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Digital Imaging for Defoliation Measurements

A.M. Stewart, K.L. Edmisten and R. Wells


 
ABSTRACT

Measurements made in defoliation trials are currently made with a visual rating. While this method seems to work well, it is subject to human subjectivity. In this study, we attempted to consistently quantify defoliation without a visual rating by means of digital images. A Kodak DC-50 digital camera was mounted to a camera stand modified for plot use. The camera was set up to shoot an image perpendicular into the center row middle of a four row test plot. The camera lens was approximately 7 feet high. Digital images were taken at 0, 7, and 14 days after treatment on plots defoliated with Finish 1.5 qt/acre+Folex/Def 0.5 pt/acre, Folex/Def 1.5 pt/acre, and an untreated control. Images were analyzed for percent defoliation, percent desiccation, and percent open bolls. Analysis was conducted with Image Tool for Windows 95 and Image Pro Plus software. Visual ratings were also taken. With the Image Tool software, the images were converted to a gray scale. Color separation was set to separate green leaf colors by manually setting a desirable threshold level, and thus producing a mask of the original image with the green leaf colors represented by black pixels and all other colors represented by white pixels. The software then counted the number of black and white pixels in the image, in order to obtain a relative leaf area for the image. With the Image Pro Plus software, an area of the original image that contained desired leaf colors was selected, and these colors were separated from the rest of the image. A black and white mask was then obtained and pixels were counted with the Image Tool software.



Reprinted from Proceedings of the 1997 Beltwide Cotton Conferences pp. 1362 - 1363
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998