Structured-illumination reflectance imaging (SIRI) for enhanced detection of fresh bruises in apples

Abstract

A structured-illumination reflectance imaging (SIRI) system was developed for the detection of fresh bruises in apples. The system consisted of a high-performance digital camera, a broadband DC-regulated light source, and a digital light engine for generating specific patterns of illumination. Sinusoidal patterns of illumination at a series of spatial frequencies were created to illuminate test samples. Experiments were first conducted on a strongly scattering nylon sample embedded with foreign objects at different depths and then on apples of three cultivars with fresh bruises. The acquired images were demodulated into two separate sets of direct component (representing uniform diffuse illumination) and alternating component (or amplitude) images for each spatial frequency. The amplitude images were found to be effective for ascertaining the sub-surface defects, and the detection resolution and depth depended on the spatial frequency of illumination. SIRI technique was able to detect fresh bruises in apples immediately after they were induced, which, otherwise, could be difficult to achieve by conventional uniform illumination-based imaging techniques. The technique is promising for effective detection of defects, like bruise, in fruit.