Multispectral line-scan imaging system for simultaneous fluorescence and reflectance measurements of apples: multitask apple inspection system

Abstract

In this methodology paper, a recently developed line-scan imaging system, capable of simultaneously acquiring a combination of multispectral reflectance and fluorescence from rapidly moving objects, is presented. The system can potentially provide multitask inspections for quality and safety attributes of apples due to its dynamic selectivity in multispectral bands, each with independent spectral bandwidth in the fluorescence and reflectance domains. Mounted on a commercial apple-sorting machine, the system was evaluated to determine the image pixel (spatial) resolution for apples at a sorting line speed of three to four apples per second. Apples loaded on the sorting machine were spaced approximately 15 cm apart. With these parameters, the resulting images showed approximately 40 line-scan images per apple, for a horizontal spatial resolution of 2 mm per pixel. In the vertical direction, with 1,002 pixels available for each line-scan image, the spatial resolution of the system can be as high as approximately 0.2 mm per pixel depending on the choice of binning. The combined spatial resolution is comparable to that in our previous studies and is adequate for image-based online inspection of defects and fecal contamination on apples.