two picture pixels

I want to calculate the corresponding pixels of the two pictures. How can I do? This is my code. clear all; load watch

[m,n,c,f]=size(xw);

fd=zeros(1,324);

a=1; for i=1:325

    fd(:,:,:,a)=mean(abs((xw(:,:,:,i+1))-(xw(:,:,:,i))));
    a=a+1;

end

but have a error ??? Subscripted assignment dimension mismatch.

Error in ==> detectiontest at 12 fd(:,:,:,a)=mean(abs((xw(:,:,:,i+1))-(xw(:,:,:,i))));

Answer 1

[Geoff]

You are addressing fd(:,:,:,a) as a 4-dimensional array, but it is declared as a 1-dimensional array.

You need to make sure that the shape of the matrix you are assigning to on the left is the same as the shape of the matrix on the right. So you need to look at that call to mean and examine the dimensions of the result (using size). Most easily checked by doing this:

size( mean(abs(xw(:,:,:,1))) )

Answer 2

[Image Analyst]

fd(:,:,:,a) is a 3D array, while the mean of a 3D array (which is what xw(:,:,:,i+1) is) is a 2D array. For example the mean of a 2D array returns the means of the columns so the mean is always one dimension less than what you took the mean of. So you're trying to assign a 2D array to a 3D array. You need to look up the definition of mean and figure out what you need to pass it to do whatever it is that you want to take the mean of.