unit 21 of the measurement unit 12, thereby generating two optical paths with an optical path difference. The convex lens 91 and the biprism 92 are optical elements included in the light branching unit 14. The convex lens 91 is disposed so that its optical axis 93 coincides with the direction in which the laser light 41 irradiated by the irradiation unit 11a travels straight. The biprism 92 is a so-called double prism, and is a triangular column-shaped prism whose cross section is an isosceles triangle with a vertex angle close to 180 degrees. The biprism 92 is disposed so that the surface including the base of the isosceles triangle shape is parallel to the light receiving surface of the light receiving unit 21. Convex lens 15a, which is an example of light focusing unit 15, is arranged so that its optical axis is perpendicular to the light receiving surface of light receiving unit 21 of measurement unit 12 and a surface including the base of the isosceles triangle shape of biprism 92, and intersects with the side including the apex angle of the isosceles triangle shape. Convex lens 15a is arranged at a position where scattered light 52-1, 52-2 that has passed through biprism 92 and arrived thereat is collected, and a speckle pattern is imaged on the light receiving surface of light receiving unit 21.

By arranging as described above, the laser light 41 irradiated by the irradiation unit 11a is diffused by the convex lens 91, and the diffused laser light is irradiated to the scattering body 32. The scattered light 52 generated by the scattering body 32 receiving the laser light passes through the biprism 92. When the scattered light 52 passes through the biprism 92, the optical action of the biprism 92 causes a double image 32D of the scattering body 32 to be formed at a slightly shifted position on the surface of the measurement object on which the laser light of the scattering body 32 is irradiated, as shown in FIG. 9(d). Here, the light that forms the double image 32D and is generated by the biprism 92 is referred to as double image light 52D. An optical path difference occurs between the scattered light 52 and the double image light 52D due to the optical action of the biprism 92. The scattered light 52 transmitted through the biprism 92 and the double image light 52D generated by the biprism 92 are condensed by the convex lens 15a and reach the light receiving surface of the light receiving unit 21.

When the scattered light 52 and the double image light 52D reach the light receiving surface of the light receiving unit 21, a speckle pattern reflecting the phase difference caused by the optical path difference is formed on the light receiving surface of the light receiving unit 21. Here, assume that the out-of-plane displacement shown in the reference light method case of FIG. 9(b) occurs in the scatterer 32, that is, the scatterer 32 is displaced not parallel to the surface of the measurement target. In this case, when the scattered light 52 and the double image light 52D reach the light receiving surface of the light receiving unit 21, a speckle pattern reflecting the phase difference caused by the optical path difference and the amount of displacement caused by the deformation of the scatterer 32 is formed on the light receiving surface of the light receiving unit 21.

By using the optical branching unit 14 to which any of the optical systems shown in Figures 9(a) to (d) is applied, a speckle pattern generated by the scatterer 32-1 before deformation and a speckle pattern generated by the scatterer 32-2 after deformation can be obtained. The square of the difference between the two speckle patterns before and after deformation is calculated to obtain an interference pattern. The brightness of the obtained interference pattern depends on the amount of displacement when the scatterer 32 is deformed, and it is darkest when the amount of displacement is an integer multiple of the wavelength of the laser light 41, and it is brightest when the amount of displacement is a half-integer multiple of the wavelength of the laser light 41. One interference pattern indicates the same amount of displacement, and when the surface of the scatterer 32 is continuous, the interference pattern can be regarded as a contour line in which the altitude is replaced by the amount of displacement. Therefore, in areas where the spacing between the interference patterns is fine, the change in the amount of displacement is large, indicating that the shape of the scatterer 32 is changing rapidly, and in areas where the spacing between the interference patterns is coarse, the change in the amount of displacement is small, indicating that the shape of the scatterer 32 is changing gradually. In this way, the speckle pattern corresponding to the measurement area is received by pixels 22-1 to 22-n of the light receiving section 21 of the measurement unit 12, and by comparing it before and after the deformation of the shape of the scatterer 32, it is possible to estimate the amount of displacement of the position of the scatterer 32 corresponding to each of pixels 22-1 to 22-n that occurs due to the deformation of the shape of the scatterer 32.

(Processing by the Measuring Device of the Second Embodiment)
The process by the measurement device 1a in the second embodiment will be described with reference to Fig. 10. Fig. 10 is a flowchart showing the flow of the process by the calculation processing unit 13a. Note that the process by the measurement device 1a will be described assuming that the optical system of the two-beam method shown in Fig. 9A is applied as the light branching unit 14 and the convex lens 15a is applied as the light focusing unit 15.

As a premise for starting the process of the flowchart in FIG. 10, the following is assumed to have been performed. The irradiation unit 11a generates laser light 41 and outputs it to the light branching unit 14. In the light branching unit 14, the half mirror 61 branches the laser light 41 irradiated by the irradiation unit 11a into a laser light that reaches the mirror 62 and a laser light that reaches the mirror 64. The mirror 62 reflects the received laser light in the direction of the optical axis 67, and the reflected laser light is diffused by the convex lens 63 to become the laser light 42. The mirror 64 reflects the received laser light in the direction of the optical axis 68, and the reflected laser light is diffused by the convex lens 65 to become the laser light 43. The laser light 42 and the laser light 43 are irradiated to the scattering body 32. The scattered light 52 generated by the scattering body 32 receiving the laser light 42 and the scattered light 53 generated by the scattering body 32 receiving the laser light 43 are collected by the convex lens 15a. The scattered light 52 collected by the convex lens 15a interferes with the scattered light 53, resulting in a speckle pattern being generated in the pixels 22-1 to 22-n on the light receiving surface of the light receiving unit 21.

When the shape of the scatterer 32 is not deformed, there is no change in the scattered light 52 and the scattered light 53, and therefore the speckle pattern generated in the pixels 22-1 to 22-n on the light receiving surface of the light receiving unit 21 also does not change. In this case, the luminance value output by each of the pixels 22-1 to 22-n upon receiving the light of the speckle pattern does not change, so the event detection unit 23 detects a luminance change of "0" from each of the pixels 22-1 to 22-n. However, in reality, due to the presence of noise, etc., the luminance change detected by the event detection unit 23 may not be "0", but will never be greater than the detection threshold. Therefore, in this case, the event detection unit 23 does not output event data.

In contrast, when the shape of the scatterer 32 is deformed, the scattered light 52 and the scattered light 53 change according to the amount of displacement when the shape of the scatterer 32 is deformed. Therefore, the speckle pattern changes according to the changes in the scattered light 52 and the scattered light 53. When the speckle pattern changes, the luminance value detected by the pixels 22-1 to 22-n corresponding to the position where the speckle pattern change occurs changes. When the event detection unit 23 detects the amount of luminance change from the luminance values output by the pixels 22-1 to 22-n and determines that the detected amount of luminance change is equal to or greater than a predetermined detection threshold, the event detection unit 23 generates and outputs event data for the pixel 22 corresponding to the amount of luminance change.

The process flow will be explained below according to the flowchart in FIG. 10. The calculation processing unit 13a takes in the event data output asynchronously by the event detection unit 23 (step Se1). The calculation processing unit 13a counts the number of event data for each of the pixels 22-1 to 22-n within a predetermined time based on the position of the pixel 22 included in each piece of event data and the detection time (step Se2).

The calculation processing unit 13a generates image data in which the number of event data for each of the pixels 22-1 to 22-n is used as the pixel value (step Se3). As described above, the brightness of the interference fringes obtained by calculating the square of the difference between the two speckle patterns before and after the deformation depends on the amount of displacement when the shape of the scatterer 32 is deformed. The bright parts of the interference fringes have a large change in luminance before and after the deformation of the scatterer 32, and therefore there is a lot of event data. In contrast, the dark parts of the interference fringes have a small change in luminance before and after the deformation of the scatterer 32, and therefore there is little event data or no event data. Therefore, the image represented by the image data generated by the calculation processing unit 13a is an image that shows the change in the interference fringes.

As described above, in areas where the spacing between the interference fringes is fine, the amount of displacement is large, indicating that the scatterer 32 is changing rapidly, and in areas where the spacing between the interference fringes is coarse, the amount of displacement is small, indicating that the scatterer 32 is changing slowly. The calculation processing unit 13a performs frequency analysis on the generated image data to calculate the fineness of the spacing between the interference fringes at the positions of each of the pixels 22-1 to 22-n. The calculation processing unit 13a calculates the amount of displacement at the positions of the scatterer 32 corresponding to each of the pixels 22-1 to 22-n from the calculated fineness of the spacing between the interference fringes at the positions of each of the pixels 22-1 to 22-n (step Se4).

9(a) and (c), that is, when the two-beam method and the two-aperture method are applied, the calculation processing unit 13a calculates the displacement amount of the scatterer 32 in the direction of the symbols 39a and 39c in FIG. 9(a) and (c), that is, in the direction parallel to the surface of the scatterer 32 to be measured. In the case of FIG. 9(b), that is, when the reference light method is applied, the calculation processing unit 13a calculates the displacement amount of the scatterer 32 in the direction of the symbol 39b in FIG. 9(b), that is, in the direction not parallel to the surface of the scatterer 32 to be measured. In the case of FIG. 9(d), that is, in the case of the lateral shift method, the calculation processing unit 13a calculates the inclination of the direction of the shift of the scatterer 32 and the double image 32D caused by the deformation due to the out-of-plane displacement of the scatterer 32 as the displacement amount of the scatterer 32. Therefore, when the shift amount of the scatterer 32 and the double image 32D is sufficiently small, the displacement amount calculated by the calculation processing unit 13a indicates the differential value of the out-of-plane displacement of the scatterer 32. Which optical system from Figures 9(a) to (d) is applied to the optical branching section 14 will be determined appropriately depending on the direction in which the amount of displacement in the scatterer 32 is to be detected.

In the measurement device 1a of the second embodiment described above, the irradiation unit 11a generates coherent light to be irradiated onto the scatterer 32, the shape of which changes. The light branching unit 14 branches the optical path from the irradiation unit 11a to the multiple pixels 22-1 to 22-n of the measurement unit 12 into two optical paths so that an optical path difference is generated. The light focusing unit 15 focuses the two optical paths branched by the light branching unit 14 to form a speckle pattern on the multiple pixels 22-1 to 22-n of the measurement unit 12. The measurement unit 12 receives light of a speckle pattern generated by interference of scattered light 52, 53 generated when the scatterer 32 receives coherent light by a plurality of pixels 22-1 to 22-n, detects pixels 22-1 to 22-n having a predetermined luminance change amount to be detected, which indicates a change in luminance value detected by each of the pixels 22-1 to 22-n receiving the light of the speckle pattern, and outputs event data including the position of the detected pixels 22-1 to 22-n, a code value indicating the direction of change in the luminance change amount of the pixels 22-1 to 22-n, and a detection time indicating the time of detection. The calculation processing unit 13a generates image data in which the number of event data for each pixel 22-1 to 22-n within a predetermined time is the pixel value, and calculates the amount of displacement caused by the deformation of the scatterer 32 based on the generated image data.

With the above configuration, when the shape of the scatterer 32 is deformed, an optical path difference corresponding to the amount of displacement when the shape of the scatterer 32 is deformed is added to the two optical paths branched by the optical branching unit 14, and a phase difference of the added optical path difference is generated. Therefore, a change corresponding to the generated phase difference appears in the speckle pattern imaged by the optical focusing unit 15 on the multiple pixels 22-1 to 22-n. Therefore, by generating image data in which the number of event data corresponding to each of the pixels 22-1 to 22-n is the pixel value, the image of the generated image data becomes an image showing the change in the speckle pattern before and after the shape of the scatterer 32 is deformed, depending on the fineness of the intervals of the interference fringes. The calculation processing unit 13a performs frequency analysis on the generated image data, and is able to calculate the amount of displacement when the shape of the scatterer 32 is deformed from the fineness of the intervals of the interference fringes. When the calculation processing unit 13a generates image data based on event data, there is no need to continuously acquire image data multiple times, as is the case with a frame camera. This makes it possible for the measurement device 1a to estimate changes in objects whose changes are not constant based on speckle patterns under conditions where there are restrictions on the measurement time interval, such as in so-called real-time measurement.

In the second embodiment, the convex lens 71 in FIG. 9(b), the convex lens 81 in FIG. 9(c), and the convex lens 91 in FIG. 9(d) are included in the light branching unit 14. In contrast, the light branching unit 14 may not include the convex lenses 71, 81, and 91, and the position of the optical element provided inside the irradiation unit 11a may be adjusted so that the irradiation unit 11a irradiates diffused laser light.

In the second embodiment described above, the optical branching unit 14 branches the optical path from the irradiation unit 11a to the pixels 22-1 to 22-n of the measurement unit 12 into two so that an optical path difference occurs, regardless of which of the optical systems in Figures 9(a) to 9(d) is applied. In contrast, the optical branching unit 14 may branch the optical path from the irradiation unit 11a to the pixels 22-1 to 22-n of the measurement unit 12 into three or more optical paths so that an optical path difference occurs. In this case, the optical focusing unit 15 focuses the three or more optical paths branched by the optical branching unit 14 to form a speckle pattern on the pixels 22-1 to 22-n of the measurement unit 12.

In the first and second embodiments described above, when the event detection unit 23 determines that the luminance change amount of a certain pixel 22 is equal to or greater than a predetermined detection threshold, the event detection unit 23 detects the pixel 22 corresponding to the luminance change amount as a pixel 22 having a luminance change amount to be detected as a pixel 22 having a predetermined luminance change amount to be detected. In contrast, when the event detection unit 23 determines that the luminance change amount of a certain pixel 22 is equal to or greater than a predetermined detection threshold, the event detection unit 23 may detect the pixel 22 corresponding to the luminance change amount as a pixel 22 having a luminance change amount to be detected as a pixel 22 having a predetermined luminance change amount to be detected. However, in this case, in the configuration in which the absolute value of the difference between the maximum and minimum luminance values of the pixels 22-1 to 22-n shown in the first embodiment is set as the detection threshold, in order to perform a correct determination, it is necessary to set the detection threshold value to a value obtained by subtracting a minute value corresponding to the determination accuracy of the event detection unit 23 from the absolute value of the difference between the maximum and minimum luminance values, rather than setting the absolute value of the difference between the maximum and minimum luminance values as the detection threshold.

The measuring device 1 of the first embodiment described above can be a measuring device that measures blood flow, or an observation device that observes blood flow, when the scatterer 30 is, for example, a human body and the moving scatterer 31 is, for example, blood. The measuring device 1a of the second embodiment can be a measuring device that measures changes in the shape of the human body, or an observation device that observes changes in the shape of the human body, when the scatterer 32 is, for example, a human body.

The calculation processing unit 13, 13a in the first and second embodiments described above may be realized by a computer. In that case, a program for realizing this function may be recorded in a computer-readable recording medium, and the program recorded in the recording medium may be read into a computer system and executed to realize the function. The term "computer system" here includes hardware such as an OS and peripheral devices. The term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into a computer system. The term "computer-readable recording medium" may also include a medium that dynamically holds a program for a short period of time, such as a communication line when a program is transmitted via a network such as the Internet or a communication line such as a telephone line, and a medium that holds a program for a certain period of time, such as a volatile memory inside a computer system that is a server or client in that case. The program may be a program for realizing part of the above-mentioned functions, or may be a program that can realize the above-mentioned functions in combination with a program already recorded in the computer system, or may be a program that is realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

The above describes an embodiment of the present invention in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and includes designs that do not deviate from the gist of the present invention.

1...measuring device, 11...irradiation unit, 12...measurement unit, 13...calculation processing unit, 21...light receiving unit, 22-1 to 22-n...pixels, 23...event detection unit, 30...scattering body, 31...moving scattering body

Claims (8)

An irradiation unit that generates coherent light;
a measurement unit that receives light of a speckle pattern generated by interference of scattered light caused by a human body receiving the coherent light with a plurality of pixels, detects pixels having a predetermined luminance change amount to be detected, the luminance change amount indicating a change in luminance value detected by each of the pixels receiving the light of the speckle pattern, and generates event data including a position of the detected pixel, a code value indicating a change direction of the luminance change amount of the pixel, and a detection time indicating a time of detection;
a calculation processing unit that calculates a physical quantity indicating a change in the human body based on the event data;
Equipped with
the human body includes blood flowing through blood vessels of the human body ;
The calculation processing unit:
calculating a blood movement speed at a position of the human body corresponding to each of the pixels as a physical quantity indicating a change in the human body based on a predetermined number of the event data for each of the pixels per unit time ;
Measuring equipment. An irradiation unit that generates coherent light;
a measurement unit that receives light of a speckle pattern generated by interference of scattered light caused by a human body receiving the coherent light with a plurality of pixels, detects pixels having a predetermined luminance change amount to be detected, the luminance change amount indicating a change in luminance value detected by each of the pixels receiving the light of the speckle pattern, and generates event data including a position of the detected pixel, a code value indicating a change direction of the luminance change amount of the pixel, and a detection time indicating a time of detection;
a calculation processing unit that calculates a physical quantity indicating a change in the human body based on the event data;
Equipped with
the human body includes blood flowing through blood vessels of the human body ;
The measurement unit is
determining whether or not each of the pixels is a pixel having the luminance change amount to be detected based on the luminance change amount corresponding to each of the pixels and a predetermined detection threshold;
The calculation processing unit:
a multiplication value is calculated by multiplying a code value indicating a change direction of the amount of change in luminance included in the event data by the detection threshold, and for each of the pixels, a value obtained by integrating the multiplication values corresponding to detection times before the detection time is calculated as an integrated value for the detection time, and a moving speed of the blood at a position of the human body corresponding to each of the pixels is calculated as a physical quantity indicating a change in the human body based on the calculated integrated value for each of the detection times of each of the pixels .
Measuring equipment. An irradiation unit that generates coherent light;
a measurement unit that receives light of a speckle pattern generated by interference of scattered light caused by a human body receiving the coherent light with a plurality of pixels, detects pixels having a predetermined luminance change amount to be detected, the luminance change amount indicating a change in luminance value detected by each of the pixels receiving the light of the speckle pattern, and generates event data including a position of the detected pixel, a code value indicating a change direction of the luminance change amount of the pixel, and a detection time indicating a time of detection;
a calculation processing unit that calculates a physical quantity indicating a change in the human body based on the event data;
Equipped with
the human body includes blood flowing through blood vessels of the human body ;
The measurement unit is
determining whether or not each of the pixels is a pixel having the amount of change in luminance to be detected based on the amount of change in luminance corresponding to each of the pixels and a predetermined detection threshold that is determined based on an absolute value of a difference between a maximum value and a minimum value of a luminance value detected by the pixel from the light of the speckle pattern;
The calculation processing unit:
calculating an occurrence interval of the event data for each of the pixels based on the detection time included in the event data, and calculating a blood movement speed at a position of the human body corresponding to each of the pixels as a physical quantity indicating a change in the human body based on the calculated occurrence interval of the event data for each of the pixels ;
Measuring equipment. An irradiation unit that generates coherent light;
a measurement unit that receives light of a speckle pattern generated by interference of scattered light caused by a human body receiving the coherent light with a plurality of pixels, detects pixels having a predetermined luminance change amount to be detected, the luminance change amount indicating a change in luminance value detected by each of the pixels receiving the light of the speckle pattern, and generates event data including a position of the detected pixel, a code value indicating a change direction of the luminance change amount of the pixel, and a detection time indicating a time of detection;
a calculation processing unit that calculates a physical quantity indicating a change in the human body based on the event data;
Equipped with
the human body includes blood flowing through blood vessels of the human body ;
The calculation processing unit:
generating image data for each of the detection times based on the code value included in the event data, and calculating a blood movement speed as a physical quantity indicating a change in the human body based on the generated image data for the two different detection times ;
Measuring equipment. An irradiation unit that generates coherent light;
a measurement unit that receives light of a speckle pattern generated by interference of scattered light caused by a human body receiving the coherent light with a plurality of pixels, detects pixels having a predetermined luminance change amount to be detected, the luminance change amount indicating a change in luminance value detected by each of the pixels receiving the light of the speckle pattern, and generates event data including a position of the detected pixel, a code value indicating a change direction of the luminance change amount of the pixel, and a detection time indicating a time of detection;
a calculation processing unit that calculates a physical quantity indicating a change in the human body based on the event data;
Equipped with
an optical branching unit that branches an optical path from the irradiation unit to the plurality of pixels of the measurement unit into a plurality of optical paths so that an optical path difference is generated;
a light focusing unit that focuses the plurality of optical paths branched by the light branching unit to form an image of the speckle pattern on the plurality of pixels included in the measurement unit,
The human body is a shape-changing human body ,
The calculation processing unit:
generating image data in which the number of the event data for each pixel within a predetermined time period is defined as a pixel value, and calculating an amount of displacement caused by the deformation of the human body as a physical quantity indicating a change in the human body based on the generated image data ;
Measuring equipment. The irradiating unit generates coherent light;
a measurement unit that receives light of a speckle pattern generated by interference of scattered light caused by the human body receiving the coherent light, using a plurality of pixels;
the measurement unit detects pixels having a luminance change amount indicating a change in luminance value detected by each of the pixels upon receiving the light of the speckle pattern, the luminance change amount being a predetermined detection target;
the measurement unit generates event data including a position of the detected pixel, a code value indicating a change direction of the amount of change in luminance of the pixel, and a detection time indicating a time of detection;
a calculation processing unit that calculates a physical quantity indicating a change in the human body based on the generated event data;
the body includes blood flowing through blood vessels of the body;
the calculation processing unit calculates a blood movement speed at a position of the human body corresponding to each of the pixels as a physical quantity indicating a change in the human body based on a predetermined number of the event data for each of the pixels per unit time;
Measurement method. The irradiating unit generates coherent light;
a measurement unit that receives light of a speckle pattern generated by interference of scattered light caused by the human body receiving the coherent light, using a plurality of pixels;
the measurement unit detects pixels having a luminance change amount indicating a change in luminance value detected by each of the pixels upon receiving the light of the speckle pattern, the luminance change amount being a predetermined detection target;
the measurement unit generates event data including a position of the detected pixel, a code value indicating a change direction of the amount of change in luminance of the pixel, and a detection time indicating a time of detection;
a calculation processing unit that calculates a physical quantity indicating a change in the human body based on the generated event data;
the body includes blood flowing through blood vessels of the body;
the measurement unit determines whether or not each of the pixels is a pixel having the luminance change amount to be detected based on the luminance change amount corresponding to each of the pixels and a predetermined detection threshold;
the calculation processing unit calculates a multiplied value by multiplying a code value indicating a change direction of the luminance change amount included in the event data by the detection threshold, calculates, for each of the pixels, a value obtained by integrating the multiplied values corresponding to detection times before the detection time as an integrated value for the detection time, and calculates a movement speed of the blood at a position of the human body corresponding to each of the pixels as a physical quantity indicating a change in the human body based on the calculated integrated value for each of the detection times of each of the pixels.
Measurement method. A program for causing a computer to function as the measurement device according to any one of claims 1 to 5 .

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