Normalized cross-correlation function
19 Ansichten (letzte 30 Tage)
Ältere Kommentare anzeigen
Manolis Michailidis
am 18 Sep. 2015
Kommentiert: devi sowjanya
am 6 Mär. 2021
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 :
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/149206/image.png)
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
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/149208/image.png)
.
1 Kommentar
Akzeptierte Antwort
Kirby Fears
am 21 Sep. 2015
Bearbeitet: Kirby Fears
am 21 Sep. 2015
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.
Weitere Antworten (2)
Kirby Fears
am 18 Sep. 2015
Bearbeitet: Kirby Fears
am 18 Sep. 2015
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 Kommentare
Kirby Fears
am 21 Sep. 2015
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
am 29 Sep. 2015
Do you have the Image Processing Toolbox? If so, why not just use the built-in function normxcorr2()?
1 Kommentar
Siehe auch
Kategorien
Mehr zu Loops and Conditional Statements finden Sie in Help Center und File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!