Image Processing Reference
In-Depth Information
Algorithm 13: Computation of Normals at Boundary Points of 2-D
Object
Algorithm: Normal-Computation-Using-MAT (NCUM)
Input: A set of contour points (C), the MAT of an object (S) derived
by the metric d(.).
Output: Normals at the boundary points.
1. For each boundary point p ∈ C, find the set of corresponding medial
disks Q
p
as follows:
1a. Compute the distances from the center o
M
of a medial disk M.
Let the distance be denoted as d(p,o
M
).
1b. Let the radius of the disk be r
M
. Then the disk corresponds to p
(i.e., M ∈ Q
p
) if
| d(p,o
M
)−r
M
|< Nthresh
where NThresh is the threshold for declaring M as
approximately touching the contour at p.
1c. Perform Steps 1a and 1b for all the medial disks in S.
2. Normal at p is expressed by the vector along N
p
, where
N
p
=
∀M∈Q
p
(po
M
)
End Normal-Computation-using-MAT (NCUM)
