DEFECT DETECTION IN APPLES BY MEANS OF X-RAY IMAGING

Abstract

X-ray radiograms were obtained for 400 to 700 each of four State of Washington apple cultivars (Fuji,Granny Smith, Red and Golden Delicious) and 79 Braeburns carrying assorted defects (bruises, senescencebrowning, rot, watercore and insect damage). Radiograms of whole apples, most out of long term storage, were obtainedwith line scanning x-ray, suitable for real-time inspection, and with high resolution film, at two orientations, followingwhich the apples were sliced and photographed. Apples were characterized as defective or not based on the appearancein these photos. Sets of x-ray images for a given cultivar/orientation (good and bad apples mixed randomly) wereinspected by human observers and the recognition rates recorded. When still images were viewed on a computer screen,acceptable recognition (= 50% of defective apples recognized, = 5% of good apples classified defective) of images wasobtained for senescence browning of Red Delicious, for watercore and stem rot in Fuji (requiring orientation), possiblyfor watercore in Red Delicious, and for codling moth damage in the first four cultivars 8 to 19 days after larval entry.However, when images were scrolled across the screen at increasing rates, simulating a three-chain sorting line,recognition fell off to unacceptable levels at rates one half that corresponding to a commercial sorting line. This decreaseis not unexpected in light of previous work in more structured situations. The implications for devising an apple sortingsystem based on x-ray are discussed.