Research And Application Of Plant Leaf Geometric Parameters Measurement

Geometric parameters measurement of plant leaf can be used for monitoring the growth condition of the plant, and it is helpful to guide the agricultural production and research on the agronomic or plant physiology. Traditional measurement means of geometric parameters on plant leaf are nine palace grid method, weighing method, coefficient method, leaf area meter, vernier calipe r method, thickness sensor, etc, which have many shortcomings such as complicated operation, depending on the human eye observation, high price, low precision, contact measurement, easy to damage the blades and so on. Therefore, this paper mainly aims at the automation, precision, non-contact nondestructive method for measuring geometric parameters of the plant leaf, including two dimensional geometric parameters measurement method based on image processing and thickness measurement method based on three dimensional surface shape recovery, with only a simple equipment consisting of low cost devices such as laser and CCD camera, which can accomplish the measurement of a high precision. The main completed contents are as follows:(1) The color image segmentation algorithm is studied in order to solve the problem of parameters measurement method based on gray level image processing, which is difficult to distinguish the complex background, the leaf and its inner region. The five color space models of RGB, YIQ, YCb Cr, HSI and Lab are analyzed and compared, and the color factor component images which can distinguish the color difference between the background, the leaf and the interior area of the leaf are extracted. The processing methods such as segmentation, morphological operations, area filtering, hole filling, etc. are used to the color factor component images to obtain the plant leaf target and its inner regions. Finally, the two dimensional geometric parameters of the target area are calculated by using the method of parameter measurement in the two value image of plant leaf.(2) The measurement system of plant leaf thickness based on dual optical laser triangulation method is designed on the basis of the traditional laser triangulation method. Casting point laser into the surface of plant leaf, then surface scattering light is received by the CCD camera and forms a laser spot image, the height variation of leaf surface shape with respect to the reference plane can reflect directly to the laser spot center offset in image. Through the anti-noise ability of the barycenter method, the sub-pixel center of the laser spot can be accurately extracted, then the spot center offset corresponding to the plant leaf surface and reference plane is calculated, and based on the geometrical optics formula of the laser triangulation method, the three dimensional shape of a plant leaf surface can be recovered. Finally, by using the laser triangulation method of double light path, the three dimensional shape difference of the upp er and lower surface of the plant leaf can be calculated, and the thickness of every point of the leaf can be obtained.(3) Taking the cactus leaves as the research object, we can built hardware test platform to measure its two-dimensional geometry which is analyzed and compared with its actual value. Then lasers, motion platform and other equipment are added in the plant leaves Acquisition System to get the laser spot image.The 3D surface topography of the leaves is recovered by laser triangulation, and thus to obtain the thickness of the 9 regions of the plant leaves. Experimental results show that under the conditions of the error in the optical system and artificial introduction, the deviation between two dimensional parameter value and actual value is less than 2 mm, and the root mean square error between thickness measurement value and actual value is about 0.3mm, which shows high precision.