MATLAB Answers


Count grid boxes inside an object in an image.

Asked by Damodara
on 11 May 2013
I want to draw grid on an image and I want to count the number of grid boxes which cover an object in that image. Some regions of that object intersect the grid. How can I count those intersect grids as well as inside of that object.?
Experts kindly get me the solution.
Regards Dams


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1 Answer

Answer by Image Analyst
on 11 May 2013
 Accepted Answer

If you draw C lines along the columns (vertically), this will split the image into (C+1) vertical strips. If you draw R lines along the rows (horizontally), this will split the image into (R+1) horizontal strips. You will then have (C+1)*(R+1) boxes in the grid. You will have C*R intersections, where the vertical and horizontal lines intersect.
If you have a binary image then you need to make a mask of the lines and multiply it or assign the binary image to be false there. Then call bwlabel to get the number of parts you chopped your object into.
[labeledImage, numberOfPieces] = bwlabel(binaryImage);
Of course that depends on where you drew your lines and will have a problem if any of the lines overlap a 1 pixel wide part. Please run this demo I made specially for you:
clc; % Clear the command window.
workspace; % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
% Synthesize an image.
grayImage = peaks(400);
% Get the dimensions of the image. numberOfColorBands should be = 1.
[rows, columns, numberOfColorBands] = size(grayImage)
% Display the original gray scale image.
fh = 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]);
% Binarize the image by thresholding it.
binaryImage = grayImage > 2.1;
% Display the image.
subplot(2, 2, 2);
imshow(binaryImage, []);
title('Binary Image', 'FontSize', fontSize);
% Make mask
columnSplitters = 16:32:columns;
rowSplitters = 16:32:rows;
splitBinaryImage = binaryImage; % Initialize.
splitBinaryImage(:, columnSplitters) = false;
splitBinaryImage(rowSplitters, :) = false;
% Display the image.
subplot(2, 2, 3);
imshow(splitBinaryImage, []);
title('Split Binary Image', 'FontSize', fontSize);
% Label each blob with 8-connectivity, so we can make measurements of it
[labeledImage, numberOfBlobs] = bwlabel(splitBinaryImage, 8);
% Apply a variety of pseudo-colors to the regions.
coloredLabelsImage = label2rgb (labeledImage, 'hsv', 'k', 'shuffle');
% Display the pseudo-colored image.
subplot(2, 2, 4);
caption = sprintf('The number of pieces = %d', numberOfBlobs)
title(caption, 'FontSize', fontSize);
message = sprintf('Done with Image Analyst demo.\nThe number of pieces = %d', numberOfBlobs);
close(fh); % Close down the figure


How can count these grid boxes which cover that object. I wanted to count for different grid size.
Regards Dams
How is that different than what I did? And your boxes are not one pixel wide. The grid lines are, but the boxes are not -they're wider than that, just like I had. What's the use of chopping your object up like this anyway?
Here grid size is not one pixel. Have tried my code which i posted.?I have given an example. I want to use it for fractal dimension. Regards Dams

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