Added method to remove the settings to IKmeansSettingsExtensions.

src/Magick.NET/Shared/Extensions/IKmeansSettingsExtensions.cs

@@ -29,5 +29,11 @@ public static void SetImageArtifacts(this IKmeansSettings self, IMagickImage<Qua
             if (!string.IsNullOrEmpty(self.SeedColors))
                 image.SetArtifact("kmeans:seed-colors", self.SeedColors);
         }
+
+        public static void RemoveImageArtifacts(this IKmeansSettings self, IMagickImage<QuantumType> image)
+        {
+            if (!string.IsNullOrEmpty(self.SeedColors))
+                image.RemoveArtifact("kmeans:seed-colors");
+        }
     }
 }

src/Magick.NET/Shared/MagickImage.cs

@@ -3747,6 +3747,8 @@ public void Kmeans(IKmeansSettings settings)
             settings.SetImageArtifacts(this);
 
             _nativeInstance.Kmeans(settings.NumberColors, settings.MaxIterations, settings.Tolerance);
+
+            settings.RemoveImageArtifacts(this);
         }
 
         /// <summary>

tests/Magick.NET.Tests/Shared/Extensions/IKmeansSettingsExtensionsTests/TheRemoveImageArtifactsMethod.cs

@@ -0,0 +1,41 @@
+// Copyright 2013-2020 Dirk Lemstra <https://github.com/dlemstra/Magick.NET/>
+//
+// Licensed under the ImageMagick License (the "License"); you may not use this file except in
+// compliance with the License. You may obtain a copy of the License at
+//
+//   https://www.imagemagick.org/script/license.php
+//
+// Unless required by applicable law or agreed to in writing, software distributed under the
+// License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+// either express or implied. See the License for the specific language governing permissions
+// and limitations under the License.
+
+using ImageMagick;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Magick.NET.Tests
+{
+    public partial class IKmeansSettingsExtensionsTests
+    {
+        [TestClass]
+        public class TheRemoveImageArtifactsMethod
+        {
+            [TestMethod]
+            public void ShouldRemoveSeedColors()
+            {
+                using (var image = new MagickImage())
+                {
+                    var settings = new KmeansSettings()
+                    {
+                        SeedColors = "red;blue",
+                    };
+
+                    settings.SetImageArtifacts(image);
+                    settings.RemoveImageArtifacts(image);
+
+                    Assert.IsNull(image.GetArtifact("kmeans:seed-colors"));
+                }
+            }
+        }
+    }
+}

tests/Magick.NET.Tests/Shared/Extensions/IKmeansSettingsExtensionsTests/TheSetImageArtifactsMethod.cs

@@ -0,0 +1,53 @@
+// Copyright 2013-2020 Dirk Lemstra <https://github.com/dlemstra/Magick.NET/>
+//
+// Licensed under the ImageMagick License (the "License"); you may not use this file except in
+// compliance with the License. You may obtain a copy of the License at
+//
+//   https://www.imagemagick.org/script/license.php
+//
+// Unless required by applicable law or agreed to in writing, software distributed under the
+// License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+// either express or implied. See the License for the specific language governing permissions
+// and limitations under the License.
+
+using ImageMagick;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Magick.NET.Tests
+{
+    public partial class IKmeansSettingsExtensionsTests
+    {
+        [TestClass]
+        public class TheSetImageArtifactsMethod
+        {
+            [TestMethod]
+            public void ShouldNotSetTheAttributesWhenTheyAreNotSpecified()
+            {
+                using (var image = new MagickImage())
+                {
+                    var settings = new KmeansSettings();
+
+                    settings.SetImageArtifacts(image);
+
+                    Assert.IsNull(image.GetArtifact("kmeans:seed-colors"));
+                }
+            }
+
+            [TestMethod]
+            public void ShouldSetSeedColors()
+            {
+                using (var image = new MagickImage())
+                {
+                    var settings = new KmeansSettings()
+                    {
+                        SeedColors = "red;blue",
+                    };
+
+                    settings.SetImageArtifacts(image);
+
+                    Assert.AreEqual("red;blue", image.GetArtifact("kmeans:seed-colors"));
+                }
+            }
+        }
+    }
+}