Homework 2 : Due Feb. 25, 2009
CS 778 / 578
February 11, 2009
Submit all Matlab code and a report containing all requested images via ecampus.
1 Segmentation using active contours
Load the ’abct’ abdominal CT image from the course webpage. Initialize the curve to be a circle
of radius = 15 with center at (x,y) = (93,162). Discretize the curve into at least 20 points. (You
may use more points if the speed of execution is adequate.) Pick parameters α, β, γ and design the
external energy so that the liver is segmented.
Display the image and curve in the x-y coordinate system (use ’axis xy’). Display the curve using
’plot’. Show images of the curve on top the image for the following cases:
•The initial state.
•At least one other time before convergence.
•The final converged state.
Describe your energy functional in the report. You may use one of the functions from the ’Snakes’
paper, or functions from another paper, a function of your own design, or a combination. The
balloon inflation force (described and referenced in the notes) which propagates the curve in the
outward normal direction may be a very useful component.
2 If you are registered for CS 778
2.1 Subdivision
Incorporate a subdivision scheme to increase the number of points in your curve during the evolution.
Use the midpoint subdivision (or a scheme of your choosing) at least 3 times during the curve
evolution process. The midpoint subdivision scheme involves doubling the number of points in the
curve by inserting new points halfway between each adjacent pair of points in the curve.
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