Calculating perimeter of object!

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Sean Farrell
Sean Farrell 2016-10-20
编辑： Image Analyst 2016-10-22
Hi Folks,
So, I want to calculate the perimeter of an object. I have posted an image to this question. I wrote a short script - which I found on Mathworks - to trace the object of interest with a green trace. I was wondering if I can calculate the perimeter of this object. The perimeter measurement would be acquired first in number of pixels, and then I would convert that number into a physical SI measurement using a value I have written down.
My question is... How would I go about this? Also, would tracing the perimeter of the object, as I have done, help? Or, does tracing just serve to be a visual aid?
Here is the figure. The green is obviously the trace of the perimeter. In advance, thank you for reading through this!

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采纳的回答

Walter Roberson
Walter Roberson 2016-10-20
Go back to the mask without the green traced in, and use regionprops() and ask for Perimeter
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Sean Farrell
Sean Farrell 2016-10-22
If I have multiple objects, as in the image shown above, how do I know what perimeter belongs to which object?
Image Analyst
Image Analyst 2016-10-22
编辑：Image Analyst 2016-10-22
regionprops can handle multiple regions by returning a structure array:
props = regionprops(labeledImage, 'Area', 'Perimeter');
allAreas = [props.Area];
allPerimeters = [props.Perimeter];
To get the outlines as an array of (x,y) coordinates, use bwboundaries() and then use plot() to plot them all over the original image, like this snippet:
% bwboundaries() returns a cell array, where each cell contains the row/column coordinates for an object in the image.
% Plot the borders of all the regions on the original grayscale image using the coordinates returned by bwboundaries.
imshow(originalImage);
title('Outlines, from bwboundaries()', 'FontSize', captionFontSize);
axis image; % Make sure image is not artificially stretched because of screen's aspect ratio.
hold on;
boundaries = bwboundaries(binaryImage);
numberOfBoundaries = size(boundaries, 1);
for k = 1 : numberOfBoundaries
thisBoundary = boundaries{k};
plot(thisBoundary(:,2), thisBoundary(:,1), 'g', 'LineWidth', 2);
end
hold off;

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更多回答（1 个）

nikhil agrawal
nikhil agrawal 2016-10-20
Go back to the mask without the green traced in and use regionprops() and Ask for Perimeter.

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