function vs = voxsize(img)
%  voxsize -- get voxel sizes in world (mm) coordinates
% vs = voxsize(img)
%
% See also: world_bb, resize_img

% By Ged Ridgway -- email bugs to drc.spm@gmail.com

% Check spm version:
if exist('spm_select','file') % should be true for spm5
    spm5 = 1;
elseif exist('spm_get','file') % should be true for spm2
    spm5 = 0;
else
    error('Can''t find spm_get or spm_select; please add SPM to path')
end

% prompt for missing arguments
if ( ~exist('img','var') || isempty(img) )
    if spm5
        img = spm_select(1, 'image', 'Choose image');
    else
        img = spm_get(1, 'img', 'Choose image');
    end
end

V = spm_vol(img); % (okay if img is already an SPM vol)

prm = spm_imatrix(V.mat);
vs = prm(7:9);