Abstract Understanding optical properties of food and agricultural products is essential to apply optical techniques for quality and safety assessment. This research was aimed at optimizing the frequency region through an inverse algorithm for better quantification of the optical absorption (μa) and reduced scattering (μs′) coefficients of two-layered food and agricultural products from spatial-frequency domain reflectance. The frequency region, defined by start and end frequencies, was first optimized for parameter estimations of the first and second layers, respectively. Estimation accuracies were then validated by comparing with the conventional all-at-once method through Monte Carlo simulations. On average, accuracies for estimating μa1, μa2 and μs2′ by using the optimized frequency region were improved by 52.9%, 63.0% and 62.1%, respectively, compared to the results by using fixed frequency region before optimization. No improvement for the estimated μs1′ was found because its mean absolute error was already very low (2.4%) and well within the acceptable level. Experimental results for two-layered solid phantoms and liquid milk samples in the wavelengths of 650–830 nm further validated the effectiveness of stepwise method with the optimized frequency region. Finally, the stepwise method, coupled with the optimized frequency region was used to estimate the optical properties of skin and flesh of apples for four cultivars (i.e., Delicious, Golden Delicious, Jonagold and Red Rome). The results were compared with those obtained using the single integrating sphere technique, followed with a discussion on the optical property discrepancies obtained by these two methods.

中文翻译：

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空间频域成像结合频率优化估计两层食品和农产品的光学特性

摘要 了解食品和农产品的光学特性对于应用光学技术进行质量和安全评估至关重要。本研究旨在通过逆算法优化频率区域，以更好地量化两层食品和农产品的光吸收 (μa) 和减少散射 (μs') 系数，从空间频率域反射。由开始和结束频率定义的频率区域首先分别针对第一层和第二层的参数估计进行优化。然后通过蒙特卡罗模拟与传统的一次性方法进行比较来验证估计精度。平均而言，使用优化的频率区域估计 μa1、μa2 和 μs2' 的精度分别提高了 52.9%、63.0% 和 62.1%，与优化前使用固定频率区域的结果进行比较。未发现估计的 μs1' 有任何改进，因为其平均绝对误差已经非常低 (2.4%) 并且完全在可接受的水平内。波长为 650-830 nm 的两层固体模型和液态奶样品的实验结果进一步验证了优化频率区域的逐步方法的有效性。最后，采用逐步法，结合优化的频率区域，用于估计四个品种（即美味、金冠、乔纳金和红罗马）的苹果皮和果肉的光学特性。将结果与使用单积分球技术获得的结果进行比较，然后讨论这两种方法获得的光学特性差异。