Add Lanczos3

Former-commit-id: ffc9b65f1a7643d7a1581dc702d507ee247aab91
Former-commit-id: e079559f8b9293a40b86a946825d4cd734ef0e69
Former-commit-id: 7b795cc9803c78b1d2b434b4d7c1479ebd42809f

src/ImageProcessor/Common/Helpers/ImageMaths.cs

@@ -0,0 +1,56 @@
+// <copyright file="ImageMaths.cs" company="James South">
+// Copyright © James South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessor
+{
+    using System;
+
+    /// <summary>
+    /// Provides common mathematical methods.
+    /// </summary>
+    internal static class ImageMaths
+    {
+        /// <summary>
+        /// Gets the result of a sine cardinal function for the given value.
+        /// </summary>
+        /// <param name="x">
+        /// The value to calculate the result for.
+        /// </param>
+        /// <returns>
+        /// The <see cref="double"/>.
+        /// </returns>
+        public static double SinC(double x)
+        {
+            const double Epsilon = .0001;
+
+            if (Math.Abs(x) > Epsilon)
+            {
+                x *= Math.PI;
+                return Clean(Math.Sin(x) / x);
+            }
+
+            return 1.0;
+        }
+
+        /// <summary>
+        /// Ensures that any passed double is correctly rounded to zero
+        /// </summary>
+        /// <param name="x">The value to clean.</param>
+        /// <returns>
+        /// The <see cref="double"/>
+        /// </returns>.
+        private static double Clean(double x)
+        {
+            const double Epsilon = .0001;
+
+            if (Math.Abs(x) < Epsilon)
+            {
+                return 0.0;
+            }
+
+            return x;
+        }
+    }
+}

src/ImageProcessor/ImageExtensions.cs

@@ -119,7 +119,7 @@ namespace ImageProcessor
             for (int i = 0; i < source.Frames.Count; i++)
             {
                 ImageFrame sourceFrame = source.Frames[i];
-                ImageFrame tranformedFrame = clone ? new ImageFrame(sourceFrame) : new ImageFrame();
+                ImageFrame tranformedFrame = clone ? new ImageFrame(sourceFrame) : new ImageFrame { FrameDelay = sourceFrame.FrameDelay };
                 action(sourceFrame, tranformedFrame);
 
                 if (!clone)

src/ImageProcessor/ImageProcessor.csproj

@@ -40,6 +40,7 @@
     <!-- A reference to the entire .NET Framework is automatically included -->
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="Common\Helpers\ImageMaths.cs" />
     <Compile Include="Common\Helpers\PixelOperations.cs" />
     <Compile Include="Filters\Contrast.cs" />
     <Compile Include="Filters\ImageFilterExtensions.cs" />
@@ -179,6 +180,7 @@
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="Numerics\Rectangle.cs" />
     <Compile Include="Numerics\Size.cs" />
+    <Compile Include="Samplers\Lanczos3Resampler.cs" />
     <Compile Include="Samplers\BicubicResampler.cs" />
     <Compile Include="Samplers\ImageSampleExtensions.cs" />
     <Compile Include="Samplers\IResampler.cs" />

src/ImageProcessor/Samplers/Lanczos3Resampler.cs

@@ -0,0 +1,33 @@
+// <copyright file="BicubicResampler.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 Lanczos3Resampler : IResampler
+    {
+        /// <inheritdoc/>
+        public double Radius => 3;
+
+        /// <inheritdoc/>
+        public double GetValue(double x)
+        {
+            if (x < 0)
+            {
+                x = -x;
+            }
+
+            if (x < 3)
+            {
+                return ImageMaths.SinC(x) * ImageMaths.SinC(x / 3f);
+            }
+
+            return 0;
+        }
+    }
+}

tests/ImageProcessor.Tests/Filters/FilterTests.cs

@@ -14,12 +14,12 @@ namespace ImageProcessor.Tests.Filters
     {
         public static readonly List<string> Files = new List<string>
         {
-            { "../../TestImages/Formats/Jpg/Backdrop.jpg"},
+            //{ "../../TestImages/Formats/Jpg/Backdrop.jpg"},
             //{ "../../TestImages/Formats/Bmp/Car.bmp" },
             //{ "../../TestImages/Formats/Png/cmyk.png" },
             //{ "../../TestImages/Formats/Gif/a.gif" },
             //{ "../../TestImages/Formats/Gif/leaf.gif" },
-            //{ "../../TestImages/Formats/Gif/ani.gif" },
+            { "../../TestImages/Formats/Gif/ani.gif" },
             //{ "../../TestImages/Formats/Gif/ani2.gif" },
             //{ "../../TestImages/Formats/Gif/giphy.gif" },
         };

tests/ImageProcessor.Tests/ImageProcessor.Tests.csproj

@@ -60,6 +60,7 @@
     <Compile Include="Numerics\PointTests.cs" />
     <Compile Include="Numerics\SizeTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="Samplers\SamplerTests.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="packages.config" />

tests/ImageProcessor.Tests/Samplers/SamplerTests.cs

@@ -0,0 +1,74 @@
+
+namespace ImageProcessor.Tests.Filters
+{
+    using System.Collections.Generic;
+    using System.Diagnostics;
+    using System.IO;
+
+    using Samplers;
+
+    using Xunit;
+
+    public class SamplerTests
+    {
+        public static readonly List<string> Files = new List<string>
+        {
+            { "../../TestImages/Formats/Jpg/Backdrop.jpg" },
+            { "../../TestImages/Formats/Bmp/Car.bmp" },
+            { "../../TestImages/Formats/Png/cmyk.png" },
+            //{ "../../TestImages/Formats/Gif/a.gif" },
+            { "../../TestImages/Formats/Gif/leaf.gif" },
+            //{ "../../TestImages/Formats/Gif/ani.gif" },
+            //{ "../../TestImages/Formats/Gif/ani2.gif" },
+            //{ "../../TestImages/Formats/Gif/giphy.gif" },
+        };
+
+        public static readonly TheoryData<string, IResampler> Samplers =
+            new TheoryData<string, IResampler>
+            {
+                { "Bicubic", new BicubicResampler() },
+                { "Lanczos3", new Lanczos3Resampler() }
+            };
+
+        [Theory]
+        [MemberData("Samplers")]
+        public void ResizeImage(string name, IResampler sampler)
+        {
+            if (!Directory.Exists("Resized"))
+            {
+                Directory.CreateDirectory("Resized");
+            }
+
+            foreach (string file in Files)
+            {
+                using (FileStream stream = File.OpenRead(file))
+                {
+                    Stopwatch watch = Stopwatch.StartNew();
+                    Image image = new Image(stream);
+                    string filename = Path.GetFileNameWithoutExtension(file) + "-" + name + Path.GetExtension(file);
+                    using (FileStream output = File.OpenWrite($"Resized/{filename}"))
+                    {
+                        image.Resize(900, 900, sampler).Save(output);
+                    }
+
+                    Trace.WriteLine($"{name}: {watch.ElapsedMilliseconds}ms");
+                }
+            }
+        }
+
+        [Theory]
+        [InlineData(-2, 0)]
+        [InlineData(-1, 0)]
+        [InlineData(0, 1)]
+        [InlineData(1, 0)]
+        [InlineData(2, 0)]
+        [InlineData(2, 0)]
+        public static void Lanczos3WindowOscillatesCorrectly(double x, double expected)
+        {
+            Lanczos3Resampler sampler = new Lanczos3Resampler();
+            double result = sampler.GetValue(x);
+
+            Assert.Equal(result, expected);
+        }
+    }
+}