Pattern Recognition and Computer Vision : 4th Chinese Conference, PRCV 2021, Beijing, China, October 29 - November 1, 2021, Proceedings, Part IV - Ma, Huimin; Lai, Jianhuang; Tan, Tieniu; Wang, Liang; Wang, Yaonan; Wu, Fei; Zhang, Changshui; Zhao, Yao (Springer, 2021)