Add ditherscale to palette API

src/ImageSharp/Processing/Extensions/Dithering/DitherExtensions.cs

@@ -13,7 +13,7 @@ namespace SixLabors.ImageSharp.Processing
     public static class DitherExtensions
     {
         /// <summary>
-        /// Dithers the image reducing it to a web-safe palette using Bayer4x4 ordered dithering.
+        /// Dithers the image reducing it to a web-safe palette using <see cref="KnownDitherings.BayerDither4x4"/>.
         /// </summary>
         /// <param name="source">The image this method extends.</param>
         /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
@@ -26,9 +26,24 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="source">The image this method extends.</param>
         /// <param name="dither">The ordered ditherer.</param>
         /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
-        public static IImageProcessingContext Dither(this IImageProcessingContext source, IDither dither) =>
+        public static IImageProcessingContext Dither(
+            this IImageProcessingContext source,
+            IDither dither) =>
             source.ApplyProcessor(new PaletteDitherProcessor(dither));
 
+        /// <summary>
+        /// Dithers the image reducing it to a web-safe palette using ordered dithering.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="dither">The ordered ditherer.</param>
+        /// <param name="ditherScale">The dithering scale used to adjust the amount of dither.</param>
+        /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
+        public static IImageProcessingContext Dither(
+            this IImageProcessingContext source,
+            IDither dither,
+            float ditherScale) =>
+            source.ApplyProcessor(new PaletteDitherProcessor(dither, ditherScale));
+
         /// <summary>
         /// Dithers the image reducing it to the given palette using ordered dithering.
         /// </summary>
@@ -42,6 +57,32 @@ namespace SixLabors.ImageSharp.Processing
             ReadOnlyMemory<Color> palette) =>
             source.ApplyProcessor(new PaletteDitherProcessor(dither, palette));
 
+        /// <summary>
+        /// Dithers the image reducing it to the given palette using ordered dithering.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="dither">The ordered ditherer.</param>
+        /// <param name="ditherScale">The dithering scale used to adjust the amount of dither.</param>
+        /// <param name="palette">The palette to select substitute colors from.</param>
+        /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
+        public static IImageProcessingContext Dither(
+            this IImageProcessingContext source,
+            IDither dither,
+            float ditherScale,
+            ReadOnlyMemory<Color> palette) =>
+            source.ApplyProcessor(new PaletteDitherProcessor(dither, ditherScale, palette));
+
+        /// <summary>
+        /// Dithers the image reducing it to a web-safe palette using <see cref="KnownDitherings.BayerDither4x4"/>.
+        /// </summary>
+        /// <param name="source">The image this method extends.</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 Dither(this IImageProcessingContext source, Rectangle rectangle) =>
+            Dither(source, KnownDitherings.BayerDither4x4, rectangle);
+
         /// <summary>
         /// Dithers the image reducing it to a web-safe palette using ordered dithering.
         /// </summary>
@@ -57,6 +98,23 @@ namespace SixLabors.ImageSharp.Processing
             Rectangle rectangle) =>
             source.ApplyProcessor(new PaletteDitherProcessor(dither), rectangle);
 
+        /// <summary>
+        /// Dithers the image reducing it to a web-safe palette using ordered dithering.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="dither">The ordered ditherer.</param>
+        /// <param name="ditherScale">The dithering scale used to adjust the amount of dither.</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 Dither(
+            this IImageProcessingContext source,
+            IDither dither,
+            float ditherScale,
+            Rectangle rectangle) =>
+            source.ApplyProcessor(new PaletteDitherProcessor(dither, ditherScale), rectangle);
+
         /// <summary>
         /// Dithers the image reducing it to the given palette using ordered dithering.
         /// </summary>
@@ -73,5 +131,24 @@ namespace SixLabors.ImageSharp.Processing
             ReadOnlyMemory<Color> palette,
             Rectangle rectangle) =>
             source.ApplyProcessor(new PaletteDitherProcessor(dither, palette), rectangle);
+
+        /// <summary>
+        /// Dithers the image reducing it to the given palette using ordered dithering.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="dither">The ordered ditherer.</param>
+        /// <param name="ditherScale">The dithering scale used to adjust the amount of dither.</param>
+        /// <param name="palette">The palette to select substitute colors from.</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 Dither(
+            this IImageProcessingContext source,
+            IDither dither,
+            float ditherScale,
+            ReadOnlyMemory<Color> palette,
+            Rectangle rectangle) =>
+            source.ApplyProcessor(new PaletteDitherProcessor(dither, ditherScale, palette), rectangle);
     }
 }

src/ImageSharp/Processing/Processors/Dithering/PaletteDitherProcessor.cs

@@ -3,6 +3,7 @@
 
 using System;
 using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing.Processors.Quantization;
 
 namespace SixLabors.ImageSharp.Processing.Processors.Dithering
 {
@@ -16,7 +17,17 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
         /// </summary>
         /// <param name="dither">The ordered ditherer.</param>
         public PaletteDitherProcessor(IDither dither)
-            : this(dither, Color.WebSafePalette)
+            : this(dither, QuantizerConstants.MaxDitherScale)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="PaletteDitherProcessor"/> class.
+        /// </summary>
+        /// <param name="dither">The ordered ditherer.</param>
+        /// <param name="ditherScale">The dithering scale used to adjust the amount of dither.</param>
+        public PaletteDitherProcessor(IDither dither, float ditherScale)
+            : this(dither, ditherScale, Color.WebSafePalette)
         {
         }
 
@@ -26,8 +37,22 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
         /// <param name="dither">The dithering algorithm.</param>
         /// <param name="palette">The palette to select substitute colors from.</param>
         public PaletteDitherProcessor(IDither dither, ReadOnlyMemory<Color> palette)
+            : this(dither, QuantizerConstants.MaxDitherScale, palette)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="PaletteDitherProcessor"/> class.
+        /// </summary>
+        /// <param name="dither">The dithering algorithm.</param>
+        /// <param name="ditherScale">The dithering scale used to adjust the amount of dither.</param>
+        /// <param name="palette">The palette to select substitute colors from.</param>
+        public PaletteDitherProcessor(IDither dither, float ditherScale, ReadOnlyMemory<Color> palette)
         {
-            this.Dither = dither ?? throw new ArgumentNullException(nameof(dither));
+            Guard.MustBeGreaterThan(palette.Length, 0, nameof(palette));
+            Guard.NotNull(dither, nameof(dither));
+            this.Dither = dither;
+            this.DitherScale = ditherScale.Clamp(QuantizerConstants.MinDitherScale, QuantizerConstants.MaxDitherScale);
             this.Palette = palette;
         }