Abstract Three-dimensional (3-D) geometry information is valuable for fruit quality evaluation. This study was aimed at exploring an emerging structured-illumination reflectance imaging (SIRI) system, coupled with phase analysis, for reconstructing surface profiles of fruit. Phase-shifted sinusoidal patterns, distorted by the fruit geometry, were acquired and processed through phase demodulation, phase unwrapping and other post-processing procedures to obtain phase difference maps relative to the phase of a reference plane. The phase maps were then transformed into height profiles based on phase-to-height calibrations. A reference plane-based approach, in conjunction with the curve fitting technique using polynomials of order 3 or higher, was utilized for phase-to-height calibrations, which achieved superior accuracies with the root-mean-squared errors (RMSEs) of 0.027–0.033 mm for a height measurement range of 0–91 mm. The 3rd-order polynomial curve fitting technique was further tested on two reference blocks with known heights, resulting in relative errors of 3.75% and 4.16%. Tests of the calibrated system for reconstructing the surface of apple samples showed that surface concavities (i.e., stem/calyx regions) could be readily discriminated from bruising defects from both the phase difference images and reconstructed height profiles. This study has laid a foundation for using SIRI for reconstructing the 3-D geometry, and thus expanded the capability of the technique for quality evaluation of horticultural products. Further research is needed to utilize the phase analysis techniques for detecting surface concavities of apples, and optimize the phase demodulation and unwrapping algorithms for faster and more reliable detection.

中文翻译：

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结构化照明反射成像与相位分析技术相结合，用于苹果表面轮廓分析 1

摘要 三维（3-D）几何信息对于水果质量评价很有价值。本研究旨在探索一种新兴的结构照明反射成像 (SIRI) 系统，结合相位分析，用于重建水果的表面轮廓。通过相位解调、相位展开和其他后处理程序获取和处理因水果几何形状而失真的相移正弦图案，以获得相对于参考平面相位的相位差图。然后基于相位到高度的校准将相位图转换为高度轮廓。基于参考平面的方法结合使用 3 阶或更高阶多项式的曲线拟合技术，用于相位到高度的校准，在 0-91 毫米的高度测量范围内，均方根误差 (RMSE) 为 0.027-0.033 毫米，实现了卓越的精度。三阶多项式曲线拟合技术在两个已知高度的参考块上进一步测试，导致相对误差分别为 3.75% 和 4.16%。用于重建苹果样品表面的校准系统的测试表明，可以很容易地从相位差图像和重建的高度轮廓中区分表面凹陷（即茎/花萼区域）和瘀伤缺陷。本研究为利用 SIRI 重建 3D 几何奠定了基础，从而扩展了该技术对园艺产品质量评估的能力。