Xcorr2 function

hello,can anybody help me how to go about using the xcorr2 function to find the cross correlation between 2 images? i need a single value of correlation between a query image and an image in the database. i have used the followin: crosscorr1=max(abs(xcorr2(double(x(:,:,1)),double(y(:,:,1))))); where x and y are d 2 images. i get a single row matrix as the output.

Answer 1

[Wayne King]

Hi, That's because you are using max() on a matrix, which returns by default the maximum values for each column. One thing you can do is to call max() on the initial max() output.

x = randn(10,10);
y = randn(10,10);
max(max(abs(xcorr2(x,y))))

Note however that xcorr2 is not a normalized cross correlation.

Wayne

[Padma]

thanks!!!

but how is it different from normxcorr2??? will make a difference if i use just xcorr2?

[RITIKA MALIK]

https://in.mathworks.com/matlabcentral/answers/95436-why-are-my-results-different-in-xcorr2-and-normxcorr2-in-matlab-7-7-r2008b#answer_104789

Answer 2

[Wayne King]

The difference is that xcorr2 depends on the scale of the values in the input matrices, while normxcorr2 normalizes the cross correlation values to lie in the interval [-1,1]. Consequently, you can interpret the output of normxcorr2 more easily. If I tell the maximum value of the cross correlation between two matrices using xcorr2 is 200, you have no way of saying whether that indicates a strong linear association or not. All you know is that the correlation is in a certain direction. On the other hand if I tell you the maximum normalized cross correlation is 0.9. That gives you information about the strength of the cross correlation.

[Padma]

hey,thank u!!