function s = SNR(y,z)
%% SNR function takes two input. One of them is matrix of original image.
%% The other is also matrix but it is matrix of corrupted image. SNR is
%% about finding a number between 0 and infinite. f this number is closer
%% to infinite it is good but it is close to 0 it is bad.

%% As first step, we take output of function gaussian noise and use input
%% of SNR function. n order to do this, The output of function must have
%% same name with input of another function.
%%y = imread('thewoman.jpg');
%%% in that step we find error rate. This is necessary becuase this is
%%% actually about measurement sensitivity  of an imaging system.

% z is the noisy image
% y is the noise free image

error = z - y;

s = 20 * log10(1/(sqrt(mean(mean(error.^2)))));