Add Lanczos5

Former-commit-id: dd83c793aea242e533c04f1ed0526319e3608c7b
Former-commit-id: 27cfda9e96a3148eb9345992050880cfa830dbd5
Former-commit-id: 4d4eb638fed3de06a05eca59d161acdd2d389b7f

src/ImageProcessor/Samplers/Resamplers/Lanczos5Resampler.cs

@@ -0,0 +1,33 @@
+// <copyright file="Lanczos5Resampler.cs" company="James South">
+// Copyright © James South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessor.Samplers
+{
+    /// <summary>
+    /// The function implements the Lanczos kernel algorithm as described on
+    /// <see href="https://en.wikipedia.org/wiki/Lanczos_resampling#Algorithm">Wikipedia</see>
+    /// </summary>
+    public class Lanczos5Resampler : IResampler
+    {
+        /// <inheritdoc/>
+        public double Radius => 5;
+
+        /// <inheritdoc/>
+        public double GetValue(double x)
+        {
+            if (x < 0)
+            {
+                x = -x;
+            }
+
+            if (x < 5)
+            {
+                return ImageMaths.SinC(x) * ImageMaths.SinC(x / 5f);
+            }
+
+            return 0;
+        }
+    }
+}

tests/ImageProcessor.Tests/Processors/Samplers/SamplerTests.cs

@@ -17,6 +17,7 @@ namespace ImageProcessor.Tests
                 { "Triangle", new TriangleResampler() },
                 { "Box", new BoxResampler() },
                 { "Lanczos3", new Lanczos3Resampler() },
+                { "Lanczos5", new Lanczos5Resampler() },
                 { "Lanczos8", new Lanczos8Resampler() },
                 { "MitchellNetravali", new MitchellNetravaliResampler() },
                 { "Hermite", new HermiteResampler() },