Image Processing Reference
In-Depth Information
Fig. 10.7
The importance of choosing the four points far apart. The
blue points
are used for
calculating the mapping between the two coordinate systems, whereas the
red points
are mapped
from image 1 to image 2 using this mapping
It is important that the four points we use are spread out across the entire image.
This will ensure a good transformation. If your points are too close together, then
the transformation might not be applicable for the entire image, but only for the
region wherein the points are located. This is illustrated in Fig.
10.7
.Thetoprow
shows two images of the same scene but captured from two different viewpoints. In
order to learn the mapping between the two, the coordinates of the blue points are
measured in the two images. From these points we can solve Eq.
10.17
and hence
obtain the two Eqs.
10.13
and
10.14
. We now use these equations to map the red
points in image 1 to image 2. We can see that the mapped points in image 2 are in
agreement with the red points in image 1. The same is now done for the images in
the second row only now the blue points are located close to each other. The effect
of this is that when mapping the red points from image 1 to image 2, they end up in
incorrect locations. The further away from the blue points a red point is in image 1,
the worse the mapping. In fact, the red point furthest away in image 1 is mapped to a
position outside image 2 and therefore not present in image 2. This example should
underline the very important point about choosing the four points as far away from
each other as possible.
