Using a Robust Active Appearance Model for Face Processing

Active appearance models are widely used to match statistical models of shape and appearance to new images rapidly. They work by finding model parameters which minimise the sum of squares of residual differences between model and target image. A limitation of AAMs is that they are not robust to a large set of gross outliers. Using a robust kernel can help, but there are potential problems in determining the correct kernel scaling parameters. We describe a method of learning two sets of scaling parameters during AAM training: a coarse and a fine scale set. Our algorithm initially applies the coarse scale and then uses a form of deterministic annealing to reduce to the fine outlier rejection scaling as the AAM converges. The algorithm was assessed on two large datasets consisting of a set of faces, and a medical dataset of images of the spine. A significant improvement in accuracy and robustness was observed in cases which were difficult for a standard AAM.