--- a/NEWS
+++ b/NEWS
@@ -112,6 +112,10 @@
  ** The transform option of imtophat has been removed (it was deprecated
     in version 2.0.0) in favour of using imbothat.
 
+ ** The function bwconncomp now returns the indices for each element in each
+    object, no longer the indices for the elements in the object boundaries
+    only. The connectivity default was changed to 8.
+
  ** Other functions that have been changed for smaller bugfixes, increased
     Matlab compatibility, or performance:
 
@@ -123,6 +127,7 @@
     number of dimensions:
 
       bestblk
+      bwconncomp
       col2im
       colfilt
       im2col

--- a/inst/bwconncomp.m
+++ b/inst/bwconncomp.m
@@ -1,4 +1,5 @@
 ## Copyright (C) 2010 Søren Hauberg <soren@hauberg.org>
+## Copyright (C) 2013 Carnë Draug <carandraug@octave.org>
 ##
 ## This program is free software; you can redistribute it and/or modify it under
 ## the terms of the GNU General Public License as published by the Free Software
@@ -14,56 +15,110 @@
 ## this program; if not, see <http://www.gnu.org/licenses/>.
 
 ## -*- texinfo -*-
-## @deftypefn {Function File} {@var{cc} = } bwconncomp (@var{BW})
-## @deftypefnx {Function File} {@var{cc} = } bwconncomp (@var{BW}, @var{connectivity})
-## Trace the boundaries of objects in a binary image.
+## @deftypefn  {Function File} {@var{cc} =} bwconncomp (@var{bw})
+## @deftypefnx {Function File} {@var{cc} =} bwconncomp (@var{bw}, @var{conn})
+## Find connected objects.
 ##
-## @code{bwconncomp} traces the boundaries of objects in a binary image @var{BW}
-## and returns information about them in a structure with the following fields.
+## Elements from the matrix @var{bw}, belong to an object if they have a
+## non-zero value.  The output @var{cc} is a structure with information about
+## each object;
 ##
-## @table @t
-## @item Connectivity
-## The connectivity used in the boundary tracing.
-## @item ImageSize
-## The size of the image @var{BW}.
-## @item NumObjects
-## The number of objects in the image @var{BW}.
-## @item PixelIdxList
+## @table @qcode
+## @item "Connectivity"
+## The connectivity used in the boundary tracing. This may be different from
+## the input argument, e.g., if @var{conn} is defined as a matrix of 1s and
+## size 3x3, the @qcode{"Connectivity"} value will still be 8.
+## @item "ImageSize"
+## The size of the matrix @var{bw}.
+## @item "NumObjects"
+## The number of objects in the image @var{bw}.
+## @item "PixelIdxList"
+## A cell array with linear indices for each element of each object in @var{bw}
 ## A cell array containing where each element corresponds to an object in @var{BW}.
 ## Each element is represented as a vector of linear indices of the boundary of
 ## the given object.
 ## @end table
 ##
-## The connectivity used in the tracing is by default 4, but can be changed
-## by setting the @var{connectivity} input parameter to 8. Sadly, this is not
-## yet implemented.
-## @seealso{bwlabel, bwboundaries, ind2sub}
+## Element connectivity @var{conn}, to define the size of objects, can be
+## specified with a numeric scalar (number of elements in the neighborhood):
+##
+## @table @samp
+## @item 4 or 8
+## for 2 dimensional matrices;
+## @item 6, 18 or 26
+## for 3 dimensional matrices;
+## @end table
+##
+## or with a binary matrix representing a connectivity array.  Defaults to
+## @code{conndef (ndims (@var{bw}), "maximal")} which is equivalent to
+## @var{conn} of 8 and 26 for 2 and 3 dimensional matrices respectively.
+##
+## @seealso{bwlabel, bwlabeln, bwboundaries, ind2sub, regionprops}
 ## @end deftypefn
 
-function CC = bwconncomp (bw, N = 4)
-  ## Check input
-  if (nargin < 1)
-    error ("bwconncomp: not enough input arguments");
-  endif
-  if (!ismatrix (bw) || ndims (bw) != 2)
-    error ("bwconncomp: first input argument must be a NxM matrix");
+function CC = bwconncomp (bw, N)
+
+  if (nargin < 1 || nargin > 2)
+    print_usage ();
+  elseif (! ismatrix (bw) || ! (isnumeric (bw) || islogical (bw)))
+    error ("bwconncomp: BW must be an a numeric matrix");
   endif
-  if (!isscalar (N) || !any (N == [4])) #, 8]))
-    error ("bwconncomp: second input argument must be 4");
+  if (nargin < 2)
+    ## Defining default connectivity here because it's dependent
+    ## on the first argument
+    N = conndef (ndims (bw), "maximal");
   endif
-  
-  ## Trace boundaries
-  B = bwboundaries (bw, N);
+  [conn, N] = make_conn ("bwconncomp", 2, ndims (bw), N);
+
 
-  ## Convert from (x, y) index to linear indexing
-  P = cell (1, numel (B));
-  for k = 1:numel (B)
-    P{k} = sub2ind (size (bw), B{k}(:, 1), B{k}(:, 2));
-  endfor
+  [bw, n_obj] = bwlabeln (logical (bw), conn);
+  ## We should probably implement this as the first part of bwlabeln
+  ## as getting the indices is the first part of its code. Here we are
+  ## just reverting the work already done.
+  P = arrayfun (@(x) find (bw == x), 1:n_obj, "UniformOutput", false);
 
   ## Return result
   CC = struct ("Connectivity",  N,
                "ImageSize",     size (bw),
-               "NumObjects",    numel (B),
+               "NumObjects",    n_obj,
                "PixelIdxList",  {P});
 endfunction
+
+%!test
+%! a = rand (10) > 0.5;
+%! cc = bwconncomp (a, 4);
+%! assert (cc.Connectivity, 4)
+%! assert (cc.ImageSize, [10 10])
+%!
+%! b = false (10);
+%! for i = 1:numel (cc.PixelIdxList)
+%!   b(cc.PixelIdxList{i}) = true;
+%! endfor
+%! assert (a, b)
+
+%!test
+%! a = rand (10, 13) > 0.5;
+%! cc = bwconncomp (a, 4);
+%! assert (cc.ImageSize, [10 13])
+%!
+%! b = false (10, 13);
+%! for i = 1:numel (cc.PixelIdxList)
+%!   b(cc.PixelIdxList{i}) = true;
+%! endfor
+%! assert (a, b)
+
+%!test
+%! a = rand (15) > 0.5;
+%! conn_8 = bwconncomp (a, 8);
+%! assert (conn_8, bwconncomp (a))
+%! assert (conn_8, bwconncomp (a, ones (3)))
+%! assert (conn_8.Connectivity, 8)
+%! assert (bwconncomp (a, ones (3)).Connectivity, 8)
+%! assert (bwconncomp (a, [0 1 0; 1 1 1; 0 1 0]).Connectivity, 4)
+
+## test that PixelIdxList is a row vector
+%!test
+%! a = rand (40, 40) > 0.2;
+%! cc = bwconncomp (a, 4);
+%! assert (rows (cc.PixelIdxList), 1)
+%! assert (columns (cc.PixelIdxList) > 1)

--- a/inst/private/make_conn.m
+++ b/inst/private/make_conn.m
@@ -32,37 +32,29 @@
 ## @code{conndef (ndims (@var{bw}), "maximal")} which is equivalent to
 ## @var{conn} of 8 and 26 for 2 and 3 dimensional matrices respectively.
 
-function conn = make_conn (func, arg_pos, n_dims, conn)
+function [conn, N] = make_conn (func, arg_pos, n_dims, conn)
+
+  persistent conn_4  = logical ([0 1 0; 1 1 1; 0 1 0]);
+  persistent conn_8  = true (3);
+  persistent conn_6  = get_conn_6 ();
+  persistent conn_18 = get_conn_18 ();
+  persistent conn_26 = true (3, 3, 3);
 
   iptcheckconn (conn, func, "CONN", arg_pos);
   if (isscalar (conn))
+    N = conn;
     if (n_dims == 2)
-      if (conn == 4)
-        conn = [0 1 0
-                1 1 1
-                0 1 0];
-      elseif (conn == 8)
-        conn = [1 1 1
-                1 1 1
-                1 1 1];
+      if     (conn == 4), conn = conn_4;
+      elseif (conn == 8), conn = conn_8;
       else
         error ("%s: CONN must have a value of 4 or 8 for 2 dimensional matrices",
                func);
       endif
 
     elseif (n_dims == 3)
-      if (conn == 6)
-        conn = false (3, 3, 3);
-        conn(:,2,2) = true;
-        conn(2,:,2) = true;
-        conn(2,2,:) = true;
-      elseif (conn == 18)
-        conn = false (3, 3, 3);
-        conn(2,:,:) = true;
-        conn(:,2,:) = true;
-        conn(:,:,2) = true;
-      elseif (conn == 26)
-        conn = true (3, 3, 3);
+      if     (conn == 6),  conn = conn_6;
+      elseif (conn == 18), conn = conn_18;
+      elseif (conn == 26), conn = conn_26;
       else
         error (["%s: CONN must have a value of 6, 18, or 26 for 3 " ...
                 "dimensional matrices"], func);
@@ -71,5 +63,27 @@
       error (["%s: CONN must be defined as a binary matrix for matrices " ...
               "with more than 3 dimensions"], func);
     endif
+  elseif (nargout > 1)
+    if     (isequal (conn, conn_4)),  N = 4;
+    elseif (isequal (conn, conn_8)),  N = 8;
+    elseif (isequal (conn, conn_6)),  N = 6;
+    elseif (isequal (conn, conn_18)), N = 18;
+    elseif (isequal (conn, conn_26)), N = 26;
+    else,                             N = conn;
+    endif
   endif
 endfunction
+
+function conn = get_conn_6 ()
+  conn = false (3, 3, 3);
+  conn(:,2,2) = true;
+  conn(2,:,2) = true;
+  conn(2,2,:) = true;
+endfunction
+
+function conn = get_conn_18 ()
+  conn = false (3, 3, 3);
+  conn(2,:,:) = true;
+  conn(:,2,:) = true;
+  conn(:,:,2) = true;
+endfunction