DEFECT DETECTION IN APPLES BY MEANS OF X-RAY IMAGING

摘要

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, senescence browning, rot, watercore and insect damage). Radiograms of whole apples, most out of long term storage, were obtained with line scanning x-ray, suitable for real-time inspection, and with high resolution film, at two orientations, following which the apples were sliced and photographed. Apples were characterized as defective or not based on the appearance in these photos. Sets of x-ray images for a given cultivar/orientation (good and bad apples mixed randomly) were inspected 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 was obtained for senescence browning of ‘Red Delicious’, for watercore and stem rot in ‘Fuji’ (requiring orientation), possibly for 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 decrease is not unexpected in light of previous work in more structured situations. The implications for devising an apple sorting system based on x-ray are discussed.