Defoliation Assessment Using Video Imagery and a Microcomputer

Abstract

A video digitizer and lightpen system integrated with a microcomputer were designed to receive and alter soybean leaf images produced by a video camera. Soybean leaves were back-lighted on a fluorescent light table to differentiate defoliated, partially defoliated, and solid leaf tissue. Comparisons of precision and accuracy for solid and defoliated object measurements were made between the area analysis system (AAS) and a Li-Cor area meter (LAM). Standard deviations from two trials of six nondefoliated objects measured 10 times were significantly lower with the AAS, and overall levels of accuracy were higher than those obtained with the LAM. Percentage defoliation assessment by both systems were inconsistent. The AAS generally produced smaller error values for objects up through 15.11 cm2; The LAM produced smaller errors for objects 29–108 cm2. Significant differences between LAM and AAS defoliation estimates were found for 5 of the 19 object size-defoliation combinations measured. Of the 19 estimates made by the AAS,15 were in error by <1% defoliation, 18 were within 2%, and all were within 3% defoliation. Fifteen of 19 LAM estimates were also in error by < 1% defoliation, 16 were within 2%, 18 were within 3%, and all were within 4% defoliation. Processing times for obtaining the total area of nondefoliated objects, Mexican bean beetle-defoliated leaves, and defoliation of the 10 leaves were 13.6 s, 65 s, and 31.5 min respectively for the LAM and 15.5 s, 20.9 s, and 10.75 min for the AAS. The cost of setting up the AAS is ca. 3,000.