Shu-huai Zhang

Measurement of 3-D Locations of Fruit by Binocular Stereo Vision for Apple Harvesting in an Orchard

This paper describes the results of measurement of 3-D locations of fruit by binocular stereo vision for apple harvesting in an orchard. In the method of image processing, a 3-D space is divided into a number of cross sections at an interval based on disparity that is calculated from a gaze distance, and is reconstructed by integrating central composite images owing to stereo pairs. Three measures to restrict false images were proposed: (1) a set of narrow searching range values, (2) comparison of an amount of color featured on the half side in a common area, and (3) the central composition of the half side. Experiments with a trial stereo system were conducted on ripe apples in red (search distance ranging from 1.5m to 5.5m) and in yellow-green (search range of 2m to 4m) in an orchard. The results showed that two measures of (1) and (3) were effective, whereas the other was effective if there was little influence of background color similar to that of the objects. The rate of fruit discrimination was about 90% or higher in the images with 20 to 30 red fruits, and from 65% to 70% in images dense with red fruit and in the images of yellow-green apples. The errors of distance measurement were about ±5%.