better support of areaOpening for label images

Author: dlegland

src/@Image/areaOpening.m

@@ -34,15 +34,22 @@
 % Created: 2011-11-08,    using Matlab 7.9.0.529 (R2009b)
 % Copyright 2011 INRA - Cepia Software Platform.
 
+% check input arguments
+if nargin < 2
+    error('Image:areaOpening', 'Need to specify the minimum number of pixels');
+end
+
+% force image to be label
 if isLabelImage(obj)
     data = obj.Data;
+    res = zeros(size(obj.Data), 'like', obj.Data);
 
 elseif isBinaryImage(obj)
     % if image is binary compute labeling
 
     % first determines connectivity to use
     conn = 4;
-    if obj.Dimension == 3
+    if ndims(obj) == 3
         conn = 6;
     end
     if ~isempty(varargin)
@@ -51,6 +58,7 @@
 
     % appply labeling, get result as 2D or 3D matrix
     data = labelmatrix(bwconncomp(obj.Data, conn));
+    res = false(size(obj.Data), 'like', obj.Data);
 
 else
     error('Image:areaOpening', 'Requires binary or label image');
@@ -62,7 +70,10 @@
 
 % select regions with areas greater than threshold
 inds = find(areas >= value);
-data = ismember(data, inds);
+
+% keep only the pixels belonging to the selected regions
+mask = ismember(data, inds);
+res(mask) = data(mask);
 
 % create new image
-res = Image.create('data', data, 'parent', obj, 'type', 'binary');
+res = Image.create('data', res, 'parent', obj);

tests/image/test_areaOpening.m

@@ -0,0 +1,58 @@
+function tests = test_areaOpening
+% Test suite for the file areaOpening.
+%
+%   Test suite for the file areaOpening
+%
+%   Example
+%   test_areaOpening
+%
+%   See also
+%     areaOpening
+
+% ------
+% Author: David Legland
+% e-mail: david.legland@inrae.fr
+% Created: 2020-11-25,    using Matlab 9.8.0.1323502 (R2020a)
+% Copyright 2020 INRAE - BIA-BIBS.
+
+tests = functiontests(localfunctions);
+
+function test_Simple_binary(testCase) %#ok<*DEFNU>
+% Test call of function without argument.
+
+% create default label image
+data = zeros(8, 8, 'uint8');
+data(2, 2) = 2;
+data(2, 4:7) = 4;
+data(4:7, 2) = 5;
+data(4:7, 4:7) = 8;
+img = Image(data>0);
+
+imgOp = areaOpening(img, 3);
+
+% expect to keep three connected components
+lbl = componentLabeling(imgOp, 4);
+assertEqual(testCase, max(lbl), 3);
+
+
+function test_Simple_label(testCase) %#ok<*DEFNU>
+% Test call of function without argument.
+
+% create default label image
+data = zeros(8, 8, 'uint8');
+data(2, 2) = 2;
+data(2, 4:7) = 4;
+data(4:7, 2) = 5;
+data(4:7, 4:7) = 8;
+img = Image(data, 'Type', 'Label');
+
+imgOp = areaOpening(img, 3);
+
+% expect result to be a label image
+assertTrue(testCase, isLabelImage(imgOp));
+
+% expect to keep three connected components
+% (recompute labels)
+labelList = unique(imgOp(imgOp>0));
+assertEqual(testCase, length(labelList), 3);
+