Normalized cross-correlation function
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Hello, i am trying to write a normilized cross-correlation method function , but i can't complete it. Here are the details of the formula :
My code is
x=rand(1,1000);
N=length(x); %// length of signal
n1=128; %// length of window
xf=framing(x,n1,n1/2,rectwin(n1)); %this function frames the signal i will get xf(128,14)
win_num=size(xf,2);
for col=1:win_num
for m=1:n1+1
for n=1:n1-m
ccor(m,col)=sum(xf(n+m,col)*(xf(n,col)))/ sqrt(sum(xf(n)^2)*sum(xf(n+m)^2) );
end
end
end
Note that i want to see the correlation values betwen -1 and 1 like in the figure but instead i get
.
1 个评论
devi sowjanya
2021-3-6
Can you please provide the framing function code
采纳的回答
Kirby Fears
2015-9-21
编辑：Kirby Fears
2015-9-21
Hi Manolis,
To directly replicate what the equations say (shifting indices with +1), the calculation would look more like this:
x=rand(1,1000);
N=length(x); %// length of signal
n1=128; %// length of window
xf=framing(x,n1,n1/2,rectwin(n1)); %this function frames the signal i will get xf(128,14)
win_num=size(xf,2);
% M0=???
ccor=NaN(M0+1,win_num);
for col=1:win_num
for m=1:M0+1,
[term1,term2,term3]=deal(0);
for n=1:N-m,
term1=term1+xf(n,col)*xf(n+m,col);
term2=term2+xf(n,col)^2;
term3=term3+xf(n+m,col)^2;
end
ccor(m,col)=term1/sqrt(term2*term3);
end
end
You would just need to explicitly specify M0. This calculation can be simplified as follows:
x=rand(1,1000);
N=length(x); %// length of signal
n1=128; %// length of window
xf=framing(x,n1,n1/2,rectwin(n1)); %this function frames the signal i will get xf(128,14)
win_num=size(xf,2);
% M0=???
ccor=NaN(M0+1,win_num);
for col=1:win_num
for m=1:M0+1,
term1=sum(xf(1:N-m,col).*xf(1+m:N,col));
term2=sum(xf(1:N-m,col).^2);
term3=sum(xf(1+m:N,col).^2);
ccor(m,col)=term1/sqrt(term2*term3);
end
end
I don't have the toolbox required to run this code, so it may have bugs. Hope this helps.
更多回答（2 个）
Kirby Fears
2015-9-18
编辑：Kirby Fears
2015-9-18
0 个投票
Hi Manolis,
You are looping n and m by starting at 1, but in the formula you posted the sum starts at 0. You will need to correct your calculations to include the 0 terms in the summation. You should also consider pre-allocating "ccor" to save yourself some computational time.
You may have access to the xcorr function which calculates cross correlations. It has several options to control normalization.
Hope this helps.
2 个评论
Manolis Michailidis
2015-9-18
Kirby Fears
2015-9-21
Indeed the loop variables are only used as indices, so you are correct. My mistake. I assumed the loop variables were also used as numeric values in the summand. I'm writing another answer below.
Image Analyst
2015-9-29
0 个投票
Do you have the Image Processing Toolbox? If so, why not just use the built-in function normxcorr2()?
1 个评论
Manolis Michailidis
2015-9-29
编辑：Manolis Michailidis
2015-9-29
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