Influence of time, bruise-type, and severity on near-infrared reflectance from apple surfaces for automatic bruise detection

Near-infrared imaging was used to characterize the influence of time, bruise-type, and severity on the near-infrared (NIR) reflectance from bruised and unbruised regions on ‘Delicious’ and ‘Golden Delicious’ apples. Images of apples were captured on five dates for both impact- and compression-type bruises. Changes in the NIR reflectance were characterized by comparing the contrast which was measured by a difference calculation between two concentric circular profiles from bruised and unbruised areas. Within 24 h after inducing damage, a maximum contrast in NIR reflectance occurred for both bruise types. Afterwards, the contrast decreased until it equaled the contrast for an unbruised region. This change usually occurred between 1 and 42 days. The time at which the contrast at a bruised region exceeded that at an unbruised one depended upon the severity and type of bruise. Changes in contrast after one day were more gradual for impact-type bruises than bruises created by compression.