binary descriptor (ORB, BRIEF)

A compact bit-string keypoint descriptor built from pairwise pixel-intensity comparisons, much cheaper to match than a gradient histogram.

BRIEF and ORB descriptors represent a keypoint's neighborhood as a bit string, one bit per predetermined pair of nearby pixels, set to $1$ or $0$ depending on which of the pair is brighter. Two such descriptors are compared with a fast Hamming distance (bit-position mismatches) instead of SIFT's Euclidean distance over a floating-point histogram, at the cost of some robustness to large scale and illumination changes ORB partially recovers with an added orientation step.

Examples

ORB matches two video frames in real time by comparing bit strings with a fast Hamming distance instead of SIFT's slower floating-point gradient histograms.