In Situ Measurement of Rod-Like Crystal Size and Surface Area During Crystallization via Virtual Stereo Imaging

In this article, a novel crystal size measurement method based on the virtual stereo imaging is proposed for monitoring rod-like crystal growth in a glass crystallizer. A microscopic binocular vision system consisting of telecentric lenses with two different magnifications is designed to ensure the depth of field (DOF) for capturing stereo images. The crystal image matching in each snapshot image pair is realized by developing an improved epipolar rectification strategy in combination with the Bézier curve fitting for extracting crystal feature contours, based on the YOLOv8 network for image segmentation. Subsequently, a virtual imaging plane is constructed based on the matched binocular crystal feature contour points to generate a virtual 2-D crystal image. Meanwhile, a criterion named the overlapping ratio is introduced to evaluate the reconstruction accuracy. By projecting each crystal image from the camera imaging plane to the virtual imaging plane, the length and width of each crystal together with its surface area are measured by the orthogonal decomposition projection. Experimental results on measuring the length, width, and surface area of $\beta $ -form L-glutamic acid (LGA) crystals in a 1-L glass crystallizer well demonstrate the effectiveness and merits of the proposed measurement method.