Graphics Reference
In-Depth Information
Figure 3.9.
Successful image composition using the Poisson equation.
(a)
(b)
(c)
Figure 3.10.
(a) The region
includes some key features of the target image. (b) Poisson image
compositing without modification creates unacceptable visual artifacts; the mountain's color is
smudged into the source region. (c) Using mixed gradients to preserve the target edges in
is
a big improvement.
We've assumed that the pixels from the source image entirely overwrite whatever
pixels used to be in the same place in the target image. However, in some cases, it
may be appropriate for the original target pixels to “show through.” For example, we
may want to maintain some of the texture of the target image, or give the sense that
the source pixels are slightly transparent. In this case, we could use a guidance vector
field given by a mixture of the source and target gradients, such as:
S
x
(
x
,
y
)
∇
T
(
x
,
y
)
if
∇
T
(
x
,
y
)
>
∇
S
(
x
,
y
)
=
(3.19)
S
y
(
x
,
y
)
∇
S
(
x
,
y
)
otherwise
. This is an example
of a non-conservative vector field, sowemust use Equation (
3.13
), not Equation (
3.11
)
(though the numerical implementation is basically the same). Figure
3.10
illustrates
an example.
This would preserve whatever gradients were stronger inside
