MATLAB: Is there a way to extract the width/diameter of the contour lines

diameterellipseImage Processing Toolboxintensity plotradius

I have this image which is an intensity plot of my laser beam:

Now I want to find the horizontal and vertical (1/e^2) diameter (distance is 100 µm/px). Do you have any suggestions on how to go about fitting an ellipse at the 1/e^2 threshold.

the countour function seams to draw nice interpolated lines would there be any idea in trying to extract the information from this plot? If I can specify the counter to only be drawn at the 1/e^2 level?

Best Answer

Get a binary image of your data where it's more than 1/e^2

binaryImage = data > 1 / exp(2);

Now get the boundaries:

boundaries = bwboundaries(binaryImage);
x = boundaries{:,2};
y = boundaries{:,1};

then use the FAQ to fit an ellipse: http://matlab.wikia.com/wiki/FAQ#How_can_I_fit_an_ellipse_or_other_shape_to_a_set_of_XY_data.3F to those x and y values.

Related Solutions

MATLAB: Highlighting the contour of a specific region and its lowest end points.

I have solved the problem. The code is as below:

crownAndSecondaryDroplet=imread('inputImage.png');
%get the row number of the lowest white pixels
lowestRow = find(sum(crownAndSecondaryDroplet, 2)>0, 1, 'last');  % Bottom white row of the image
hp = impixelinfo(); %to check the output of the lowest row
%find the column numbers of the lowest row
colummsOfLowestRow= find(crownAndSecondaryDroplet(lowestRow,:)==1);
%find the x value for the leftmost and the rightmost pixels of the lowest row
lowestLeftXvalue = min(colummsOfLowestRow);
lowestRightXvalue = max(colummsOfLowestRow);
%get the boundary of the contour
boundary = bwtraceboundary(crownAndSecondaryDroplet,[lowestRow, lowestLeftXvalue],'N'); 
%display the image
figure, imshow(crownAndSecondaryDroplet, []);
title('Image with Rim Contour', 'FontSize', fontSize, 'Interpreter', 'None'); 
axis on;
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
hold on;
%plot the contour and lowest end points
plot(boundary(:,2),boundary(:,1),'g','LineWidth',2);
plot(lowestLeftXvalue , lowestRow, 'r+', 'LineWidth', 3, 'MarkerSize', 20 ); 
plot(lowestRightXvalue , lowestRow, 'r+', 'LineWidth', 3, 'MarkerSize', 20 ); 
hold off;

MATLAB: Points on a contour and meshgrid

How about doing interpolation with the contour points and mesh grid points with no extrapolation. If the meshgrid point lies on the contour, it will result into some value, if not a NaN; this helps in finding out whether point lies on contour or not.

Best Answer

Related Solutions

MATLAB: Highlighting the contour of a specific region and its lowest end points.

MATLAB: Points on a contour and meshgrid

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