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Gradient-based optical flow: a critical review

Optical flow, or the distribution of the apparent movement of the brightness pattern in an image, proved to be an important tool in image sequence analysis. A class of techniques that received a special interest for its simplicity and computational efficiency is the one based on the idea of conservation of image intensity. This class of techniques is known as the gradient-based techniques and is composed of two sub-classes, namely, global and local. This paper presents a critical review from the theoretical point of the main directions within the global subclass.