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d = d(k 0 ,l 0 ) = min
k,l
d(k, l),
(7.2)
where d is the inter-frame deformation of the object, and v =(k 0 ,l 0 )
is the motion vector representing the velocity of the movement of
the object. If more than one (k 0 ,l 0 ) gives the same minimum value,
d(k 0 ,l 0 ), the shortest (k 0 ,l 0 ) vector is then chosen as motion vector
v.
y ( F -1 )
y ( F )
Search range
Macro-block
( b , b )
( b , b )
xy
xxy
d ( k , l )
( b + k , b + l )
( b + k , b + l )
x
x
y
y
Reference frame
Current frame
Fig. 7.3. Block-matching method.
Criteria Using Motion Information
We first define the following terminology.
WMIP r i,j of a pixel in a motion picture: It is a measure representing the de-
gree of imperceptibility of a luminance change at a pixel (i, j). If, for ex-
ample, the WMIP of pixel (1,0) is larger than that of pixel (2,0), a change
in luminance at pixel (1,0) is less perceptible than one at pixel (2,0).
As described in the analysis of WM imperceptibility, the element r i,j of a
pixel in a motion picture depends on two kinds of motion information and on
the still picture properties. Thus, r i,j is a function of d, v,ands i,j :
r i,j = f (d, v,s i,j ),
(7.3)
where s i,j is the pixel WMIP based only on the still picture properties 3 .
3
Various methods of determining s i,j have been presented; we use the one reported
by Echizen and coworkers [12]. It uses the one-dimensional luminance standard
deviation to prevent contour distortion by WMs. See Ref. [12] for details.
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