How I can repeatedly divide a binary image ?

I want to divide a binary image into 4 equal parts first. Then each parts again to 4 parts and so on. I want to repeat this work upto certain no of times . How to do that?

Answer 1

[darova]

Use mat2cell()

clc,clear
A = imread('fig3.png');
I = im2bw(A);
k = 128;                % divide matrix into 128 parts
[m,n] = size(I);

rows_rest = mod(m,k);
cols_rest = mod(n,k);
nrows = (m-rows_rest)/k *ones(1,k);
ncols = (n-cols_rest)/k *ones(1,k);
nrows(1:rows_rest) = nrows(1:rows_rest) + 1;
ncols(1:cols_rest) = ncols(1:cols_rest) + 1;
C = mat2cell(I,nrows,ncols);

[Zara Khan]

You are diving the whole image into 128 blocks that I don't want. I want to di this work step by step. First want to divide the image into 4 equal parts then each part to again 4 parts and so on.

[darova]

Why cant you rebuild that code with loops?

[Zara Khan]

No

[Image Analyst]

You CAN do this with loops if you want. You can maybe do it with other ways like reshape or permute or something -- I'd have to spend time to look into it.

Would you want all the chunks of this divided-up image to be stacked as slices in a 3D array - this is more efficient than a cell array?

[Zara Khan]

Actually after dividing each image I want calculate the no of white pixels of each parts then will store it in a excel sheet. I am working with 1000 dataset. So it will be 1000x no of cols

[Zara Khan]

Image Analyst: what will be the easiest way ??

[darova]

The best way is to pay someone

Answer 2

[Image Analyst]

Your image is not a power of 2.

Try this code:

clc;    % Clear the command window.
clear all;
close all;  % Close all figures (except those of imtool.)
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;

%===============================================================================
% Get the name of the image the user wants to use.
baseFileName = 'fig3.png';
folder = pwd;
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
	% The file doesn't exist -- didn't find it there in that folder.
	% Check the entire search path (other folders) for the file by stripping off the folder.
	fullFileNameOnSearchPath = baseFileName; % No path this time.
	if ~exist(fullFileNameOnSearchPath, 'file')
		% Still didn't find it.  Alert user.
		errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
		uiwait(warndlg(errorMessage));
		return;
	end
end
%=======================================================================================
% Read in demo image.
grayImage = imread(fullFileName);
% Get the dimensions of the image.
[rows, columns, numberOfColorChannels] = size(grayImage)
if numberOfColorChannels > 1
	grayImage = grayImage(:, :, 3);
end
% Make sure it's square
if rows ~= columns
	grayImage = imresize(grayImage, [rows, rows]);
	% Get the dimensions of the image.
	[rows, columns, numberOfColorChannels] = size(grayImage)
end
% Display image.
subplot(2, 2, 1);
imshow(grayImage, []);
impixelinfo;
axis('on', 'image');
caption = sprintf('Original image: %d rows by %d columns', rows, columns);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0.05 1 0.95]);
% Get rid of tool bar and pulldown menus that are along top of figure.
% set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')
drawnow;

% Define the function that we will apply to each block.
% First in this demo we will take the median gray value in the block
% and create an equal size block where all pixels have the median value.
% Image will be the same size since we are using ones() and so for each block
% there will be a block of 8 by 8 output pixels.
nnzFunction = @(theBlockStructure) nnz(theBlockStructure.data(:));

% Now do a loop to divide by half each time and count the number of non-zeros.
counter = 1;
newRows = rows;
newCols = columns;
while newRows >= 1
	% Round sizes.
	newRows = floor(newRows);
	newCols = floor(newCols);
	% Resize the image.
	grayImage = imresize(grayImage, [newRows, newCols], 'nearest');
	% Get the dimensions of the image.
	[rows, columns, numberOfColorChannels] = size(grayImage)

	% Show the image
	subplot(2, 2, 2);
	imshow(grayImage);
	axis('on', 'image');
	caption = sprintf('%d rows by %d columns', newRows, newCols);
	title(caption, 'FontSize', fontSize);
	
	% Count the number of non-zero pixels.
	whitePixelCount(counter) = nnz(grayImage);
	% Display counts so far.
	subplot(2, 2, 3:4);
	plot(whitePixelCount, 'b.-', 'MarkerSize', 30);
	grid on;
	title('White Pixel Count', 'FontSize', fontSize);
	xlabel('Image number', 'FontSize', fontSize);
	ylabel('Count (Number of White Pixels)', 'FontSize', fontSize);
	drawnow;
	
	% Compute half the number of rows and columns.
	% May be a fractional number if the rows and columns are not a power of 2.
	newRows = (rows / 2);
	newCols = (columns / 2);
	
	% Show user the results.
	promptMessage = sprintf('%d white pixels in this image.\nDo you want to Continue processing,\nor Quit processing?', whitePixelCount(counter));
	titleBarCaption = 'Continue?';
	buttonText = questdlg(promptMessage, titleBarCaption, 'Continue', 'Quit', 'Continue');
	if contains(buttonText, 'Quit')
		return;
	end
	
	% Increment index for whitePixelCount array.
	counter = counter + 1;
end
% Show in command window.
whitePixelCount

[Zara Khan]

Image Analyst:

You are always making two equal parts of this image. But at every steps I want to get 4 equal parts as long as we can get. Please can you give me any hints in this case.

[Zara Khan]

I am using this :

q1=image(1:size(image,1)/2,1:size(image,2)/2,:);
q2=image(size(image,1)/2+1:size(image,1),1:size(image,2)/2,:);
q3=image(1:size(image,1)/2,size(image,2)/2+1:size(image,2),:);
q4=image(size(image,1)/2+1:size(image,1),size(image,2)/2+1:size(image,2),:);

But its becoming difficult when repeating the process at every steps, too many variables I need to handle. How can I loop over the process ?

[Image Analyst]

Start with a small image of 16 by 16 pixels and explain step by step what you want as the output at each step.

[Zara Khan]

I want to set a label like :

Label 1: 16X16 will be divided into 4 equal quadrants ,now will store number of white pixels from 4 quadrants

Label 2: Each 8X8 will be divided into 4 equal quadrants again , now will store number of white pixels from 4(previous) + 32(now)

This will continue as many labels we want.

note: I am taking the complement of the 'fig3.png'

Answer 3

[Walter Roberson]

Code for repeatedly dividing was provided at https://www.mathworks.com/matlabcentral/answers/456856-how-can-i-loop-over-a-binary-image-to-get-4-equal-quadrants-always#answer_371003

[Zara Khan]

I want label here. I want to provide labels and want to store number if white pixels like I mentioned

I want to set a label like : Label 1: 16X16 will be divided into 4 equal quadrants ,now will store number of white pixels from 4 quadrants Label 2: Each 8X8 will be divided into 4 equal quadrants again , now will store number of white pixels from 4(previous) + 32(now) This will continue as many labels we want. note: I am taking the complement of the 'fig3.png'

[Walter Roberson]

What does it mean to "set a label" ?

[Zara Khan]

I mean I want define how long I want to divide the image. But at every step we will get 4 quadrants

[Image Analyst]

Do you know how to do recursive functions?

[Walter Roberson]

function splitted = rsplit4(img, sd)
  [r, c, p] = size(img);
  if sd <= 0 || mod(r,2) || mod(c,2)
      splitted = img;
  else
      splitted = {rsplit4(img(1:end/2,1:end/2, :), sd-1), rsplit4(img(1:end/2,end/2+1:end, :), sd-1);
                  rsplit4(img(end/2+1:end,1:end/2,:), sd-1), rsplit4(img(end/2+1:end,end/2+1:end,:)), sd-1};
  end
end

Now you call rsplit4 passing in the image and the maximum number of subdivisions.

[Zara Khan]

can I store white pixels counts from each blocks gradully in an array format?

Like said

step 1: 16X16 will be divided into 4 equal quadrants ,now will store number of white pixels from 4 quadrants

step 2: Each 8X8 will be divided into 4 equal quadrants again , now will store number of white pixels from 4(previous) + 32(now)

For one image it will be 1X32

for 10 image ---10X32 in this format.

white pixels count from 32 blocks .

[Zara Khan]

Image Analyst : No