METHOD FOR DETECTING AND TRACKING MOVING SUBJECTS IN A DIGITAL IMAGE SEQUENCE HAVING A STATIONARY BACKGROUND

摘要

A method for detecting and tracking moving subjects in a digital image sequence having a stationary background by comparing the image sequence to a calculated background image sequence, whereby a sequence of binary subject masks is calculated whose segments reproduce the shapes and positions of the moving subjects, and whereby the motion vectors of the moving subjects are calculated by matching these segments. Also, a sequence of background images is calculated by spatially selective and chronologically recursive averaging of the input image sequence in which the moving subjects are not contained but in which other modifications of the background that are not caused by moving subjects are contained. Further, a sequence of binary subject masks is calculated by binarization of the difference image sequence from the input image sequence and the background image sequence using a threshold whose value is used for controlling the spatial selectivity in the calculation of the background image sequence and whose segments are determined together with their sizes and center of gravity positions. Finally, motion vectors of the detected subjects are determined by minimization of the squared gray scale value differences averaged over the intersection of the shifted mask segments, whereby differences between the center of gravity vectors of corresponding segments are utilized as start vectors in the minimization.