image scrambling in matlab

i want to simply divide a given digital image into small segments and scramble them(jumble). thus encrypting them and also decrypt them.plz help

[Matt Kindig]

How are the "small segments" defined? Are you trying to make a puzzle? Where does the encryption/decryption come into play?

Also, "provide necessary code!" comes across as demanding to the readers of this forum. At worst, someone with sufficient privileges could tag this with the "doit4me" tag, which would essentially doom your chances of getting any help from us. I'd recommend editing your question to a) provide more details as to what you are trying to do, and b) to come across as more polite and respectful of the time of the (volunteer) forum contributors.

[Walter Roberson]

Anyone with a reputation of 5 or higher can add tags.

[vardhit]

thanx for your reply :) you are right...i apologize for the same :) i want a simple encryption technique using scrambling. i am a newbie that is why i asked for code/function. i want an image to be split into smaller images(cells). if i have 100x100 pixel image .then i want it to be divided into 10x10 smaller segments. i want them to be scrambles/jumbled so that the original image is hidden. i also want to decrypt it. plz guide me. :)

Answer 1

[Jan]

If you are talking about an RGB image:

img       = rand(100, 100, 3);
block     = reshape(img, [10, 10, 10, 10, 3]);
block     = permute(block, [1, 3, 2, 4, 5]);
block     = reshape(block, [100, 10, 10, 3]);
mix       = randperm(100);
scrambled = reshape(block(mix, :, :, :), 100, 100, 3);  % EDITED: reshape added

And the descrambling runs the other way around.

[vardhit]

thank you for ur help :) i'll try it out !

[vardhit]

i have a doubt regarding decryption. while encryption we jumbled the blocks randomly now if i want to decrypt the encrypted image,i have to put the blocks in its original location as before. how i can achieve that?

[Jan]

You have to store the result of randperm together with the image, e.g. in the comment section. Or you can replace the dynamic call of randperm by one specific reply of randperm.

[vardhit]

here block,mix and scrambled are 4 d arrays. when i use command imshow or imwrite on them. it shows an error !

imshow(scrambled) ??? Error using ==> imageDisplayValidateParams>validateCData at 114 Unsupported dimension

Error in ==> imageDisplayValidateParams at 31 common_args.CData = validateCData(common_args.CData,image_type);

Error in ==> imageDisplayParseInputs at 79 common_args = imageDisplayValidateParams(common_args);

Error in ==> imshow at 199 [common_args,specific_args] = ...

[Jan]

Then use reshape(scrambled, 100, 100, 3) to obtain the standard RGB arrays.

[Manpreet]

Sir, On reshaping we will get a new image which will contains scrambled value only not image pixels value.

[Walter Roberson]

No, Manpreet, the code Jan provided moves all three bit planes for a pixel together and does not change the representation. Every output pixels has an RGB that can be tracked directly to an input pixel. If you wish to verify this experimentally then replace Jan's original line

img = rand(100,100,3);

with

img = repmat(reshape(1:100*100)/(100*100),[100,100]), [1, 1, 3]);

this will produce an RGB image containing shades of grey, with the R, G, and B all being the same. You can image() it to observe this. Then when you look at the resulting image "scrambled" you will find that it continues to contain shades of grey and that the R, G, and B planes for any one location are all the same, and differ from every other location; this establishes that the planes were all moved together and establishes that the values are just moved around, not calculated or interpolated.

Answer 2

[Image Analyst]

Try the File Exchange, and you might find similar things to what you want, such as the 15 tile sliding puzzles:

http://www.mathworks.com/matlabcentral/fileexchange/28222-fifteen

http://www.mathworks.com/matlabcentral/fileexchange/13900-n-puzzle-dynamic-size-and-solver

[Image Analyst]

Also take a look at http://www.mathworks.com/matlabcentral/fileexchange/17981-randblock