This preview shows page 1. Sign up to view the full content.
Unformatted text preview: constraining the vectors representing y0 and y1 to
be within the same pixel in image coordinates.
The tracking consists in running for each frame the
optimization algorithm described above. Thus, given
the target model, the new location of the target in the
current frame minimizes the distance (18) in the neighborhood of the previous location estimate. e cient (17) is approximated as (after some manipulations)
s
m
m
qu
^
1 X pp (^ )^ + 1 X p (y)
^^
^u y0 qu 2 ^u
p(y) q] 2
pu (^ 0 )
^y
u=1
u=1
(23)
where it is assumed that the target candidate
fpu (y)gu=1:::m does not change drastically from the
^
initial fpu (^ 0 )gu=1:::m , and that pu (^ 0 ) > 0 for all
^y
^y
u = 1 : : : m. Introducing now (21) in (23) we obtain!
nh
m
2
Xp
X
^^1
pu (^ 0 )^u + Ch wi k y ; xi
^yq 2
p(y) q] 2
h
u=1
i=1
(24)
s
m
where
X
qu :
^
wi =
b(xi ) ; u] p (^ )
(25)
^y
u0 u=1 Thus, to minimize the distance (18), the second term
in equation (24) has to be maximized, the rst term
being independent of y. The second term represents
the density estimate computed with kernel pro le k at
y in the current frame, with the data being weighted by
wi (25). The maximization can be e ciently achieved
based on the mean shift iterations, using the following
algorithm.
^^
Bhattacharyya Coe cient p(y) q] Maximization
Given the distribution fqu gu=1:::m of the target model
^
^
and the estimated location y0 of the target in the previous frame:
1. Initialize the location of the target in the cur^
rent frame with y0 , compute the distribution
fpu (^ 0 )gu=1:::m , and evaluate
^y
p
^y ^
^yq
p(^ 0) q] = Pm=1 pu(^ 0 )^u :
u 4.3 Scale Adaptation The scale adaptation scheme exploits the property
of the distance (18) to be invariant to changes in the
object scale. We simply modify the radius h of the
kernel pro le with a certain fraction (we used 10%),
let the tracking algorithm to converge again, and choose
the radius yielding the largest decrease in the distance
(18). An IIR lter is used to derive the new radius
based on the cu...
View
Full
Document
This note was uploaded on 11/27/2011 for the course MATH 3484 taught by Professor Staff during the Fall '10 term at University of Central Florida.
 Fall '10
 Staff
 Math, The Land

Click to edit the document details