diff --git a/src/ImageProcessorCore/Filters/Alpha.cs b/src/ImageProcessorCore/Filters/Alpha.cs
new file mode 100644
index 000000000..545639afa
--- /dev/null
+++ b/src/ImageProcessorCore/Filters/Alpha.cs
@@ -0,0 +1,60 @@
+//
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+//
+
+namespace ImageProcessorCore
+{
+ using Processors;
+
+ ///
+ /// Extension methods for the type.
+ ///
+ public static partial class ImageExtensions
+ {
+ ///
+ /// Alters the alpha component of the image.
+ ///
+ /// The pixel format.
+ /// The packed format. long, float.
+ /// The image this method extends.
+ /// The new opacity of the image. Must be between 0 and 100.
+ /// A delegate which is called as progress is made processing the image.
+ /// The .
+ public static Image Alpha(this Image source, int percent, ProgressEventHandler progressHandler = null)
+ where T : IPackedVector
+ where TP : struct
+ {
+ return Alpha(source, percent, source.Bounds, progressHandler);
+ }
+
+ ///
+ /// Alters the alpha component of the image.
+ ///
+ /// The pixel format.
+ /// The packed format. long, float.
+ /// The image this method extends.
+ /// The new opacity of the image. Must be between 0 and 100.
+ ///
+ /// The structure that specifies the portion of the image object to alter.
+ ///
+ /// A delegate which is called as progress is made processing the image.
+ /// The .
+ public static Image Alpha(this Image source, int percent, Rectangle rectangle, ProgressEventHandler progressHandler = null)
+ where T : IPackedVector
+ where TP : struct
+ {
+ AlphaProcessor processor = new AlphaProcessor(percent);
+ processor.OnProgress += progressHandler;
+
+ try
+ {
+ return source.Process(rectangle, processor);
+ }
+ finally
+ {
+ processor.OnProgress -= progressHandler;
+ }
+ }
+ }
+}
diff --git a/src/ImageProcessorCore/Filters/Processors/AlphaProcessor.cs b/src/ImageProcessorCore/Filters/Processors/AlphaProcessor.cs
new file mode 100644
index 000000000..b4595ac4b
--- /dev/null
+++ b/src/ImageProcessorCore/Filters/Processors/AlphaProcessor.cs
@@ -0,0 +1,75 @@
+//
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+//
+
+namespace ImageProcessorCore.Processors
+{
+ using System.Numerics;
+ using System.Threading.Tasks;
+
+ ///
+ /// An to change the Alpha of an .
+ ///
+ /// The pixel format.
+ /// The packed format. long, float.
+ public class AlphaProcessor : ImageProcessor
+ where T : IPackedVector
+ where TP : struct
+ {
+ ///
+ /// Initializes a new instance of the class.
+ ///
+ /// The percentage to adjust the opacity of the image. Must be between 0 and 100.
+ ///
+ /// is less than 0 or is greater than 100.
+ ///
+ public AlphaProcessor(int percent)
+ {
+ Guard.MustBeBetweenOrEqualTo(percent, 0, 100, nameof(percent));
+ this.Value = percent;
+ }
+
+ ///
+ /// Gets the alpha value.
+ ///
+ public int Value { get; }
+
+ ///
+ protected override void Apply(ImageBase target, ImageBase source, Rectangle targetRectangle, Rectangle sourceRectangle, int startY, int endY)
+ {
+ float alpha = this.Value / 100f;
+ int sourceY = sourceRectangle.Y;
+ int sourceBottom = sourceRectangle.Bottom;
+ int startX = sourceRectangle.X;
+ int endX = sourceRectangle.Right;
+ Vector4 alphaVector = new Vector4(1, 1, 1, alpha);
+
+ using (IPixelAccessor sourcePixels = source.Lock())
+ using (IPixelAccessor targetPixels = target.Lock())
+ {
+ Parallel.For(
+ startY,
+ endY,
+ y =>
+ {
+ if (y >= sourceY && y < sourceBottom)
+ {
+ for (int x = startX; x < endX; x++)
+ {
+ Vector4 color = sourcePixels[x, y].ToVector4();
+ color *= alphaVector;
+
+ T packed = default(T);
+ packed.PackVector(color);
+ targetPixels[x, y] = packed;
+ }
+
+ this.OnRowProcessed();
+ }
+ });
+
+ }
+ }
+ }
+}
diff --git a/src/ImageProcessorCore/Filters/Processors/BrightnessProcessor.cs b/src/ImageProcessorCore/Filters/Processors/BrightnessProcessor.cs
index 3b3be22a5..f9197d143 100644
--- a/src/ImageProcessorCore/Filters/Processors/BrightnessProcessor.cs
+++ b/src/ImageProcessorCore/Filters/Processors/BrightnessProcessor.cs
@@ -9,7 +9,7 @@ namespace ImageProcessorCore.Processors
using System.Threading.Tasks;
///
- /// An to change the brightness of an .
+ /// An to change the brightness of an .
///
/// The pixel format.
/// The packed format. long, float.
diff --git a/tests/ImageProcessorCore.Tests/Processors/Filters/AlphaTest.cs b/tests/ImageProcessorCore.Tests/Processors/Filters/AlphaTest.cs
new file mode 100644
index 000000000..6176cbb71
--- /dev/null
+++ b/tests/ImageProcessorCore.Tests/Processors/Filters/AlphaTest.cs
@@ -0,0 +1,47 @@
+//
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+//
+
+namespace ImageProcessorCore.Tests
+{
+ using System.IO;
+
+ using Xunit;
+
+ public class AlphaTest : FileTestBase
+ {
+ public static readonly TheoryData AlphaValues
+ = new TheoryData
+ {
+ 20 ,
+ 80 ,
+ };
+
+ [Theory]
+ [MemberData("AlphaValues")]
+ public void ImageShouldApplyAlphaFilter(int value)
+ {
+ const string path = "TestOutput/Alpha";
+ if (!Directory.Exists(path))
+ {
+ Directory.CreateDirectory(path);
+ }
+
+ foreach (string file in Files)
+ {
+ using (FileStream stream = File.OpenRead(file))
+ {
+ string filename = Path.GetFileNameWithoutExtension(file) + "-" + value + Path.GetExtension(file);
+
+ Image image = new Image(stream);
+ using (FileStream output = File.OpenWrite($"{path}/{filename}"))
+ {
+ image.Alpha(value)
+ .Save(output);
+ }
+ }
+ }
+ }
+ }
+}
\ No newline at end of file