Methods for estimating chlorophyll content of leaves

Abstract

The present invention relates to a method for estimating the chlorophyll content of a leaf (12), the method comprising: providing an apparatus (10), wherein the apparatus comprises: a mobile computing device (14) comprising a digital camera (16); and a peripheral device (18) removably attached to the mobile computing device, the peripheral device comprising a light source (20), when the peripheral device is removably attached to the mobile computing device, the light source is aligned with the digital camera so that the light source (20) can illuminate the lens of the digital camera (16), wherein the peripheral device provides the light source (20) and the digital camera (16) a space (19) between the digital camera (16); capturing a first image (34a) of the light source turned on by the digital camera (16) when the leaf (12) is not inserted between the digital camera and the light source; extracting exposure data of the first image; capturing a second image (34b) by the digital camera when the leaf is inserted between the digital camera and the light source turned on; extracting exposure data of the second image; and estimating the chlorophyll content of the leaf based on the extracted exposure data of the first image and the second image using a processor, wherein the exposure data includes at least one of exposure time, F number and ISO value.

Description

Technical Field

[0001] The present invention relates to a method for estimating the chlorophyll content of a leaf, a computer program product, a computer-readable storage medium, an electrical signal and a mobile computing device. Background Art

[0002] The chlorophyll content of plant leaves is related to the nutritional status of the plant. Therefore, by measuring the chlorophyll content, it is possible to determine whether the plant needs additional fertilizer.

[0003] The SPAD-502Plus from Konica Minolta is a portable measuring device for the chlorophyll content of leaves. The SPAD-502Plus determines the relative amount of chlorophyll present by measuring the absorbance of the leaves in two wavelength regions using two LED (light emitting diode) elements and a silicone photodiode. However, this dedicated device is relatively expensive and therefore may not be available to everyone.

[0004] In addition, WO2019081729 discloses a handheld device (e.g., a smart phone or tablet) for determining the state of a plant, comprising: a multi-pixel digital color sensor; a light source (e.g., a flash of a smart phone) arranged to provide broadband illumination, wherein the light source and the multi-pixel digital color sensor are arranged in substantially the same plane; a light guide for guiding light from the light source into the direction of the multi-pixel digital color sensor; a sampling space provided between the multi-pixel digital color sensor and the light source for inserting at least a portion of the plant therein; and a processing unit arranged to control at least the multi-pixel digital color sensor and the light source. The light guide can be detachably attached to a smart phone or tablet. The processing unit may be arranged to control the multi-pixel digital color sensor and the light source so as to obtain a first image of the plant part when the light source is turned on and a second image of the plant part when the light source is turned off, wherein the multi-pixel digital color sensor is arranged to obtain at least red (R), green (G) and blue (B) color components, the red (R), green (G) and blue (B) color components together forming a set of color components, and wherein the processing unit is arranged to perform at least the following operations: (i) determining a first color value, the first color value representing the difference in intensity values ​​of the first color component of the color components in the first and second images; (ii) determining a second color value, the second color value representing the difference in intensity values ​​of the second color component of the color components in the first and second images; (iii) using the first color value and the second color value to calculate a value representing the state of the plant. Although the device in WO2019081729 can reduce costs because it can use existing smartphones or tablets, there is still room for improvement in the versatility and use of processing power.

[0005] Furthermore, in the article “Feasibility of using smart phones to estimate chlorophyll content in cornplants” by Versali et al., December 2017, in Photosyntica, Vol. 55, No. 4, pp. 603-610, a smart phone and a lamp holder having an LED (light emitting diode) attached to the smart phone are disclosed, wherein an image of a leaf on top of the LED is captured in light-assisted spectral absorption photometry. In the light-assisted spectral absorption photometry, all settings of the smart phone camera including ISO, exposure time, etc. are kept constant. R, G, and B components and various indices are extracted from the acquired image. However, a disadvantage of the solution of Versali et al. is that it may require considerable processing power. Summary of the invention

[0006] It is an object of the present invention to overcome or at least alleviate the above mentioned problems.

[0007] According to a first aspect of the present invention, this and other objects are achieved by a method for estimating the chlorophyll content of a leaf, the method comprising: providing an apparatus, wherein the apparatus comprises: a mobile computing device including a digital camera; and a peripheral device removably attached to the mobile computing device, the peripheral device comprising a light source, when the peripheral device is removably attached to the mobile computing device, the light source is aligned with the digital camera so that the light source can illuminate a lens of the digital camera, wherein the peripheral device provides a space between the light source and the digital camera so that the leaf can be inserted between the digital camera and the light source; capturing a first image of the light source turned on by the digital camera without the leaf being inserted between the digital camera and the light source; extracting exposure data of the first image; capturing a second image by the digital camera with the leaf inserted between the digital camera and the turned on light source; extracting exposure data of the second image; and estimating the chlorophyll content of the leaf based on the extracted exposure data of the first image and the second image using a processor, wherein the exposure data comprises at least one of exposure time, F number and ISO value. That is, the processor may estimate the chlorophyll content of the leaf based on at least one of the exposure time, F number and ISO value of the first image and the second image. The processor may be included in the aforementioned mobile computing device. The method may be (at least in part) computer-implemented.

[0008] The peripheral device may also be referred to as an accessory for the mobile computing device. The peripheral device may, for example, include a U-shaped clamp that clamps the peripheral device to the mobile computing device and a holder that holds a light source in front of the digital camera so that the light source can illuminate the lens of the digital camera. In addition, the first and second images captured by the digital camera may be recorded images or live images. In the latter case, the extracted exposure data may be a real-time reading from a sensor of the digital camera. In addition, the first image and the second image may be automatically captured by the digital camera while the mobile computing device instructs the user to insert / remove the blade.

[0009] The present invention is based on the understanding that exposure data (preferably Exif data) of a first and a second image without and with a leaf can be conveniently used to estimate the chlorophyll content of the leaf. That is, depending on the chlorophyll content, the leaf will absorb more or less light emitted by the light source, which typically results in, for example, a longer exposure time and / or a smaller F number (wider aperture) of the second image compared to the first image, as indicated by the exposure data. By means of the present invention, the processing power required to estimate the chlorophyll content of the leaf is greatly reduced compared to more advanced image analysis techniques. Therefore, less powerful and generally less expensive mobile computing devices, such as low-end smartphones, can also be used. In addition, the device (method) is highly accurate relative to the cost. In addition, since the light source is external to the mobile computing device and no light guide is used, a peripheral device that can be removably attached or attachable to the mobile computing device and includes the light source can be designed to fit most mobile computing devices including digital cameras, making the present device (method) very versatile.

[0010] The exposure data may be Exif (Exchangeable Image File Format) data. Exif is a standard that specifies image formats for devices that process image files recorded by digital cameras. Exif data is convenient for use in the present invention because it is readily available in many mobile computing devices that include digital cameras.

[0011] As described above, the exposure data may include at least one of exposure time, F number, and ISO value. The exposure time is the length of time the sensor of the digital camera is exposed to light, the F number is the ratio of focal length to aperture in a digital camera, and the ISO value is the "film speed".

[0012] The mobile computing device may control the digital camera so that the first image and the second image are captured at the same exposure time and ISO value, and the chlorophyll content of the leaf is estimated based on any change in the F-number of the first image and the second image. For example, for the two images, the exposure time and ISO value may be set to 1 / 125s and ISO 100, respectively, and the F-number may be reduced from, for example, 5.6 to 4 (digital camera in shutter priority mode), wherein the reduction is indicative of the chlorophyll content of the leaf. Generally, the more chlorophyll, the larger the aperture opening required (the smaller the F-number). In another embodiment, the mobile computing device may control the digital camera so that the first image and the second image are captured at the same F-number and ISO value, and the chlorophyll content of the leaf is estimated based on any change in the exposure time of the first image and the second image (digital camera in aperture priority mode). In any case, by keeping the exposure time and ISO value constant or the F-number and ISO value constant, the digital camera only needs to calculate a single parameter (F-number or exposure time), which can provide a fast estimate of the chlorophyll content of the leaf.

[0013] In yet another embodiment, the mobile computing device may control the digital camera so that the first and second images are captured using the same value of at least one of the exposure time, the F number, and the ISO value. That is, only one of the three parameters / values ​​may be kept constant here. Preferably, the F number is kept constant because the ISO value is easier to control, i.e., more dynamic than the F number.

[0014] Estimating the chlorophyll content of the leaves based on the extracted exposure data of the first image and the second image (by the mobile computing device) may include determining illuminance values ​​of the first image and the second image based on the extracted exposure data of the first image and the second image and determining an attenuation value based on the determined illuminance value. The illuminance value (lux) may be defined as lux=C*(N*N) / (S*t), where C is a constant depending on the digital camera, N is the F number, S is the ISO value, and t is the exposure time. As described above, S and t may be the same for the two images, while N may vary. The illuminance value may alternatively be defined as lux=C*(2^EV) / S, where EV is the exposure value. The exposure value may be included in the aforementioned exposure data. The attenuation value is defined as (lux 具有叶片 ) / (lux 没有叶片 ). The advantage of using the attenuation value is that it is unitless and independent of the constant C mentioned above.

[0015] Estimating the chlorophyll content of the leaves (by the mobile computing device) may be further based on a predefined thickness of the leaves, which is based on the crop type and sowing date input from a user of the mobile computing device. The user may, for example, enter the type of crop (e.g., wheat, rice, corn, etc.) and the number of days after sowing (e.g., 10 days or 15 days) or the crop stage week via a user interface (e.g., touch screen) of the mobile computing device, whereupon the mobile computing device may (be configured to) extract the thickness of the leaves from a table showing average thickness of leaves at different growth stages. Alternatively, the user may measure the actual thickness of the leaves and input it into the mobile computing device.

[0016] The method may also include calculating (by a mobile computing device) a (proprietary) value indicating the chlorophyll content of the leaf based on the determined attenuation value and a predefined thickness of the leaf. The proprietary value may be, for example, an Ntester value. The Ntester value may be calculated as Ntester value = weight 1 * ln (attenuation value) + weight 2 * predetermined leaf thickness, where ln is a natural logarithm function. Early trials of the device showed a strong correlation (0.769-0.811) between the results obtained using this equation and Yara's Ntester. Only a single equation is required to calculate the current Ntester value using the attenuation value. In addition, the inventors have discovered a linear relationship between the Ntester value and the natural logarithm of the attenuation value, which means that the Ntester value can be calculated significantly faster and with less processing power than more advanced image analysis techniques. Weight 1 and weight 2 for a particular digital camera can be calculated using four calibration papers of known thickness, Ntester value and attenuation.

[0017] The mobile computing device may automatically set the focus of the digital camera on the turned-on light source (and if possible, focus on the turned-on light source) for capturing the first image, and control the digital camera to use the same focus when capturing the second image (i.e., the first image and the second image may be captured with the same focus). This typically means that the digital camera's photometry is also "focused" on the turned-on light source. The turned-on light source is typically the brightest spot in the scene. Using the same focus may speed up processing because the digital camera does not need to be adjusted to introduce the leaf. Furthermore, this allows estimation of the precise position of the leaf independent of the digital camera and the light source.

[0018] The light source may be adapted to emit light that is at least partially absorbable by the chlorophyll pigments, chlorophyll a and chlorophyll b.

[0019] The light source may be adapted to emit light of a single predetermined wavelength, for example 650 nm or in the range of 640-649 nm or in the range of 651-670 nm. 650 nm is useful because both chlorophyll a and chlorophyll b have a high absorption of light at this wavelength.

[0020] The light source is preferably an LED (Light Emitting Diode).

[0021] The light source may be provided with a hollow light guide, such as a cylinder, for blocking ambient light when the light source is aligned with the digital camera. This may improve chlorophyll content estimation.

[0022] The mobile computing device may be a smartphone or a tablet computer.

[0023] Throughout the document, the image taken without the blade inserted between the light source and the camera is referred to as the first image, and the image taken with the blade inserted between the light source and the camera is referred to as the second image. However, this does not mean that the image without the blade must be taken before the image with the blade. It is also possible to first place the blade between the light source and the camera, capture a picture under the light source turned on with the blade inserted between the light source and the camera, remove the blade, and capture another picture of the light source with the blade not inserted.

[0024] According to a second aspect of the present invention, there is provided a computer program product comprising a computer program code, which, when executed on a mobile computing device, performs the following steps: capturing, by a digital camera of the mobile computing device, a first image of a light source that is turned on and is removably attached to a peripheral device of the mobile computing device, the first image being captured without inserting a leaf between the digital camera and the light source; extracting exposure data of the first image; capturing, by the digital camera, a second image, wherein the leaf is inserted between the digital camera and the turned-on light source; extracting exposure data of the second image; and estimating the chlorophyll content of the leaf based on the extracted exposure data of the first image and the second image, wherein the exposure data comprises at least one of an exposure time, an F number, and an ISO value. The computer program product may be a non-transitory computer program product. The computer program product may be an app (application program) (for a smart phone or tablet). This aspect may exhibit the same or similar features and technical effects as the first aspect, and vice versa.

[0025] According to a third aspect of the present invention, there is provided a computer readable storage medium comprising the computer program product according to the second aspect.

[0026] According to a fourth aspect of the present invention, there is provided an electrical signal embodied on a carrier wave and propagating on a dielectric medium, the electrical signal comprising a computer program product according to the second aspect.

[0027] According to a fifth aspect of the present invention, there is provided a mobile computing device comprising the computer-readable storage medium according to the third aspect.

[0028] According to a sixth aspect of the present invention, there is provided a device for estimating the chlorophyll content of a leaf, the device comprising: a mobile computing device including a digital camera; and a peripheral device removably attached or attachable to the mobile computing device, the peripheral device comprising a light source aligned with the digital camera when the peripheral device is removably attached to the mobile computing device, wherein the mobile computing device is configured to extract exposure data of a first image of the light source turned on, the first image being captured by the digital camera when the leaf is not inserted between the digital camera and the light source, extract exposure data of a second image captured by the digital camera when the leaf is inserted between the digital camera and the turned-on light source, and estimate the chlorophyll content of the leaf based on the extracted exposure data of the first image and the second image. This aspect may exhibit the same or similar features and technical effects as any one of the other aspects, and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention.

[0030] Figure 1a -b is a schematic side view of an apparatus according to an embodiment of the present invention.

[0031] Figure 2a -b is according to an embodiment Figure 1a -b A device's peripheral perspective.

[0032] Figure 3a -b is according to another embodiment Figure 1a -b A device's peripheral perspective.

[0033] Figure 4 is a graph illustrating exemplary performance of the present invention.

[0034] Figure 5 is a flow chart of a method according to one or more embodiments of the invention. DETAILED DESCRIPTION

[0035] Figure 1a -b is a schematic side view of an apparatus 10 for estimating the chlorophyll content of a leaf 12 according to one embodiment of the present invention.

[0036] The device 10 includes a mobile computing device 14, which may be handheld. The mobile computing device 14 may be, for example, a smart phone (such as an iPhone or an Android phone) or a tablet computer (such as an iPad).

[0037] The mobile computing device 14 includes a digital camera 16, as described in further detail below. In addition, the mobile computing device 14 may include a processor, memory, storage, and a user interface. The user interface may include a touch screen.

[0038] The digital camera 16 may be arranged, for example, on the back of the mobile computing device 14. The digital camera 16 may include a sensor, a lens, a photometer function (for exposure control), and an autofocus function. The digital camera 16 may be configured to provide exposure data, i.e., Exif data, of an image captured by the digital camera 16. The captured image may be a recorded image (e.g., stored in the above-mentioned storage device) and / or a live image (i.e., a real-time sensor reading). The Exif data may include exposure time, F number (aperture), and ISO value.

[0039] The device 10 also includes a peripheral device 18. The peripheral device 18 may also be referred to as an accessory of the mobile computing device 14. The peripheral device 18 is removably attached or removably attachable to the mobile computing device 14 and includes a light source 20 that is aligned with the digital camera 14 when the peripheral device 18 is removably attached to the mobile computing device 14. As shown, the peripheral device 18 provides a space 19 between the light source 20 and the digital camera 16. The light source 20 is adapted to emit a single predetermined wavelength of light 21, here 650nm, i.e., visible red light. The light source 20 is preferably at least one LED (light emitting diode). The peripheral device 18 may also include a battery electrically connected to the light source 20 and adapted to power the light source 20. The peripheral device 18 may also include a switch that allows a user to turn on / off the light source 20. In this way, the peripheral device 18 may be self-contained and only mechanically connected to the mobile computing device 14.

[0040] Further references Figure 2a-b, the peripheral device 18 may include a U-shaped clamp 22 that clamps the peripheral device 18 to the mobile computing device 14. The clamp 22 includes a first leg 24a that abuts the back of the mobile computing device 14, and a curved second leg 24b having a distal end portion 26b that abuts the front of the mobile computing device 14. The clamp 22 may be slightly flexible so as to fit mobile computing devices with different depths. The clamp 22 may be made of plastic, for example. The first leg 24a includes an opening 25 that exposes the lens of the digital camera 16. The opening 25 may also serve as a lens cover for the digital camera 16. The peripheral device 18 also includes a holder 28 connected at the distal end portion 26a of the first leg 24a and holding the light source 20 in front of the digital camera 16. The holder 28 may be arranged above the first leg 24a. The holder 28 holds the light source 20 and aligns it with the digital camera 16 so that the light source 20 can illuminate the lens of the digital camera 16 and so that the light source 20 is within the field of view of the digital camera 16. The blade 12 may be placed between the holder 28 and the first leg 24a so that the blade 12 is inserted (placed) between the digital camera 16 and the light source 20. In addition, the holder 28 may be pivotally connected to the first leg 24a so that it may be temporarily raised to facilitate placement of the blade 12.

[0041] exist Figure 3a In another embodiment of the peripheral device shown in -b, the holder 28 is arranged substantially perpendicular to the first leg 24a, where the first leg 24a does not need to have an opening 25. In addition, the light source 20 can be provided with a "lens cover" in the form of a (straight circular hollow) cylinder 30 for blocking ambient light.

[0042] Next, the mobile computing device 14 may be configured to perform various specific steps or actions described in detail below with the aid of an application 32 (computer program product). The application 32 may be downloaded to the mobile computing device 14 and stored in the above-mentioned storage device of the mobile computing device 14. The application 32 may run or be executed on the mobile computing device 14 using the above-mentioned processor and memory of the mobile computing device 14.

[0043] Specifically, the mobile computing device 14 is configured to extract exposure data of a first image 34a of the light source 20 being turned on, the first image 34a being taken when the blade 12 is not interposed between the digital camera 16 and the light source 20 ( Figure 1a , 2a and 3a) are captured by the digital camera 16. The extracted exposure data may include exposure time, F number (aperture) and ISO value, for example 1 / 1000s, 2.8 and ISO 100.

[0044] The first image 34a may be automatically captured by the digital camera 16 while the mobile computing device 14 instructs the user to remove any blades 12 placed between the digital camera 16 and the light source 20. To this end, an appropriate message ("Remove blades") may be displayed on the aforementioned touch screen of the mobile computing device 14, for example.

[0045] In addition, the mobile computing device 14 can be configured to automatically set the focus 36 of the digital camera 16 on the center of the turned-on light source 20 for capturing the first image 34a. This may include performing Gaussian low-pass filtering, RGB to HSV (hue saturation value) conversion, red bandpass filtering, extracting contours using Suzuki boundary tracking, extracting bounding boxes with smaller areas, and finding the center of the bounding box. Setting the focus 36 on the turned-on light source 20 can also “focus” the photometry of the digital camera 16 on the turned-on light source 20.

[0046] The mobile computing device 14 is also configured to, in the event that the blade 12 is inserted between the digital camera 16 and the turned-on light source 20 which is still aligned with the digital camera 16 ( Figure 1b , 2b and 3b) extracting exposure data of a second image 34b captured by the digital camera 16, as will be discussed in more detail below.

[0047] While the mobile computing device 14 instructs the user to place the blade 12 between the digital camera 16 and the light source 20, the second image may be automatically captured by the digital camera 16. In addition, the mobile computing device 14 may be configured to control the digital camera 16 so as to use the same focus 36 when capturing the second image 34b, and so that the first and second images 34a-b are captured at least at the same ISO value (e.g., ISO 100), while the exposure time and F-number are selected by the digital camera 16 using the light meter function to obtain the correct exposure (the digital camera 16 is in program mode). The selected exposure time and F-number may be, for example, 1 / 60s and 1.3. Therefore, the extracted exposure data of the second image 34b may include, for example, 1 / 60s, 1.3, and ISO 100. Here, it is noted that the exposure time has been increased from 1 / 1000s to 1 / 60s, and the F-number has been changed from 2.8 to 1.3 (i.e., a wider aperture is used for the second image 34b).

[0048] The mobile computing device 14 is also configured to estimate the chlorophyll content of the leaf 12 based on the extracted exposure data of the first and second images 34a - b .

[0049] Specifically, the mobile computing device 14 may be configured to determine the illuminance values ​​of the first and second images 34a-b based on the extracted exposure data of the first and second images 34a-b, and determine the attenuation value based on the determined illuminance values. The illuminance value (lux) may be defined as lux=C*(N*N) / (S*t), where C is a constant depending on the digital camera, N is the F number, S is the ISO value, and t is the exposure time. Based on the exposure data given above, Lux 没有叶片 =78.39*C*(first image), and Lux 具有叶片 =1.014*C*(second image). The attenuation value is defined as (lux 具有叶片 ) / (lux 没有叶片 ). For the exemplary exposure data given above, the attenuation value is 0.0129. It is worth noting that the attenuation value is independent of C.

[0050] The mobile computing device 14 may also be configured to calculate an N tester value based on the determined attenuation value and a predefined thickness of the blade 12, wherein the N tester value indicates the chlorophyll content. The predefined thickness of the blade 12 may be based on the crop type and sowing day input by the user to the mobile computing device 14. The user may enter, for example, the crop type (e.g., wheat, rice, corn, etc.) and the number of days after sowing (e.g., 90 or 105 days) or the crop stage week via the above-mentioned touch screen of the mobile computing device 14. "Wheat" and the 4th crop stage week may, for example, result in a blade thickness of 0.2886 mm.

[0051] The Ntester value can be calculated as Ntester value = Weight 1 * ln (attenuation value) + Weight 2 * predefined blade thickness, where Weight 1 and Weight 2 for a specific digital camera 14 can be calculated using four calibration papers of known thickness, Ntester value and attenuation value.

[0052] Figure 4 is a graph showing the relationship between the natural logarithm of the attenuation value (obtained from experiments of the present invention) and the Ntester value (calculated) obtained from experiments of the present invention.

[0053] Figure 5 is a flow chart of a method of estimating the chlorophyll content of a leaf 12. The method may be performed, for example, using the apparatus 10. The method may thus correspond to the operation of the apparatus 10.

[0054] The method may be initiated by a user attaching the peripheral device 18 to the mobile computing device 14 , and turning on the light source 20 (step S1 ).

[0055] The mobile computing device 14 may prompt the user to remove any blades 12 placed between the digital camera 16 and the light source 20 (step S2).

[0056] The mobile computing device 14 may then automatically set the focus 36 of the digital camera 16 on the turned-on light source 20 for capturing the first image 34a (step S3).

[0057] The mobile computing device 14 may then automatically capture a first image 34a of the turned-on light source 20 without the blade 12 interposed between the digital camera 16 and the light source 20 (step S4 ).

[0058] In step S5 , the method comprises extracting exposure data of the first image 34 a . The extracted exposure data may be stored in a memory and / or storage device of the mobile computing device 14 .

[0059] The mobile computing device 14 may then prompt the user to place the blade 12 between the digital camera 16 and the light source 20 (step S6). The user may (at this point) place the blade 12 in the space 19 between the digital camera 16 and the light source 20.

[0060] In step S7 , the mobile computing device 14 may set the focus, exposure time, and ISO value of the digital camera 16 to be the same as that used for the first image 34 a .

[0061] The mobile computing device 14 may then automatically capture the second image 34 b in step S8 using the settings from step S7 with the blade 12 inserted between the digital camera 14 and the turned-on light source 20 .

[0062] The first and second images 34a-b are preferably captured continuously. Furthermore, the time between capturing the first and second images 34a-b is preferably less than 1 hour, in particular less than 30 minutes. Furthermore, the brightness and position of the light source 20 are preferably kept constant for both images 34a-b.

[0063] In step S9 , the method comprises extracting exposure data of the second image 34 b . The extracted exposure data may be stored in a memory and / or storage device of the mobile computing device 14 .

[0064] The mobile computing device 14 may then determine illumination values ​​for the first and second images 34a - b based on the exposure data extracted in steps S5 and S9 , and thereby determine an attenuation value (step S10 ).

[0065] Furthermore, the user may input the crop type and the number of days after sowing (or crop stage week) via the aforementioned touch screen of the mobile computing device 14 , whereby the mobile computing device 14 may extract the predetermined thickness of the blade 12 (step S11 ).

[0066] In step S12 , the mobile computing device 14 may calculate an Ntester value based on the attenuation value determined in step S10 and the predefined thickness of the blade from step S11 .

[0067] Based on the calculated N tester value, it can be determined whether the plant from which the leaf 12 comes needs additional fertilizer. The calculated N tester value can be presented, for example, on a touch screen of the mobile computing device 14. The calculated N tester value can also be sent remotely from the device 10 / 14, for example, along with GPS location data and / or other data available in the mobile computing device 14.

[0068] Steps S10 - S12 may be collectively referred to as estimating the chlorophyll content of the leaf 12 based (at least in part) on the exposure data of the first and second images 34a - b .

[0069] Those skilled in the art realize that the present invention is by no means limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

[0070] For example, instead of setting the exposure time and ISO value in step S7, the mobile computing device 14 may set the F-number and ISO value of the digital camera 16 to be the same as for the first image 34a, and the digital camera 16 uses the light meter function to select the exposure time of the second image 34b to obtain the correct exposure (the digital camera 16 is in aperture priority mode). This may be useful if the digital camera 16 has a fixed aperture. As other alternatives, just use the same ISO value (as in the example on page 12) or the same F-number.

[0071] also, Figure 5 At least some of the steps in the method need not be Figure 5 The method may be performed in the exact order shown. For example, the illumination value of the first image 34a may be determined directly after step S5. The user may also enter the crop type and the number of days after sowing earlier in the method. Furthermore, the second image 34b may be captured before the first image 34a.

[0072] Furthermore, capturing a second image by the digital camera with the blade inserted between the digital camera and the switched-on light source and extracting exposure data of the second image may comprise capturing at least two images of different parts of the blade and extracting (average) exposure data of those images.

[0073] Furthermore, peripheral devices 18 may be provided without mobile computing device 14 .

Claims

1. A method for estimating the chlorophyll content of a leaf (12), the method comprising: A device (10) is provided, wherein the device (10) comprises: a mobile computing device (14) comprising a digital camera (16); and a peripheral device (18) removably attached to the mobile computing device, the peripheral device comprising a light source (20), wherein when the peripheral device (18) is removably attached to the mobile computing device (14), the light source (20) is aligned with the digital camera (16) such that the light source (20) can illuminate a lens of the digital camera (16), wherein the light source (20) is adapted to emit light that is at least partially absorbable by a chlorophyll pigment comprising chlorophyll a and chlorophyll b, and wherein the peripheral device (18) provides a space (19) between the light source (20) and the digital camera (16) such that the leaf (12) can be inserted between the digital camera (16) and the light source (20); capturing (S4) a first image (34a) of the turned-on light source (20) by the digital camera (16) when the blade (12) is not inserted between the digital camera (16) and the light source (20); extracting (S5) exposure data of the first image (34a); capturing (S8) a second image (34b) by the digital camera (16) with the blade (12) inserted between the digital camera (16) and the turned-on light source (20); extracting (S9) exposure data of the second image (34b); and Using a processor, estimating the chlorophyll content of the leaf (12) based on the extracted exposure data of the first image and the second image (34a, 34b), wherein the processor estimates the chlorophyll content of the leaf based on at least one of exposure time, F-number and ISO value of the first image and the second image, and wherein the first and second images are captured using the same value of at least one of exposure time, F-number and ISO value, the method further comprising: determining illuminance values ​​of the first image and the second image based on the extracted exposure data of the first image and the second image and determining the attenuation value based on the determined illuminance values; and A value indicative of the chlorophyll content of the leaf is calculated based on the determined attenuation value.

2. The method according to claim 1, wherein: The mobile computing device (14) controls the digital camera (16) so that the first image and the second image (34a, 34b) are captured at the same F number.

3. A method according to any one of the preceding claims, wherein: Estimating the chlorophyll content of the leaf (12) based on the extracted exposure data of the first and second images (34a, 34b) includes determining illumination values ​​of the first and second images (34a, 34b) based on the extracted exposure data of the first and second images (34a, 34b) and determining an attenuation value based on the determined illumination values.

4. The method according to claim 1 or 2, wherein: Estimating the chlorophyll content of the leaf (12) is also based on a predefined thickness of the leaf (12), the predefined thickness of the leaf (12) being based on crop type and days after planting from user input to the mobile computing device (14).

5. The method according to claim 4, comprising calculating a proprietary value indicative of the chlorophyll content of the blade (12) based on the determined attenuation value and a predefined thickness of the blade (12).

6. The method according to claim 1 or 2, wherein: The mobile computing device (14) automatically sets a focus (36) of the digital camera (16) on the activated light source (20) for capturing the first image (34a), and controls the digital camera (16) to use the same focus when capturing the second image (34b).

7. The method according to claim 1 or 2, wherein: The light source (20) is adapted to emit light of a single predetermined wavelength.

8. The method according to claim 7, wherein: The single predetermined wavelength is 650 nm.

9. The method according to claim 1 or 2, wherein: The light source (20) is a light emitting diode (LED).

10. The method according to claim 1 or 2, wherein: The light source is provided with a hollow light guide (30) for blocking ambient light when the light source (20) is aligned with the digital camera (16).

11. The method according to claim 1 or 2, wherein: The mobile computing device (14) is a smartphone or a tablet computer.

12. A computer program product (32) comprising computer program code which, when executed on a mobile computing device (14) comprising a digital camera (16), performs the following steps: capturing, by the digital camera (16) of the mobile computing device (14), a first image (34a) of an activated light source (20) of a peripheral device (18) removably attached to the mobile computing device (14), the first image being captured without a blade (12) interposed between the digital camera and the light source (20), wherein: The light source is adapted to emit light that is at least partially absorbable by chlorophyll pigments, the chlorophyll pigments comprising chlorophyll a and chlorophyll b; extracting exposure data of the first image (34a); capturing a second image (34b) by the digital camera (16) with the blade (12) interposed between the digital camera (16) and the activated light source (20); extracting exposure data of the second image (34b); as well as estimating the chlorophyll content of the leaf (12) based on the extracted exposure data of the first image and the second image (34a, 34b), wherein the processor of the mobile computing device estimates the chlorophyll content of the leaf based on at least one of exposure time, F-number and ISO value of the first image and the second image, and wherein the first and second images are captured using the same value of at least one of exposure time, F-number and ISO value, the steps further comprising: determining illuminance values ​​of the first image and the second image based on the extracted exposure data of the first image and the second image and determining the attenuation value based on the determined illuminance values; and A value indicative of the chlorophyll content of the leaf is calculated based on the determined attenuation value.

13. A computer-readable storage medium comprising the computer program product according to claim 12.

14. A mobile computing device (14) comprising the computer-readable storage medium of claim 13.

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