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ea_conncomp.m
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ea_conncomp.m
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function cc = ea_conncomp(A)
% conncomp Find connected components in 2D grayscale or label image
% Four-connected neighborhood is used.
%
% CC = CONNCOMP(A) returns the connected components CC found in A.
% A is a two dimensional array (image) of sixe I-by-J. Elements in A should
% be positive, if A(i,j)==0 it is handled as background and not assigned to a
% component, and cc.Labels(i,j) = 0. class(A) should be uint8, uint16 or double.
%
% CC is a structure with the following fields:
%
% Connectivity is always 4, two-dimensional four-connected neighborhood
%
% ImageSize Size of A, i.e. [I, J] = size(A).
%
% NumObjects Number of connected components (objects) in A.
%
% PixelIdxList 1-by-NumObjects cell array where the kth element
% in the cell array is a vector containing the linear
% indices of the pixels in the kth object.
%
% NumPixels 1-by-NumObjects array where the kth element is the
% number of pixels in the kth object.
%
% LenBorder 1-by-NumObjects array where the kth element is the
% length of the border (to other components) for the kth object
%
% OutBorder 1-by-NumObjects array where the kth element is the
% length of the border (to outside) for the kth object
%
% Labels I-by-J label image
%
% Example 1
% ---------
% A = [1,2,2,2,2,2; 1,1,2,2,2,2; 1,1,1,2,3,2; 1,1,1,3,3,3; 1,1,1,3,3,3];
% cc = conncomp(A)
% A([1,2,29,30])=0;
% cc = conncomp(A)
%
% See also bwconncomp (in Matlab images toolbox)
% or grayconncomp (an older more complicated version made by K. Skretting,
% and which is usually faster).
%----------------------------------------------------------------------
% Copyright (c) 2012. Karl Skretting. All rights reserved.
% University of Stavanger (Stavanger University), Signal Processing Group
% Mail: karl.skretting@uis.no Homepage: http://www.ux.uis.no/~karlsk/
%
% HISTORY: dd.mm.yyyy
% Ver. 1.0 11.09.2012 Made function
% Ver. 1.1 18.09.2012 Added OutBorder field
% Ver. 2.0 28.09.2012 Included conncomp_mex (to speed up the program)
%----------------------------------------------------------------------
mfile = 'conncomp';
[I,J] = size(A); IJ = I*J;
cc = struct('Connectivity', 4, ...
'ImageSize', [I,J], ...
'NumObjects', 0, ... % fill in this in the end
'PixelIdxList', [], ... % fill in this in the end
'NumPixels', zeros(IJ,1), ... % but these as processing goes on
'LenBorder', zeros(IJ,1), ...
'OutBorder', zeros(IJ,1), ...
'Labels', zeros(I,J) );
% an alternative to function n4 = n4list(n,I,J)
% use more memory, and does not increase speed
% n = repmat((1:I)',1,J) + repmat(I*(0:(J-1)),I,1);
% n41 = [zeros(I,1),n(:,2:J)-I];
% n42 = [zeros(1,J); n(2:I,:)-1];
% n43 = [n(1:(I-1),:)+1; zeros(1,J)];
% n44 = [n(:,1:(J-1))+I, zeros(I,1)];
% clear n
% stack is implemented as a simple array here, not a class
lenStack = 4000; % IJ is large enough!
incStack = 2000;
stack = zeros(IJ,1);
idxStack = 0;
maxStack = 0;
idxPlist = zeros(IJ,1); % idxPlist(k) is index in plist for last pixel in component k
plist = zeros(IJ,1);
count = 0; % number of labeled pixels
p1 = 0; % first pixel in previous (or current) component
k = 0; % current component
while 1 % (p <= IJ)
% find next (first) pixel (in new component) to process,
p = p1 + 1;
if (p > IJ); break; end; % all are processed
while ((cc.Labels(p) > 0) || (A(p) == 0))
p = p + 1;
if (p > IJ); break; end; % all are processed
end
if (p > IJ); break; end; % all are processed
% p is current pixel, here first pixel in new component
p1 = p;
pv = A(p); % current pixel value
k = k + 1; % current component
cc.Labels(p) = k;
while 1 % process this component pixel by pixel
count = count + 1;
plist(count) = p;
cc.NumPixels(k) = cc.NumPixels(k)+1;
% disp([' count=',int2str(count),', p=',int2str(p),...
% ', pv=',int2str(pv),', k=',int2str(k)]);
% add to borders and push neighbors in this component to the stack
for n4 = n4list(p,I,J)
% for n4 = [n41(p),n42(p),n43(p),n44(p)] % is not faster
if n4 % > 0
if (A(n4) == pv) && (cc.Labels(n4) == 0)
% push n4 to stack
idxStack = idxStack + 1;
maxStack = max(maxStack, idxStack);
if (idxStack > lenStack)
stack = [stack; zeros(incStack,1)]; %#ok<AGROW>
lenStack = numel(stack);
end
stack(idxStack) = n4;
cc.Labels(n4) = k; % label it right away
end
if (A(n4) ~= pv)
if A(n4) % ~= 0
cc.LenBorder(k) = cc.LenBorder(k)+1;
else
cc.OutBorder(k) = cc.OutBorder(k)+1;
end
end
else % (n4 == 0)
cc.OutBorder(k) = cc.OutBorder(k)+1;
end
end
if (idxStack == 0); break; end
% next pixel
p = stack(idxStack);
idxStack = idxStack - 1;
end % loop for this component
% finishing the component
idxPlist(k) = count; % last pixel for component k in plist
end
cc.NumObjects = k;
cc.NumPixels = cc.NumPixels(1:k);
cc.LenBorder = cc.LenBorder(1:k);
cc.OutBorder = cc.OutBorder(1:k);
cc.PixelIdxList = cell(k,1);
n = 1;
for k=1:cc.NumObjects
cc.PixelIdxList{k} = plist(n:idxPlist(k));
% cc.PixelIdxList{k} = sort(plist(n:idxPlist(k))); % ordered perhaps ??
n = idxPlist(k)+1;
end
function n4 = n4list(n,I,J)
n4 = [n-I, n-1, n+1, n+I];
if (n <= I); n4(1) = 0; end;
if (rem(n-1,I) == 0); n4(2) = 0; end;
if (rem(n,I) == 0); n4(3) = 0; end;
if (n > (J-1)*I); n4(4) = 0; end;
% n4 = nonzeros(n4);
return