error 'index exceeds matrix dimensions'

figure
for i=1:11
    y(:,:,k3)=idwt2(llf(:,:,i),lhf(:,:,i),hlf(:,:,i),hhf(:,:,i),'haar');
    s=mat2gray(y(:,:,k3));
    subplot(4,4,i)
    imshow(s);
     k3=k3+1;

end
figure
    i1=1;
   j1=1;
        a1(i1:i1+63, j1:j1+63)=mat2gray(cell2mat(P(1)));
        a1(i1:i1+63, 65:65+63)=mat2gray(cell2mat(P(2)));
        a1(i1:i1+63, 129:129+63)=mat2gray(cell2mat(P(3)));
        a1(i1:i1+63, 193:193+63)=mat2gray(cell2mat(P(4)));
        a1(65:65+63, j1:j1+63)=mat2gray(cell2mat(P(5)));
        a1(65:65+63, 65:65+63)=mat2gray(s(:,:,1));
        a1(65:65+63, 129:129+63)=mat2gray(s(:,:,2));
        a1(65:65+63, 193:193+63)=mat2gray(s(:,:,3));
        a1(129:129+63, j1:j1+63)=mat2gray(s(:,:,4));
        a1(129:129+63, 65:65+63)=mat2gray(s(:,:,5));
        a1(129:129+63, 129:129+63)=mat2gray(s(:,:,6));
        a1(129:129+63, 193:193+63)=mat2gray(s(:,:,7));
        a1(193:193+63, j1:j1+63)=mat2gray(s(:,:,8));
        a1(193:193+63, 65:65+63)=mat2gray(s(:,:,9));
        a1(193:193+63, 129:129+63)=mat2gray(s(:,:,10));
        a1(193:193+63, 193:193+63)=mat2gray(s(:,:,11));
        imshow(a1);

i use this part of code to reassemble the watermarked blocks of an image. but it shows the error 'Index exceeds matrix dimensions.

Error in aftrR2 (line 185)
        a1(65:65+63, 129:129+63)=mat2gray(s(:,:,2)); ' . 
can anyone help me solve the error.thanks in advance.

[KSSV]

Check the dimensions of every matrix you are using and see the loop's which you are using to call the matrices.

Answer 1

[Jan]

The message means, that the variable "s" does not have the size 2 in the third dimension. Check this:

dbstop if error

Then runm your code again until Matlab stops at the error. Now check the size of the variables unsed in the failing line.

I guess the problem is here:

s = mat2gray(y(:,:,k3));

After the loop "s" is the last gray image, which is a 2D matrix. Then mat2gray(s(:,:,2)) accesses a not existing 3rd dimension and tries to convert it to gray levels again.