NONDESTRUCTIVE DETERMINATION OF LEAF-AREA IN TOMATO PLANTS USING IMAGE-PROCESSING

The objectives of this study were to validate the use of image process ing for the measurement of leaf areas in intact tomato plants and to e xamine the potential of taut-string bounding area as a parameter for w ilting. This was achieved by taking images of 18 tomato plants, viewed from the top, from the side and from an oblique angle. In the case of side and oblique views the images were taken as the plant was rotated through 360 degrees with 45 degrees steps. An average value of the le af area was then calculated for each view. Regression of true leaf are a on image-calculated areas for individual views resulted in a second order polynomial which adequately described the relationship. The regr ession coefficient, R(2), adjusted for degrees of freedom, was 0.98. M ultiple regression of true leaf area against areas obtained from two v iews increased R(2) to 0.99. When all three view points were taken int o consideration, R(2) increased further, albeit modestly, to 0.993. Ta ut-string boundary provides information about the plant's compactness as it grows. A boundary was obtained by rotating the image co-ordinate system through 16 different angles. After every rotation the extreme points of the image were determined. These points formed the corners o f a bounding polygon that approximated to the taut string boundary. Th e polygon area was calculated from the co-ordinates of the polygon cor ners. Regression of true leaf area on taut string image area for indiv idual views resulted in a second-order polynomial which adequately des cribed the relationship. Multiple regression improved the regression c oefficient. To test the potential usefulness of taut-string area, two plants were water stressed, then irrigated and monitored while they re covered from wilted to turgid. The change in taut string area detected (50-55%) was sufficient to recommend its use as a meaningful paramete r for wilting.