How do I make 3D sphere for convolution?
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Lieke Pullen
el 12 de En. de 2022
Comentada: Lieke Pullen
el 13 de En. de 2022
Hi all,
I want to make a 3D sphere where the x, y and z coordinates are being solved in a 3D array, so I can convolute this with a kernel I have. But, I don't seem to both save the coordinates and get the shape right at the same time. I have the following code:
figure;
half=50;
for k=1:100
for j=1:100
for i=1:100
mesh_sphere(i,j,k)=((i-half).^2)+((j-half).^2)+((k-half).^2);
end
end
surf(mesh_sphere(:,:,k));
hold on
end
hold off
After this, I also want to use other shapes that I can test my kernel on, such as a hollow sphere and an ellipsoid. How can I make those and also same them in a 3D array? Thank you in advance!
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Rik
el 12 de En. de 2022
If you want a sphere in a 3D array, you should probably do something like this:
array_width=21;%must be odd
radius=5;%must be smaller than half the array width for the sphere to fit
a=(array_width-1)/2;
a=linspace(-a,a,array_width);
[X,Y,Z]=meshgrid(a);
solid_sphere= sqrt(X.^2 + Y.^2 + Z.^2) <= radius;
For a shell you can repeat this with two radii and use the or operator |. For an elipsoid you need you can scale the coordinate values in each direction according to the partial radius you want.
9 comentarios
Image Analyst
el 13 de En. de 2022
Editada: Image Analyst
el 13 de En. de 2022
@Lieke Pullen like I showed in my answer below, the strel() function creates the sphere in one line of code. The convolution is also done in one line of code.
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Image Analyst
el 12 de En. de 2022
Editada: Image Analyst
el 13 de En. de 2022
SE = strel('sphere',r) % creates a 3-D spherical structuring element whose radius is r pixels.
out = convn(inputImage, SE.Neighborhood);
3 comentarios
Rik
el 12 de En. de 2022
I don't remember this object notation. Admittedly, I haven't used this function in years, but I will look up this function in the release notes to see whether I forgot, or if they changed it.
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