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Material Type: Notes; Professor: Jacobs; Class: Image Processing; Subject: Computer Science; University: University of Maryland; Term: Unknown 1989;
Typology: Study notes
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-^
-^
considering all.^ • These can be hard to find. – Local methods: pick solution, then improve it withsmall changes, until it can’t be improved.^ • Can almost always be done, but doesn’t always find best
answer.
Sometimesedge detectorsfind theboundary prettywell.
Sometimesit’s notenough.
Humans integrate contour information.
How do wedecide howgood a pathis? Which oftwo paths isbetter?
•Strength of gradient.
•Low curvature•Low change of direction ofgradient.
A Curve is a path through the grid.Cost depends on each step of thepath.We want to minimize cost.
Weight represents cost of goingfrom one pixel to another. Nextterm in sum.
p
q c
First, smooth the image to reduce noise.
-^ c can be computed using a cross-correlation filter^ – assume it is centered at p -^ Also typically scale c by it’s length^ – set c = (max-|filter response|) * length(c) - where max = maximum |filter response| over all pixels inthe image
(Seitz)
Defining the costs
p
q c
w
c can be computed using a cross-correlation filter– assume it is centered at p
-^ Also typically scale c by it’s length– set c = (max-|filter response|) * length(c) - where max = maximum |filter response| over all pixels inthe image
(Seitz)
Dijkstra’s shortest path algorithm
Algorithm 1.^
init node costs to
∞, set p = seed point, cost(p) = 0
2.^
expand p as follows:for each of p’s neighbors q that are not expanded
-^ set cost(q) = min( cost(p) + c
, cost(q) )pq
» if q’s cost changed, make q point back to p
-^ put q on the ACTIVE list
5 3 (if not already there) 1
Dijkstra
’s
shortest path algorithm
Algorithm 1.^
init node costs to
∞, set p = seed point, cost(p) = 0
2.^
expand p as follows:for each of p’s neighbors q that are not expanded
-^ set cost(q) = min( cost(p) + c
, cost(q) )pq
» if q’s cost changed, make q point back to p
-^ put q on the ACTIVE list
(if not already there)
3.^
set r = node with minimum cost on the ACTIVE list
4.^
repeat Step 2 for p = r
