Page 185 - Video Coding for Mobile Communications Efficiency, Complexity, and Resilience

162 Chapter 7. Reduced-Complexity Motion Estimation Techniques

Horizontal displacement, d
x
-6 -5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5 +6
-6
3 4
-5
5 5 5
-4
3 2 5 3 5 4
-3
5 5 5
-2
Vertical displacement, d y +1
1 1 1
2
2
1
-1
0

+2
1
+3

+4
+5

+6

searched location minimum at a given step

direction of minimum at final motion vector
a given step
Figure 7.1: An example of the TDL search with d m = 6 pels

the search pattern of the )rst step. At each step, the search pattern is centered
around the minimum of the previous step. In the given example, the minimum
in the )rst step is at (0; −2). Thus, the search pattern in the second step is
centered around this minimum location. The step size is reduced by a factor
of 2 if the minimum is in the center of the search pattern or at the boundary
of the search window. In the fourth step of the given example, the mini-
mum is at (+2; −4), which is the center of the search pattern. Therefore, the
spacing between the search locations is halved in the )fth step. Since halving