ORB

ORB (Oriented FAST and Rotated BRIEF) (RRKB11) is derived from the combination of the FAST keypoint detector and the BRIEF descriptor, modified to be rotation invariant. Since FAST does not provide orientation information, ORB computes it by determining the intensity centroid within the patch surrounding the keypoint: the vector connecting the keypoint to the centroid is invariant to rotation and sufficiently robust to illumination changes.

Using this angle, ORB rotates the BRIEF pattern (i.e., it employs precomputed rotated patterns, for example by quantizing the full rotation into 30 discrete parts) to generate a binary descriptor that is robust to rotation, known as rBRIEF. Additionally, by applying FAST and BRIEF across multiple levels of an image pyramid, scale invariance is also achieved.

ORB delivers performance comparable to SIFT and SURF in terms of accuracy, while offering significantly higher speed and, most importantly, being free of patent restrictions.