How can I unscramble a scrambled image?

Hi! I'm just a beginner. I scrambled an image using the following source.

if true
---------- scramble an 512*512 image as 8 by 8 blocks---------------------
I = imread('lena_org.bmp'); 
row = size(I, 1) / 64;
col = size(I, 2) / 64;
I_scramble = mat2cell(I, ones(1, row) * 64, ones(1, col) * 64, size(I, 3));
I_scramble = cell2mat(reshape(I_scramble(randperm(row * col)), row, col));
imshow(I_scramble);
---------------------------------------------------------------------------
end

Anyone knows how to unscramble the image as it was? I spent a lot of time solving the problem, but I am going around in circles. Thanks a lot for your help in advance!

Answer 1

[harjeet singh]

Dear @eulerphi, use this code:

I = imread('Lena512.bmp'); 
row = size(I, 1) / 64;
col = size(I, 2) / 64;
I_scramble = mat2cell(I, ones(1, row) * 64, ones(1, col) * 64, size(I, 3));
a=randperm(row * col);
I_scramble = cell2mat(reshape(I_scramble(a), row, col));
figure(1)
imshow(I_scramble);

drawnow

b=1:length(a);
com=[a' b'];
com=sortrows(com,1);

I_scramble = mat2cell(I_scramble, ones(1, row) * 64, ones(1, col) * 64, size(I, 3));
I_scramble = cell2mat(reshape(I_scramble(com(:,2)), row, col));
figure(2)
imshow(I_scramble);

drawnow

[eulerphi]

I deeply appreciate your help! That's what I exactly wanted! Thank you! :)

[BHAGYASHREE HEGDE]

Can you please tell what is 64 here in this example??

[Image Analyst]

@BHAGYASHREE HEGDE the 64 is so that you get exactly 8 blocks vertically and horizontally.

numBlocks = 512/64

numBlocks = 8

Answer 2

[Image Analyst]

See my attached demo that scrambles an image element by element. You could adapt it to scramble a cell array element by element also.

[eulerphi]

Thanks a lot for your help! Your code seems so nice for me to study. Thank you for your help! :)

[hayat ali]

Image Analyst

thank you for your efforts

can you tell me how to scramble the grayscale image? Itried this code in below but did not get a picture of scramble and unscramble. they are apear as a white image.

please help me to correct this code

the code :

clc

close all;

rgbImage = imread('pepper.bmp');

I=rgb2gray(rgbImage);

[row col]=size(I);

%figuer

subplot(2, 2, 1);

imshow(I)

% Get the order to scramble them in

scrambleorder=randperm(row*col);

% Scramble according to the scrambling order.

b=scrambleorder;

% Reshape into a 2D image

sec_b=reshape(b,[row,col]);

% Display the scrambled color image.

subplot(2, 2, 2);

imshow(sec_b);

% Recover the image, knowing the sort order

recoverOrder = zeros([row*col], 2);

recoverOrder(:, 1) = 1 : (row*col);

recoverOrder(:, 2) = b;

% Sort this to find out where each scrambled location needs to be sent to.

newOrder = sortrows(recoverOrder, 2);

% Extract just column 1, which is the order we need.

newOrder = newOrder(:,1);

% Unscramble according to the recoverOrder order.

b = b(newOrder);

% Reshape into a 2D image

b = reshape(b, [row, col]);

% Display the original color image.

subplot(2, 2, 3);

imshow(b);

[Image Analyst]

See code altered to work on a gray scale image.

% Demo to use randperm() to scramble the pixel locations in a gray scale image, then undo the scrambling to obtain the original image again.
clc;
clearvars;
close all;
workspace;
fontSize = 16;

% Read in a gray scale demo image.
folder = fileparts(which('cameraman.tif')); % Determine where demo folder is (works with all versions).
baseFileName = 'cameraman.tif';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
	% Didn't find it there.  Check the search path for it.
	fullFileName = baseFileName; % No path this time.
	if ~exist(fullFileName, 'file')
		% Still didn't find it.  Alert user.
		errorMessage = sprintf('Error: %s does not exist.', fullFileName);
		uiwait(warndlg(errorMessage));
		return;
	end
end
grayImage = imread(fullFileName);
% Get the dimensions of the image.  numberOfColorBands should be = 1.
[rows, columns, numberOfColorBands] = size(grayImage);
if numberOfColorBands > 1
	grayImage = rgb2gray(grayImage); % Convert to gray level.
end
% Display the original gray scale image.
subplot(2, 2, 1);
imshow(grayImage);
title('Original Gray Scale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off') 

% Get the order to scramble them in 
scrambleOrder = randperm(rows*columns);

% Scramble according to the scrambling order.
grayImage = grayImage(scrambleOrder);

% Reshape into a 2D image
scrambledImage = reshape(grayImage, [rows, columns]);

% Display the scrambled gray scale image.
subplot(2, 2, 2);
imshow(scrambledImage);
title('Scrambled Gray Scale Image', 'FontSize', fontSize);

% Recover the image, knowing the sort order
recoverOrder = zeros([rows*columns], 2);
recoverOrder(:, 1) = 1 : (rows*columns);
recoverOrder(:, 2) = scrambleOrder;
% Sort this to find out where each scrambled location needs to be sent to.
newOrder = sortrows(recoverOrder, 2);
% Extract just column 1, which is the order we need.
newOrder = newOrder(:,1);
% Unscramble according to the recoverOrder order.
grayImage = grayImage(newOrder);
% Reshape into a 2D image
scrambledImage = reshape(grayImage, [rows, columns]);

% Display the original gray scale image.
subplot(2, 2, 3);
imshow(scrambledImage);
title('Unscrambled Gray Scale Image', 'FontSize', fontSize);

[hayat ali]

thank you very much. I wish you success.