How to find the Alpha Hull of 2-D image

i would like to know how to find the alpha hull of the image like convex hull for 2-D image

Answer 1

[Sean de Wolski]

You will need to binarize the image (however, you need to do that), find the points on the perimeter ( find/bwperim , or bwboundaries) and then call alphaShape on those points.

Simple example:

I = imread('onion.png');

BW = I(:,:,2)>100 & I(:,:,1)<150;

[r,c] = find(bwperim(BW));

ah = alphaShape(c,r);

plot(ah)

This is about as simple of an example as it gets. You might want to do more advanced things like calling regionprops with 'SubarrayIdx' so that you find the alpha hull of each object in the image, etc.

[ganesh s]

Thanks for the answer Sir but getting the error Undefined function 'alphaShape' for input arguments of type 'double'. Even tough i changed the data type from the double to logical i am getting the same error.

[Steven Lord]

The documentation page for alphaShape indicates it was introduced in release R2014b. Are you using an earlier release?

[ganesh s]

Yes sir, I am using earlier version. How to find it for the older version.

[Sean de Wolski]

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