keepMaxObj.m

function Imx = keepMaxObj(X)
%Function to keep only the maximum sized (biggest) object in an image
%SCd 11/30/2010
%
%Updates:
%   -02/03/2011: Added ability to handle an image directly
%
%Usage:
%   Imx = keepMaxObj(CC);
%   Imx = keepMaxObj(V);
%
%Input Arguments:
%   -CC: Connected components returned from bwconncomp
%   -V: Logical image with parts you want true
%   
%Output Arguments:
%   -Imx: Logical volume with only the biggest object left true.
%
%See Also: bwconncomp
%
    %Error checking:
    assert(islogical(X)||isstruct(X),'The first input argument is expected to be a struct or a logical');
    if isstruct(X)
        CC = X;
        parts = {'PixelIdxList','ImageSize'};
        assert(all(ismember(parts,fieldnames(CC))),'CC is expected to be the output from bwconncomp');
    else
        CC = bwconncomp(X);
    end  
    clear X;
    %Preallocate and find number of voxels/object
    Nvox = zeros(CC.NumObjects,1);
    for ii = 1:CC.NumObjects
        Nvox(ii) = numel(CC.PixelIdxList{ii});
    end
    %Find the biggest object's index, warn and save all if there are multiples
    [mx,midx] = max(Nvox);
    more_than1_max = sum(mx==Nvox);
    if more_than1_max > 1
        midx = find(mx == Nvox);
        warning('Multiple:Maxima', 'There were %i objects with the maximum size.\n  They are all left on!',more_than1_max);
    end    
    %Create the final image
    Imx = false(CC.ImageSize);
    Imx([CC.PixelIdxList{midx}]) = true;
end