Examples
Template Matching
 The comparison of two images is done based on correlation
coefficient.
 The quantitative measure of the degree of association of two
distinct variables is often coined as correlation coefficient, which
typically ranges between -1 and 1.
 Pearson Correlation coefficient
Template Matching (Cont’d)
 Steps to be performed for finding the correlation coefficient between
two vectors or matrices
Template Matching (Cont’d)
This denotes that the matrix A and B are highly correlated.
MATLAB Code
A= [1 4 7; 2 5 8; 3 6 9]
B = A*2;
%Find the average of the matrix A
meanA = mean2(A);
%Find the average of the matrix B
meanB = mean2(B);
%Subtract the average value from matrix A
Asub = A-meanA;
%Subtract the average value from matrix B
Bsub = B-meanB;
Example: 2
%Covariance of matrix A and matrix B
%Assign new values to B
covAB = mean2(Asub.*Bsub);
B = [9 6 3;8 5 2; 7 4 1];
%Find the standard deviation of the matrix A
Rho = corr2(A,B)
stdA = std(A(:),1);
%Find the standard deviation of the matrix B
stdB = std(B(:),1);
%Find the correlation Cofficient
Rho = covAB./(stdA*stdB)
In the first example, both A and B are highly
correlated. The correlation coefficient is 1, whereas
in example 2, the correlation coefficient is -1.
Template Matching in Spatial Domain
%Read an Image A(Template)
A1 = imread('benten.jpg');
%Read the Target Image
B1 = imread('watch.jpg');
A = A1(:,:,1);
B = B1(:,:,1);
corr_map = zeros([size(A,1),size(A,2)]);
for i = 1:size(A,1)-size(B,1)
for j = 1:size(A,2)-size(B,2)
%Construct the correlation map
corr_map(i,j) = corr2(A(i:i+size(B,1)-1,j:j+size(B,2)-1),B);
end
end
Template Matching in Spatial Domain (Cont’d)
figure,imagesc(corr_map);colorbar;
%Find the maximum value
maxpt = max(corr_map(:));
[x,y]=find(corr_map==maxpt);
%Display the image from the template
figure,imagesc(B1);title('Target Image');colormap(gray);axis image
grayA = rgb2gray(A1);
Res = A;
Res(:,:,1)=grayA;
Res(:,:,2)=grayA;
Res(:,:,3)=grayA;
Res(x:x+size(B,1)-1,y:y+size(B,2)-1,:)=A1(x:x+size(B,1)1,y:y+size(B,2)-1,:);
figure,imagesc(Res);