Add indexed png encoder benchmark [skip ci]

tests/ImageSharp.Benchmarks/Image/EncodeIndexedPng.cs

@@ -0,0 +1,104 @@
+// <copyright file="EncodeIndexedPng.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp.Benchmarks.Image
+{
+    using System.IO;
+
+    using BenchmarkDotNet.Attributes;
+
+    using ImageSharp;
+    using ImageSharp.Formats;
+    using ImageSharp.Quantizers;
+
+    /// <summary>
+    /// Benchmarks saving png files using different quantizers. System.Drawing cannot save indexed png files so we cannot compare.
+    /// </summary>
+    public class EncodeIndexedPng : BenchmarkBase
+    {
+        // System.Drawing needs this.
+        private Stream bmpStream;
+        private Image bmpCore;
+
+        [Params(false)]
+        public bool LargeImage { get; set; }
+
+        [Setup]
+        public void ReadImages()
+        {
+            if (this.bmpStream == null)
+            {
+                string path = this.LargeImage
+                                  ? "../ImageSharp.Tests/TestImages/Formats/Jpg/baseline/jpeg420exif.jpg"
+                                  : "../ImageSharp.Tests/TestImages/Formats/Bmp/Car.bmp";
+                this.bmpStream = File.OpenRead(path);
+                this.bmpCore = new Image(this.bmpStream);
+                this.bmpStream.Position = 0;
+            }
+        }
+
+        [Cleanup]
+        public void Cleanup()
+        {
+            this.bmpStream.Dispose();
+            this.bmpCore.Dispose();
+        }
+
+        [Benchmark(Baseline = true, Description = "ImageSharp Octree Png")]
+        public void PngCoreOctree()
+        {
+            using (MemoryStream memoryStream = new MemoryStream())
+            {
+                PngEncoderOptions options = new PngEncoderOptions() { Quantizer = new OctreeQuantizer<Color>(), Quality = 256 };
+
+                this.bmpCore.SaveAsPng(memoryStream, options);
+            }
+        }
+
+        [Benchmark(Description = "ImageSharp Octree NoDither Png")]
+        public void PngCoreOctreeNoDIther()
+        {
+            using (MemoryStream memoryStream = new MemoryStream())
+            {
+                PngEncoderOptions options = new PngEncoderOptions { Quantizer = new OctreeQuantizer<Color> { Dither = false }, Quality = 256 };
+
+                this.bmpCore.SaveAsPng(memoryStream, options);
+            }
+        }
+
+        [Benchmark(Description = "ImageSharp Palette Png")]
+        public void PngCorePalette()
+        {
+            using (MemoryStream memoryStream = new MemoryStream())
+            {
+                PngEncoderOptions options = new PngEncoderOptions { Quantizer = new PaletteQuantizer<Color>(), Quality = 256 };
+
+                this.bmpCore.SaveAsPng(memoryStream, options);
+            }
+        }
+
+        [Benchmark(Description = "ImageSharp Palette NoDither Png")]
+        public void PngCorePaletteNoDither()
+        {
+            using (MemoryStream memoryStream = new MemoryStream())
+            {
+                PngEncoderOptions options = new PngEncoderOptions { Quantizer = new PaletteQuantizer<Color> { Dither = false }, Quality = 256 };
+
+                this.bmpCore.SaveAsPng(memoryStream, options);
+            }
+        }
+
+        [Benchmark(Description = "ImageSharp Wu Png")]
+        public void PngCoreWu()
+        {
+            using (MemoryStream memoryStream = new MemoryStream())
+            {
+                PngEncoderOptions options = new PngEncoderOptions() { Quantizer = new WuQuantizer<Color>(), Quality = 256 };
+
+                this.bmpCore.SaveAsPng(memoryStream, options);
+            }
+        }
+    }
+}