How to calculate the correlation coefficient in an image?

In order to find the correlation between two adjacent pixels (horizontal, vertical and diagonal), I have randomly selected 3000 pairs of adjacent pixels from the original and encrypted images. I used the inbuilt MATLAB function corrcoef but I'm not getting the result. Do I need to find the mean, variance and covariance of the pixels before calculating the correlation coefficient?If I do where do I use it in the function? This function doesnt seem to use any of the values. I used the following code to calculate for horizontally adjacent pixels

           m1 = A(:,1:end-1,1);  %# All rows and columns 1 through 255 
           n1 = A(:,2:end,1);    %# All rows and columns 2 through 256 
                                 % A is the original image

           randIndex1 = randperm(numel(m1));  %# A random permutation of the integers
                                              %#   from 1 to numel(m1)
           randIndex1 = randIndex1(1:3000);   %# Pick the first 3000 indices
           m1Rand = m1(randIndex1);          %# 3000 random values from m1
           n1Rand = n1(randIndex1);          %# The corresponding 3000 values from n1 

           r_mn1 = corrcoef(m1Rand(:),n1Rand(:)); disp('r_mn1=');disp(r_mn1);

I do have the formulas for calculating mean, variance, covariance and correlation coefficient.I want to know whether the inbuilt function can be used in this case or should I calculate using the formulas? Please help. Thanks in advance.

Answer 1

[Ali Broumandnia]

function  r_xy=AdjancyCorrPixel( P )
%UNTITLED3 Summary of this function goes here
%   Detailed explanation goes here
x1 = double(P(:,1:end-1));
y1 = double(P(:,2:end));
randIndex1 = randperm(numel(x1));
randIndex1 = randIndex1(1:3000);
x = x1(randIndex1);
y = y1(randIndex1);
r_xy = corrcoef(x,y);
scatter(x,y);
xlabel('Pixel gray value on location (x,y)')
ylabel('Pixel gray value on location (x+1,y)')
end

[Wisal Adnan]

hello Ali

i am using this code put how can calcalate corr in direction ( hor.,ver.,dig.)

Thanks

[Abubakar Abba]

Hello, @Wisal Adnan Have you done the calculation for Hori Corr?

Answer 2

[Ranjit Shrestha]

what if we have more than two images? I mean a sequence of images.