MATLAB: How to segment this metal bead correctly as shown in the attached images

Image Processing Toolboximage segmentationmetalweld

I tried to segment the bead on the joint of the metal in the image below, but the results seem to be not meaningful. I am interested in trying some other algorithms like random walker, level sets, and snake algorithms to do the segmentation. I have attached the combined real image and the expected results.

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Try converting to grayscale and calling stdfilt(). Then threshold. Mask off the known locations of the white background to dark plate boundaries. Call imfill() on what's left, then call bwareafilt() and bwboundaries(). Let me know if you can't figure it out, and attach the test image alone as a PNG file.

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MATLAB: How to find the centroid of cells in an image

Continue your code with this:

% Find the centroids of the mask.
props = regionprops(mask, grayImage, 'Centroid', 'WeightedCentroid');
allCentroids = vertcat(props.Centroid);
% Plot centroids over image in the overlay
hold on;
for k = 1 : size(allCentroids, 2)
    x = allCentroids(k, 1);
    y = allCentroids(k, 2);
    plot(x, y, 'r.', 'MarkerSize', 25)
    % You can plot the Weighted Centroids (weighted by the gray level) instead if you want.
end

MATLAB: Automatically crop an object from a solid background as close as possible to the object edges.

From the looks of your code, it looks like you should come to Answers before Stack Overflow. For example, you last double loop can be done vectorized. Anyway, if you want as close as possible, why are you dilating your image and doing an activecontour? Both of these will give you a boundary slightly off your "true" boundary. I'd recommend converting to hsv colorspace and threshold for high saturation. The objects will be selected and the white background will not be selected (because white and shadows have low S value). See the color segmentation demos in my File Exchange, especially this one: http://www.mathworks.com/matlabcentral/fileexchange/28512-simple-color-detection-by-hue

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MATLAB: How to find the centroid of cells in an image

MATLAB: Automatically crop an object from a solid background as close as possible to the object edges.

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