System and method for face detection using candidate image region selection

Abstract

A face detection system and a method of pre-filtering an input image for face detection utilize a candidate selector that selects candidate regions of the input image that potentially contains a picture of a human face. The candidate selector operates in conjunction with an associated face detector that verifies whether the candidate regions contain a human face. In the preferred embodiment, the candidate selector includes a linear matched filter and a non-linear filter that operate in series to select the candidate regions from the input image. Initially, the linear matched filter performs a linear correlation on the input image using a filtering kernel to derive a correlation image. The linear matched filter selects regions of the input image that have a local maximum in the correlation image and have correlation values greater than a threshold correlation value. Preferably, the linear correlation is performed in the discrete cosine transform (DCT) domain. The non-linear filter then examines contrast values from various sub-regions of the image regions that were selected by the linear matched filter to screen for suitable candidate regions. The filtering kernel used by the linear matched filter is calculated during a training period, or a non-face detecting period, by a filtering-kernel generator. The filtering kernel is preferably computed utilizing a database of training face images that have been averaged and then masked to remove DC, illumination and noise components.