# Level Set algorithm not working properly

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Warid Islam on 12 Oct 2022
I am trying to segment gastric tumor. 'b1.png' is the original image. After applying level set segmentation, I get the result as definded in 'b2.png' which is not correct. As eviden, the red lines in the top left corder of the image is not right. I am trying to start the contour around the middle of the image(where I have the mass). But I am not getting the desired result. Any suggestions would be very much appreciated. Thank you.
Img=double(I(:,:,1));
%% parameter setting
timestep=1; % time step
mu=0.2/timestep; % coefficient of the distance regularization term R(phi)
iter_inner=5;
iter_outer=20;
lambda=5; % coefficient of the weighted length term L(phi)
alfa=-3; % coefficient of the weighted area term A(phi)
epsilon=1.5; % papramater that specifies the width of the DiracDelta function
sigma=.8; % scale parameter in Gaussian kernel
G=fspecial('gaussian',15,sigma); % Caussian kernel
Img_smooth=conv2(Img,G,'same'); % smooth image by Gaussiin convolution
f=Ix.^2+Iy.^2;
g=1./(1+f); % edge indicator function.
% initialize LSF as binary step function
c0=2;
initialLSF = c0*ones(size(Img));
% generate the initial region R0 as two rectangles
initialLSF(25:35,20:25)=-c0;
initialLSF(25:35,40:50)=-c0;
phi=initialLSF;
figure(1);
mesh(-phi); % for a better view, the LSF is displayed upside down
hold on; contour(phi, [0,0], 'r','LineWidth',2);
title('Initial level set function');
view([-80 35]);
figure(2);
imagesc(Img,[0, 255]); axis off; axis equal; colormap(gray); hold on; contour(phi, [0,0], 'r');
title('Initial zero level contour');
pause(0.5);
potential=2;
if potential ==1
potentialFunction = 'single-well'; % use single well potential p1(s)=0.5*(s-1)^2, which is good for region-based model
elseif potential == 2
potentialFunction = 'double-well'; % use double-well potential in Eq. (16), which is good for both edge and region based models
else
potentialFunction = 'double-well'; % default choice of potential function
end
% start level set evolution
for n=1:iter_outer
phi = drlse_edge(phi, g, lambda, mu, alfa, epsilon, timestep, iter_inner, potentialFunction);
if mod(n,2)==0
figure(2);
imagesc(Img,[0, 255]); axis off; axis equal; colormap(gray); hold on; contour(phi, [0,0], 'r');
end
end
% refine the zero level contour by further level set evolution with alfa=0
alfa=0;
iter_refine = 10;
phi = drlse_edge(phi, g, lambda, mu, alfa, epsilon, timestep, iter_inner, potentialFunction);
finalLSF=phi;
figure(2);
imagesc(Img,[0, 255]); axis off; axis equal; colormap(gray); hold on; contour(phi, [0,0], 'r');
hold on; contour(phi, [0,0], 'r');
str=['Final zero level contour, ', num2str(iter_outer*iter_inner+iter_refine), ' iterations'];
title(str);
figure;
mesh(-finalLSF); % for a better view, the LSF is displayed upside down
hold on; contour(phi, [0,0], 'r','LineWidth',2);
view([-80 35]);
str=['Final level set function, ', num2str(iter_outer*iter_inner+iter_refine), ' iterations'];
title(str);
axis on;
[nrow, ncol]=size(Img);
axis([1 ncol 1 nrow -5 5]);
set(gca,'ZTick',[-3:1:3]);
set(gca,'FontSize',14)

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