Can anyone help me check is this the correct way of formulating this formula

I am currently working on watermarking approach. I want to calculate the correlation without using the MATLAB inbuilt formular corr2. when i compared my answer with corr2 and my formula (i.e.

1. . without any attacks on the watermarked image both values are the same =1
2. . without attacks implemented answers are different e.g. with corr2 = 0.9+ whilst using the formula answer are 1.12+ or 1.0023 etc.)

so, i'm having doubt the way i formulated the formula in the attached for NC Below is my formulation?

host = double(host);

watermarked = double(watermarked);

NCtopF=0;

NCdownF=0;

NCdown= 0;

NCtop1=0;

for i=1:64

for j=1:64

NCtop = host(i,j) .*watermarked(i,j);

NCtop1= NCtop1 + NCtop;

NCdown = NCdown + host(i,j).^2;

end

NCtopF = NCtopF + NCtop1;

NCdownF = NCdownF + NCdown;

end

NCsum = NCtopF/NCdownF;

NC1 = corr2(host,watermarked);

fprintf('\n normalized correlation (corr2) : %d \n', NC1);

fprintf('\n normalized correlation Y : %d \n', NCsum);

[Rik]

https://www.mathworks.com/matlabcentral/answers/416759-a-guide-to-flag-or-close-questions

Have a read here and here. It will greatly improve your chances of getting an answer.