MATLAB: Extract outermost contour from a set of contours.

contourimage processingImage Processing Toolboximage segmentation

I have an N X 2 matrix with the x,y co-ordinate values of the edges. I plot these co-ordinates (plotted in red displayed below in "Input Plot")
I want to extract the outermost contour (enclosing the largest area). How can this be done?
I have attached the N X 2 matrix with all x, y values (of input plot). I have also attached a .fig file of the input plot.
Regards.

Best Answer

I think using contour is the wrong approach, but I could be wrong. You don't even want all the contours -- you just want the outer boundary . What I would do is to threshold your image, then call imfill() to make the binary image solid, and then call bwareaopen() to get rid of the small noisy exterior regions. Then call bwboundaries to get a list of the outer perimeter's (x,y) coordinates.
binaryImage = grayImage > thresholdValue; % Threshold/binarize the image.
binaryImage = imfill(binaryImage, 'holes'); % Fill holes.
binaryImage = bwareaopen(binaryImage, 2000); % Remove small blobs.
boundaries = bwboundaries(binaryImage); % Get list of (x,y) coordinates of outer perimeter.
Attach your image if you want more help.
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