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

### Mohsin Shah (view profile)

on 14 Mar 2018
Latest activity Commented on by Image Analyst

on 14 Mar 2018

### Walter Roberson (view profile)

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

### Walter Roberson (view profile)

on 14 Mar 2018

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

Mohsin Shah

### Mohsin Shah (view profile)

on 14 Mar 2018
Yes, I did consider blockproc() but I am making a mistake in using blockproc().
if true
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."

### Image Analyst (view profile)

on 14 Mar 2018

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

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Walter Roberson

### Walter Roberson (view profile)

on 14 Mar 2018
fh = @(block_struct) fwht2d(block_struct.data);
Mohsin Shah

### Mohsin Shah (view profile)

on 14 Mar 2018
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.
Image Analyst

### Image Analyst (view profile)

on 14 Mar 2018
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.