Application of 3D Scanning Technique and Colour Measurement on Pearl Sorting

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.