Learning a Rare Event Detection Cascade by Direct Feature Selection

Abstract

Face detection is a canonical example of a rare event detection prob- lem, in which target patterns occur with much lower frequency than non- targets. Out of millions of face-sized windows in an input image, for ex- ample, only a few will typically contain a face. Viola and Jones recently proposed a cascade architecture for face detection which successfully ad- dresses the rare event nature of the task. A central part of their method is a feature selection algorithm based on AdaBoost. We present a novel cascade learning algorithm based on forward feature selection which is two orders of magnitude faster than the Viola-Jones approach and yields classifiers of equivalent quality. This faster method could be used for more demanding classification tasks, such as on-line learning.