Rotation Equivariance for Diamond Identification

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Floris De Feyter, Bram Claes, Toon Goedemé

Published: 2023, Last Modified: 27 Sept 2025VISIGRAPP (5: VISAPP) 2023EveryoneRevisionsBibTeXCC BY-SA 4.0
Abstract: To guarantee integrity when trading diamonds, a certified company can grade the diamonds and give them a unique ID. While this is often done for high-valued diamonds, it is economically less interesting to do this for lower-valued diamonds. While integrity could be checked manually as well, this involves a high labour cost. Instead, we present a computer vision-based technique for diamond identification. We propose to apply a polar transformation to the diamond image before passing the image to a CNN. This makes the network equivariant to rotations of the diamond. With this set-up, our best model achieves an mAP of 100% under a stringent evaluation regime. Moreover, we provide a custom implementation of the polar warp that is multiple orders of magnitude faster than the frequently used implementation of OpenCV.