A Two Phase Approach for Pedestrian Detection

Abstract

Most of current pedestrian detectors have pursued high detection rate without carefully considering sample distributions. In this paper, we argue that the following characteristics must be considered; (1) large intra-class variation of pedestrians (multi-modality), and (2) data imbalance between positives and negatives. Pedestrian detection can be regarded as one of finding needles in a haystack problems (rare class detection). Inspired by a rare class detection technique, we propose a two-phase classifier integrating an existing baseline detector and a hard negative expert by separately conquering recall and precision. Main idea behind the hard negative expert is to reduce sample space to be learned, so that informative decision boundaries can be effectively learned. The multi-modality problem is dealt with a simple variant of a LDA based random forests as the hard negative expert. We optimally integrate two models by learned integration rules. By virtue of the two-phase structure, our method achieve competitive performance with only little additional computation. Our approach achieves 38.44 % mean miss-rate for the reasonable setting of Caltech Pedestrian Benchmark.