diff --git a/src/ImageProcessor/Filters/Alpha.cs b/src/ImageProcessor/Filters/Alpha.cs
new file mode 100644
index 000000000..672e5263a
--- /dev/null
+++ b/src/ImageProcessor/Filters/Alpha.cs
@@ -0,0 +1,56 @@
+// <copyright file="Alpha.cs" company="James South">
+// Copyright © James South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessor.Filters
+{
+    using System;
+
+    /// <summary>
+    /// An <see cref="IImageProcessor"/> to change the Alpha of an <see cref="Image"/>.
+    /// </summary>
+    public class Alpha : ParallelImageProcessor
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Alpha"/> class.
+        /// </summary>
+        /// <param name="percent">The percentage to adjust the opacity of the image. Must be between 0 and 100.</param>
+        /// <exception cref="ArgumentException">
+        /// <paramref name="percent"/> is less than 0 or is greater than 100.
+        /// </exception>
+        public Alpha(int percent)
+        {
+            Guard.MustBeBetweenOrEqualTo(percent, 0, 100, nameof(percent));
+            this.Value = percent;
+        }
+
+        /// <summary>
+        /// Gets the alpha value.
+        /// </summary>
+        public int Value { get; }
+
+        /// <inheritdoc/>
+        protected override void Apply(ImageBase target, ImageBase source, Rectangle targetRectangle, Rectangle sourceRectangle, int startY, int endY)
+        {
+            double alpha = this.Value / 100.0;
+            int sourceY = sourceRectangle.Y;
+            int sourceBottom = sourceRectangle.Bottom;
+            int startX = sourceRectangle.X;
+            int endX = sourceRectangle.Right;
+
+            for (int y = startY; y < endY; y++)
+            {
+                if (y >= sourceY && y < sourceBottom)
+                {
+                    for (int x = startX; x < endX; x++)
+                    {
+                        Bgra color = source[x, y];
+                        double a = color.A * alpha;
+                        target[x, y] = new Bgra(color.B, color.G, color.R, a.ToByte());
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/src/ImageProcessor/Filters/Contrast.cs b/src/ImageProcessor/Filters/Contrast.cs
index 6c3336fca..d08bcfcc2 100644
--- a/src/ImageProcessor/Filters/Contrast.cs
+++ b/src/ImageProcessor/Filters/Contrast.cs
@@ -17,7 +17,7 @@ namespace ImageProcessor.Filters
         /// </summary>
         /// <param name="contrast">The new contrast of the image. Must be between -100 and 100.</param>
         /// <exception cref="ArgumentException">
-        /// <paramref name="contrast"/> is less than -100 is greater than 100.
+        /// <paramref name="contrast"/> is less than -100 or is greater than 100.
         /// </exception>
         public Contrast(int contrast)
         {
@@ -34,35 +34,45 @@ namespace ImageProcessor.Filters
         protected override void Apply(ImageBase target, ImageBase source, Rectangle targetRectangle, Rectangle sourceRectangle, int startY, int endY)
         {
             double contrast = (100.0 + this.Value) / 100.0;
+            int sourceY = sourceRectangle.Y;
+            int sourceBottom = sourceRectangle.Bottom;
+            int startX = sourceRectangle.X;
+            int endX = sourceRectangle.Right;
 
             for (int y = startY; y < endY; y++)
             {
-                for (int x = sourceRectangle.X; x < sourceRectangle.Right; x++)
+                if (y >= sourceY && y < sourceBottom)
                 {
-                    Bgra color = source[x, y];
+                    for (int x = startX; x < endX; x++)
+                    {
+                        Bgra sourceColor = source[x, y];
+                        sourceColor = PixelOperations.ToLinear(sourceColor);
 
-                    double r = color.R / 255.0;
-                    r -= 0.5;
-                    r *= contrast;
-                    r += 0.5;
-                    r *= 255;
-                    r = r.ToByte();
+                        double r = sourceColor.R / 255.0;
+                        r -= 0.5;
+                        r *= contrast;
+                        r += 0.5;
+                        r *= 255;
+                        r = r.ToByte();
 
-                    double g = color.G / 255.0;
-                    g -= 0.5;
-                    g *= contrast;
-                    g += 0.5;
-                    g *= 255;
-                    g = g.ToByte();
+                        double g = sourceColor.G / 255.0;
+                        g -= 0.5;
+                        g *= contrast;
+                        g += 0.5;
+                        g *= 255;
+                        g = g.ToByte();
 
-                    double b = color.B / 255.0;
-                    b -= 0.5;
-                    b *= contrast;
-                    b += 0.5;
-                    b *= 255;
-                    b = b.ToByte();
+                        double b = sourceColor.B / 255.0;
+                        b -= 0.5;
+                        b *= contrast;
+                        b += 0.5;
+                        b *= 255;
+                        b = b.ToByte();
 
-                    target[x, y] = new Bgra((byte)b, (byte)g, (byte)r, color.A);
+                        Bgra destinationColor = new Bgra(b.ToByte(), g.ToByte(), r.ToByte(), sourceColor.A);
+                        destinationColor = PixelOperations.ToSrgb(destinationColor);
+                        target[x, y] = destinationColor;
+                    }
                 }
             }
         }
diff --git a/src/ImageProcessor/Filters/ImageFilterExtensions.cs b/src/ImageProcessor/Filters/ImageFilterExtensions.cs
index 674f4f0e4..351a1921e 100644
--- a/src/ImageProcessor/Filters/ImageFilterExtensions.cs
+++ b/src/ImageProcessor/Filters/ImageFilterExtensions.cs
@@ -6,7 +6,7 @@
 namespace ImageProcessor.Filters
 {
     /// <summary>
-    /// Exstensions methods for <see cref="Image"/> to apply filters to the image.
+    /// Extensions methods for <see cref="Image"/> to apply filters to the image.
     /// </summary>
     public static class ImageFilterExtensions
     {
@@ -16,6 +16,48 @@ namespace ImageProcessor.Filters
         /// <param name="source">The image this method extends.</param>
         /// <param name="amount">The new contrast of the image. Must be between -100 and 100.</param>
         /// <returns>The <see cref="Image"/>.</returns>
-        public static Image Contrast(this Image source, int amount) => source.Process(new Contrast(amount));
+        public static Image Contrast(this Image source, int amount)
+        {
+            return Contrast(source, amount, source.Bounds);
+        }
+
+        /// <summary>
+        /// Alters the contrast component of the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="amount">The new contrast of the image. Must be between -100 and 100.</param>
+        /// <param name="sourceRectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to draw.
+        /// </param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image Contrast(this Image source, int amount, Rectangle sourceRectangle)
+        {
+            return source.Process(sourceRectangle, new Contrast(amount));
+        }
+
+        /// <summary>
+        /// Alters the alpha component of the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="percent">The new opacity of the image. Must be between 0 and 100.</param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image Alpha(this Image source, int percent)
+        {
+            return Alpha(source, percent, source.Bounds);
+        }
+
+        /// <summary>
+        /// Alters the alpha component of the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="percent">The new opacity of the image. Must be between 0 and 100.</param>
+        /// <param name="sourceRectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to draw.
+        /// </param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image Alpha(this Image source, int percent, Rectangle sourceRectangle)
+        {
+            return source.Process(sourceRectangle, new Alpha(percent));
+        }
     }
 }
diff --git a/src/ImageProcessor/ImageProcessor.csproj b/src/ImageProcessor/ImageProcessor.csproj
index a7ec6d89a..53b0946a9 100644
--- a/src/ImageProcessor/ImageProcessor.csproj
+++ b/src/ImageProcessor/ImageProcessor.csproj
@@ -43,6 +43,7 @@
     <Compile Include="Colors\Cmyk.cs" />
     <Compile Include="Common\Helpers\ImageMaths.cs" />
     <Compile Include="Common\Helpers\PixelOperations.cs" />
+    <Compile Include="Filters\Alpha.cs" />
     <Compile Include="Filters\Contrast.cs" />
     <Compile Include="Filters\ImageFilterExtensions.cs" />
     <Compile Include="ImageExtensions.cs" />
@@ -181,6 +182,7 @@
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="Numerics\Rectangle.cs" />
     <Compile Include="Numerics\Size.cs" />
+    <Compile Include="Samplers\Resamplers\Lanczos5Resampler.cs" />
     <Compile Include="Samplers\Resamplers\Lanczos8Resampler.cs" />
     <Compile Include="Samplers\Resamplers\WelchResampler.cs" />
     <Compile Include="Samplers\Resamplers\CatmullRomResampler.cs" />
diff --git a/tests/ImageProcessor.Tests/Processors/Filters/FilterTests.cs b/tests/ImageProcessor.Tests/Processors/Filters/FilterTests.cs
index dac009328..4d6cb78a5 100644
--- a/tests/ImageProcessor.Tests/Processors/Filters/FilterTests.cs
+++ b/tests/ImageProcessor.Tests/Processors/Filters/FilterTests.cs
@@ -1,12 +1,10 @@
 
 namespace ImageProcessor.Tests
 {
-    using System.Collections.Generic;
     using System.Diagnostics;
     using System.IO;
 
     using ImageProcessor.Filters;
-    using ImageProcessor.Samplers;
 
     using Xunit;
 
@@ -16,6 +14,7 @@ namespace ImageProcessor.Tests
         {
             { "Contrast-50", new Contrast(50) },
             { "Contrast--50", new Contrast(-50) },
+            { "Alpha--50", new Alpha(50) },
         };
 
         [Theory]
@@ -43,30 +42,5 @@ namespace ImageProcessor.Tests
                 }
             }
         }
-
-        [Fact]
-        public void ResizeImage()
-        {
-            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.GetFileName(file);
-                    using (FileStream output = File.OpenWrite($"Resized/{ Path.GetFileName(filename) }"))
-                    {
-                        image.Resize(400, 400).Save(output);
-                    }
-
-                    Trace.WriteLine($"{ filename }: { watch.ElapsedMilliseconds}ms");
-                }
-            }
-        }
     }
 }
diff --git a/tests/ImageProcessor.Tests/Processors/Samplers/SamplerTests.cs b/tests/ImageProcessor.Tests/Processors/Samplers/SamplerTests.cs
index ffa4c5d54..c35ff951e 100644
--- a/tests/ImageProcessor.Tests/Processors/Samplers/SamplerTests.cs
+++ b/tests/ImageProcessor.Tests/Processors/Samplers/SamplerTests.cs
@@ -46,7 +46,8 @@ namespace ImageProcessor.Tests
                     string filename = Path.GetFileNameWithoutExtension(file) + "-" + name + Path.GetExtension(file);
                     using (FileStream output = File.OpenWrite($"Resized/{filename}"))
                     {
-                        image.Resize(image.Width / 2, image.Height / 2, sampler).Save(output);
+                        //image.Resize(image.Width / 2, image.Height / 2, sampler).Save(output);
+                        image.Resize(500, 500, sampler, new Rectangle(0, 0, 100, 100), new Rectangle(0, 0, 500, 500)).Save(output);
                     }
 
                     Trace.WriteLine($"{name}: {watch.ElapsedMilliseconds}ms");