What is number of iterations deciding factor in the following code?
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clc;
clearvars;
close all;
workspace;
fontSize = 33;
grayImage = imread('cameraman.tif');
subplot(1,2,1);
imshow(grayImage);
[rows, columns, numberOfColorChannels] = size(grayImage);
N=rows;
T=1.4938*N+40.8689;
disp(T);
t=0;
T2=ceil(T);
disp(T2);
c = T
iscram= grayImage;
while t<T2
for i= 1 : rows
for j= 1 : columns
r = mod(i+j,N)+1;
c = mod(i+(2*j)+1,N)+1;
imscram(i,j)=iscram(r,c);
end
end
t=t+1;
fprintf('t = %f, T2 = %f\n', t, T2);
end
subplot(1,2,2);
imshow(imscram);
(1) why should we use linear approximation of arnolds cat map, T=1.4938N+40.8689?
(2) which denotes the number of iterations in the above code?
(3) Even if i change t<700 or t<4, the output i got is the same..and also there is no change/improvement in NPCR and UACI value...
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Accepted Answer
Walter Roberson
on 30 Dec 2016
After your fprintf() you need to add
iscram = imscram;
Otherwise you are just repeating the same work over and over again instead of doing multiple iterations of the transform.
More Answers (1)
Image Analyst
on 30 Dec 2016
That code is from someone else's post and it's wrong. I redid that code and a "fixed" version is attached. I don't use that T number he computed. It doesn't seem needed at all.
From Wikipedia, it seems that the code only works on square images. I tried to generalize it for rectangular images and always got the image wrapped around vertically. It never reconstituted itself. So maybe you'll have to use other scrambling methods.
5 Comments
Image Analyst
on 30 Jan 2021
Make sure the imwrite() is not commented out like I had it in the demo:
% Save the image, if desired.
filename = sprintf('Arnold Cat Iteration %d.png', iteration);
% imwrite(currentScrambledImage, filename); % Uncomment this if you want to save the images.
fprintf('Saved image file %s to disk.\n', filename);
So take away the % and you should see Arnold Cat Iteration 67.png
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