Chlorophyll fluorescence image acquisition device

Abstract

This chlorophyll fluorescence image acquisition device comprises: a camera that outputs an image corresponding to the intensity of received light; a filter unit that is disposed between the camera and a plant leaf to be measured, and that makes it possible to switch between a first filter and a second filter that transmit light in different wavelength bands; and a computer that uses the image output by the camera to acquire a chlorophyll fluorescence image. The computer performs an operation for acquiring a first image, an operation for acquiring a second image, an operation for acquiring a whiteboard intensity ratio, an operation for acquiring a corrected image, and an operation for acquiring a chlorophyll fluorescence image that is based on the chlorophyll fluorescence transmitted through the second filter, by subtracting the light intensity of the first image from the light intensity of the corrected image.

Description

Chlorophyll fluorescence image acquisition device

[0001] The present invention relates to a chlorophyll fluorescence image acquisition device.

[0002] In recent years, agriculture that utilizes cutting-edge technologies such as IoT has been attracting attention. This new form of agriculture is also known as smart agriculture. The market for smart agriculture is expanding year by year. For example, the robotics field, such as drones used in smart agriculture, is expected to have a market of approximately 10 billion yen, and this market is expected to continue to expand. Furthermore, the international price of chemical fertilizer has risen significantly in recent years due to factors such as increased demand for grains and rising energy prices, as well as international geopolitical risks. Against this backdrop, systems that combine remote sensing and drone technology to apply only the amount of fertilizer needed where it is needed (variable fertilization systems) are becoming increasingly popular.

[0003] Variable fertilization systems allow for pinpoint application of fertilizer only to areas deemed to be experiencing poor growth. As a result, this not only eliminates variations in crop growth, but also contributes to reducing excess fertilizer and labor. With the spread of such variable fertilization systems, the importance of technology for monitoring crop growth conditions is increasing.

[0004] Kenji Masuda, "Technologically developed vegetation remote sensing measurement method and research support," Shizuoka University Academic Repository Technical Report, Shizuoka University, Japan, March 30, 2021, Vol. 26, pp. 21-26.

[0005] For example, Non-Patent Document 1, written by the present inventor, discloses a technique for obtaining image information that can be used to diagnose the growth status of plants. Non-Patent Document 1 focuses on a fluorescence intensity distribution image obtained using an F780 filter under sunlight. Non-Patent Document 1 then compares this fluorescence intensity distribution image with other evaluation methods that can be used to diagnose the growth status of plants (thermal images and Normalized Difference Vegetation Index (NDVI)). In this technical field, it is desirable to further improve the accuracy of image information that can be used to diagnose the growth status.

[0006] Therefore, the present invention provides a chlorophyll fluorescence image acquisition device that can improve the accuracy of image information that can be used to diagnose the growth status.

[0007] One aspect of the present invention is a chlorophyll fluorescence image acquisition device that acquires a chlorophyll fluorescence image based on chlorophyll fluorescence emitted due to photosynthetic activity of plant leaves exposed to sunlight, the device comprising: a camera that outputs an image corresponding to the intensity of the received light; a filter unit that is disposed between the plant leaf as a measurement object and the camera and that is capable of switching between a first filter and a second filter that transmit light with different wavelength bands; and a processing unit that acquires a chlorophyll fluorescence image using the image output by the camera, the transmission wavelength band of the first filter not including the wavelength of chlorophyll fluorescence and the transmission wavelength band of the second filter including the wavelength of chlorophyll fluorescence, and the processing unit that extracts a chlorophyll fluorescence image based on the components of plant leaf reflected light that are caused by sunlight reflected by the plant leaf by passing the light through the first filter. The method includes the following operations: causing transmitted light, including a component of reference body reflected light due to sunlight reflected by a reference body placed near the plant leaf, to be incident on a camera to obtain a first image; causing transmitted light, including a component of plant leaf reflected light, a component of reference body reflected light, and a component of chlorophyll fluorescence emitted due to photosynthetic activity of the plant leaf, to be incident on a camera by passing it through a second filter to obtain a second image; obtaining a reflection intensity ratio by dividing the light intensity of the component of reference body reflected light contained in the first image by the light intensity of the component of reference body reflected light contained in the second image; obtaining a corrected image by multiplying the second image by the reflection intensity ratio; and obtaining a chlorophyll fluorescence image based on the chlorophyll fluorescence that has passed through the second filter by subtracting the light intensity of the first image from the light intensity of the corrected image.

[0008] This chlorophyll fluorescence image acquisition device obtains image data based on chlorophyll fluorescence using the second image obtained through the second filter. Images based on chlorophyll fluorescence can provide more accurate image information that can be used to diagnose growth conditions than images based on excess energy fluorescence with a peak wavelength of 780 nm.

[0009] In the above-mentioned chlorophyll fluorescence image acquisition device, the sunlight received by the plant leaves has a photosynthetically active radiation (PAR) of 600 μmol m －２ s －１ It may be the following:

[0010] In the chlorophyll fluorescence image acquisition device, the transmission wavelength band of the second filter may have a center wavelength of 750 nm.

[0011] According to the present invention, a chlorophyll fluorescence image acquisition device is provided that can improve the accuracy of image information that can be used to diagnose the growth status.

[0012] FIG. 1 is a diagram that schematically illustrates the relationship between photosynthesis and chlorophyll fluorescence, and conceptually illustrates the configuration of a chlorophyll fluorescence image acquisition device. FIG. 2 is a graph that shows the spectra of chlorophyll fluorescence and excess energy fluorescence, along with the optical characteristics of several filters. FIG. 3 is a diagram that simply illustrates the physical configuration of the computer included in the chlorophyll fluorescence image acquisition device. FIG. 4 is a flowchart illustrating the main steps of a method for obtaining a chlorophyll fluorescence image, which is executed by the chlorophyll fluorescence image acquisition device. FIGS. 5(a), (c), (e), and (g) are images acquired in an environment that satisfies appropriate lighting conditions. FIGS. 5(b), (d), (f), and (h) are images acquired in an environment that satisfies strong lighting conditions.

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0014] <Relationship between photosynthesis and chlorophyll fluorescence> Figure 1 shows a schematic diagram of the relationship between photosynthesis and chlorophyll fluorescence. Specifically, Figure 1 shows the relationship between photosynthesis and chlorophyll fluorescence under appropriate light conditions (PAR 600 μmol m －２ s －１ Schematic diagram of the photosynthetic reaction when

[0015] The induced energy of sunlight L8 is first collected by the chlorophyll in photosystem II (PSII). Of the energy collected by the chlorophyll, only the amount that can be used for photosynthesis is sent to photosystem I (PSI). Photosynthesis is most active at the saturation value. For example, the saturation value is when the photosynthetically active radiance (PAR) is 600 μmol m －２ s －１ The extent can be exemplified.

[0016] The chlorophyll in photosystem I combines with a protein (Rubisco) to carry out photosynthesis. As a result, the chlorophyll in photosystem I produces carbohydrates such as sugars and oxygen from carbon dioxide and water. Chlorophyll fluorescence L91 (F740), which has a peak at a wavelength of 740 nm, is emitted from the chlorophyll in photosystem I.

[0017] Most of the excess light energy not used in photosynthesis is converted into heat and dissipated in the carotenoids. Some of it is emitted from photosystem II as excess energy fluorescence L92 (F685) with a peak wavelength of 685 nm. In other words, chlorophyll fluorescence L91 (F740) with a peak wavelength of 740 nm is emitted only from photosystem I. Excess energy fluorescence L92 (F685) with a peak wavelength of 685 nm is emitted only from photosystem II.

[0018] <Chlorophyll Fluorescence Image Acquisition Device> Fig. 1 is a conceptual diagram showing the configuration of a chlorophyll fluorescence image acquisition device 1. The chlorophyll fluorescence image acquisition device 1 acquires a chlorophyll fluorescence image D44 based on plant fluorescence (SIF: Solar-Induced Fluorescence) induced by sunlight L8. The chlorophyll fluorescence image D44 is captured in a chlorophyll fluorescence image D44 with a photosynthetically active radiation (PAR) of 600 μmol m －２ s －１ This is based on the chlorophyll fluorescence L91 emitted due to the photosynthetic activity of the plant leaf 9 exposed to sunlight L8.

[0019] The chlorophyll fluorescence image acquisition device 1 has, as physical components, a filter unit 2, a camera 3, and a computer (processing unit) 4. As will be described later, when acquiring the chlorophyll fluorescence image D44, a white plate 5 (reference body) is used, which is placed near the plant leaf 9, which is the measurement object. This white plate 5 may also be included as a component of the chlorophyll fluorescence image acquisition device 1.

[0020] The filter unit 2 is disposed on the optical axis of the camera 3, between the camera 3 and the plant leaves 9. For example, the filter unit 2 may be disposed immediately before the lens of the camera 3. The filter unit 2 provides the camera 3 with light of a specific wavelength band. The filter unit 2 has two or more optical filters that transmit wavelengths different from each other. In the example of FIG. 1 , the filter unit 2 has a first filter 21 and a second filter 22. These filters are selectively disposed on the optical axis of the camera 3. Switching between the first filter 21 and the second filter 22 may be performed manually or mechanically.

[0021] 2 shows the spectrum (G31) of chlorophyll fluorescence L91, the optical characteristics (G32) of the first filter 21, and the optical characteristics (G33) of the second filter 22. The spectrum (G31) of chlorophyll fluorescence L91 was obtained under sunlight L8 that satisfies appropriate light conditions. The appropriate light conditions include, for example, a light source with a photosynthetically active radiation (PAR) of 600 μmol m －２ s －１ 2 also shows the spectrum (G34) of excess energy fluorescence L92. Note that the spectrum (G34) of excess energy fluorescence L92 was obtained under sunlight L8, which satisfies the strong light condition. Graph G35 shows the optical characteristics of a filter with a center wavelength of 780 nm.

[0022] As shown in graph G31, the spectrum of chlorophyll fluorescence L91 ranges from approximately 730 nm to approximately 820 nm. Therefore, chlorophyll fluorescence L91 does not contain any wavelength components longer than 820 nm. Here, the light components of sunlight L8 are present in a wide range, for example, from 300 nm to 1200 nm. Therefore, the light components of sunlight L8 are present in the range from approximately 730 nm to approximately 820 nm, where the light components of chlorophyll fluorescence L91 exist, and also in a range longer than approximately 820 nm, where the light components of chlorophyll fluorescence L91 do not exist. In other words, the light components of white-plate reflected light L5 originating from the white plate 5 are included in the wavelength range longer than 820 nm. The light components of sunlight L8 in the wavelength range not including the light components of chlorophyll fluorescence L91 are used to obtain the white-plate intensity ratio D42 (reflection intensity ratio), which will be described later.

[0023] The optical characteristic (G32) of the first filter 21 is set to a range that does not include the light component of chlorophyll fluorescence L91. For example, the optical characteristic (G32) of the first filter 21 has a transmission wavelength band with a center wavelength of 850 nm and a half-width of 10 nm. The light component of chlorophyll fluorescence L91 does not exist within the range of the optical characteristic (G32) of the first filter 21. On the other hand, the optical characteristic (G33) of the second filter 22 is set to a range that includes the light component of chlorophyll fluorescence L91. For example, the optical characteristic (G33) of the second filter 22 has a transmission wavelength band with a center wavelength of 750 nm and a half-width of 10 nm. The center wavelength of the transmission wavelength band of this second filter 22 does not coincide with 740 nm, the wavelength of chlorophyll fluorescence. The center wavelength of the transmission wavelength band of this second filter 22 is longer than the wavelength of chlorophyll fluorescence. More specifically, the center wavelength of the transmission wavelength band of this second filter 22 is longer by 10 nm than the wavelength of chlorophyll fluorescence.

[0024] The camera 3 outputs an image based on the light transmitted through the filter unit 2. The camera 3 may be, for example, a cooled CCD camera unit equipped with a wide-angle lens (focal length: 10 mm to 20 mm) as the camera body. The filter unit 2 described above is placed immediately in front of the wide-angle lens.

[0025] The camera 3 generates a first image D31 and a second image D32 and passes these images to the computer 4. The first image D31 was obtained with the first filter 21 placed in front of the wide-angle lens. Based on the optical characteristics (G32) of the first filter 21, the first filter 21 does not transmit the light component of chlorophyll fluorescence L91 but transmits the light component of reflected sunlight L9 reflected by the plant leaves 9 (plant leaf reflected light). Therefore, the first image D31 does not include the light component of chlorophyll fluorescence L91 and is composed of the light component of reflected sunlight L9 reflected by the plant leaves 9.

[0026] On the other hand, the second image D32 was obtained with the second filter 22 placed in front of the wide-angle lens. Based on the optical characteristic (G33) of the second filter 22, the second filter 22 transmits the light component of chlorophyll fluorescence L91 and also transmits the light component of reflected sunlight L9 reflected by the plant leaves 9. Therefore, the second image D32 is composed of the light component of chlorophyll fluorescence L91 and the light component of reflected sunlight L9 reflected by the plant leaves 9. The white-plate reflected light L5 from the white plate 5 is used to calculate the white-plate intensity ratio D42.

[0027] The computer 4 obtains a chlorophyll fluorescence image D44 using the first image D31 and the second image D32 provided by the camera 3. FIG. 3 is a diagram showing the basic physical configuration of the computer 4. The computer 4 has a processor 401, which is a central processing unit (CPU), a main memory 402, an auxiliary memory 403, a communication control unit 404, an input unit 405, and an output unit 406. The chlorophyll fluorescence image acquisition device 1 is composed of one or more computers 4 configured with this hardware and software such as programs.

[0028] When the chlorophyll fluorescence image acquisition device 1 includes multiple computers 4, these computers 4 may be connected locally or via a communication network such as the Internet or an intranet. This connection logically constitutes a single chlorophyll fluorescence image acquisition device 1.

[0029] The processor 401 executes an operating system, application programs, etc. The main memory 402 is composed of a read-only memory (ROM) and a random access memory (RAM). The auxiliary memory 403 is a storage medium composed of a hard disk, a flash memory, etc. The auxiliary memory 403 generally stores a larger amount of data than the main memory 402. At least a portion of the components constituting the chlorophyll fluorescence image acquisition device 1 is realized by the auxiliary memory 403. At least a portion of the components constituting the chlorophyll fluorescence image acquisition device 1 may be realized by a communication control unit 404. The input unit 405 is composed of a keyboard, a mouse, a touch panel, a microphone for voice input, etc. The output unit 406 is composed of a display, a printer, etc. For example, the chlorophyll fluorescence image acquisition device 1 may display the first image D31, the second image D32, the corrected image D43, the chlorophyll fluorescence image D44, etc. on a display or the like.

[0030] The auxiliary storage unit 403 stores in advance a program P for obtaining a chlorophyll fluorescence image D44 and data necessary for the processing. The program P causes the computer 4 to execute each functional element of the chlorophyll fluorescence image acquisition device 1. For example, the program P is loaded by the processor 401 or the main storage unit 402, and causes at least one of the processor 401, the main storage unit 402, the auxiliary storage unit 403, the communication control unit 404, the input unit 405, and the output unit 406 to operate. For example, the program P reads and writes data from and to the main storage unit 402 and the auxiliary storage unit 403.

[0031] The program P may be provided in the form of a tangible recording medium such as a CD-ROM, a DVD-ROM, a semiconductor memory, etc. The program P may also be provided as a data signal via a communication network.

[0032] 1, the computer 4 has several functional components, which are realized by the processor 401 executing a program P for generating a fluorescent image.

[0033] The data input unit 41 receives the first image D31 and the second image D32 from the camera 3. The data input unit 41 is the input unit 405 shown in FIG. 3 . For example, if the camera 3 and the computer 4 are connected by wire, the data input unit 41 may be a USB port. If the camera 3 and the computer 4 are connected wirelessly, the data input unit 41 may be a wireless LAN port. Furthermore, if the first image D31 and the second image D32 are transferred from the camera 3 to the computer 4 via a recording medium such as a memory card, the data input unit 41 may be a card reader. The data input unit 41 stores the received first image D31 and second image D32 in the auxiliary storage unit 403.

[0034] The intensity ratio calculation unit 42 obtains a white-board intensity ratio D42. The white-board intensity ratio D42 is the ratio of the light intensity of the first image D31 to the light intensity of the second image D32. In other words, the white-board intensity ratio D42 is a value that corrects for differences in the radiant intensity of sunlight L8 due to the transmission wavelength bands (750 nm and 850 nm) of the filters 21 and 22. The white-board intensity ratio D42 is obtained by dividing the average value of all pixel values ​​constituting the first image D31 of the white-board reflected light L5 (reference-object reflected light) by the average value of all pixel values ​​constituting the second image D32.

[0035] The intensity ratio calculation unit 42 obtains a luminance value corresponding to the light intensity for a pixel constituting the second image D32. Next, the intensity ratio calculation unit 42 extracts a pixel constituting the first image D31 that corresponds to the extracted pixel in the second image D32. The intensity ratio calculation unit 42 then obtains a luminance value for the pixel. The intensity ratio calculation unit 42 then divides the luminance value obtained from the first image D31 by the luminance value obtained from the second image D32. As a result, a whiteboard intensity ratio D42 for the selected pixel can be obtained.

[0036] The above-mentioned "certain pixel" is extracted from a portion (reflected light intensity reference region) in the first image D31 and the second image D32 that corresponds to the white board 5. In other words, the luminance value of the "certain pixel" corresponds to the intensity of the light component of the white board reflected light L5.

[0037] The corrected image calculation unit 43 corrects the second image D32 using the white board intensity ratio D42. Correcting the second image D32 means adjusting the intensity of the light component of the white board reflected light L5 in the second image D32 to match the intensity of the light component of the white board reflected light L5 in the first image D31. The relationship between the intensity of the light component of the white board reflected light L5 in the second image D32 and the intensity of the light component of the white board reflected light L5 in the first image D31 is clear from the white board intensity ratio D42 described above. Therefore, the corrected image calculation unit 43 first obtains the second image D32 and the white board intensity ratio D42 from the auxiliary storage unit 403. Next, the corrected image calculation unit 43 multiplies the luminance values ​​set for the pixels constituting the second image D32 by the white board intensity ratio D42. As a result, a corrected luminance value is obtained. The corrected image calculation unit 43 performs a process of multiplying the luminance values ​​of all pixels constituting the second image D32 by the white board intensity ratio D42. As a result, a corrected image D43 configured by the corrected luminance values ​​can be obtained. The corrected image calculation unit 43 records the corrected image D43 in the auxiliary storage unit 403.

[0038] The chlorophyll fluorescence image calculation unit 44 obtains a chlorophyll fluorescence image D44. The chlorophyll fluorescence image D44 is obtained by subtracting the first image D31 from the corrected image D43. The corrected image D43 contains the light component of chlorophyll fluorescence L91 and the light component of sunlight L9 reflected by the plant leaves 9. The first image D31 does not contain the light component of chlorophyll fluorescence L91; it contains only the light component of sunlight L9 reflected by the plant leaves 9. Therefore, by subtracting the luminance value of the first image D31 from the luminance value of the corrected image D43, the light component of sunlight L9 reflected by the plant leaves 9 that was included in the corrected image D43 is canceled. As a result, an image composed only of the light component of chlorophyll fluorescence can be obtained. This image is the chlorophyll fluorescence image D44.

[0039] The light intensity of reflected sunlight L9 (excluding fluorescence) originating from the plant leaf 9 is equal to the light intensity of white-plate-reflected light L5 originating from the white plate 5 multiplied by the reflectance (the reflected light intensity of the plant leaf 9 divided by the reflected light intensity of the white plate 5). Here, the plant leaf intensity ratio is a value that corrects for differences in the radiant intensity of sunlight due to the filter's transmission wavelength band (750 nm and 850 nm). However, the plant leaf intensity ratio cannot be measured directly. The plant leaf intensity ratio can be obtained by dividing the light intensity obtained when reflected sunlight L9 reflected by the plant leaf 9 passes through a filter (F850) by the light intensity obtained when reflected sunlight L9 passes through a filter (F750). In other words, it can also be said that the plant leaf intensity ratio is equal to the white plate intensity ratio.

[0040] Then, all pixel values ​​of the first image D31 are subtracted from the product of all pixel values ​​(1360 x 1024 pixels) of the second image D32 multiplied by the white board intensity ratio D42, thereby obtaining a chlorophyll fluorescence image D44.

[0041] Next, a method for obtaining the chlorophyll fluorescence image D44 will be described with reference to the flow shown in FIG.

[0042] First, the first filter 21 is placed in front of the wide-angle lens of the camera 3 (S1). The placement of the first filter 21 may be performed manually by an operator, or may be performed mechanically when a switch is pressed.

[0043] Next, a first image D31 is obtained (S2). This step is performed by the first filter 21, the camera 3, and the data input unit 41 of the computer 4. For example, the computer 4 records the data of the first image D31 in the auxiliary storage unit 403.

[0044] Next, the first filter 21 is removed from in front of the wide-angle lens of the camera 3, and then the second filter 22 is placed in front of the wide-angle lens (S3). As with step S1, step S3 may also be performed manually by an operator, or may be performed mechanically when a switch is pressed.

[0045] Next, a second image D32 is obtained (S4). This step is performed by the second filter 22, the camera 3, and the data input unit 41 of the computer 4. For example, the computer 4 records the data of the second image D32 in the auxiliary storage unit 403.

[0046] Next, a white board intensity ratio D42 is obtained (S5). This step is executed by the intensity ratio calculation unit 42 of the computer 4. The processor 401 of the computer 4 reads out the first image D31 and the second image D32 from the auxiliary storage unit 403. Then, the processor 401 obtains the white board intensity ratio D42 using the first image D31 and the second image D32. The specific process for obtaining the white board intensity ratio D42 is as described in the explanation of the intensity ratio calculation unit 42. Then, the processor 401 stores the white board intensity ratio D42 in the auxiliary storage unit 403.

[0047] Next, a corrected image D43 is obtained (S6). This step is executed by the corrected image calculation unit 43 of the computer 4. The processor 401 of the computer 4 reads out the second image D32 and the white board intensity ratio D42 from the auxiliary storage unit 403. The specific processing for obtaining the corrected image D43 is as described in the explanation of the corrected image calculation unit 43. Then, the processor 401 stores the corrected image D43 in the auxiliary storage unit 403.

[0048] Next, a chlorophyll fluorescence image D44 is obtained (S7). This step is executed by the chlorophyll fluorescence image calculation unit 44 of the computer 4. The processor 401 of the computer 4 reads out the corrected image D43 and the first image D31 from the auxiliary storage unit 403. The specific processing for obtaining the chlorophyll fluorescence image D44 is as described above in the explanation of the chlorophyll fluorescence image calculation unit 44. The processor 401 then stores the chlorophyll fluorescence image D44 in the auxiliary storage unit 403.

[0049] Thereafter, the computer 4 may perform an output operation such as displaying the chlorophyll fluorescence image D44 on a display in accordance with a predetermined rule or an operation by an operator.

[0050] <Effects> The chlorophyll fluorescence image acquisition device 1 acquires a chlorophyll fluorescence image D44 based on chlorophyll fluorescence L91 emitted due to the photosynthetic activity of plant leaves 9 exposed to sunlight L8. The chlorophyll fluorescence image acquisition device 1 includes a camera 3 that outputs an image corresponding to the intensity of the received light, a filter unit 2 that is disposed between the plant leaves 9 (the object to be measured) and the camera 3 and is capable of switching between a first filter 21 and a second filter 22 that transmit light with different wavelength bands, and a computer 4 that acquires a chlorophyll fluorescence image D44 using the image output by the camera 3. The transmission wavelength band of the first filter 21 does not include the wavelength of the chlorophyll fluorescence L91, and the transmission wavelength band of the second filter 22 includes the wavelength (740 nm) of the chlorophyll fluorescence L91. The computer 4 performs an operation of passing the transmitted light, which includes a component of reflected sunlight L9 resulting from sunlight L8 reflected by the plant leaves 9 and a component of white-plate reflected light L5 resulting from white-plate reflected light L5 reflected by a white plate 5 arranged near the plant leaves 9, through the first filter 21, and making the transmitted light incident on the camera 3 to obtain a first image D31; and by passing the transmitted light through the second filter 22, making the transmitted light incident on the camera 3 to obtain a first image D31, making the transmitted light including a component of reflected sunlight L9, a component of white-plate reflected light L5, and a component of chlorophyll fluorescence L91 emitted due to the photosynthetic activity of the plant leaves 9 3 to obtain a second image D32; an operation of obtaining a white-board intensity ratio D42 by dividing the light intensity of the component of the white-board reflected light L5 contained in the first image D31 by the light intensity of the component of the white-board reflected light L5 contained in the second image D32; an operation of obtaining a corrected image D43 by multiplying the second image D32 by the white-board intensity ratio D42; and an operation of obtaining a chlorophyll fluorescence image D44 based on the chlorophyll fluorescence L91 that has passed through the second filter 22 by subtracting the light intensity of the first image D31 from the light intensity of the corrected image D43.

[0051] The chlorophyll fluorescence image acquisition device 1 obtains a chlorophyll fluorescence image D44 based on the chlorophyll fluorescence L91 using a second image D32 obtained through a second filter 22 with a central wavelength of 750 nm in the transmission wavelength band. The image based on the chlorophyll fluorescence L91 can provide image information that can be used to diagnose the growth condition with higher accuracy than an image based on the excess energy fluorescence L92 with a peak wavelength of 780 nm.

[0052] <Study on differences in sunlight conditions 1: Chlorophyll fluorescence image> Figure 5(a) is an image obtained using a visible light filter (F560) in an environment satisfying appropriate light conditions. Figure 5(b) is an image obtained using a visible light filter (F560) in an environment satisfying strong light conditions.

[0053] Figure 5(c) shows the results in an environment with appropriate light conditions (PAR = 542 μmol m －２ s －１ ) and Fig. 5(d) shows a chlorophyll fluorescence image obtained under high light conditions (PAR = 1356 μmol m －２ s －１ ) is a chlorophyll fluorescence image obtained by the chlorophyll fluorescence image D44. The image shown in Figure 5(c) indicates that in an environment with appropriate lighting conditions, the intensity value of the chlorophyll fluorescence image D44 is high, indicating that photosynthesis is activated. More specifically, in an environment with appropriate lighting conditions, sunlight L8 pours down vertically. In Figure 5(c), the value of the white solid-line frame in the crown area on the right-center side where PAR is highest is 700 countsms. －１ pixel －１ In Figure 5(c), the value of the white dashed frame at the base of the tree leaves with the lowest PAR is 100 countsms. －１ pixel －１ Therefore, it was found that there was a seven-fold change in these values. On the other hand, the image shown in Figure 5(d) shows that under strong light conditions that do not satisfy the appropriate light conditions, the intensity value of the chlorophyll fluorescence image D44 becomes extremely small, indicating that photosynthetic activity is reduced.

[0054] Therefore, the chlorophyll fluorescence image acquisition device 1 described in this embodiment can acquire images of plants with a photosynthetically active radiation (PAR) of 600 μmol m －２ s －１ For example, the chlorophyll fluorescence image acquisition device 1 may be provided with a sensor for measuring PAR as an additional element. The chlorophyll fluorescence image acquisition device 1 then determines whether the value obtained by the sensor for measuring PAR satisfies the appropriate light conditions (e.g., if the measured value is 600 μmol m or less). －２ s －１ If the appropriate lighting conditions are met, a chlorophyll fluorescence image D44 may be generated.

[0055] <Study 2 on Differences in Sunlight Conditions: In the Case of Excess Energy Fluorescence Images> Various information can be used to evaluate the growth status of plants. For example, an image based on excess energy fluorescence L92 (hereinafter referred to as excess energy fluorescence image) can be used as an image related to photosynthesis. As described at the beginning of the detailed description of the invention, excess energy fluorescence L92 is fluorescence emitted from photosystem II (PSII) and has a peak wavelength at 685 nm. The excess energy fluorescence image can be obtained by using a filter whose transmission wavelength band has a central wavelength of 685 nm.

[0056] Figure 5(e) is an excess energy fluorescence image obtained in an environment that satisfies the appropriate lighting conditions. Figure 5(f) is an excess energy fluorescence image obtained in an environment that does not satisfy the appropriate lighting conditions. The appropriate lighting conditions and intense lighting conditions are the same as those in Study 1 above. Comparing Figure 5(e) and Figure 5(f) reveals that the intensity value of the excess energy fluorescence image obtained under the intense lighting conditions is higher than that of the excess energy fluorescence image obtained under the appropriate lighting conditions. These results indicate that the excess energy fluorescence image can capture the activation of heat dissipation pathways, but cannot directly capture the activation of photosynthesis.

[0057] <Study 3 on differences in sunlight conditions: In the case of the Normalized Difference Vegetation Index (NDVI)> The Normalized Difference Vegetation Index (NDVI) is sometimes used as a parameter for evaluating the degree of plant activity. The Normalized Difference Vegetation Index (NDVI) is defined by the following formula (1): In formula (1), R ＮＩＲ can be obtained by using a filter whose central wavelength of the transmission wavelength band is 850 nm. Rｅｄ can be obtained by using a filter with a central wavelength of 680 nm in the transmission wavelength band. The reflectance of the plant leaf was calculated by dividing the reflection intensity of the plant by the reflection intensity of the white board. The reflectance is in the red region (R Ｒｅｄ ) and is low in the near-infrared region (R ＮＩＲ ) where the normalized difference vegetation index (NDVI) in equation (1) is calculated based on the near-infrared reflectance (R) at 850 nm, which is less affected by fluorescence and water vapor. ＮＩＲ ) and the red region of 680 nm (R Ｒｅｄ ) is calculated using the reflectance of the red region (R Ｒｅｄ ) reflectance decreases, and chlorophyll absorbs in the red region (R Ｒｅｄ ) increases the light energy absorption rate, and both photosynthetic activity and NDVI increase.

[0058] Figure 5(g) is an NDVI image obtained in an environment that satisfies the appropriate lighting conditions. Figure 5(h) is an NDVI image obtained in an environment that does not satisfy the appropriate lighting conditions. The appropriate lighting conditions and intensity lighting conditions are the same as those in Study 1 above. Examining Figure 5(g) reveals that the NDVI value has increased, indicating that the photosynthetic pathway is activated. On the other hand, examining Figure 5(h) reveals that the NDVI value has slightly decreased, indicating that the photosynthetic pathway is degraded. Although the NDVI has decreased to 0.7-0.6, this is not considered to be inactivation.

[0059] Furthermore, as in "Study 1: Chlorophyll Fluorescence Images Due to Differences in Sunlight Conditions," comparing the value (0.7) in the black box at the crown with the value (0.6) in the dashed box at the base of the tree, the rate of change was found to be 1.2 times. Meanwhile, in the case of chlorophyll fluorescence images, as mentioned above, the rate of change was 7 times. This is thought to be due to the fact that NDVI is obtained from reflectance and tends to have a small rate of change. On the other hand, chlorophyll fluorescence images are obtained from intensity differences and tend to have a large rate of change. Therefore, chlorophyll fluorescence images with a large rate of change indicate high measurement accuracy.

[0060] 1...chlorophyll fluorescence image acquisition device, 2...filter unit, 3...camera, 4...computer

Claims

1. A chlorophyll fluorescence image acquisition device for acquiring a chlorophyll fluorescence image based on chlorophyll fluorescence emitted due to photosynthetic activity of plant leaves exposed to sunlight, comprising: a camera for outputting an image corresponding to the intensity of the received light; a filter unit arranged between the plant leaf, which is an object to be measured, and the camera, capable of switching between a first filter and a second filter, the first filter and the second filter having different wavelength bands of transmitted light; and a processing unit for acquiring the chlorophyll fluorescence image using an image output by the camera, wherein the transmission wavelength band of the first filter does not include the wavelength of the chlorophyll fluorescence, and the transmission wavelength band of the second filter includes the wavelength of the chlorophyll fluorescence, and the processing unit performs the operations of: passing the transmitted light, which includes a component of plant leaf reflected light due to the sunlight reflected by the plant leaf and a component of reference body reflected light due to the sunlight reflected by a reference body arranged near the plant leaf, into the camera to acquire a first image by passing the transmitted light through the first filter; A chlorophyll fluorescence image acquisition device which performs the following operations: by passing the transmitted light, which includes a component of the plant leaf reflected light, a component of the reference body reflected light, and a component of the chlorophyll fluorescence emitted due to the photosynthetic activity of the plant leaf, through the second filter and incident on the camera to obtain a second image; by dividing the light intensity of the component of the reference body reflected light contained in the first image by the light intensity of the component of the reference body reflected light contained in the second image, to obtain a reflection intensity ratio; by multiplying the second image by the reflection intensity ratio, to obtain a corrected image; and by subtracting the light intensity of the first image from the light intensity of the corrected image, to obtain the chlorophyll fluorescence image based on the chlorophyll fluorescence that has passed through the second filter.

2. The sunlight received by the plant leaves has a photosynthetically active radiation (PAR) of 600 μmolm －２ s －１ The chlorophyll fluorescence image acquisition device according to claim 1, wherein:

3. A chlorophyll fluorescence image acquisition device as described in claim 1 or 2, wherein the transmission wavelength band of the second filter has a center wavelength of 750 nm.

Images