STREL3D creates a 3D sphere as a structuring element. Three-dimensional structuring elements are much better for morphological reconstruction and operations of 3D datasets. Otherwise the traditional MATLAB "strel" function will only operate on a slice-by-slice approach. This function uses the aribtrary neighborhood for "strel."
sesize - desired diameter size of a sphere (any positive integer)
the structuring element as a strel class (can be used directly for imopen, imclose, imerode, etc)
2014/09/26 - LX
2014/09/27 - simplification by Jan Simon
Luke Xie (2021). 3D structuring element (sphere) (https://www.mathworks.com/matlabcentral/fileexchange/47937-3d-structuring-element-sphere), MATLAB Central File Exchange. Retrieved .
I've found it useful to use ellipsoidal elements. This seems to work. xr,yr,zr are the radii of the ellipsoid in each direction. Might need some refining?
%% 3D ellipsoid
xbase = 1:2*xr+1;
ybase = 1:2*yr+1;
zbase = 1:2*zr+1;
[xm,ym,zm] = ndgrid( xbase , ybase , zbase) ;
xc = xr + 1;
yc = yr + 1;
zc = zr + 1;
mask = ( ((xm-xc).^2/(xr.^2)) + ((ym-yc).^2/(yr.^2)) + ((zm-zc).^2/(zr.^2)) <= 1 ) ;
se = strel('arbitrary',mask);
I received the same error and cannot get around it. Seems like 3D structuring elements are not supported by gpuArray. If you discover anything in the future, please share.
Very useful code. But when I tried to use it with the GPU array I encountered this hurdle:
'gpuarrayIM must be a gpuArray of type uint8 or logical. When used with a gpuarray, the structuring element must be flat and two-dimensional.'
Any idea if there is a way to sneak a 3D strel onto the gpu?
Jan Simon -
Excellent catch. Your simplification is ~1.2x faster. The code is now updated.
sw = (sesize-1)/2;
ses2 = ceil(sesize/2);
[y,x,z] = meshgrid(-sw:sw, -sw:sw, -sw:sw);
m = sqrt(x.^2 + y.^2 + z.^2);
b = (m <= m(ses2, ses2, sesize));
se = strel('arbitrary', b);
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