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Workshop proceeding - final.pdf - Faculty of Information and ...

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speed, several methods can be utilized. Here we use the changeable resolution algorithm to accelerate<br />

it. The key step <strong>of</strong> the changeable resolution algorithm is to reduce the resolution at first, then roughly<br />

do image registration in the lower resolution images, <strong>and</strong> then do it accurately near the possible<br />

positions in the full resolution images, <strong>final</strong>ly we can get the registration results.<br />

Optical image<br />

IR image<br />

Edge extraction<br />

Edge extraction<br />

Resolution Reducing<br />

Resolution Reducing<br />

NCC<br />

Roughly registration<br />

NCC at certain positions<br />

Selecting optimal position<br />

Rotation angle estimation<br />

Image registration parameters<br />

Fig 1 Flow diagram <strong>of</strong> changeable resolution algorithm based on NCC<br />

Suppose Im O <strong>and</strong> Im IR (image size is M×N) st<strong>and</strong>s for the optical <strong>and</strong> IR image respectively, f is<br />

the image zoom factor, Im Ol <strong>and</strong> Im IRl (image size is Mh×Nh) st<strong>and</strong>s for the lower resolution one,<br />

accordingly, Im Oe , Im IRe , Im Ole , Im IRle are the edged images <strong>of</strong> the corresponding images, then the<br />

generalize cross correlation can be expressed as<br />

ρ ( u,<br />

v)<br />

=<br />

l<br />

ρ(<br />

k,<br />

l)<br />

=<br />

Mh<br />

Nh<br />

∑∑<br />

i= 0 j=<br />

0<br />

M<br />

N<br />

∑∑<br />

i= 0 j=<br />

0<br />

(Im<br />

(Im<br />

Oleu, v<br />

( i,<br />

j)<br />

− ImIRle<br />

( i,<br />

j))<br />

σ<br />

lu,<br />

v<br />

k , l<br />

σ<br />

IR<br />

IRl<br />

Oek, l<br />

( i,<br />

j)<br />

− ImI<br />

Re<br />

( i,<br />

j))<br />

σ<br />

σ<br />

Where ρ<br />

l<br />

( u,<br />

v)<br />

is the cross correlation coefficient calculated from the lower resolution image pair<br />

Im Ole <strong>and</strong> Im IRle , (u,v) is the coordinate index <strong>of</strong> the optical image Im Ole , Im Oleu,v<br />

is an image located in<br />

(u,v)th <strong>of</strong> the image Im Ole <strong>and</strong> its size is the same as image Im IRle , σ lu,v <strong>and</strong> σ IRl are the st<strong>and</strong>ard<br />

deviation <strong>of</strong> the corresponding images respectively; ρ ( k,<br />

l)<br />

is the cross correlation coefficient<br />

calculated from the raw resolution image pair Im Oe <strong>and</strong> Im IRe , (k,l) is the coordinate index <strong>of</strong> the<br />

(1)<br />

(2)<br />

28

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