Solutions to uneven light distribution and measurement distance variation in optical-based food inspection: A review

The demand for high-efficiency quality control in the food industry has driven the adoption of emerging techniques such as spectroscopy and imaging. The spectral and imaging detection processes are subject to various interferences, which may affect the detection results. This review summarizes the interferences and correction methods in the food inspection based on spectroscopy and imaging. This review finds that these interferences can be classified into two categories: uneven light distribution and measurement distance. The uneven light distribution was divided into specular light and vignetting. The problem of measurement distance variation was divided into two categories: variation caused by the morphological characteristic of the sample itself and that caused by the undesired movement of the detector. Furthermore, solutions to the abovementioned problems were discussed. For uneven light distribution, specular light was mainly corrected by polarization guided approaches using a self-developed cross-polarized system, while vignetting was mainly corrected based on an algorithm and applied to spherical food that can be approximated as a Lambertian object. For measurement distance variation, diameter correction method has gained attention in recent studies to mitigate the impact of size on transmission spectra of spherical fruits. Methods for regulating the distance between the food sample and the camera can be categorized into image reference based-methods and multi sensor-based methods. By providing a holistic insight into the mechanisms of interference factors in the optical detection process and the corresponding correction methods, this review contributes to the improvement of the accuracy for spectroscopy and imaging-based food inspection.