Pedestrian detection is a difficult problem in the field of object detection. This paper applies the boosted cascade algorithm which originates from face detection to pedestrian detection. We improve the algorithm by first project the high dimensional hog(histogram of gradient) feature to 1 dimension

then estimate the posterior probability with lookup table so as to apply the gentle adaboost algorithm. Experiments indicate our algorithm is both efficient in training and detection. The detection rate is close to the state of the arts.