Compute block-wise standard deviation

i have converted 80*80 image into blocks. next i converted blocks to linear array. now i need to find standard deviation of first 8 arrays. then standard deviation of next 8 arrays and so on. please send code.std2(tv(:,me:nn*nnn), 2). it show error

 for i=1:4:nr-3

    for j=1:4:nc-3

      block=I(i:i+3,j:j+3);

      %convert 4X4 into 16X1 column vector
      tv(:,col)=reshape(block,16,1);

      col=col+1;
      count=count+1;
      column=column+4;

    end

   row=row+4;

 end

[Jan]

Please post the code, which produces the error and the complete error message.

Answer 1

[Matt J]

Not sure I fully understand. You can get the standard deviations of each 4x4 block, all in just 2 lines, by using SEPBLOCKFUN ( Download )

     sz=[4,4]; 

     Imeans=sepblockfun(I,sz,@mean);

   result=sqrt(sepblockfun(I.^2, sz,@mean  ) - Imeans.^2   );

Or, if you set sz=[32,4] this will do the same across blocks of size [32,4] which is what you get if you group consecutive sets of eight 4x4 blocks together.

Answer 2

[Image Analyst]

You can use blockproc:

% Block process the image to replace every pixel in the 
% 8 pixel by 8 pixel block by the standard deviation
% of the pixels in the block.
% Image will be smaller since we are not using ones() and so for each block
% there will be just one output pixel, not a block of 8 by 8 output pixels.
blockSize = [8 8];
StDevFilterFunction = @(theBlockStructure) std(double(theBlockStructure.data(:)));
blockyImageSD = blockproc(grayImage, blockSize, StDevFilterFunction);

See attached demos.