How to turn all parts of a binary image outside of an ellipse to zero.
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I have the centeroid, major axis length, minor axis length, and orientation of an ellipse and I want to make everything outside of the ellipse on a binary image 0/black. How would I approach this?
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Answers (1)
Matt J
on 23 Dec 2019
Edited: Matt J
on 23 Dec 2019
Express the elliptical region in equality form
(x-c).'*Q*(x-c)<=1
where c is the centroid, Q is the 2x2 matrix,
Q=R.'*diag(1./[a,b]).^2*R;
and R is a 2x2 rotation matrix.
Then test all pixels to see which satisfy the inequality. This can be vectorized as follows,
[x,y]=ndgrid((1:Nx)-cx,(1:Ny)-cy);
delta=[x(:),y(:)].';
mask= all( sum( (Q*delta).*delta )<=1 );
mask=reshape(mask, Nx,Ny);
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