MATLAB 2x2 maximum fill

Hello guys ,

I have a problem.I have an image file and you also know it is matrix.I want to implement 2x2 maximum fill as an image that i upload. I want to search the all 2x2 pixels , finding the maximum value and fill 2x2 area (that we searched) with the maximum value.Can anyone help me. Thank you

Answer 1

[Stephen23]

Method One: blockproc:

>> ipt = [128,25,12,26;240,200,15,25;128,128,255,15;35,35,35,155]
ipt =
   128    25    12    26
   240   200    15    25
   128   128   255    15
    35    35    35   155
>> blk = [2,2];
>> fun = @(s)max(s.data(:))*ones(blk);
>> otp = blockproc(ipt,blk,fun)
otp =
   240   240    26    26
   240   240    26    26
   128   128   255   255
   128   128   255   255

Method Two: mat2cell, cellfun, and cell2mat:

>> blk = [2,2];
>> spl = size(ipt)./blk;
>> col = repmat(blk(1),1,spl(1));
>> row = repmat(blk(2),1,spl(2));
>> C = mat2cell(ipt,col,row);
>> foo = @(m)max(m(:))*ones(blk);
>> otp = cell2mat(cellfun(foo,C,'Uni',0))
otp =
   240   240    26    26
   240   240    26    26
   128   128   255   255
   128   128   255   255

Method Three: kron and accumarray:

>> blk = [2,2];
>> idx = size(ipt)./blk;
>> idx = reshape(1:prod(idx),idx);
>> idx = kron(idx,ones(blk)); % (repelem also works)
>> vec = accumarray(idx(:),ipt(:),[],@max);
>> otp = vec(idx)
otp =
   240   240    26    26
   240   240    26    26
   128   128   255   255
   128   128   255   255

Method Four: reshape, permute, and kron:

>> idx = size(ipt)./blk;
>> tmp = reshape(ipt,blk(1),idx(1),blk(2),idx(2));
>> tmp = permute(tmp,[2,4,1,3]);
>> tmp = max(max(tmp,[],4),[],3);
>> otp = kron(tmp,ones(blk))
otp =
   240   240    26    26
   240   240    26    26
   128   128   255   255
   128   128   255   255

[Fabio Corres]

in blockproc: method i had and error like :

Function BLOCKPROC encountered an error while evaluating the user supplied function handle, FUN.

The cause of the error was:

Error using .* Integers can only be combined with integers of the same class, or scalar doubles.

Error in @(s)max(s.data(:))*ones(block)

Error in blockprocFunDispatcher (line 14) output_block = fun(block_struct);

Error in blockprocInMemory (line 81) [ul_output fun_nargout] = blockprocFunDispatcher(fun,block_struct,...

Error in blockproc (line 237) result_image = blockprocInMemory(source,fun,options);

Error in bitirmetest1 (line 24) otp = blockproc(img_backup_ycbcr,block,fun);

///////////////// then i use im2double function image and it compiled.Did i make the true addition ?

Thank you so much :)

[Stephen23]

This error occurs if the input matrix is not double. It can be fixed by specifying the class of the ones in fun:

>> ipt = uint8([128,25,12,26;240,200,15,25;128,128,255,15;35,35,35,155]);
>> blk = [2,2];
>> fun = @(s)max(s.data(:))*ones(blk,class(s.data));
>> otp = blockproc(ipt,blk,fun)
otp =
  240  240   26   26
  240  240   26   26
  128  128  255  255
  128  128  255  255

[Fabio Corres]

It works thank you