Asked by sumaya
on 24 Mar 2014

clc; clear all; close all; A = imread('cameraman.tif'); imshow(A); N=256; T=1.4938*N+40.8689; disp(T); t=0; T2=ceil(T); disp(T2); c=[T]; iscram=A; while t<T2 for i=[0:N-1] for j=[0:N-1] iscram(i,j)=iscram(mod(i+j,N),mod(i+(2*j),N)); end end t=t+1; end figure,imshow(imscram);

Answer by Image Analyst
on 23 Nov 2014

Edited by Image Analyst
on 30 Dec 2016

Accepted Answer

I don't really know what this code is doing or if I'm even doing it correctly, but here's a version of the code that "works": [OLD CODE DELETED]

**[EDIT] - See vastly improved working code in my comment further down, and also attached here.**

Walter Roberson
on 4 Feb 2016

catherine, you apply the transform enough more times in a row that eventually the pixels move back to the original location.

Or you use the technique I describe http://www.mathworks.com/matlabcentral/answers/262451-in-a-code-of-encryption-if-y-mod-x-256-is-used-how-can-i-apply-the-same-statement-in-decryption-p#comment_340207

Veera Kalyani S
on 30 Dec 2016

Image Analyst
on 30 Dec 2016

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Answer by Manpreet
on 1 May 2015

I am doing a project on Image watermarking using Discrete Wavelet Transform(DWT) and Encryption. It is carried out in the following steps 1.) Select the host image( Image in which watermark will be hided). 2.) Select the watermark. 3.) Encrypt the watermark using the following code as given by sir(Image analyst) 4.) Watermarking using DWT.

5.) Recover the Encrypted watermark using recovery formula.

6.) Decryption of watermark using the following code which is also attached. This is also given by Image Analyst

My Question is that I have made many attacks on Watermarked Image like Rotation, Scaling, Croping but PSNR and MSE between (Watermark and Decrypted watermark) after and before attack remain Infinity and Zero respectively.

I think During Decryption, I have used same ran permutation that I used to ENCRYPT the image. So I think, Attacks have no effect on decrypted image.

Question is how to improve my code or what suggestions you can give me.

I need Help. Though, I am trying but yr valuable suggestions can make code more effective and fast

Thanks............

Walter Roberson
on 4 May 2015

iron man
on 28 Jul 2016

manpreet , could u please help me ..i m having a same problem with using RSA in watermarking.

Walter Roberson
on 28 Jul 2016

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## 2 Comments

## namita chandrakar (view profile)

Direct link to this comment:https://www.mathworks.com/matlabcentral/answers/122907-can-i-get-the-matlab-code-for-scrambling-a-digital-image-based-on-arnold-transformations#comment_251366

I tried your code but its seems like its not working. Its giving error of "Attempted to access iscram(0,0); index must be a positive integer or logical.

Error in ==> iscram(i,j)=iscram(mod(i+j,N),mod(i+(2*j),N)); "

how can i solve this error ??

## myetceteramail myetceteramail (view profile)

Direct link to this comment:https://www.mathworks.com/matlabcentral/answers/122907-can-i-get-the-matlab-code-for-scrambling-a-digital-image-based-on-arnold-transformations#comment_417094

add a 1 to both the coordinates after the mod

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