Synchronous Measurement Of Three Dimensional Illuminance And Deformation Of Plant Leaves Based On The 3D-DIC And Hotometry

The growth of plant leaves and light is in close relationship. Leaf growth occurs after a leaf absorbs nutrition, which results in the generation of force within the leaf and its subsequent morphological changes. However, so far there is no relevant research on the mechanical mechanism of leaf growth. In order to study three dimensional(3D) illumination and deformation of the process of plant leaf growth, a very precise light control in the greenhouse is required. As the machine vision technology has advantages of non-contact, continuous and High-accuracy, this paper proposed a method for synchronous measurement illuminance and deformation of plant leaves with texture, which is based on 3D digital image correlation(3D-DIC) technique and photometry, and the concrete research steps are as follows:(1) Because there is a lot of texture information on plant leaves. The texture information on plant leaves never disappear in leaf growth process, thus their growth dynamics can be captured by digital image correlation method as they gradually grow. First of all, this assay used two cameras to acquire leaf images, according to the texture information of leaf image, used digital image correlation method and the principle of binocular vision for 3D shape reconstruction, and calculated leaf surface point to the left camera distance by the 3D coordinates. Secondly, according to the imaging principle and combining Lamber's cosine theorem. The assay derived the relation between image and illumination, achieved the illuminance measurement by leaf image. Finally, 3D deformation(displacement field, strain field) of plant leaves were meausured by the 3D-DIC based on the collection and comparison of plant leaves.(2) According to the analysis of 3D illumination and deformation measurement principle of plant leaves, this paper designed and implemented a system of measuring 3D illuminance and deformation of leaves. the hardware system included camera, light source, illuminance sensor, synchronous controller, adjustable bracket; the software system mainly consisted of 5 parts, and its functions are as follows: 1) the equipment control unit controled 2 cameras and illuminance sensor synchronization; 2) the data acquisition unit achieved the acquisition of calibration target image, leaf image and illuminance; 3) the calibration unit achieved the calibration of the camera parameters and the relation between leaf surface illuminatio n and image gray values; 4) the measurement unit according to the parameters and the relation of the calibration to synchronously measure the 3D coordinates, illuminance distribution, displacement field, strain field; 5) the visualization unit achieved the visualization of measurement results. The system can be achieved through the C++ programming combined with opencv image library and MATLAB tool.(3) This assay simulated 2 cameras, flat plates and curved surface with random speckle information through the CAD, the measurement precision was guaranteed through the reconstruction of the flat and curved surface and the further analysis of its accuracy. Taking the fittonia as the study object, 3D reconstruction, illuminance distribution visualization, displacement field visualization and strain field visualization in the leaf growth process were achieved.In summary, for leaf size 1280*1204pixel image, we took 57 pixel as matching size, calculated the interval 7pixel, 3D reconstruction effect best, Through comparative analysis of image measurement average values and acquisition values,the correlation was 0.9963, the relative error was less than 6%. The results show that the measurement system can achieve the synchronous measurement of 3D morphology, illuminance distribution, displacement field, strain field of plant leaf with texture, and provide a method for the study on growth mechanics of plant leaves, meanwhile supply data support for greenhouse intelligent optical control.