Computer Vision Approaches to Pedestrian Detection: Visible Spectrum Survey David Ger´ onimo, Antonio L´ opez, and Angel D. Sappa Computer Vision Center, Universitat Aut`onoma de Barcelona Edifici O, 08193 Bellaterra, Barcelona, Spain {dgeronimo,antonio,asappa}@cvc.uab.es www.cvc.uab.es/adas Abstract. Pedestrian detection from images of the visible spectrum is a high relevant area of research given its potential impact in the design of pedestrian protection systems. There are many proposals in the liter- ature but they lack a comparative viewpoint. According to this, in this paper we first propose a common framework where we fit the different approaches, and second we use this framework to provide a comparative point of view of the details of such different approaches, pointing out also the main challenges to be solved in the future. In summary, we expect this survey to be useful for both novel and experienced researchers in the field. In the first case, as a clarifying snapshot of the state of the art; in the second, as a way to unveil trends and to take conclusions from the comparative study. 1 Introduction Pedestrian accidents are the second source of traffic injuries and fatalities in the European Union. In this sense, advanced driver assistance systems (ADAS), and specifically pedestrian protection systems (PPS), have become an important field of research to improve traffic safety. Of course, in order to avoid collisions with pedestrians they must be detected, being camera sensors key due to the rich amount of cues and high resolution they provide. Currently there are two main lines of work, one based on images of the visi- ble spectrum, and the other, mainly motivated by nighttime, based on thermal infrared. The former has accumulated more literature because the easier avail- ability of either CCD or CMOS sensors working in the visible spectrum, their cheaper price, better signal–to–noise ratio and resolution, and because most of the accidents happen at daytime. Therefore, we restrict the discussion presented in this paper to works based on images of the visible spectrum. In this context, difficulties of the pedestrian detection task for PPS arise both from working with a mobile platform in an outdoor scenario, recurrent challenge in all ADAS applications, and from dealing with a so aspect–changing class like pedestrians. Difficulties can be summarized in the followings: (a) targets have a very high intra–class variability; (b) background can be cluttered and changes in milliseconds; (c) targets and camera usually follow different unknown J. Mart´ı et al. (Eds.): IbPRIA 2007, Part I, LNCS 4477, pp. 547–554, 2007. c  Springer-Verlag Berlin Heidelberg 2007