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Pixel Shuffling and inverse shuffling

Asked by Renjith V Ravi on 5 Feb 2017
Latest activity Edited by Walter Roberson
on 7 May 2018
I have tried to shuffle the image using tinkerbell map and Henon Map and obtained the output.But I cant do the inverse shuffling processes.The code is given below
clear all
clc
g=imread('cameraman.tif');
% g=double(g)/255;
subplot(231)
imshow(g)
original=g;
[m,n]=size(g);
mo=m;
num = 12;
K=10.^10;
% K=19;
%....................Shuffling.......................
disp('........................Started Shuffling.....................')
%Tinkerbell shuffling
a=0.3;b=0.6000;c=2.0;d=0.27;
for k= 1:num
for i=1:m
for j=1:n
r = mod([round(abs((i^2)-(j^2)+(a*i)+(b*j))),round(abs((2*i*j)+(c*i)+(d*j)))], [m,n]);
% r = mod([(i+j),(j+K*sin(((i+1)*n)/2*pi))],mo);
% r = [((i-1)+(K*sin(j-1))),((j-1)+i)];
% r = uint8(r);
ggg(i,j)=g(r(1)+1,r(2)+1);
% ggg(i,j)=g(r(1),r(2));
end
end
g=ggg;
end
subplot(232)
x=ggg;
imshow(ggg,[]);
title('Tinkerbell shuffled')
%henon Shuffling
[m,n]=size(x);
a = 1.4;b=0.3;
% num_iter=input('Enter the round for Arnold shuffling');
num_iter = 5;
% a=1.4;
% b=0.3;
for k=1:num_iter
for i=1:m
for j=1:m
r = mod([round(abs(1-(a*(i^2))+j)),round(abs(b*i))],[m n]);
xxx(i,j)=x(r(1)+1,r(2)+1);
end
end
x=xxx;
end
subplot(233)
imshow(xxx);
title('henon Shuffled Image')
save xxx x
disp('........................Shuffling process completed succesfully.....................')
%...................Inverse Shufling.............................
disp('........................Started Inverse Shuffling.....................')
%Henon Inverse Shuffling
for k=1:num_iter
for i=1:m
for j=1:n
r = mod([round(abs(1-(a*(i^2))+j)),round(abs(b*i))],[m n]);
x1(r(1)+1,r(2)+1)=xxx(i,j);
end
end
xxx=x1;
end
subplot(234)
imshow(x1);
title('henon Inverse Shuffled')
%Tinkerbell inverse shuffling
a=0.3;b=0.6000;c=2.0;d=0.27;
for k=1:num
for i=1:m
for j=1:n
r = mod([round(abs((i^2)-(j^2)+(a*i)+(b*j))),round(abs((2*i*j)+(c*i)+(d*j)))], [m,n]);
g1(r(1)+1,r(2)+1)=x1(i,j);
end
end
xxx=g1;
end
subplot(224)
imshow(g1)
title('Tinkerbell_inverse_shuffled')
disp('........................Inverse Shuffling process completed succesfully.....................')
psnr = psnr(g1,original)
ssim=ssim(g1,original)

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2 Answers

Answer by Walter Roberson
on 5 Feb 2017
Edited by Walter Roberson
on 5 Feb 2017
 Accepted Answer

Suppose your shuffled image is S. Then
temp = reshape(1:numel(S), size(S));
temp will be an array of linear indices -- temp(k) will be k.
Now apply your forward shuffling routine to temp, generating temp_mapped . Each value in temp_mapped will appear only once, and the location temp_mapped == k is the place that the shuffle maps pixel #k to. So you can undo it:
unshuffled = zeros(size(S), class(S));
unshuffled(temp_map) = S;
and you can cross-check by shuffling this and checking that you get out S.
By the way, once you have temp_mapped, you can use it to do all future shuffling,
S1 = unsuffled(temp_map);
S2 = S1(temp_map);
S3 = S2(temp_map);
and S3 would be unsuffled shuffled 3 times, without having to do any further computation of indices.

  9 Comments

what can be done for unique henon map code, its values are repeating??
Are you able to get the correct inverse shuffling?
am not getting the inverse
its showing error
Index exceeds matrix dimensions.
Error in rough (line 62)
x1(r(1)+1,r(2)+1)=xxx(i,j);
pleae help me to resolve

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Answer by Hyelda Kefas on 7 May 2018
Edited by Walter Roberson
on 7 May 2018

I was able to do the INVERSE SHUFFLE for the Henon map. I don't know whether it is perfectly correct or not. Let's rub minds and get the perfect solution for you. Thanks
clear all
clc
g=imread('cameraman.tif');
g = imresize(g, [256 256]);
g=g(:,:,1);
subplot(2,2,1)
imshow(g,[])
title('Original Image')
%HENON SHUFFLING
[m,n]=size(g);
a = 3;
b = 3;
num_iter = 1;
for k=1:num_iter
for i=1:m
for j=1:n
r = mod([round(abs(1-(a*(i^2))+j)),round(abs(b*i))],[m n]);
x(i,j)=g(r(1)+1,r(2)+1);
end
end
g=x;
end
subplot(2,2,2)
imshow(x,[]);
title('Henon Shuffled Image')
%HENON INVERSE SHUFFLING
[m,n]=size(x);
a = 3;
b = 3;
num_iter = 1;
for k=1:num_iter
for i=1:m
for j=1:n
r1 = mod([round(abs(1-(a*(i^2))+j)),round(abs(b*i))],[m n]);
x1(r1(1)+1,r1(2)+1)=x(i,j);
%x(i,j)=x1(r(1)+1,r(2)+1);
end
end
x=x1;
end
subplot(2,2,3)
imshow(x1,[]);
title('Henon Inverse Shuffled')
set(gcf,'units','normalized','outerposition',[0 0 1 1]);

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