How to divide a 1024 * 1024 image into 128 *128 equal parts?

Image size is 1024*1024. I need to divide this image into equal parts of size 128*128 and then i need to calculate local variance map for each parts. Can anyone please help me to do this. Thanks in advance.

[Jan]

How cool is this! It would be useful to learn, how accepting two answers works intentionally.

Answer 1

[Walter Roberson]

blockproc()

[Aynesh Rathna]

thank u :)

Answer 2

[Image Analyst]

Here's how to do it:

% Demo of blockproc.
% Uses an anonymous function to return a block of pixels
% the same size as the sliding window block.
% Blocksize is 128 and image is 1024 wide so there will be 8 values across.
try
  clc; % Clear the command window.
  close all; % Close all figures (except those of imtool.)
  workspace; % Make sure the workspace panel is showing.
  fontSize = 20;

  % Change the current folder to the folder of this m-file.
  if(~isdeployed)
    cd(fileparts(which(mfilename)));
  end

  % Read in standard MATLAB demo image.
  grayImage = imread('moon.tif');
  [rows, columns, numberOfColorChannels] = size(grayImage);
  % Resize it to be 1024 by 1024 for demo for Aynesh, who has that size images.
  grayImage = imresize(grayImage, [1024, 1024]);
  [rows, columns, numberOfColorChannels] = size(grayImage);
  % Display the original image.
  subplot(2, 2, 1);
  imshow(grayImage, []);
  caption = sprintf('Original Image\n%d by %d pixels', ...
  rows, columns);
  title(caption, 'FontSize', fontSize);
  % Enlarge figure to full screen.
  set(gcf, 'Position', get(0,'Screensize'));
  set(gcf, 'name','Image Analysis Demo', 'numbertitle','off')

  % Now let's use an anonymous function.
  % We'll take the standard deviation in the blocks.
  windowSize = 128;
  myFilterHandle2 = @(block_struct) ...
  std2(block_struct.data(:));
  blockyImageSD = blockproc(grayImage, [windowSize windowSize], myFilterHandle2);
  [rowsSD, columnsSD, numberOfColorChannelsSD] = size(blockyImageSD);
  subplot(2, 2, 2);
  imshow(blockyImageSD, []);
  caption = sprintf('Image Processed in %d by %d Blocks\nStd. Dev. Output Image is %d by %d pixels\nAnonymous Standard Deviation Filter', ...
  windowSize, windowSize, rowsSD, columnsSD);
  title(caption, 'FontSize', fontSize);

  % Note: the image size of blockyImageSD is 8x8, smaller than the original.
  
  % Convert to variance image by squaring:
  varianceImage = blockyImageSD .^2;
  subplot(2, 2, 3);
  imshow(varianceImage, []);
  caption = sprintf('Image Processed in %d by %d Blocks\nVariance Output Image is %d by %d pixels\nIt equals Std. Dev. Image Squared.', ...
  windowSize, windowSize, rowsSD, columnsSD);
  title(caption, 'FontSize', fontSize);

  uiwait(msgbox('Done with demo'));
  catch ME
    errorMessage = sprintf('Error in blockproc_demo():\n\nError Message:\n%s', ME.message);
    uiwait(warndlg(errorMessage));
  end

[Aynesh Rathna]

thank u so much :)