In order to develop a system for the automatic detection of leaf wilting, several methods of leaf region extraction were examined. Color images of bean, cucumber, and melon plants were obtained under artificial light in a growth chamber, under sunlight in the laboratory near a window, and under sunlight in a glasshouse, respectively. The optimum method for leaf region extraction seemed to depend on image acquisition conditions. For example, under artificial light, leaf region was satisfactorily extracted by using an intensity thresholding, whereas under sunlight in the laboratory, fairly good performance was obtained by using saturation thresholding or by G/B ratio thresholding.
When these optimal methods were applied for leaf region extraction, the y-coordinate of the center of gravity of the extracted area was used as an index of the leaf wilting.
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