How does this function "regionprops" to find the orientation of any object?

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marian wagdy
marian wagdy 2013-10-22
评论： Simone conigliaro 2017-8-31
How does this function "regionprops" to find the orientation of any object?
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Image Analyst
Image Analyst 2017-8-29
You'd use [y, x, z] = find(binaryImage) and then pass them into pca(). I don't have a demo for exactly that, but I'm attaching a demo of using pca to determine axes for a color gamut, for whatever that's worth.
Simone conigliaro
Simone conigliaro 2017-8-31
thanks for your replay. i have another question to ask you. i would like to know what is the method that regionprops label the object? because i used this function to get centroid and volume(sum voxel for each blob)but i don't understand this aspect. thank you very much

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David Legland
David Legland 2013-10-22
Hi Marian,
the code is in the regionprops function, you can access it via "edit regionprops", and checking the "ComputeEllipseParams" function.
The principle is to compute the inertia ellipse of a shape. It is obtained by computing normalised centered moments. The matrix of Inertia is obtained from the normalised moments of order 2 : Ixx, Ixy, and Iyy. By extracting eigen values and eigen vectors of the inertia matrix, it is possible to obtain the direction of the first eigen vector, that is converted into angle.

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Image Analyst
Image Analyst 2013-10-22
It fits the blob to an ellipse and then gets the angle of the major axis of the ellipse from the horizontal. Note: the major axis of the fitted ellipse is not the farthest distance between two points in the blob.

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