*Article* **Image Measurement of Crystal Size Growth during Cooling Crystallization Using High-Speed Imaging and a U-Net Network**

**Yan Huo, Xin Li \* and Binbin Tu**

College of Information Engineering, Shenyang University, Shenyang 110044, China **\*** Correspondence: li\_xin@syu.edu.cn

**Abstract:** In this paper, an image measurement method using a high-speed imaging system is proposed for the evolution of crystal population sizes during cooling crystallization processes. Firstly, to resist the negative effect from solution stirring and particle motion during crystallization, a U-net network-based image processing method is established to efficiently detect sufficiently clear crystals from the online captured microscopic images. Accordingly, the crystal size distribution model is analyzed in terms of the counted probability densities of these crystal images. Subsequently, a measurement method of size growth rate based on crystal population distribution is proposed to estimate the growth condition. An experimental case on a crystallization process of β-form LGA is used to show the effectiveness of the proposed strategy.

**Keywords:** crystal image analysis; deep learning; size measurement; crystal growth rate
