How can I fix this when the value is constantly changing when measuring PSNR?

clc

k=imread('clue.jpg');
k=rgb2gray(k);
subplot(3,3,1);

imshow(k)

ks=double(k);

%Periodic noise
%diagonal noise
[x,y]=meshgrid(1:512,1:512);
p=1+sin(x+y);
tp=(ks/128+p)/4;

%Vertical noise
sig=30/255;
ks(:,:) = ks(:,:)/255;
for i=1:3:512
    y=randn;
    ks(:,i) = ks(:,i) + sig*y;
end
ts=(tp+ks)/2;
subplot(3,3,2);
imshow(ts)

%Frequency domain
tf=fftshift(fft2(tp));
tfs=10*log(1+abs(tf));
subplot(3,3,3);
imshow(tfs,[])

%lpf design
fr=zeros(512,512);
row=512;
col=512;
pok1=70;
pok2=70;

%Rectangle
for x=row/2-pok1:1:row/2+pok1
    for y=col/2-pok2:1:col/2+pok2
        fr(x,y)=1;
    end
end


%Rhombus
R = [350 250 ; 
    250 350 ; 
    150 250 ; 
    250 250] ; 
[X,Y] = meshgrid(1:512,1:512) ; 
idx = inpolygon(X,Y,R(:,1),R(:,2)) ; 
fr(idx) = 1 ; 

U = [350 250 ; 
    250 150 ; 
    150 250 ; 
    250 250] ; 
[X,Y] = meshgrid(1:512,1:512) ; 
idx = inpolygon(X,Y,U(:,1),U(:,2)) ; 
fr(idx) = 1 ;

subplot(3,3,4);
imshow(fr)

 

%noise reduction
J=tf.*fr;
subplot(3,3,5);
imshow(J);

J1=ifftshift(J);
j=ifft2(J1);
subplot(3,3,6);
j=abs(j);
imshow(j);

%measure psnr
peaksnr=psnr(j,ks);
fprintf('The PSNR value is %0.4f.\n',peaksnr);

double ks value keeps changing...ㅠ

How can I get a fixed PSNR value?

[Walter Roberson]

We expect ks to keep changing: you are adding randn() to it.

randn() has a statistical distribution; you should not expect that two different random runs will give you exactly the same PSNR -- not unless you use rng() to set a particular random number seed.

[Ju Hee Hwang]

rng('default');
 y=randn();

This change made the value fixed.

It was very helpful:)