how to divide an image to equal parts and convert it to a matrix?

Hi there, i'm doing on a statistical project,in one step i wanna disassemble an image.for this i need to divide the image into e.g. 9 parts as a matrix and then constantly translocate the components till after "i" relocations it reaches the first matrice(first image).

I wanna know how to do that?

[Rahul Krishna]

Hello Image Analyst,

I have used your code (Another way to split the image up into blocks is to use indexing.). Could you please help me to use the image3D(:,:,slicenumber) to further divide the parts into another 4 parts.?

Thanks and Regards,

Rahul.

Answer 1

[Image Analyst]

Not sure what "relocations" means to you but here's my demo for splitting an image into blocks:

% Demo to divide a color image up into blocks.
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);
    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.');

[Shahryar]

Thank you for the answer,But I couldn't find sth that i neeeded.I just want you to introduce me exactly the function of converting an image to a matrix with real components,I mean how can I segment an image to 9 parts and define a 3x3 matrix which each of it's components are 1 of those 9 parts so that if I change the places of 2 components with each other it gives me that image in other formation,for example here this code changes 2 components of matrix a::

>>a = [1 2;3 4];

t = [1 2;3 4];

for i=1:4

b=floor(rand*2)+1

c=floor(rand*2)+1

d=floor(rand*2)+1

e=floor(rand*2)+1

f=a(b,c)

a(b,c)=a(d,e)

a(d,e)=f

if a==t

    break

end

x(i)=i

end

i

now I just want the components of [a] being e.g. 4 parts of an image...appreciate your answers..

[Image Analyst]

Looks like you're on the right track and will have it solved shortly. For checking that a = t, you might use this:

if mean2(a == t) == 1 % All elements match

[Shahryar]

Yes,you were right!I've solved it for a chessboard-like picture,But yet i have problem with the RGB picture,i have an idea but it doesn't work,what the problem is with this code?

||a=bw((1:25),(1:25)) b=bw((25:50),(1:25)) c=bw((1:25),(25:50)) d=bw((25:50),(25:50)) ||

e=[a b;c d] , e should give the matrix of imread('bw')(bw is 50x50),But doesn't. CATHORSE error...Why??

[Rahul Krishna]

Hello shahryar,

you have divided the image into overlapping blocks, so matlab cannot concatenate the matrices if its rows doesnt match correctly. So it gives a error like ''CAT arguments dimensions are not consistent''.

[Image Analyst]

Shahryar, you're overlapping the 25th row and column, plus you're not arranging the subimages in the correct layout when you assemble "e". Try going from 26 to 50 instead of 25 to 50, like this:

a=bw( 1:25,  1:25);
b=bw(26:50,  1:25);
c=bw( 1:25, 26:50);
d=bw(26:50, 26:50);
e=[a, c; b, d];  % Different order than what you had.

If this (finally) answers your question, please mark it as Accepted. Thanks in advance.

[sushmitha kemisetti]

I have divided an image into 9 parts and I have done some operations like circular shifts then how to concatenate that 9 parts of an image again?

[Image Analyst]

Try this:

fullImage = [image1, image2, image3;
             image4, image5, image6;
             image7, image8, image9];

[sushmitha kemisetti]

Error using vertcat Dimensions of matrices being concatenated are not consistent.

This error is coming... please help.

[Walter Roberson]

sushmitha kemisetti: what code are you using?

[sushmitha kemisetti]

for the above code fullImage to combine 9 parts of an image to get full image

[sushmitha kemisetti]

I have divided an image into 9 parts and I have done some operations like circular shifts on the parts of Image, then how to concatenate that 9 parts of an image again?

[Image Analyst]

fullImage = [image1, image2, image3;
             image4, image5, image6;
             image7, image8, image9];

[edit] I already told you this, above in the now-hidden comments. So why are you asking again?

[sushmitha kemisetti]

Image Analyst, I am getting error for the above code. The error is "Error using vertcat Dimensions of matrices being concatenated are not consistent" That's why I asked again.

[Image Analyst]

At least one of your 9 images is not the same size as the others. What are the sizes of them all?

[sushmitha kemisetti]

I have taken 256x256 "color image" but I am getting gray Image after combining those 9 image parts through the "fullImage = [image1, image2, image3; image4, image5, image6; image7, image8, image9];". How can I get colored Image?

[Walter Roberson]

sushmitha kemisetti: are those pieces the 85 x 85 and 86 x 86 that you mentioned somewhere else?

If you have [85 x 85 (A), 86 x 86 (B); 86 x 86 (C), 85 x 85 (D)] then MATLAB would attempt to proceed by doing the [85 x 85 (A), 86 x 86 (B)] first. That would fail because of the different number of rows.

You could attempt to reorder that by using [[85 x 85 (A); 86 x 86 (C)], [86 x 86 (B); 85 x 85 (D)]] so that the two parts being "," together have the same number of rows. That would, however, fail, because in the [85 x 85 (A); 86 x 86 (C)] the ";" operator would be trying to work with different number of columns.

In a situation like this, the easiest approach is to copy the pieces into the output array one-by-one:

output(1:size(A,1),1:size(A,2),:) = A;
output(1:size(B,1),size(A,2)+1:size(A,2)+size(B,2),:) = B;
output(size(A,1)+1:size(A,1)+size(C,1), 1:size(C,2),:) = C;
output(size(B,1)+1:size(B,1)+size(D,1), size(C,2)+1:size(C,2)+size(D,2), :) = D;

[sushmitha kemisetti]

Walter Roberson: sir, After doing this also I am getting gray Image, Is there any possibility to get color Image after combining the parts of original(color) Image

Thank you

[sushmitha kemisetti]

Img = imread('D:\misc\house_256.tiff');

imshow(Img)

A =Img(1:85, 1:85)

B =Img(1:85, 86:171)

C =Img(1:85, 172:256)

D =Img(86:171, 1:85)

E =Img(86:171, 86:171)

F =Img(86:171, 172:256)

G =Img(172:256, 1:85)

H =Img(172:256, 86:171)

I =Img(172:256, 172:256)

figure,imshow(A)

here I am getting output of the part A in gray color, how should I get colored one?

[Walter Roberson]

A =Img(1:85, 1:85, :)

B =Img(1:85, 86:171, :)

C =Img(1:85, 172:256, :)

and so on. Your existing code is only selecting the Red pane from the image.

[sushmitha kemisetti]

thank you sir...

[sushmitha kemisetti]

I want to do circular right shift for the part A "A =Img(1:85, 1:85, :)" then how can I get it?

Thanks in advance

[Walter Roberson]

positions_to_shift_right = 5;
A = circshift(A, positions_to_shift_right, 2);

[sushmitha kemisetti]

Img = imread('D:\misc\house_256.tiff');

imshow(Img)

A =Img(1:85, 1:85, :)

B =Img(1:85, 86:171, :)

C =Img(1:85, 172:256, :)

[m,n]=size(A);

k=3;l=8;

%circular Right shift for the matrix A

            for i=1:m
              for j=1:n
                  ARight(i,j)=mod(A(i,j),2^k)*2^(l-k) + floor(A(i,j)/2^k);  
              end
            end
    image(ARight);
    figure, imshow(ARight)

I am getting ARight matrix with 85x255, but I need 85x85 matrix, how can I combine the ARight Matrix to get 85x85?

[Walter Roberson]

That code does a bit-wise right circular shift, not an element-wise right circular shift. If that is your intention then it would be better if you documented that.

As to the cause of your difficulty: read this https://www.mathworks.com/help/matlab/ref/size.html#output_argument_d0e920671 carefully:

"If fewer than ndims(A) output arguments are specified, then all remaining dimension lengths are collapsed into the last argument in the list. For example, if A is a 3-D array with size [3 4 5], then [sz1,sz2] = size(A) returns sz1 = 3 and sz2 = 20."