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How to process each non-overlapped block of an image after it's sub-division?

Asked by Mohsin Shah on 14 Mar 2018
Latest activity Commented on by Image Analyst
on 14 Mar 2018
My function sub-divides an image into non-overlapping blocks (each block is a cell matrix). I wonder how to process each block and then recombine them to make a processed image? Let's say I want to apply fast Walsh Hadamard transform (fwht2) on each block. Here is my function:
if true
function Blocks = imageBlock(I)
[m,n] = size(I);
Blocks = cell(m/8,n/8);
counti = 0;
for i = 1:8:m-7
counti = counti + 1;
countj = 0;
for j = 1:8:n-7
countj = countj + 1;
Blocks{counti,countj} = I(i:i+7,j:j+7);
end
end
end

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2 Answers

Answer by Walter Roberson
on 14 Mar 2018
 Accepted Answer

cellfun() to process them. cell2mat() to recombine.
Have you considered using blockproc() instead of the steps you are taking now?

  1 Comment

Yes, I did consider blockproc() but I am making a mistake in using blockproc().
if true
I = imread('lena.jpg');
fh = @fwht2d;
Ip = blcokproc(I, [8, 8], fh);
end
where fwht2d is a user-defined function. This code gives the following error: "BLOCKPROC encountered an error while evaluating the user-supplied function handle, FUN.
The cause of the error was:
Conversion to double from struct is not possible."

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Answer by Image Analyst
on 14 Mar 2018

Use blockproc() and give it your function. It can be whatever you want. See attached examples.

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fh = @(block_struct) fwht2d(block_struct.data);
It worked. Thank you, Walter Roberson. I wonder which answer to accept and which to vote. Both answers (from Image Analyst and Walter Roberson) have solved my problem.
You can only accept one, but you can Vote for mine. Voting will also give the answerer reputation points. You can vote for as many as you want.

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