Error ' index exceeds matrix dimensions'? i had done arnold transform(48 iterations) and took DWT for each iteration. Here i need iterations from 19 to 29 only. but i got the error. what is the problem in my code. Help me resolve the problem. thank u

imag1 = imread('peppers.png');imag2=rgb2gray(imag1);
imag3= imresize(imag2, [64, 64]);
subplot(1,2,1);
imshow(imag3);
k=1;
for i=1:48
    [rows, columns] = size(imag3);
N=rows;
T=1.4938*N+40.8689;
disp(T);
t=0;
T2=ceil(T);
disp(T2);
c = T;
iscram= imag3;
while t< T2
  for i= 1 : rows
    for j= 1 : columns
      r = mod(i+j,N)+1;
      c = mod(i+(2*j)+1,N)+1;
      imscram(i,j,k)=iscram(r,c);
             %subplot(8,8,i);
            imshow(imscram(:,:,k));
    end
    end
  t=t+1;
    k=k+1;

  %fprintf('t = %f, T2 = %f\n', t, T2);
   end
%subplot(1,2,2);
%figure

end
k1=1;
for i=19:29
    imag4=imscram(:,:,i);
    subplot(7,7,i);
    imshow(imag4);
[lllo,lhlo,hllo,hhlo]=dwt2(double(imag4),'haar');
llw(:,:,k1)=lllo(:,:);
lhw(:,:,k1)=lhlo(:,:);
hlw(:,:,k1)=hllo(:,:);
hhw(:,:,k1)=hhlo(:,:);
k1=k1+1;
end

[Massimo Zanetti]

Where do you get an error in all these lines of code?

Answer 1

[Guillaume]

It's not clear where the error comes from in your code. In theory, there's no indexing that exceeds any matrix dimension, unless any of imscram, llw, lhw, hlw or hhw already exists is not 64x64x? prior to running your script.

However, there are several issues with your code.

First,

for i = 1:48
   %bunch of code that does not depend on i and should be before the loop
   for i = 1 : rows

You're using the same variable for two different loops. While that works (in matlab, in some other languages, it'll go very wrong), it's really not a good idea. Within the inner loop, you don't have access to the i of the outer loop. Don't do that.

Secondly, I'll point out you're not doing 48 iterations. You're doing 48 times the same iteration, each time discarding the result of the previous one. It may be because you've mistyped imscram as iscram in

   imscram(i,j,k)=iscram(r,c);

Finally, you actually don't need the inner i and j loops. The following will be much faster:

[i, j] = ndgrid(1:rows, 1:columns);
r = mod(i+j,N)+1;
c = mod(i+(2*j)+1,N)+1;
imscram(:, :, k) = iscram(sub2ind(size(iscram), r, c));

Note however that if iscram is meant to be imscram, the above won't work if sub2ind(size(iscram), r, c) is not a permutation of 1:4096. It appears to be a permutation with the modulo operation that you have, so it's not an issue.

[SIBI SIVA]

i get in the error in the second for loop.

[Guillaume]

There's not much point investigating what is wrong with the second loop (which I assume you mean the for i = 19:29, which is actually the fourth loop), until you've fixed the problems in the first one.

Once, it's sorted, what is

size(imscram)
size(llw)
size(lhw)
size(hlw)
size(hhw)