Watermarking and pseudo random generator

Hi I want to access 8x8 matrix from the the 512x512 main matrix.Can I access the block through the blockproc function from the image toolbox?Do we get the indexing of these blocks?

I also tried doing it in the different way by writing the following code for one dimension.

a=rand(512);

y=zeros;

for i=2:64

    m=1;

    y(i)=a(m+8:8*i);

    m=m+1;

    %i=i+1;

end

But I am getting the below mentioned error.

"In an assignment A(I) = B, the number of elements in B and I must be the same."

What wrong am I doing and also could somebody tell me about the pseudo random number system where we can control the seed and get the key.

Thx, Sreeni

Answer 1

[Matt J]

You can use MAT2TILES, available here, to break the image into 8x8 cells

 y=mat2tiles(a,[8,8]);

Then you can get the (i,j)-th block just by doing y{i,j}.

Answer 2

[Walter Roberson]

Change

y(i)=a(m+8:8*i);

to

y{i} = a(m+8:8*i);

If you are using a relatively recent version of MATLAB, see the documentation for rng()