Since Chapter 10, we have been devoting our discussion to motion analysis and motion-compensated coding. Following a general description in Chapter 10, three major techniques — block matching, pel recursion, and optical flow — are covered in Chapters 11, 12, and 13, respectively. In this chapter, before concluding this subject, we provide further discussion and a summary. A general characterization for 2-D motion estimation, thus for all three techniques, is given in Section 14.1. In Section 14.2