AST Based Feature Detectors
AST is an acronym standing for Accelerated Segment Test. This test is a relaxed version of the SUSAN corner criterion. Instead of evaluating the circular disc only the pixels in a Bresenham circle of radius around the candidate point are considered. If contiguous pixels are all brighter than the nucleus by at least or all darker than the nucleus by, then the pixel under the nucleus is considered to be a feature. This test is reported to produce very stable features. The choice of the order in which the pixels are tested is a so-called Twenty Questions problem. Building short decision trees for this problem results in the most computationally efficient feature detectors available.
The first corner detection algorithm based on the AST is FAST (Features from Accelerated Segment Test). Although can in principle take any value, FAST uses only a value of 3 (corresponding to a circle of 16 pixels circumference), and tests show that the best results are achieved with being 9. This value of is the lowest one at which edges are not detected. The order in which pixels are tested is determined by the ID3 algorithm from a training set of images. Confusingly, the name of the detector is somewhat similar to the name of the paper describing Trajkovic and Hedley's detector.
Read more about this topic: Corner Detection
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