Rejection Based Classifier for Target Detection In Images
February 21st , 2003
High Dimensional Data Day, Redwood Neuroscience Institute - Invited Talk

One of the most fundamental problems in the treatment of high-dimensional data is classification of a cloud of points in R^D into several sub-classes based on training data. An important such task is the pattern detection problem in images, which requires a separation between ‘Target’ and ‘Clutter’ classes, where every instance of a pattern in each of these classes appears as a sequence of D pixels. In most cases, the following properties hold true for the target detection task: (i) the probability of the ‘Target’ class is substantially smaller compared to that of the ‘Clutter’ ; (ii) the volume occupied by the target class in R^D is far smaller than that held by the clutter set ; and (iii) The target set is either convex or can be divided to several sub-sets each being convex.

In this talk we describe a new classifier that exploits these properties, yielding a low complexity yet effective target detection algorithm. This algorithm, called the Maximal Rejection Classifier (MRC), is based on successive rejection operations. Each such rejection stage is performed using a linear projection followed by thresholding. The projection direction is designed to maximize the number of rejected ‘Clutter’ points from further consideration. An application of detecting frontal and vertical faces in images is demonstrated using the MRC with encouraging results.