How to find cells corresponding to zero lag in an autocorrelation function

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Olalekan Ajayi
Olalekan Ajayi 2019-9-4
评论： Ajay Pattassery 2019-9-19
Hi,
I am looking to identify the cells corresponding to zero lag for an autocorrelation function. To do that I wrote the following as input:
I = imread('001.tif');
acf = autocorr2d(I);
[M,N]=size(acf);
lag_x = [1:N]'-ceil((N+1)/2);
lag_y = [1:M]'-ceil((M+1)/2);
[r_0,c_0] = find_r0c0(acf, lag_x,lag_y);
The response I keep getting is: undefined function or variable find_r0c0. How can this be done?
  1 个评论
KALYAN ACHARJYA
KALYAN ACHARJYA 2019-9-4
编辑：KALYAN ACHARJYA 2019-9-4
May be ?
I = imread('2.png');
acf = autocorr2d(I);
[M,N]=size(acf);
lag_x = [1:N]'-ceil((N+1)/2);
lag_y = [1:M]'-ceil((M+1)/2);
[r_0,c_0] = find(acf,lag_x,lag_y);
%..................still ^^ seems issue here

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Ajay Pattassery
Ajay Pattassery 2019-9-18
编辑：Ajay Pattassery 2019-9-18
The zero lag produces the highest value in the autocorrelation output. Hence simply finding the maximum value of the autocorrelation matrix and finding its coordinates gives the pixel location.
In the below example xcorr2 functions compute the 2-D autocorrelation.
I = imread('cameraman.tif');
acf = xcorr2(I);
maximum = max(max(acf));
[r_0,c_0]=find(acf==maximum);
Also, the following code will work since the maximum value of the autocorrelation output will be at the middle position.
I = imread('cameraman.tif');
[m,n] = size(I);
r_0 = ceil((m+n-1)/2);
c_0 = ceil((m+n-1)/2);
Refer the following link for further information on xcorr2.
https://www.mathworks.com/help/signal/ref/xcorr2.html

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