The Harris operator proposed a formal mathematical definition for corners (or, more generally, interest points) based on the rate of intensity changes in two perpendicular directions. Although this constitutes a sound definition, it requires the computation of the image derivatives, which is a costly operation, especially considering the fact that interest point detection is often just the first step in a more complex algorithm.

In this recipe, we present another feature point operator, called FAST (short for Features from Accelerated Segment Test). This one has been specifically designed to allow quick detection of interest points in an image; the decision to accept or not to accept a keypoint is based on only a few pixel comparisons.