propagates channel names when creating new image from parent

Author: dlegland

src/@Image/Image.m

@@ -283,6 +283,12 @@ function copyFields(obj, that)
         if ~isempty(that.UnitName)
             obj.UnitName     = that.UnitName;
         end
+        
+        % copy channel names if images have same number of channels
+        if size(obj.Data,4) == size(that.Data,4) && ~isempty(that.ChannelNames)
+            obj.ChannelNames = that.ChannelNames;
+        end
+        
         if ~isempty(that.AxisNames)
             obj.AxisNames(1:nd)  = that.AxisNames(1:nd);
         end

tests/image/test_crop.m

@@ -25,3 +25,15 @@ function test_2d(testCase)  %#ok<*DEFNU>
 img2 = img.crop([51 200 51 150]);
 
 assertEqual(testCase, [150 100], size(img2));
+
+
+function test_keepChannelNames(testCase)  %#ok<*DEFNU>
+
+img = Image.read('peppers.png');
+clearCalibration(img);
+img.ChannelNames = {'Rot', 'Gruen', 'Blau'};
+
+img2 = img.crop([51 200 51 150]);
+
+assertEqual(testCase, [150 100], size(img2));
+assertEqual(testCase, img2.ChannelNames, img.ChannelNames);