diff --git a/UVtools.Core/EmguCV/EmguContours.cs b/UVtools.Core/EmguCV/EmguContours.cs
index 397d025..6688094 100644
--- a/UVtools.Core/EmguCV/EmguContours.cs
+++ b/UVtools.Core/EmguCV/EmguContours.cs
@@ -108,6 +108,33 @@ namespace UVtools.Core.EmguCV
             return result;
         }
 
+        /// <summary>
+        /// Gets contours that are positive pixels and group them by areas
+        /// Only compatible with Tree type of contour detection
+        /// </summary>
+        /// <returns></returns>
+        public static List<VectorOfVectorOfPoint> GetPositiveContoursInGroups(VectorOfVectorOfPoint contours, int[,] hierarchy)
+        {
+            var result = new List<VectorOfVectorOfPoint>();
+            var vectorSize = contours.Size;
+            var processedContours = new bool[vectorSize];
+            for (int i = 0; i < vectorSize; i++)
+            {
+                if (processedContours[i]) continue;
+                processedContours[i] = true;
+                var index = result.Count;
+                result.Add(new VectorOfVectorOfPoint(contours[i]));
+                for (int n = i + 1; n < vectorSize; n++)
+                {
+                    if (processedContours[n] || hierarchy[n, EmguContour.HierarchyParent] != i) continue;
+                    processedContours[n] = true;
+                    result[index].Push(contours[n]);
+                }
+            }
+
+            return result;
+        }
+
         /// <summary>
         /// Gets contours inside contours that are black pixels and group them by areas
         /// Only compatible with Tree type of contour detection
@@ -123,12 +150,13 @@ namespace UVtools.Core.EmguCV
                 if (processedContours[i]) continue;
                 processedContours[i] = true;
                 if (hierarchy[i, EmguContour.HierarchyParent] == -1) continue;
+                var index = result.Count;
                 result.Add(new VectorOfVectorOfPoint(contours[i]));
                 for (int n = i + 1; n < vectorSize; n++)
                 {
                     if (processedContours[n] || hierarchy[n, EmguContour.HierarchyParent] != i) continue;
                     processedContours[n] = true;
-                    result[^1].Push(contours[n]);
+                    result[index].Push(contours[n]);
                 }
             }
 
diff --git a/UVtools.WPF/MainWindow.LayerPreview.cs b/UVtools.WPF/MainWindow.LayerPreview.cs
index cc2ec8a..f1306e4 100644
--- a/UVtools.WPF/MainWindow.LayerPreview.cs
+++ b/UVtools.WPF/MainWindow.LayerPreview.cs
@@ -1214,22 +1214,7 @@ namespace UVtools.WPF
                         using var vec = EmguContours.GetContoursInside(LayerCache.LayerContours, LayerCache.LayerContourHierarchy, operation.Location);
                         if (vec.Size > 0) CvInvoke.DrawContours(LayerCache.ImageBgr, vec, -1, new MCvScalar(color.B, color.G, color.R), -1);
 
-                        /*var hollowGroups = new List<VectorOfVectorOfPoint>();
-                        var processedContours = new bool[LayerCache.LayerContours.Size];
-                        for (int i = 0; i < LayerCache.LayerContours.Size; i++)
-                        {
-                            if(processedContours[i]) continue;
-                            processedContours[i] = true;
-                            if (LayerCache.LayerContourHierarchy[i, EmguContour.HierarchyParent] == -1) continue;
-                            hollowGroups.Add(new VectorOfVectorOfPoint(LayerCache.LayerContours[i]));
-                            for (int n = i + 1; n < LayerCache.LayerContours.Size; n++)
-                            {
-                                if (processedContours[n] || LayerCache.LayerContourHierarchy[n, EmguContour.HierarchyParent] != i) continue;
-                                processedContours[n] = true;
-                                hollowGroups[^1].Push(LayerCache.LayerContours[n]);
-                            }
-
-                        }
+                        /*var hollowGroups = EmguContours.GetPositiveContoursInGroups(LayerCache.LayerContours, LayerCache.LayerContourHierarchy);
 
                         foreach (var vec in hollowGroups)
                         {