Image analysis methods for real-time color grading of stonefruit

Abstract An image analysis system consisting of an illumination chamber, color camera, frame grabber, and microcomputer was developed to evaluate the color of stonefruit. Algorithms were developed for realtime maturity grading of fresh market peaches. The 13 ground color references used by the California Tree Fruit Agreement (CTFA) were measured and found to be out of order and unevenly spaced. A revised color chart was made using only six of the color references. Experimental work was conducted on four peach cultivars: O'Henry, CalRed, Summerset, and Carnival. Image analysis classification agreed with manual classification in 46% of the tests and within one color standard in 75% of the tests. Manual grading differed from image analysis and colorimeter results for the late-season cultivars due to a less blushed surface and off-scale ground colors. Blush surface area estimates by image analysis were different for the mid and late-season cultivars because of differences in their blush color and blush density.