Abstract: Pearl shape symmetry is an important quality indicator. New pearl shape symmetry detection algorithm is presented, which is called Four-Quadrant Edge Chain Code Self-Similarity（FQECCSS）, which is the self-similarity of pearl by computing each quadrant edge chain code. The pearl shape-feature image is filtered with the four directions edge operator, and divided into four quadrants. The different quadrant edges are described in the same quadrant, and the edges are coded with 8-direction Freeman chain code. The self-similarity of the edges is calculated in different quadrants. Experiment shows that the FQECCSS can well describe the pearl shape symmetry, and has certain practical application value.

Key words: pearl detection, shape symmetry, edge detection, self-similarity, Freeman chain code

摘要： 珍珠形状匀称性是衡量珍珠质量的重要指标之一。提出了一种新的珍珠形状匀称性检测算法——四象限边缘链码自相似性检测算法，是通过计算各个象限中边缘链码之间的相似度来判定珍珠形状的匀称性算法。采用四个方向的边缘算子对珍珠形状特征面进行边缘检测、融合，把已融合的珍珠边缘划分在四个象限；通过旋转、翻转方法把不同象限的珍珠边缘表示在同一象限；对表示在同一象限中的珍珠边缘进行8方向数链码编码，根据边缘链码计算出珍珠边缘的自相似性。实验显示，四象限边缘链码自相似性能够很好地描述珍珠形状匀称性，具有一定的实用价值。

关键词: 珍珠检测, 形状匀称性, 边缘检测, 自相似性, Freeman链码