459 views (last 30 days)

Image Analyst
on 15 Apr 2013

Here's my standard "split an image up into blocks" demo. It does this two ways (you can pick your favorite way), and for two types of images (gray scale and color). It's very general so it could be shortened some if you have certain conditions, like you know that there is an integer number of blocks in the image (i.e., no partial blocks at the edges).

% Demo to divide an image up into blocks (non-overlapping tiles).

% The first way to divide an image up into blocks is by using mat2cell().

% In this demo, I demonstrate that with a color image.

% Another way to split the image up into blocks is to use indexing.

% In this demo, I demonstrate that method with a grayscale image.

clc; % Clear the command window.

close all; % Close all figures (except those of imtool.)

workspace; % Make sure the workspace panel is showing.

fontSize = 20;

% Read in a standard MATLAB color demo image.

folder = fullfile(matlabroot, '\toolbox\images\imdemos');

baseFileName = 'peppers.png';

% Get the full filename, with path prepended.

fullFileName = fullfile(folder, baseFileName);

if ~exist(fullFileName, 'file')

% Didn't find it there. Check the search path for it.

fullFileName = baseFileName; % No path this time.

if ~exist(fullFileName, 'file')

% Still didn't find it. Alert user.

errorMessage = sprintf('Error: %s does not exist.', fullFileName);

uiwait(warndlg(errorMessage));

return;

end

end

% Read the image from disk.

rgbImage = imread(fullFileName);

% Test code if you want to try it with a gray scale image.

% Uncomment line below if you want to see how it works with a gray scale image.

% rgbImage = rgb2gray(rgbImage);

% Display image full screen.

imshow(rgbImage);

% Enlarge figure to full screen.

set(gcf, 'units','normalized','outerposition',[0 0 1 1]);

drawnow;

% Get the dimensions of the image. numberOfColorBands should be = 3.

[rows columns numberOfColorBands] = size(rgbImage)

%==========================================================================

% The first way to divide an image up into blocks is by using mat2cell().

blockSizeR = 150; % Rows in block.

blockSizeC = 100; % Columns in block.

% Figure out the size of each block in rows.

% Most will be blockSizeR but there may be a remainder amount of less than that.

wholeBlockRows = floor(rows / blockSizeR);

blockVectorR = [blockSizeR * ones(1, wholeBlockRows), rem(rows, blockSizeR)];

% Figure out the size of each block in columns.

wholeBlockCols = floor(columns / blockSizeC);

blockVectorC = [blockSizeC * ones(1, wholeBlockCols), rem(columns, blockSizeC)];

% Create the cell array, ca.

% Each cell (except for the remainder cells at the end of the image)

% in the array contains a blockSizeR by blockSizeC by 3 color array.

% This line is where the image is actually divided up into blocks.

if numberOfColorBands > 1

% It's a color image.

ca = mat2cell(rgbImage, blockVectorR, blockVectorC, numberOfColorBands);

else

ca = mat2cell(rgbImage, blockVectorR, blockVectorC);

end

% Now display all the blocks.

plotIndex = 1;

numPlotsR = size(ca, 1);

numPlotsC = size(ca, 2);

for r = 1 : numPlotsR

for c = 1 : numPlotsC

fprintf('plotindex = %d, c=%d, r=%d\n', plotIndex, c, r);

% Specify the location for display of the image.

subplot(numPlotsR, numPlotsC, plotIndex);

% Extract the numerical array out of the cell

% just for tutorial purposes.

rgbBlock = ca{r,c};

imshow(rgbBlock); % Could call imshow(ca{r,c}) if you wanted to.

[rowsB columnsB numberOfColorBandsB] = size(rgbBlock);

% Make the caption the block number.

caption = sprintf('Block #%d of %d\n%d rows by %d columns', ...

plotIndex, numPlotsR*numPlotsC, rowsB, columnsB);

title(caption);

drawnow;

% Increment the subplot to the next location.

plotIndex = plotIndex + 1;

end

end

% Display the original image in the upper left.

subplot(4, 6, 1);

imshow(rgbImage);

title('Original Image');

%==============================================================================

% Another way to split the image up into blocks is to use indexing.

% Read in a standard MATLAB gray scale demo image.

folder = fullfile(matlabroot, '\toolbox\images\imdemos');

baseFileName = 'cameraman.tif';

fullFileName = fullfile(folder, baseFileName);

% Get the full filename, with path prepended.

fullFileName = fullfile(folder, baseFileName);

if ~exist(fullFileName, 'file')

% Didn't find it there. Check the search path for it.

fullFileName = baseFileName; % No path this time.

if ~exist(fullFileName, 'file')

% Still didn't find it. Alert user.

errorMessage = sprintf('Error: %s does not exist.', fullFileName);

uiwait(warndlg(errorMessage));

return;

end

end

grayImage = imread(fullFileName);

% Get the dimensions of the image. numberOfColorBands should be = 1.

[rows columns numberOfColorBands] = size(grayImage);

% Display the original gray scale image.

figure;

subplot(2, 2, 1);

imshow(grayImage, []);

title('Original Grayscale Image', 'FontSize', fontSize);

% Enlarge figure to full screen.

set(gcf, 'units','normalized','outerposition',[0 0 1 1]);

% Divide the image up into 4 blocks.

% Let's assume we know the block size and that all blocks will be the same size.

blockSizeR = 128; % Rows in block.

blockSizeC = 128; % Columns in block.

% Figure out the size of each block.

wholeBlockRows = floor(rows / blockSizeR);

wholeBlockCols = floor(columns / blockSizeC);

% Preallocate a 3D image

image3d = zeros(wholeBlockRows, wholeBlockCols, 3);

% Now scan though, getting each block and putting it as a slice of a 3D array.

sliceNumber = 1;

for row = 1 : blockSizeR : rows

for col = 1 : blockSizeC : columns

% Let's be a little explicit here in our variables

% to make it easier to see what's going on.

row1 = row;

row2 = row1 + blockSizeR - 1;

col1 = col;

col2 = col1 + blockSizeC - 1;

% Extract out the block into a single subimage.

oneBlock = grayImage(row1:row2, col1:col2);

% Specify the location for display of the image.

subplot(2, 2, sliceNumber);

imshow(oneBlock);

% Make the caption the block number.

caption = sprintf('Block #%d of 4', sliceNumber);

title(caption, 'FontSize', fontSize);

drawnow;

% Assign this slice to the image we just extracted.

image3D(:, :, sliceNumber) = oneBlock;

sliceNumber = sliceNumber + 1;

end

end

% Now image3D is a 3D image where each slice,

% or plane, is one quadrant of the original 2D image.

msgbox('Done with demo! Check out the two figures.');

Samantha Villanueva
on 9 Sep 2020

Walter Roberson
on 9 Sep 2020

Image Analyst
on 9 Sep 2020

Ashwin
on 20 Sep 2016

Edited: Walter Roberson
on 20 Sep 2016

Simple, use this function

function dividedImage = divideIntoBlocks(InputImage,BlockSize)

img1 = InputImage;

TOTAL_BLOCKS = size(img1,1)*size(img1,2) / (BlockSize*BlockSize);

dividedImage = zeros([BlockSize BlockSize TOTAL_BLOCKS]);

row = 1;

col = 1;

try

for count=1:TOTAL_BLOCKS

dividedImage(:,:,count) = img1(row:row+BlockSize-1,col:col+BlockSize-1);

col = col + BlockSize;

if(col >= size(img1,2))

col = 1;

row = row + BlockSize;

if(row >= size(img1,1))

row = 1;

end

end

end

end

Subhajit Chatterjee
on 5 Feb 2017

Thomas
on 22 Mar 2012

Try this example:

A=rand(16,16); %matrix of 16*16

[a b] = size(A); % get the size of A =16*16

c=4;d=4; % reshape it into 4*4 matrices

l=0;

for i=1:c:a-3

for j=1:d:b-3

C=A((i:i+3),(j:j+3));

eval(['out_' num2str(l) '=C'])

l=l+1;

end

end

You should get 16 4*4 matrices with names out_0 to out_15

aya elfatyany
on 11 Feb 2015

Image Analyst
on 11 Feb 2015

W.Khan
on 14 Oct 2017

Edited: Image Analyst
on 14 Oct 2017

Hello, I divide my image into multiple blocks, but I want to save these new blocks to a folder. But I can't save it to another folder.

for i=1:10

a=rgbBlock;

imwrite (a,sprintf('%d.jpg',i));

end

All the new blocks are the same. I mean that the new blocks replace the old blocks of the image. Can you help how to do it? Also, how to do it for multiple images. Kindly comments

Pandu Ananto
on 8 May 2019

i still dont understand how to change the total of the blocks...

if i want to get 4x4 blocks, i have to change

blockSizeR = 64;

blockSizeC = 64;

right? so that i get 4x4 each of them have 64 pixel row and col

i get this error

Subscripted assignment dimension

mismatch.

Error in coba_split (line 77)

image3D(:, :, sliceNumber)

= oneBlock;

why? pls help...

Image Analyst
on 9 May 2019

In blockproc() the parameters are the block sizes (horizontal and vertical). You can get the number of blocks by dividing the rows and columns by the block size. It's a simple relationship

rowsInImage = blockSizeR * numberOfBlocksVertically;

Do whatever math on that equation to get the parameter you need.

Opportunities for recent engineering grads.

Apply TodayFind the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!
## 5 Comments

## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/33103-divide-256-256-image-into-4-4-blocks#comment_69601

⋮## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/33103-divide-256-256-image-into-4-4-blocks#comment_69601

## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/33103-divide-256-256-image-into-4-4-blocks#comment_143287

⋮## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/33103-divide-256-256-image-into-4-4-blocks#comment_143287

## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/33103-divide-256-256-image-into-4-4-blocks#comment_233021

⋮## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/33103-divide-256-256-image-into-4-4-blocks#comment_233021

## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/33103-divide-256-256-image-into-4-4-blocks#comment_401954

⋮## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/33103-divide-256-256-image-into-4-4-blocks#comment_401954

## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/33103-divide-256-256-image-into-4-4-blocks#comment_401964

⋮## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/33103-divide-256-256-image-into-4-4-blocks#comment_401964

Sign in to comment.