Page 139 - Video Coding for Mobile Communications Efficiency, Complexity, and Resilience

116 Chapter 4. Basic Motion Estimation Techniques

Akiyo @ 30 f.p.s. (skip=1) Table Tennis @ 7.5 f.p.s. (skip=4)
1 0.8
0.8 0.6
0.6 0.4
P(d x ,d y ) 0.4 P(d x ,d y )
0.2 0.2
0 0
15 15
10 10 15
5 15 5 10
0 5 10 0 5
−5 0 −5 −5 0
−10 −10 −5 −10 −10
−15 −15 −15 −15
d y
d x
d y
d x
(a) AKIYO at 30 frames/s (skip=1) (b) TABLE TENNIS at 7.5 frames/s (skip = 4)
Figure 4.10: Center-biased distribution of block-motion eld
Foreman at 25 frames/s 1
Akiyo, skip=1
0.9 Table Tennis, skip=4
ρ x = . 0 56 ρ x = . 0 69 ρ x = . 0 64 0.8
ρ = . 0 33 ρ = . 0 49 ρ = . 0 46
y y y 0.7
ρ = . 0 66 ρ = . 0 72 0.6
x current x P(C dx −L dx ) 0.5
ρ y = . 0 48 block ρ y = . 0 63 0.4
0.3
ρ x = . 0 64 ρ x = . 0 76 ρ x = . 0 68 0.2
ρ = . 0 43 ρ = . 0 61 ρ = . 0 56 0.1
y y y
0
−30 −20 −10 0 10 20 30

C dx L dx
(a) Correlation coefficients (b) Distribution of the diffference between
betwee the motion vector the horizontal component of the current vec-
of a block and its eight neigh- tor and that of its left neighbor
boring blocks
Figure 4.11: Highly correlated block-motion elds

sequences with higher motion content and at lower frame rates, as illustrated
in Figure 4.10(b) for TABLE TENNIS at 7:5 frames=s (frame skip of 4).
Property 4.6.7.2 The block motion eld is smooth and varies slowly. In other
words, there is high correlation between the motion vectors of adjacent blocks.
Thus, it is very common to nd neighboring blocks with identical or nearly
identical motion vectors. This is evident in Figure 4.11(a), which shows the
correlation coe!cients between the motion vector of a block and its eight