tc_expandVoxelSelection.m

function [voxel_list_expanded]=tc_expandVoxelSelection(dim_of_volume,voxel_list_to_expand,expand_factors)
%% [voxel_list_expanded]=tc_expandVoxelSelection(dim_of_volume,voxel_list_to_expand,expand_factors)
% selects voxel around a given set of voxel. E.g. if a 3x4x2 box around central 1
% voxel V in a 10x10x10 volume is asked to be selected, then call
% V_new = tc_expandVoxelSelection([10,10,10],V,[3,4,2]);
% V_new will contain 9 indices of the initial volume centering around V
%
% note: 
% - all indices that are smaller than 1 will be set to 1
% - all indices in a dimension that are greater than this dimension will be
% set to the size of this dimension
% - voxel_list_to_expand is a vector of voxel indices (not boolean indices)
% -> use (find(boolean_indices) to provide valid values)
% - expand_factors can be a scalar (equal in every direction or a vector of 
% size 1x Ndim). In the second case the expansion in the respective
% direction can be choosen independently
% - the expansion factor will be added to both sides of the center voxel. 
% Hence a 3x3x3 box around a voxel will be created using an expansion
% factor of 1 -> [center - 1, center, center + 1]
%
% BTW: the method below is hundreds of times (~500-1000) faster than a for
% loop. The bottleneck however is now memory. So
% selecting an expansion factor of > 4 will result in a massive memory
% explosion

if size(voxel_list_to_expand,1)>size(voxel_list_to_expand,2)
   voxel_list_to_expand=voxel_list_to_expand'; 
end

if numel(dim_of_volume)~=numel(expand_factors) && numel(expand_factors)~=1
    error('Please provide valid expansion vector')
end

if numel(expand_factors)==1
    expand_factors=ones(size(dim_of_volume))*expand_factors;
end

if numel(dim_of_volume)==2
    [seedX,seedY]=ind2sub(dim_of_volume,voxel_list_to_expand);
    add_those=repmat(combvec(-expand_factors(1):1:expand_factors(1),-expand_factors(2):1:expand_factors(2)),1,size(voxel_list_to_expand,2));
    inds=repmat([seedX;seedY],1,size(add_those,2)/size(voxel_list_to_expand,2))+add_those;
elseif numel(dim_of_volume)==3
    [seedX,seedY,seedZ]=ind2sub(dim_of_volume,voxel_list_to_expand);
    
    % compute all possible deviations from the center voxel
    add_those=repmat(combvec(-expand_factors(1):1:expand_factors(1),-expand_factors(2):1:expand_factors(2),-expand_factors(3):1:expand_factors(3)),1,size(voxel_list_to_expand,2));
    
    % add all those combinations
    inds=repmat([seedX;seedY;seedZ],1,size(add_those,2)/size(voxel_list_to_expand,2))+add_those;
else
    error('please provide valid dimensions')
end

for n=1:numel(dim_of_volume)
    inds(n,inds(n,:)>dim_of_volume(n))=dim_of_volume(n);
end
inds(inds<1)=1;

if numel(dim_of_volume)==2
    voxel_list_expanded=sub2ind(dim_of_volume,inds(1,:),inds(2,:));
else
    voxel_list_expanded=sub2ind(dim_of_volume,inds(1,:),inds(2,:),inds(3,:));
end