An adaptive background model aiming at outdoor vehicle detection is presented in this paper. This model is an improved
model of PICA (pixel intensity classification algorithm), it classifies pixels into K-distributions by color similarity, and
then a hypothesis that the background pixel color appears in image sequence with a high frequency is used to evaluate all
the distributions to determine which presents the current background color. As experiments show, the model presented in
this paper is a robust, adaptive and flexible model, which can deal with situations like camera motions, lighting changes
and so on.