1. Computer Vision Center and Computer Science Department, Universitat Autonoma de Barcelona, Barcelona, Spain
2. xotazu@cvc.uab.cathttp://www.cvc.uab.es/~xotazu
3. Computer Vision Center, Vall d’Hebron Research Institute, and Computer Science Department, Universitat Autonoma de Barcelona, Barcelona, Spain
4. xcerda@cvc.uab.cathttp://www.cvc.uab.es