MIDTERM WED. OCT.21
October 6, 1998
1
Modified Hough Algorithm
(More Efficient)
• Note that for p-parameters a1,a2,…,ap containing 2
translation parameters that the accumulator array is now
(p-2) dimensional.
• Also note reduction in the number of pixels that are
effectively visited:
– Instead of examining all pixels as a possible ‘center’ for the shape
we now only examine edge points as possible boundary points for
the shape.
October 6, 1998
2
GENERALIZED HOUGH
ALGORITHM
R-TABLE
f 1
f2
(Xc,Yc)
f
October 6, 1998
f
n
r1,r2,…,,rn
r1,r2,…,,rn
r1,r2,…,,rn
1
3
BINARY SETS AND THEIR
PROPERTIES
October 6, 1998
4
S
T
S + T
S - T
October 6, 1998
5
MORPHOLOGICAL OPENING AND CLOSING
OPENING S
T = (S - T) + T
CLOSING
T = (S + T) - T
S
S
T
S T
S T
S T T
October 6, 1998
6
EUCLIDEAN DISTANCE TRANSFORM
• For a set S the Euclidean Distance
Transform is the non-negative scalar
function d(x,S) where x is a point in S and
d(x,S) is the shortest distance from x to the
boundary of S.
October 6, 1998
7
“SKELETONS” AND THE MEDIAL AXIS
TRANSFORM
S
Locus of centers of largest circles
contained in S such that circles are
tangent at 2 or more points.
October 6, 1998
8
October 6, 1998
9