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Topic: Shadow Removal Using Entropy minimization
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Posts: 3
Registered: 10/6/09
Shadow Removal Using Entropy minimization
Posted: Oct 6, 2009 8:18 AM
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Hi all,

I am trying to implement a shadow removal algorithm in matlab. I follow the paper
written by Mr.Graham.Finalyson i.e, "Shadow removal using Entropy minimization".
First of all i am trying to get 1-D illuminant invariant image by assuming that we
know the projection angle. I took some known images from the above mentioned
paper so that i know the projection angle and there is no need of entropy calculation.
The program which wrote works with some images and seems to be failed with some images. Please help me if some one has some experience with this algorithm. I am appending small part of my matlab code which is written to produce a 1-D illumination invariant image.

I = imread('file1.tiff');
J = im2double(I);

R = J(:,:,1);
G = J(:,:,2);
B = J(:,:,3);

[len,wid] = size(R);

% Generation of 2-D Log Chromaticity Image.
for i = 1:len
for j = 1:wid
if ((R(i,j)*G(i,j)*B(i,j))~= 0)
c1(i,j) = R(i,j)/((R(i,j)*G(i,j)*B(i,j))^(1/3));
c2(i,j) = G(i,j)/((R(i,j)*G(i,j)*B(i,j))^(1/3));
c3(i,j) = B(i,j)/((R(i,j)*G(i,j)*B(i,j))^(1/3));
c1(i,j) = 1;
c2(i,j) = 1;
c3(i,j) = 1;

rho1 = mat2gray(log(c1));
rho2 = mat2gray(log(c2));
rho3 = mat2gray(log(c3));

X1 = mat2gray(rho1*1/(sqrt(2)) - rho2*1/(sqrt(2))); %(1/sqrt(2); -1/sqrt(2); 0)
X2 = mat2gray(rho1*1/(sqrt(6)) + rho2*1/(sqrt(6)) - rho3*2/(sqrt(6))); %(1/sqrt(6); 1/sqrt(6); -2/sqrt(6))

theta = 120;

InvariantImage = cos(theta*pi/180)*X1 + sin(theta*pi/180)*X2;


Thank you all,
Sandeep P

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