A handheld device for leaf area measurement

Abstract

Advanced electronic technology makes handheld devices (HHD) suitable for leaf area (LA) measurement with image processing techniques. This article presents the development of an HHD applied to measure LA through image processing. The procedure is essentially a module of mobile phone software developed in Java ME that uses a HHD touch panel monitor to estimate LA. The system is composed of a control module to run specially developed software, an ultrasonic ranging module to calculate the plane distance between the leaf and the HHD, and an inclination angular measuring module to determine the plane inclination angle between the leaf and the HHD. The image processing operations on each image are as follows: semi-automatic image segmentation, binarization, noise filtering, and LA calculation. The measurement accuracy of the HHD surpasses 0.005cm2, and the cost is less than one tenth of a traditional machine vision system. Squares of 400mm2 and circles of 314.15mm2 were used to test the effects of distance and inclination angle of the HHD. The distance between the HHD and objects with inclination angle at 0°, 5°, 10° and 30° was set to 150mm and between distances of 200 and 800mm at 100-mm intervals. The results showed that the deviations were in the range of −0.62% to 0.79% at the same inclination angle. There were distinguishable errors between different angles by 5°. Leaf samples of tomato, eggplant, and maple representing varied shapes and sizes were used to compare the measurement performance of the HHD and an existing leaf area meter (Li-3100; LICOR, Lincoln, NE, USA). The results indicate that the HHD was an accurate device for LA measurement when the distances were in the range of 300–600mm; especially at the 400-mm point, the maximum error of the HHD compared with Li-3100 was 0.455%, and the minimum error was 0.04%. Overall the result indicated that the developed image processing method using the HHD provided a feasible non-destructive alternative to measure LA. This new technology enables agriculture and forestry workers to conveniently, accurately, and reliably estimate the area of leaves without using expensive instruments.