Abstract: Direction is an important feature of crowd movement. The force between each other is small and the possibility of collision is low in orderly crowd movement,while they are higher in messy crowd movement which can leads security incidents,i.e. stampede. A new algorithm is proposed in this paper which detects the direction of abnormal crowd movement. First,this algorithm computes the velocity matrix and direction matrix by using optical follow method,and by these two matrices an index－“different movement index of frame” is computed.This index can indicate whether abnormal crowd phenomenon is appeared. The experiment results show that this index is relative with the messy degree of crowd movement. This algorithm can detect the abnormal movement effectively,which can avoid danger caused by messy movement.

Key words: Optical flow algorithm,Movement direction,Abnormal crowd movement,Public safety