Game Development Reference
In-Depth Information
corner positions have already been estimated, only the thickness (
d
u
, d
o
) and the
opening heights (
o
u
, o
o
) of the lips in the
mouth-open
case (ref. Figure 4), as well
as the lip thickness (
d
u
, d
o
) and the value of the parameter
t
in the
mouth-closed
case (ref. Figure 4) need to be estimated. A perpendicular bisector of the line
l
connecting both mouth corner positions in the mouth area
M
is defined as the
search area for these parameters (ref. Figure 6). Different values of these
parameters create different forms of the 2D mouth models. In order to determine
these parameters, the similarity between the selected 2D mouth model with the
geometrical form of the real mouth in the image is measured using a cost
function. This cost function utilizes texture characteristics of the real mouth by
means of the selected 2D mouth model.
It is observed that there are texture characteristics existing in the mouth area:
1.
The areas of the lips have almost the same chrominance value. In the
mouth-open
case, an additional area, mouth-inside, exists and is strongly
distinguished from the lip areas. Mouth-insides normally have different
luminance values due to, e.g., teeth (white) and shadow areas (black). But,
it has an almost uniform chrominance value.
2.
On the lip, the luminance values of the contours strongly vary.
In the following, only the
mouth-open
case is discussed as an example. The
solution to the
mouth-closed
case can be derived from the
mouth-open
case.
Let
df
stand for the cost function used in the
mouth-open
case.
Based on the texture characteristics mentioned above, the cost function
)
(
,
d
,
o
,
o
)
open
u
o
u
o
f
(
d
,
d
,
o
,
o
for the
mouth-open
case is defined as follows:
open
u
o
u
o
f
(
d
,
d
,
o
,
o
)
=
c
×
f
(
d
,
d
,
o
,
o
)
+
c
×
f
(
d
,
d
,
o
,
o
)
(1)
open
u
o
u
o
1
open
1
u
o
u
o
2
open
2
u
o
u
o
f
(
d
,
d
,
o
,
o
)
where
describes the first texture characteristic and
open
1
u
o
u
o
df
describes the second texture characteristic. The coeffi-
cients
c
1
and
c
2
are constant weighting factors. The choice of these two
coefficients is dependent on the trade-off between those two assumptions. In the
experiments in the final section, the values of
c
1
and
c
2
are assigned to be 1.
The term
(
,
d
,
o
,
o
)
open
2
u
o
u
o
df
consists of the means and variances of chromi-
nance values
U
in the area of the upper lip
A
u
, in the area of the lower lip
A
o
and
in the area of the mouth-inside
A
b
. The areas of
A
u
,
A
o
and
A
b
are defined using
the 2D mouth model (ref. Figure 4) and are dependent on the parameters (
d
u
,
d
o
, o
u
, o
o
) to be estimated. The means of chrominance in the lip areas should be
(
,
d
,
o
,
o
)
open
1
u
o
u
o
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