error when I execute RGB scrambling

I want to do RGB scrambling as part of image cryptography. While executing a code, I got an error message

"Subscript indices must either be real positive integers or logicals".

The code is given below;

 iscram=cipher;
N=256;
T=1.4938*N+40.8689;
disp(T);
t=0;
T2=ceil(T);
disp(T2);
c=[T];
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

How do I solve this. Can anyone help me?

Answer 1

[Walter Roberson]

MATLAB subscript start at 1 not 0

[A.Mariya Jomet]

then do I need to edit as i=(1:N) and j=(1:N)

[Walter Roberson]

Yes. You might need to adjust your mod() calculation.

[A.Mariya Jomet]

Thank you so much. I did some adjustments in the mod calculation and got the results as per the requirement. Thank you for your suggestions.

[rousol makki]

mrs mariya can you give me the code of this code please .... i realy need it in my project

[Image Analyst]

Like I said, it's Arnold's cat map and I gave code in my answer below. I've also attached it here. You can probably use that. It's been a while since she logged in so she may not answer you.

Answer 2

[Image Analyst]

That looks like it's Arnold's cat map. See my Arnold's cat map demo, attached.

[A.Mariya Jomet]

Thank you. Sir, I am not familiar with these scrambling methods. I just need RGB scrambling for color image encryption. I require any simple method. is this the simplest method?

[A.Mariya Jomet]

@ Image Analyst I did the code you have provide. But didn't get any results, instead the program continue to execute with out ending. Why that so?

[Walter Roberson]

Due to the laws of the United States, we cannot assist you on "encryption". On the other hand, we can suggest that some people are interested in the mathematical properties of "chaotic maps" such as the Arnold Cat Map.

[A.Mariya Jomet]

it's ok sir, thank you so much for your kind replay and valuable suggestion.

[Image Analyst]

See https://en.wikipedia.org/wiki/Arnold%27s_cat_map

The Arnold's cat map is a way of scrambling, not encrypting, the image. I'm not changing the values really, just rearranging them. The original values are all still there. If you repeatedly run my cat map demo on the output, eventually the original RGB image will be recovered. So it's cyclic, periodic. After each iteration, you should get a scrambled image. Eventually you will see the original image displayed. Not sure what you meant by not getting any results - it should show a series of images - one at each iteration - like below.

For the toysflash.png demo image, you'll see in the command window:

Back to Original after 68 Iterations.
Elapsed time = 8.3 seconds.

[A.Mariya Jomet]

I got results by executing the code that you provided.But that wasn't exactly what I required. I did some adjustments in the mod() calculation part, by using the conditions provided in your code,and I got desired output. Thank you so much for your suggestions.