Added filtered png load benchmarks

tests/ImageSharp.Benchmarks/Image/DecodeFilteredPng.cs

@@ -0,0 +1,67 @@
+// <copyright file="DecodePng.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;
+
+    public class DecodeFilteredPng
+    {
+        private MemoryStream filter0;
+        private MemoryStream filter1;
+        private MemoryStream filter2;
+        private MemoryStream filter3;
+        private MemoryStream filter4;
+
+        [Setup]
+        public void ReadImages()
+        {
+            this.filter0 = new MemoryStream(File.ReadAllBytes("../ImageSharp.Tests/TestImages/Formats/Png/filter0.png"));
+            this.filter1 = new MemoryStream(File.ReadAllBytes("../ImageSharp.Tests/TestImages/Formats/Png/filter1.png"));
+            this.filter2 = new MemoryStream(File.ReadAllBytes("../ImageSharp.Tests/TestImages/Formats/Png/filter2.png"));
+            this.filter3 = new MemoryStream(File.ReadAllBytes("../ImageSharp.Tests/TestImages/Formats/Png/filter3.png"));
+            this.filter4 = new MemoryStream(File.ReadAllBytes("../ImageSharp.Tests/TestImages/Formats/Png/filter4.png"));
+        }
+
+        private Image LoadPng(MemoryStream stream)
+        {
+            return new Image(stream);
+        }
+
+        [Benchmark(Baseline = true, Description = "None-filtered PNG file")]
+        public Image PngFilter0()
+        {
+            return LoadPng(filter0);
+        }
+
+        [Benchmark(Description = "Sub-filtered PNG file")]
+        public Image PngFilter1()
+        {
+            return LoadPng(filter1);
+        }
+
+        [Benchmark(Description = "Up-filtered PNG file")]
+        public Image PngFilter2()
+        {
+            return LoadPng(filter2);
+        }
+
+        [Benchmark(Description = "Average-filtered PNG file")]
+        public Image PngFilter3()
+        {
+            return LoadPng(filter3);
+        }
+
+        [Benchmark(Description = "Paeth-filtered PNG file")]
+        public Image PngFilter4()
+        {
+            return LoadPng(filter4);
+        }
+    }
+}