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function vol = thinbinvol(vol, layer, nobd)
%
% vol=thinbinvol(vol,layer,nobd)
%
% thinning a binary volume by a given pixel width
% this is similar to bwmorph(vol,'thin',n) except
% this does it in 3d and only run thinning for
% non-zero elements (and hopefully faster)
%
% author: Qianqian Fang, <q.fang at neu.edu>
%
% input:
% vol: a volumetric binary image
% layer: number of iterations for the thickenining
% nobd: (optional) if set to 1, boundaries will not
% erode. if not given, nobd=0.
%
% output:
% vol: the volume image after the thinning operations
%
% -- this function is part of iso2mesh toolbox (http://iso2mesh.sf.net)
%
dim = size(vol);
dxy = dim(1) * dim(2);
fulllen = prod(dim);
if (nargin < 3)
nobd = 0;
end
if (nobd == 1)
bdmask = vol;
if (ndims(vol) == 2)
bdmask(2:end - 1, 2:end - 1) = 0;
elseif (ndims(vol) == 3)
bdmask(2:end - 1, 2:end - 1, 2:end - 1) = 0;
end
end
for i = 1:layer
idx = find(~vol);
idxnew = [idx + 1; idx - 1; idx + dim(1); idx - dim(1); idx + dxy; idx - dxy];
idxnew = idxnew(find(idxnew > 0 & idxnew < fulllen));
vol(idxnew) = 0;
if (nobd)
vol = vol | bdmask;
end
end
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