Chapter 4 - Basic Motion Estimation Techniques

Abstract

This chapter reviews some basic motion estimation techniques developed specifically for video coding. In video coding, motion is estimated by observing the spatiotemporal variation of intensity between frames. This is called the “apparent motion.” An important parameter in motion estimation is the reign of support. It is the set of pels to which the motion model applies. Block-matching motion estimation (BMME) is the most widely used motion-estimation method for video coding. The chapter discusses different parameters of the basic block-matching algorithm (BMA) of Jain and Jain evaluates the impact of those parameters on performance. The BMA assumes that each block of pels moves with a uniform translational motion. Because this assumption does not always hold true, the method is known to produce blocking artefacts in the reconstructed frames. One method that reduces this effect is overlapped motion compensation (OMC). Some basic properties of the BMME algorithm when applied to typical video sequences are that the distribution of the block motion field is center-biased, the block motion field is smooth and varies slowly, and the error surface is usually multimodal. The chapter also presents the results of a comparative study on various motion estimation methods—such as differential methods, pel-recursive methods, frequency-domain methods, and block-matching methods—to find out the best motion-estimation algorithm for video coding.