how to divide a 512*512 image block by pseudo randomly permuting into 8*8 blocks?

the data hider pseudo-randomly selects Np encrypted pixels that will be used to carry the parameters for data hiding.here,Np is a small positive integer,for example,Np=20.the other(N-Np) encrypted pixels are pseudo randomly permuted and divided into number of groups,each of which contains L pixels.here what is the permutation needed and the code used to divide?

[Walter Roberson]

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Answer 1

[the cyclist]

I thought I understood the title of your post, but I have to admit I did not really understand your question at all. But, maybe this will help a tiny bit. It randomizes the 4,096 blocks of size 8*8 that tile your 512*512 array.

% Pretend data
A = rand(512);

% Random linear index to the blocks
r = randperm(4096)';

% (i,j) subscripts instead of linear index
[i,j] = ind2sub([64 64],r)

% Example of grabbing the 37th randomly found block
whichBlock = 37;
randomBlock = A(8*(i(whichBlock)-1)+(1:8),8*(j(whichBlock)-1)+(1:8))

[Tia]

Hello Sir, After randomBlock, could you tell me how to show all randomBlock in 512x512array? i followed your codes,and i added loop for example

for whichBlock = 1:64;
randomBlock = A(8*(i(whichBlock)-1)+(1:8),8*(j(whichBlock)-1)+(1:8));
end

i want random 64block.then, what should i do?

thank you