Pattern recognition and computer vision 4th Chinese Conference, PRCV 2021, Beijing, China, October 29 - November 1, 2021 : proceedings, part II - Ma, Huimin; Wang, Liang; Zhang, Changshui 19XX-; Wu, Fei; Tan, Tieniu; Wang, Yaonan; Lai, Jianhuang; Zhao, Yao (Springer, 2021)