Application of 3D Scanning Technique and Colour Measurement on Pearl Sorting
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摘要: 基于3D扫描技术及色度测量CIE L*a*b*技术, 提出了珍珠的数字化分选方法，从而可以有效克服传统人工筛选的弊端。通过非接触式3D扫描技术获取珍珠的点云数据，并对数据进行拼接处理，得到完整的珍珠三维模型以及珍珠的大小、形状、光洁度对应数据。分光光度计可对珍珠颜色及光泽度进行测量并且进行基于标准色空间CIE L*a*b*的转换，获得可量化指标。利用该技术，企业可根据实际情况并结合国家分级标准GB/T 18781-2008对不同等级珍珠标准品的大小、形状、光洁度、颜色及光泽度进行测量及数据录入，运用算法对样品的测量数据与标准品的数据进行阈值判别，从而实现数字化分选。本文通过实验验证了3D扫描及颜色测量技术在珍珠分选上具有较高的可行性，且未来二者的结合对于珍珠企业实行批量化机械分选，实现自动化生产，缩减生产成本具有巨大潜力。Abstract: An original method for automatic pearl sorting is proposed based on 3D scanning technique and CIE L*a*b* colorimetry, which is able to overcome the shortcomings of manual pearl sorting. The point cloud data of pearl will be extracted by non-contact 3D scanner and processed to splicing module to obtain a three-dimensional (3D) pearl model. The information of size, shape and surface perfection has been involved in the 3D model. The numerical colour as well as luster data of pearl is measured and converted by the colorimeter base on the standard colour space CIE L*a*b*. Pearl companies are able to test and record the standard samples from various detection ranges on the five factors mentioned above based on the judgement index of national pearls grading standard GB/T 18781-2008, and then calculate the threshold between the standard samples and other samples using corresponding algorithm to achieve automatic sorting. The authors verified the high feasibility for automatic pearl sorting using 3D scanning and colour measurement technology based on experiments. Furthermore, the integration of the two technologies has great potential for pearl companies to implement mechanical sorting, realize automatic production and reduce production costs in the future.
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图 5 扫描仪识别珍珠形状的原理图
a.对样品进行三角度切割; b-d.对应样品不同切面的周长识别结果
Figure 5. Schematic of shape identification of pearls via scanner
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图 6 经扫描的珍珠样品表面瑕疵：腰线(a)及凹陷(b)
Figure 6. Surface defects of scanned pearl samples: Waist line (a) and pits (b)
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图 8 人工与仪器检测结果吻合程度
Figure 8. Coincidence degree between the results of manual test and instrument test
表 1 珍珠样品的外形及颜色特征
Table 1 Appearance and colour characteristics of pearl samples
样品编号 颜色 光洁度 光泽度 最长直径/mm 最短直径/mm 1 浅粉色 小暇 强 11.9 9.8 2 银紫色 瑕疵 中 12.6 10.2 3 浅黄色 微暇 强 12.8 8.5 4 银白色 重瑕 中 12.2 8.7 注：最长直径，最短直径均以卡尺(mm)进行测定 
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表 2 珍珠样品大小及形状分选结果
Table 2 Sorting outcome of shapes and sizes of pearl samples
样品号 大小/mm 直径差/% 形状等级 1 12.437 × 10.594 ≤20.0 短椭圆B1 2 12.316 × 10.389 ≤ 20.0 高形扁圆C1 3 8.825 ≤ 12.0 近圆A3 4 11.750 × 8.682 > 20.0 长椭圆B2
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表 3 基于颜色测量的珍珠样品分选结果
Table 3 Sorting results based on colour measurement of pearl samples
样品编号 体色色系 颜色 光泽 1 红色 浅粉色 强 2 红色 浅紫红色 中 3 黄色 浅黄色 中 4 白色 银白色 弱
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