Plant body evaluation method and photographing device

Abstract

To provide a technique capable of evaluating the state of stress on a plant body in more detail.SOLUTION: An evaluation method includes a measurement step and an evaluation step. The measurement step measures the state of a plant body at a plurality of different elapsed times. The measurement step includes an irradiation step of irradiating the plant body with a laser beam, a separation step of separating the laser beam with which the plant body is irradiated and that is reflected on the plant body into first linearly polarized light and second linearly polarized light, and simultaneously photographing the first linearly polarized light and the second linearly polarized light obtained through the separation in the separation step. The evaluation step evaluates a change with time of speckles in the first linearly polarized light and a change with time of speckles in the second linearly polarized light, from a plurality of speckle images acquired for a plurality of pieces of photographed data obtained through the photographing at the different elapsed times. The speckle images include the speckles in the first linearly polarized light and the speckles in the second linearly polarized light.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an evaluation method for evaluating a stress state on a plant body and an imaging device for the plant body. [Background technology]

[0002] In food production, plant phenotyping has attracted attention as a way to produce a large amount of high-quality crops. The phenotype of a plant is manifested in its morphology and composition, including color, shape, environmental stress tolerance, taste, texture, etc. Phenotypes are significantly influenced not only by genetic factors but also by environmental factors such as the cultivation environment and cultivation method. Phenotyping requires continuous, non-destructive measurement of the plant. For example, Non-Patent Document 1 discloses a method in which the appearance of a plant is photographed with a photographing device such as a camera and the color and shape of the plant are evaluated from the photographed data. By continuously photographing the appearance of the plant non-destructively, the stress state on the plant is evaluated from changes in the plant's appearance. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Fei Zhao, Hideo Yoshida, Eiji Goto and Shoko Hikosaka, “Development of an Automatic Irrigation Method Using an Image-Based Irrigation System for High-Quality Tomato Production,” Agronomy 2022, 12, 106. Summary of the Invention [Problem to be solved by the invention]

[0004] As disclosed in Non-Patent Document 1, in general, non-destructive and continuous phenotyping involves photographing the external appearance of a plant to evaluate the stress state of the plant. However, the phenotype of a plant is manifested not only in the external appearance of the plant, but also in the internal appearance of the plant. The method disclosed in Non-Patent Document 1 has the problem that it can only evaluate the external appearance of the plant.

[0005] The present specification discloses a technique that enables more detailed evaluation of the stress state of a plant body. [Means for solving the problem]

[0006] An evaluation method according to a first aspect of the technology disclosed in this specification evaluates the stress state of a plant body. The evaluation method includes a measurement step and an evaluation step. The measurement step measures the state of the plant body at multiple different elapsed times. The measurement step includes an irradiation step of irradiating the plant body with laser light, a separation step of separating the laser light reflected from the plant body in the irradiation step into first linearly polarized light and second linearly polarized light that are orthogonal to each other, and an imaging step of simultaneously capturing the first linearly polarized light and the second linearly polarized light separated in the separation step. The evaluation step evaluates changes over time in speckle of the first linearly polarized light and changes over time in speckle of the second linearly polarized light from multiple speckle images acquired for each of multiple pieces of imaging data captured at different elapsed times in the measurement step. The speckle images include speckle of the first linearly polarized light and speckle of the second linearly polarized light.

[0007] In the evaluation method described above, in the separation step, the light reflected from the plant body is separated into orthogonal first and second linearly polarized light, and in the imaging step, the separated first and second linearly polarized light are simultaneously imaged. This allows light reflected from the surface of the plant body and light reflected inside the plant body to be separately imaged. Therefore, by evaluating the change over time in the speckles of one of the first and second linearly polarized light, it is possible to evaluate the change over time in the surface (i.e., the appearance) of the plant body, and by evaluating the change over time in the speckles of the other of the first and second linearly polarized light, it is possible to evaluate the change over time inside the plant body. Furthermore, since the plant body is simply irradiated with laser light, it is possible to nondestructively image the plant body over time. Therefore, not only the change in the appearance of the plant body but also the change in the interior of the plant body can be evaluated nondestructively over time.

[0008] Furthermore, a photographing device according to a first aspect of the technology disclosed in this specification photographs a plant body to evaluate a state of stress on the plant body. The photographing device includes a light source that emits laser light, a photographing unit that photographs the laser light emitted from the light source reflected from the plant body, and an optical element that is disposed between the plant body and the photographing unit and that separates the reflected light from the plant body into first linearly polarized light and second linearly polarized light that are orthogonal to each other. The photographing unit photographs a speckle image including speckles of the first linearly polarized light and speckles of the second linearly polarized light.

[0009] In the above-mentioned photographing device, the optical element separates the reflected light from the plant body into orthogonal first and second linearly polarized light, and the photographing unit simultaneously photographs the separated first and second linearly polarized light, thereby achieving the same effects as the above-mentioned evaluation method. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of an imaging device according to an embodiment. [Figure 2] 1 is a flowchart showing an example of a method for evaluating the stress state of a plant body. [Figure 3]10 is a flowchart showing an example of a measurement process. [Figure 4] FIG. 10 is a diagram showing an example of a speckle image. [Figure 5] This figure explains texture analysis. (a) shows a speckle image and the trimming range within the image. (b) shows the 32-level brightness values ​​of the trimming range. (c) shows the normalized matrix of (b). [Figure 6] Graph showing changes in feature values ​​and chlorophyll fluorescence after salt stress. [Figure 7] Graph showing changes in feature values ​​and chlorophyll fluorescence after water stress. DETAILED DESCRIPTION OF THE INVENTION

[0011] The main features of the embodiments described below are listed below. Note that the technical elements described below are independent technical elements that exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

[0012] In the evaluation method according to the second aspect of the technology disclosed in this specification, in the evaluation method according to the first aspect, the evaluation step may include an analysis step of analyzing the brightness pattern of the speckle image by performing texture analysis on the speckle image. With this configuration, it is possible to quantify and evaluate changes over time.

[0013] In the evaluation method according to the third aspect of the technology disclosed herein, in the evaluation method according to the first or second aspect, the measuring step may further include a stress application step of applying water stress or salt stress to the plant body before the irradiating step. With this configuration, water stress or salt stress on the plant body can be evaluated.

[0014] Furthermore, in a second aspect of the technology disclosed in this specification, the imaging device of the first aspect described above may further include a calculation unit. The imaging unit may simultaneously capture the first linearly polarized light and the second linearly polarized light separated by the optical element. The calculation unit may acquire multiple speckle images captured at different times from the imaging unit, and evaluate changes over time in the first linearly polarized light and the second linearly polarized light from the multiple speckle images acquired from the imaging unit. [Example]

[0015] An imaging device 10 according to an embodiment will be described with reference to the drawings. The imaging device 10 is used to photograph a plant 50 and evaluate the state of stress on the plant 50 from the photographed image. As shown in FIG. 1, the imaging device 10 includes a light source 12, an ND filter 14, a polarizing filter 16, a lens 18, an aperture 20, a Rochon prism 22, a lens 24, a CCD camera 26, and a computing unit 30.

[0016] The light source 12 is configured to emit laser light. In this embodiment, the light source 12 is a semiconductor laser device and emits laser light of a specific wavelength (in this embodiment, a wavelength of approximately 520 nm). The light source 12 is configured to be turned on when an operator turns on a power supply (not shown) for the light source 12, and to be turned off when the operator turns off the power supply. The light source 12 may be controlled by a calculation unit 30, which will be described later. Specifically, the calculation unit 30 may be connected to an input device (not shown) for turning the light source 12 on and off. Then, when an operator operates the input device, the input device may instruct the calculation unit 30 to turn the light source 12 on and off, and the calculation unit 30 may control the light source 12 on and off according to the input instruction.

[0017] The laser light emitted from the light source 12 is emitted to the polarizing filter 16 via the ND filter 14. The ND filter 14 adjusts the amount of laser light. The polarizing filter 16 emits linearly polarized light from the laser light. The linearly polarized light emitted from the polarizing filter 16 is irradiated onto the plant body 50. Specifically, the linearly polarized laser light is irradiated onto the leaves of the plant body 50. The light source 12 is positioned so that linearly polarized light (S-polarized light) is irradiated at an incident angle of 10° perpendicular to the plane of incidence of the photographing site of the plant body 50 (in this embodiment, the leaves of the plant body 50).

[0018] A portion of the linearly polarized light irradiated onto the plant body 50 is reflected by the surface of the plant body 50, and another portion enters the interior of the plant body 50. The linearly polarized light reflected by the surface of the plant body 50 remains linearly polarized light vibrating in the direction in which it entered the plant body 50 (i.e., S-polarized light). On the other hand, the linearly polarized light that enters the interior of the plant body 50 is diffusely reflected inside the plant body 50 and becomes unpolarized light vibrating in various directions. Therefore, the reflected light from the plant body 50 includes S-polarized light reflected by the surface of the plant body 50 and unpolarized light diffused inside the plant body 50.

[0019] Light reflected from the plant body 50 enters the Rochon prism 22 via the lens 18 and the aperture 20. The Rochon prism 22 separates the incident light into two linearly polarized light beams that are orthogonal to each other and then emits the separated light. Therefore, the reflected light incident on the Rochon prism 22 is separated into two linearly polarized light beams that are orthogonal to each other. Specifically, the Rochon prism 22 transmits S-polarized light that is perpendicular to the incident surface of the subject, and refracts and emits P-polarized light that is perpendicular to the S-polarized light. Therefore, the S-polarized light exits the Rochon prism 22 approximately coaxial with the optical axis that enters the Rochon prism 22. The P-polarized light exits the Rochon prism 22 at an angle (refracted angle) different from the optical axis that enters the Rochon prism 22.

[0020] As described above, the reflected light from the plant 50 includes S-polarized light reflected on the surface of the plant 50 and unpolarized light diffused inside the plant 50. Therefore, almost all of the S-polarized light emitted from the Rochon prism 22 is light reflected on the surface of the plant 50. Note that the S-polarized light emitted from the Rochon prism 22 also includes S-polarized light from the unpolarized light diffused inside the plant 50. However, the amount of S-polarized light contained in the unpolarized light diffused inside the plant 50 is small compared to the S-polarized light reflected on the surface of the plant 50. Therefore, almost all of the S-polarized light emitted from the Rochon prism 22 can be considered to be light reflected on the surface of the plant 50. Note that the P-polarized light emitted from the Rochon prism 22 is only P-polarized light from the unpolarized light diffused inside the plant 50. Therefore, the P-polarized light emitted from the Rochon prism 22 is light diffused inside the plant 50.

[0021] The S-polarized light and P-polarized light exiting the Rochon prism 22 are emitted from the Rochon prism 22 at different angles and input to the CCD camera 26 via the lens 24. This allows the CCD camera 26 to separate and simultaneously capture the S-polarized light and the P-polarized light (see FIG. 4). The CCD camera 26 outputs the captured data (hereinafter also referred to as "captured data") to the calculation unit 30. The calculation unit 30 stores the input captured data in a memory (not shown).

[0022] The calculation unit 30 is configured by a microcomputer (microprocessor) that includes a CPU, ROM, RAM, etc. The calculation unit 30 is connected to the CCD camera 26 and controls the CCD camera 26.

[0023] The calculation unit 30 also acquires the photographic data captured by the CCD camera 26 to obtain a speckle image. Speckle is a spotted pattern observed when an object is irradiated with coherent light such as laser light. The calculation unit 30 acquires images including S-polarized speckle and P-polarized speckle from the CCD camera 26. The calculation unit 30 is also configured to acquire multiple speckle images from the photographic data of the plant body 50 photographed over time, and to execute an analysis process and a stress assessment process for evaluating the changes over time in the S-polarized speckle and the P-polarized speckle, respectively, from the multiple speckle images. The analysis process (analysis step) and the stress assessment process (stress assessment step) will be described in detail later.

[0024] Next, a method for evaluating the stress state of the plant 50 using the imaging device 10 of this embodiment will be described. When the plant 50 is subjected to stress, the external appearance and internal phenotype of the plant 50 change. Examples of stress that the plant 50 is subjected to include water stress caused by the plant 50 not being provided with water, and salt stress caused by the plant 50 being irrigated with water having a high salt concentration. Below, a method for evaluating the stress state that the plant 50 is subjected to when stress is applied to the plant 50 will be described.

[0025] 2, first, a measurement step is performed (S100). The measurement step is a step of measuring the state of the plant body 50 at a plurality of different elapsed times. In the measurement step of this embodiment, the photographing device 10 is used to photograph the plant body 50 at a plurality of different elapsed times.

[0026] The measurement step will be described with reference to FIG. 3. As shown in FIG. 3, in the measurement step, a stress application step is first executed (S12). In the stress application step, stress is applied to the plant 50. For example, when salt stress is applied to the plant 50, the plant 50 is irrigated with an aqueous solution containing a high concentration of NaCl. Furthermore, when water stress is applied to the plant 50, irrigation of the plant 50 is stopped (water supply is suspended). The application of stress to the plant 50 continues until multiple measurements (photographing) of the plant 50 are completed. For example, when salt stress is applied to the plant 50, the plant 50 is irrigated with an aqueous solution containing a high concentration of NaCl until multiple measurements (photographing) of the plant 50 are completed. Furthermore, when water stress is applied to the plant 50, irrigation of the plant 50 is stopped until multiple measurements (photographing) of the plant 50 are completed.

[0027] Next, a laser light irradiation step (S14), a separation step (S16), and an imaging step (S18) are performed. The laser light irradiation step (S14), the separation step, and the imaging step are performed using the imaging device 10.

[0028] The laser light irradiation step of step S14 is a step of irradiating the plant body 50 with laser light. Specifically, the laser light irradiation step is performed in the following procedure. An operator turns on the power supply (not shown) of the light source 12 to turn on the light source 12. When the light source 12 is controlled by the calculation unit 30, the operator inputs an instruction to turn on the light source 12 from an input device (not shown), and the calculation unit 30 turns on the light source 12 in accordance with the input instruction. When the light source 12 is turned on, laser light is emitted from the light source 12. The laser light emitted from the light source 12 is irradiated onto the plant body 50 via the ND filter 14 and the polarizing filter 16. As described above, by passing through the polarizing filter 16, S-polarized light is irradiated onto the plant body 50. The light reflected from the plant body 50 is irradiated toward the CCD camera 26. As described above, the light reflected from the plant body 50 includes S-polarized light reflected on the surface of the plant body 50 and unpolarized light diffused inside the plant body 50.

[0029] The separation process of step S16 is a process of separating the light reflected from the plant 50 into two orthogonal linearly polarized lights. As described above, the imaging device 10 includes a Rochon prism 22 disposed between the plant 50 and the CCD camera 26. The light reflected from the plant 50 is irradiated onto the CCD camera 26 via the Rochon prism 22, whereby the light reflected from the plant 50 is separated into two orthogonal linearly polarized lights, S-polarized light and P-polarized light. The S-polarized light emitted from the Rochon prism 22 is light reflected from the surface of the plant 50, and the P-polarized light emitted from the Rochon prism 22 is light scattered inside the plant 50.

[0030] The imaging step of step S18 is a step of simultaneously imaging the two orthogonal linearly polarized light beams (S-polarized light and P-polarized light beam) separated in the separation step of step S16. As described above, in the imaging device 10, of the S-polarized light and P-polarized light emitted from the Rochon prism 22, the S-polarized light is emitted coaxially with the axis of incidence on the Rochon prism 22, and the P-polarized light is refracted and emitted. Therefore, when the S-polarized light and the P-polarized light are incident on the CCD camera 26, they are simultaneously incident at different positions. This allows the CCD camera 26 to separate the S-polarized light and the P-polarized light and capture them simultaneously (see FIG. 4). The imaging data captured by the CCD camera 26 is linked to the date and time of the image capture (hereinafter also referred to as the image capture time) and stored in a memory (not shown) of the calculation unit 30.

[0031] After the photographing process in step S18 is completed, it is determined whether or not the plant 50 has been photographed at all of the preset multiple different elapsed times (S20). Photographing of the plant 50 is performed at a preset time. Specifically, the photographing time and the number of days for photographing are set. For example, the plant 50 is set to be measured (photographed) at 9:00, 12:00, and 15:00 every day for four days, including the day on which stress is applied to the plant 50. In this case, all photographing is completed when the plant 50 is photographed at 15:00, three days after the day on which stress is applied to the plant 50 (day 0). The process in step S20 may be performed by an operator, or may be configured to be performed by the calculation unit 30 by storing the above conditions (photographing times) in a memory (not shown) of the calculation unit 30. If the plant 50 has been photographed at all of the preset multiple different elapsed times (YES in step S20), the measurement process shown in FIG. 3 is completed, and the process proceeds to step S200 (see FIG. 2).

[0032] On the other hand, if the plant body 50 has not been photographed at all of the plurality of different elapsed times set in advance (NO in step S20), it is determined whether or not the next photographing time has arrived (S22). The processing of step S22 may also be performed by an operator, or may be configured to be performed by the calculation unit 30. If the next photographing time has not arrived (NO in step S22), the system waits until the next photographing time arrives. If the next photographing time arrives (YES in step S22), the system returns to the processing of step S14, and the processing of steps S14 to S20 is repeated. This allows the plant body 50 to be photographed at a plurality of different elapsed times.

[0033] As shown in FIG. 2, after the measurement step is completed, the image acquisition step is executed (S200). The image acquisition step is a step of acquiring speckle images for each of the photographed data at different elapsed times in the measurement step of step S100. The image acquisition step is executed by the calculation unit 30. The image acquisition step may also be executed by an external device (e.g., another computer) of the photographing device 10. For example, the external device can execute the image acquisition step by outputting the photographed data from the memory (not shown) of the calculation unit 30 to the external device. As described above, the CCD camera 26 simultaneously captures S-polarized light and P-polarized light at different positions. Therefore, as shown in FIG. 4, S-polarized speckles and P-polarized speckles appear at different positions in the speckle images photographed at each photographing time. S-polarized light indicates reflection from the surface of the plant body 50, and P-polarized light indicates diffusion inside the plant body 50. The Rochon prism 22 emits almost all of the reflection (S-polarized light) from the surface of the plant body 50, while emitting only P-polarized light from the scattering (unpolarized light) inside the plant body 50. Therefore, in a speckle image, the intensity of S-polarized light is greater than the intensity of P-polarized light.

[0034] After the image acquisition step is completed, the evaluation step is executed (S300). The evaluation step is a step of evaluating the time-dependent changes in the S-polarized speckle and the P-polarized speckle from multiple speckle images corresponding to the photographed data at each photographing time. The evaluation step includes an analysis step and a stress evaluation step.

[0035] The analysis step is a step of calculating feature quantities of S-polarized speckles and P-polarized speckles in one speckle image in order to evaluate changes over time in S-polarized speckles and P-polarized speckles. In this embodiment, the brightness patterns of S-polarized and P-polarized light in one speckle image are analyzed by texture analysis. Note that the analysis method used in the analysis step is not limited to texture analysis, and any known method can be selected as appropriate.

[0036] In this example, the analysis process is performed using a gray level co-occurrence matrix (GLCM), an example of texture analysis. GLCM is a method for calculating statistics related to the brightness of two pixels in a specific positional relationship, and is a method for capturing the uniformity of a pattern and its statistical characteristics. As shown in Figure 5, GLCM calculates a matrix whose elements are the probability p(i,j) that a pixel value j exists at a point separated from pixel value i by an offset δ = (θ, d), which is described by a distance d and an angle θ. Texture is characterized by calculating features from the calculated matrix. The offset and the function for calculating the feature must be determined in advance. In this example, a preliminary experiment was conducted to examine the offset and the function for calculating the feature using image data of a plant body 50 photographed under unpolarized light. As a result, the offset was set to δ = (0, 5). The following formula (1) was used as the function for calculating the feature. Note that f2 is called a constant and represents the moment of inertia from the diagonal in GLCM.

[0037]

number

[0038] The value of f2 increases exponentially as the difference in brightness at the offset δ = (θ, d), which is the relative position in the image, increases. In the analysis process, the captured image data is cropped to 50 × 50 pixels (see Figure 5(a)), and the number of brightness levels in the cropped image data is changed from 256 to 32 (see Figure 5(b)). The elements of the matrix created using the data with the changed number of brightness levels are then normalized by dividing them by the sum of the matrix (see Figure 5(c)). The feature value f2 is calculated from the normalized matrix using the formula (1) above. Furthermore, the feature value f2 for S-polarized light and the feature value f2 for P-polarized light are calculated for each captured image data. That is, in the analysis process, the feature value f2 for S-polarized light at each captured image time and the feature value f2 for P-polarized light at each captured image time are calculated.

[0039] The stress assessment step is a step of assessing the stress state of the plant 50 using the analysis results from the analysis step. In this embodiment, the analysis step calculates the S-polarized light feature value f2 and the P-polarized light feature value f2 at each imaging time. This allows for evaluating the change in the S-polarized light feature value f2 and the change in the P-polarized light feature value f2 over time. For example, a change in the surface phenotype of the plant 50 can be identified from the change in the S-polarized light feature value f2 over time (e.g., a decrease in the S-polarized light feature value f2). Furthermore, a change in the internal phenotype of the plant 50 can be identified from the change in the P-polarized light feature value f2 over time (e.g., a decrease in the P-polarized light feature value f2). The stress assessment step may be performed by an operator based on the analysis results, or may be performed by the calculation unit 30 (or another computer). For example, when the calculation unit 30 (or another computer) performs the stress assessment step, a threshold value for indicating a decrease in the S-polarized light feature value f2 and a threshold value for indicating a decrease in the P-polarized light feature value f2 may be set, and it may be evaluated that a change has occurred when the threshold value is exceeded.

[0040] In this embodiment, by photographing the plant 50 using the photographing device 10, it is possible to simultaneously and separately acquire S-polarized speckles (surface reflection of the plant 50) and P-polarized speckles (internal diffusion of the plant 50). Furthermore, by using speckle images of the plant 50 photographed at multiple different times, it is possible to evaluate the time-dependent changes in the S-polarized speckles and the P-polarized speckles. Therefore, it is possible to evaluate the time-dependent changes in the S-polarized speckles (surface reflection of the plant 50) and the P-polarized speckles (internal diffusion of the plant 50). For example, when stress is applied to the plant 50, it is possible to evaluate the changes in the external phenotype of the plant 50 and the changes in the internal phenotype of the plant 50. Furthermore, it is also possible to compare and evaluate the changes in the external phenotype of the plant 50 with the changes in the internal phenotype of the plant 50. Furthermore, the evaluation method of this embodiment allows for non-destructive evaluation of not only the external phenotype of the plant 50 but also the internal phenotype of the plant 50.

[0041] In addition, experiments conducted by the present inventors have confirmed that the stress state of a plant 50 can be evaluated using the above-mentioned stress evaluation method. Experiments to evaluate the stress state included an evaluation experiment for salt stress (hereinafter also referred to as a salt stress evaluation experiment) and an evaluation experiment for water stress (hereinafter also referred to as a water stress evaluation experiment). In these experiments, soybeans (Glycine max L., Fukuyutaka) were used as the plant 50. Soybeans were sown in cell trays filled with potting soil and vermiculite and grown in a plant incubator. The growth conditions were a 12-hour light period at 27°C and a 12-hour dark period at 23°C. A fluorescent lamp was used as the light source during the light period. The fluorescent lamp was installed on the inside surface of the plant incubator, and PPFD was set to approximately 120 μmol / L. -2 s -1 The plants (hereinafter simply referred to as samples) that had been grown for 3 to 4 weeks after sowing were photographed with the above-mentioned photographing device 10.

[0042] On the day before the start of imaging, the sample was placed at a distance of approximately 120 cm under a metal halide lamp in a darkroom, and the imaging device 10 was set up so as to image the area of ​​the sample to be imaged. The metal halide lamp was turned on between 6:00 and 18:00. The PPFD at the imaging position was approximately 100 μmol / m. -2 s -2 The temperature in the darkroom was kept at approximately 25°C by air conditioning, and humidity was left constant. In the salt stress evaluation experiment, salt stress was applied to the samples starting at 9:00 on the first day of photography (day 0). Salt stress was applied by irrigating the samples with a 150 mM NaCl solution. During the photography period, 50 ml of the above NaCl solution was sub-irrigated to the samples every morning at 9:00. In the water stress evaluation experiment, sub-irrigation was performed at 9:00 on the first day of photography (day 0), and watering was stopped thereafter.

[0043] The above sample was photographed using the imaging device 10. The day on which stress was applied was designated as day 0 (day 0), and photography was performed three times each day at 9:00, 12:00, and 15:00 (12 times in total during the entire photography period) over a period of four days up to day 3 (day 3). The photography data was stored in the memory (not shown) of the calculation unit 30 of the imaging device 10. The above analysis process was then performed on the photography data at each photography time, and the feature amount f2 of S-polarized light and the feature amount f2 of P-polarized light at each photography time were calculated.

[0044] In addition, in the experiment, the chlorophyll fluorescence of the samples was measured as plant physiological information to understand the condition of the samples. Chlorophyll fluorescence measurements were performed using the central portion of the first true leaf of the stressed plants, avoiding the midrib, immediately after photographing the speckles. Chlorophyll fluorescence measurements were performed using a chlorophyll fluorometer (e.g., Photon Systems' FluorPen E-FP110 / D). While chlorophyll fluorescence was measured as plant physiological information in this example, this configuration is not limiting. For example, other plant physiological information, such as leaf temperature, carbon dioxide emissions, and SPAD values, may also be measured. As a comparative example, unstressed soybeans were also photographed and their chlorophyll fluorescence measured using the photographing device 10. For the salt-stressed samples, photographing and chlorophyll fluorescence measurements were performed on three individuals, and for the water-stressed samples, photographing and chlorophyll fluorescence measurements were performed on three individuals. For the comparative example, photographing and chlorophyll fluorescence measurements were performed on two individuals.

[0045] Figure 6 shows the feature value f2 and chlorophyll fluorescence at each image capture time in the salt stress evaluation experiment, and Figure 7 shows the feature value f2 and chlorophyll fluorescence at each image capture time in the water stress evaluation experiment. The feature value f2 was normalized to 1 at 9:00 AM on day 0 (day 0). Figures 6 and 7 show the average and standard error for three samples of this example (the salt-stressed sample in Figure 6 and the water-stressed sample in Figure 7). For the comparative example, only the average value is shown because only two samples were used. Graph A shows the feature value f2 for S-polarized light (surface reflection) of the sample of this example. Graph B shows the feature value f2 for P-polarized light (internal diffusion) of the sample of this example. Graph C shows the feature value f2 for S-polarized light (surface reflection) of the comparative example. Graph D shows the feature value f2 for P-polarized light (internal diffusion) of the comparative example. Graph E shows the chlorophyll fluorescence of the sample of this example, and Graph F shows the chlorophyll fluorescence of the comparative example.

[0046] In the salt stress evaluation experiment, as shown in Figure 6, no significant change was observed in the feature value f2 between day 0 (day 0) and day 1 (day 1). For the sample of this example, at 9:00 AM on day 2 (day 2), the feature value f2 for S-polarized light (surface reflection) increased, while the feature value f2 for P-polarized light (internal diffusion) significantly increased. Subsequently, from 12:00 PM on day 2 (day 2) to 3:00 PM on day 3 (day 3) (the last photo), the feature value f2 for S-polarized light (surface reflection) continued to increase gradually, while the feature value f2 for P-polarized light (internal diffusion) increased significantly. In the comparative example, neither the feature value f2 for S-polarized light (surface reflection) nor the feature value f2 for P-polarized light (internal diffusion) changed significantly between day 0 (day 0) and day 3 (day 3) (the last photo). Furthermore, although the chlorophyll fluorescence of the sample of this example gradually decreased from day 0 (day 0), it remained within the normal range from day 0 (day 0) to day 2 (day 2). Thereafter, the chlorophyll fluorescence of the sample in this example showed a significant decrease at 9:00 on day 3, and continued to decrease significantly at 12:00 and 15:00 on day 3. These results showed that when salt stress was applied to plant body 50, changes in the internal phenotype appeared earlier than changes in the surface (external) phenotype.

[0047] In the water stress evaluation experiment, as shown in Figure 7, no significant change in the feature value f2 was observed between day 0 (day 0) and day 1 (day 1). For the sample of this example, the feature value f2 of P-polarized light (internal diffusion) increased at 9:00 AM on day 2 (day 2). The feature value f2 of P-polarized light (internal diffusion) continued to increase thereafter, reaching approximately seven times its initial value by 9:00 AM on day 3 (day 3). Meanwhile, the feature value f2 of S-polarized light (surface reflection) increased at 9:00 AM on day 3 (day 3) and continued to increase gradually thereafter. Furthermore, the chlorophyll fluorescence of the sample of this example decreased at 12:00 AM on day 2 (day 2) and then rapidly decreased at 9:00 AM on day 3 (day 3). After 12:00 AM on day 3 (day 3), the leaves cracked due to drying, making it impossible to measure chlorophyll fluorescence. These results demonstrate that even when water stress is applied to plant 50, internal phenotypic changes appear before surface (appearance) phenotypic changes. In this way, it was confirmed that the stress state on the surface and inside of the plant body 50 can be evaluated by using the stress evaluation method of this example.

[0048] In this embodiment, the Rochon prism 22 is used to separate the incident light into two orthogonal linearly polarized lights (S-polarized light and P-polarized light), but the present invention is not limited to this configuration. Instead of the Rochon prism 22, other optical elements (e.g., a Wollaston prism) that separate the incident light into two orthogonal linearly polarized lights and emit them may be used. Furthermore, in this embodiment, the speckle image is captured using the CCD camera 26, but the present invention is not limited to this configuration. For example, the speckle image may be captured using other cameras such as a CMOS camera.

[0049] Although specific examples of the technology disclosed in this specification have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of those objectives itself has technical utility. [Explanation of symbols]

[0050] 10: Imaging device 12:Light source 16: Polarizing filter 22: Rochon Prism 26: CCD camera 30: Arithmetic section 50: Plant body

Claims

1. A method for evaluating a stress state of a plant, comprising: A measuring step of measuring the state of the plant body at a plurality of different elapsed times, The measuring step an irradiation step of irradiating the plant body with laser light; a separation step of separating the laser light irradiated in the irradiation step and reflected from the plant body into first linearly polarized light and second linearly polarized light which are orthogonal to each other; the measuring step including an imaging step of simultaneously imaging the first linearly polarized light and the second linearly polarized light separated in the separating step; an evaluation step of evaluating a change over time in the speckles of the first linearly polarized light and a change over time in the speckles of the second linearly polarized light from a plurality of speckle images acquired for each of a plurality of pieces of photographed data photographed at different elapsed times in the measurement step; Equipped with The evaluation method, wherein the speckle image includes speckles of the first linearly polarized light and speckles of the second linearly polarized light.

2. The evaluation method according to claim 1 , wherein the evaluation step includes an analysis step of analyzing a pattern of brightness of the speckle image by performing texture analysis on the speckle image.

3. The evaluation method according to claim 1 , wherein the measuring step further comprises a stress applying step of applying water stress or salt stress to the plant body before the irradiating step.

4. An imaging device for photographing a plant body in order to evaluate a stress state applied to the plant body, a light source that emits laser light; an imaging unit that images the laser light emitted from the light source and reflected from the plant body; an optical element disposed between the plant body and the imaging unit, which separates the reflected light from the plant body into first linearly polarized light and second linearly polarized light that are orthogonal to each other; The imaging unit captures a speckle image including speckles of the first linearly polarized light and speckles of the second linearly polarized light.

5. The apparatus further includes a calculation unit, the imaging unit simultaneously images the first linearly polarized light and the second linearly polarized light separated by the optical element, The calculation unit acquiring a plurality of speckle images captured at different times from the imaging unit; The imaging device according to claim 4 , wherein a change over time of the first linearly polarized light and a change over time of the second linearly polarized light are evaluated from the plurality of speckle images acquired from the imaging section.

Images