An image processing apparatus for tracking faces in an image stream
iteratively receives an acquired image from the image stream potentially
including one or more face regions. The acquired image is sub-sampled at
a specified resolution to provide a sub-sampled image. An integral image
is then calculated for a least a portion of the sub-sampled image. Fixed
size face detection is applied to at least a portion of the integral
image to provide a set of candidate face regions. Responsive to the set
of candidate face regions produced and any previously detected candidate
face regions, the resolution is adjusted for sub-sampling a subsequent
acquired image.