Fix up code and tests

src/ImageSharp/Processing/Extensions/LightnessExtension.cs

@@ -1,34 +0,0 @@
-// Copyright (c) Six Labors and contributors.
-// Licensed under the Apache License, Version 2.0.
-using SixLabors.ImageSharp.Processing.Processors.Filters;
-using SixLabors.Primitives;
-
-namespace SixLabors.ImageSharp.Processing
-{
-    /// <summary>
-    /// Defines extensions that allow to change image lightness.
-    /// </summary>
-    public static class LightnessExtension
-    {
-        /// <summary>
-        /// Alters the lightness parameter of the image.
-        /// </summary>
-        /// <param name="source">The image this method extends.</param>
-        /// <param name="lightness">Lightness parameter of image.</param>
-        /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
-        public static IImageProcessingContext Lightness(this IImageProcessingContext source, float lightness)
-            => source.ApplyProcessor(new LightnessProcessor(lightness));
-
-        /// <summary>
-        /// Alters the lightness parameter of the image.
-        /// </summary>
-        /// <param name="source">The image this method extends.</param>
-        /// <param name="lightness">Lightness parameter of image.</param>
-        /// <param name="rectangle">
-        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to alter.
-        /// </param>
-        /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
-        public static IImageProcessingContext Lightness(this IImageProcessingContext source, float lightness, Rectangle rectangle)
-            => source.ApplyProcessor(new LightnessProcessor(lightness), rectangle);
-    }
-}

src/ImageSharp/Processing/Extensions/LightnessExtensions.cs

@@ -0,0 +1,44 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using SixLabors.ImageSharp.Processing.Processors.Filters;
+using SixLabors.Primitives;
+
+namespace SixLabors.ImageSharp.Processing
+{
+    /// <summary>
+    /// Defines extensions that allow the alteration of the lightness component of an <see cref="Image"/>
+    /// using Mutate/Clone.
+    /// </summary>
+    public static class LightnessExtensions
+    {
+        /// <summary>
+        /// Alters the lightness component of the image.
+        /// </summary>
+        /// <remarks>
+        /// A value of 0 will create an image that is completely black. A value of 1 leaves the input unchanged.
+        /// Other values are linear multipliers on the effect. Values of an amount over 1 are allowed, providing lighter results.
+        /// </remarks>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="amount">The proportion of the conversion. Must be greater than or equal to 0.</param>
+        /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
+        public static IImageProcessingContext Lightness(this IImageProcessingContext source, float amount)
+            => source.ApplyProcessor(new LightnessProcessor(amount));
+
+        /// <summary>
+        /// Alters the lightness component of the image.
+        /// </summary>
+        /// <remarks>
+        /// A value of 0 will create an image that is completely black. A value of 1 leaves the input unchanged.
+        /// Other values are linear multipliers on the effect. Values of an amount over 1 are allowed, providing lighter results.
+        /// </remarks>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="amount">The proportion of the conversion. Must be greater than or equal to 0.</param>
+        /// <param name="rectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to alter.
+        /// </param>
+        /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
+        public static IImageProcessingContext Lightness(this IImageProcessingContext source, float amount, Rectangle rectangle)
+            => source.ApplyProcessor(new LightnessProcessor(amount), rectangle);
+    }
+}

src/ImageSharp/Processing/KnownFilterMatrices.cs

@@ -436,23 +436,26 @@ namespace SixLabors.ImageSharp.Processing
         /// Create a lightness filter matrix using the given amount.
         /// </summary>
         /// <remarks>
-        /// A value of -1 will create an image that is completely black. A value of 1 makes the image completely white.
+        /// A value of 0 will create an image that is completely black. A value of 1 leaves the input unchanged.
+        /// Other values are linear multipliers on the effect. Values of an amount over 1 are allowed, providing lighter results.
         /// </remarks>
-        /// <param name="amount">The proportion of the conversion. Must be between -1 and 1.</param>
+        /// <param name="amount">The proportion of the conversion. Must be greater than or equal to 0.</param>
         /// <returns>The <see cref="ColorMatrix"/></returns>
         public static ColorMatrix CreateLightnessFilter(float amount)
         {
-            Guard.MustBeBetweenOrEqualTo(amount, -1F, 1F, nameof(amount));
+            Guard.MustBeGreaterThanOrEqualTo(amount, 0, nameof(amount));
+            amount--;
+
             return new ColorMatrix
-                   {
-                       M11 = 1F,
-                       M22 = 1F,
-                       M33 = 1F,
-                       M44 = 1F,
-                       M51 = amount,
-                       M52 = amount,
-                       M53 = amount
-                   };
+            {
+                M11 = 1F,
+                M22 = 1F,
+                M33 = 1F,
+                M44 = 1F,
+                M51 = amount,
+                M52 = amount,
+                M53 = amount
+            };
         }
 
         /// <summary>

src/ImageSharp/Processing/Processors/Filters/LightnessProcessor.cs

@@ -4,23 +4,27 @@
 namespace SixLabors.ImageSharp.Processing.Processors.Filters
 {
     /// <summary>
-    /// Applies a lightness filter matrix using
+    /// Applies a lightness filter matrix using the given amount.
     /// </summary>
     public sealed class LightnessProcessor : FilterProcessor
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="LightnessProcessor"/> class.
         /// </summary>
-        /// <param name="lightness">Lightness of image</param>
-        public LightnessProcessor(float lightness)
-        : base(KnownFilterMatrices.CreateLightnessFilter(lightness))
+        /// <remarks>
+        /// A value of <value>0</value> will create an image that is completely black. A value of <value>1</value> leaves the input unchanged.
+        /// Other values are linear multipliers on the effect. Values of an amount over 1 are allowed, providing lighter results.
+        /// </remarks>
+        /// <param name="amount">The proportion of the conversion. Must be greater than or equal to 0.</param>
+        public LightnessProcessor(float amount)
+            : base(KnownFilterMatrices.CreateLightnessFilter(amount))
         {
-            this.Lightness = lightness;
+            this.Amount = amount;
         }
 
         /// <summary>
-        /// Gets Lightness of image.
+        /// Gets the proportion of the conversion
         /// </summary>
-        public float Lightness { get; }
+        public float Amount { get; }
     }
 }

tests/ImageSharp.Tests/Processing/Filters/LightnessTest.cs

@@ -15,7 +15,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Effects
             this.operations.Lightness(.5F);
             LightnessProcessor processor = this.Verify<LightnessProcessor>();
 
-            Assert.Equal(.5F, processor.Lightness);
+            Assert.Equal(.5F, processor.Amount);
         }
 
         [Fact]
@@ -24,7 +24,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Effects
             this.operations.Lightness(.5F, this.rect);
             LightnessProcessor processor = this.Verify<LightnessProcessor>(this.rect);
 
-            Assert.Equal(.5F, processor.Lightness);
+            Assert.Equal(.5F, processor.Amount);
         }
     }
 }

tests/ImageSharp.Tests/Processing/Processors/Filters/LightnessTest.cs

@@ -19,7 +19,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Effects
         = new TheoryData<float>
         {
             .5F,
-            .5F
+           1.5F
         };
 
         [Theory]
@@ -27,4 +27,4 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Effects
         public void ApplyLightnessFilter<TPixel>(TestImageProvider<TPixel> provider, float value)
             where TPixel : struct, IPixel<TPixel> => provider.RunValidatingProcessorTest(ctx => ctx.Lightness(value), value, this.imageComparer);
     }
-}
+}

tests/Images/External

@@ -1 +1 @@
-Subproject commit 99a2bc523cd4eb00e37af20d1b2088fa11564c57
+Subproject commit 58b2c01f9b66dd42d2b5b040b85e6846083b5e5f