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Detection of Particle Orientation
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Qaisar Latif
on 18 Jul 2020
Commented: Image Analyst
on 17 Oct 2022
How can I detect the orientation of the bright region with respect to the center of the particle using matlab?? I have done a rough analysis using paint and simple trignometry and it turns out to be around 45 degree (considering the center of the bright region and the center of the particle).
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Accepted Answer
Image Analyst
on 18 Jul 2020
Use regionprops():
% Code to detect angle of a blob.
% By Image Analyst
clc; % Clear the command window.
fprintf('Beginning to run %s.m ...\n', mfilename);
close all; % Close all figures (except those of imtool.)
clear; % Erase all existing variables. Or clearvars if you want.
workspace; % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 15;
%--------------------------------------------------------------------------------------------------------
% READ IN IMAGE
folder = pwd;
baseFileName = 'ZoomIn_100f.jpg';
% Get the full filename, with path prepended.
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
grayImage = imread(fullFileName);
% Get the dimensions of the image.
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
% It's not really gray scale like we expected - it's color.
% Use weighted sum of ALL channels to create a gray scale image.
% grayImage = rgb2gray(grayImage);
% ALTERNATE METHOD: Convert it to gray scale by taking only the green channel,
% which in a typical snapshot will be the least noisy channel.
grayImage = grayImage(:, :, 1); % Take red channel.
end
% Crop it to the right lines.
% grayImage = grayImage(1750:2250, 800:end);
subplot(2, 2, 1);
imshow(grayImage, []);
impixelinfo;
title('Red Channel Image', 'FontSize', fontSize, 'Interpreter', 'None');
hFig = gcf;
hFig.WindowState = 'maximized'; % May not work in earlier versions of MATLAB.
drawnow;
subplot(2, 2, 2);
imhist(grayImage);
grid on;
title('Histogram of Original Image', 'FontSize', fontSize, 'Interpreter', 'None');
%--------------------------------------------------------------------------------------------------------
% SEGMENTATION OF IMAGE
% Get a binary image by interactively thresholding using the function at
% https://www.mathworks.com/matlabcentral/fileexchange/29372-thresholding-an-image
% 91 seems good for this image.
lowThreshold = 91;
highThreshold = 255;
% [lowThreshold, highThreshold] = threshold(lowThreshold, highThreshold, grayImage)
mask = grayImage > lowThreshold & grayImage < highThreshold;
mask = imclearborder(mask);
mask = imfill(mask, 'holes');
% Take largest blobs.
mask = bwareafilt(mask, 1);
subplot(2, 2, 3);
imshow(mask, []);
impixelinfo;
caption = sprintf('Mask of White SemiCircles');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
% Measure centroid and orientation.
props = regionprops(mask, 'Centroid', 'Orientation')
xCenter = props.Centroid(1);
yCenter = props.Centroid(2);
hold on;
plot(xCenter, yCenter, 'r+', 'MarkerSize', 40, 'LineWidth', 2);
% Display the masked image.
subplot(2, 2, 4);
overlayImage = imoverlay(grayImage, mask, 'r');
imshow(overlayImage, []);
impixelinfo;
caption = sprintf('Masked Image. Angle = %.2f degrees.', props.Orientation);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hFig = gcf;
hFig.WindowState = 'maximized'; % May not work in earlier versions of MATLAB.
drawnow;
% Make a line at that angle at the centroid.
slope = tan(props.Orientation)
x = 1 : columns;
y = slope * (x - xCenter) + yCenter;
hold on;
plot(x, y, 'r-', 'LineWidth', 2);
fprintf('Done running %s.m ...\n', mfilename);
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/333690/image.png)
9 Comments
Venkata Manikantah Sai Ganesh Tanuku
on 17 Oct 2022
Hi Image analyst,
I want to track the same orientation orientation in a video, where one record theta with respect to the deviation from intital position (X0,Y0).
First instance define a unit vector at (X0,Y0) and as particle move to the position (X1 Y1) record the deviation of orientation angle.
Image Analyst
on 17 Oct 2022
@Tanuku please start a new discussion thread after you read this:
Attach your video.
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