Drop Dither property from interface, rename diffuser.

src/ImageSharp/Processing/Quantization/FrameQuantizers/FrameQuantizerBase{TPixel}.cs

@@ -39,8 +39,8 @@ namespace SixLabors.ImageSharp.Processing.Quantization.FrameQuantizers
         {
             Guard.NotNull(quantizer, nameof(quantizer));
 
-            this.Dither = quantizer.Dither;
-            this.DitherType = quantizer.DitherType;
+            this.Diffuser = quantizer.Diffuser;
+            this.Dither = this.Diffuser != null;
             this.singlePass = singlePass;
         }
 
@@ -48,7 +48,7 @@ namespace SixLabors.ImageSharp.Processing.Quantization.FrameQuantizers
         public bool Dither { get; }
 
         /// <inheritdoc />
-        public IErrorDiffuser DitherType { get; }
+        public IErrorDiffuser Diffuser { get; }
 
         /// <inheritdoc/>
         public virtual QuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> image)

src/ImageSharp/Processing/Quantization/FrameQuantizers/IFrameQuantizer{TPixel}.cs

@@ -19,9 +19,9 @@ namespace SixLabors.ImageSharp.Processing.Quantization.FrameQuantizers
         bool Dither { get; }
 
         /// <summary>
-        /// Gets the dithering algorithm to apply to the output image.
+        /// Gets the error diffusion algorithm to apply to the output image.
         /// </summary>
-        IErrorDiffuser DitherType { get; }
+        IErrorDiffuser Diffuser { get; }
 
         /// <summary>
         /// Quantize an image frame and return the resulting output pixels.

src/ImageSharp/Processing/Quantization/FrameQuantizers/OctreeFrameQuantizer{TPixel}.cs

@@ -121,7 +121,7 @@ namespace SixLabors.ImageSharp.Processing.Quantization.FrameQuantizers
                     if (this.Dither)
                     {
                         // Apply the dithering matrix. We have to reapply the value now as the original has changed.
-                        this.DitherType.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height);
+                        this.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height);
                     }
 
                     output[(y * source.Width) + x] = pixelValue;

src/ImageSharp/Processing/Quantization/FrameQuantizers/PaletteFrameQuantizer{TPixel}.cs

@@ -77,7 +77,7 @@ namespace SixLabors.ImageSharp.Processing.Quantization.FrameQuantizers
                     if (this.Dither)
                     {
                         // Apply the dithering matrix. We have to reapply the value now as the original has changed.
-                        this.DitherType.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height);
+                        this.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height);
                     }
 
                     output[(y * source.Width) + x] = pixelValue;

src/ImageSharp/Processing/Quantization/FrameQuantizers/WuFrameQuantizer{TPixel}.cs

@@ -290,7 +290,7 @@ namespace SixLabors.ImageSharp.Processing.Quantization.FrameQuantizers
                     if (this.Dither)
                     {
                         // Apply the dithering matrix. We have to reapply the value now as the original has changed.
-                        this.DitherType.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height);
+                        this.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height);
                     }
 
                     output[(y * source.Width) + x] = pixelValue;

src/ImageSharp/Processing/Quantization/IQuantizer.cs

@@ -13,14 +13,9 @@ namespace SixLabors.ImageSharp.Processing.Quantization
     public interface IQuantizer
     {
         /// <summary>
-        /// Gets a value indicating whether to apply dithering to the output image.
+        /// Gets the error diffusion algorithm to apply to the output image.
         /// </summary>
-        bool Dither { get; }
-
-        /// <summary>
-        /// Gets the dithering algorithm to apply to the output image.
-        /// </summary>
-        IErrorDiffuser DitherType { get; }
+        IErrorDiffuser Diffuser { get; }
 
         /// <summary>
         /// Creates the generic frame quantizer

src/ImageSharp/Processing/Quantization/OctreeQuantizer.cs

@@ -18,7 +18,16 @@ namespace SixLabors.ImageSharp.Processing.Quantization
         /// Initializes a new instance of the <see cref="OctreeQuantizer"/> class.
         /// </summary>
         public OctreeQuantizer()
-            : this(255)
+            : this(true)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="OctreeQuantizer"/> class.
+        /// </summary>
+        /// <param name="maxColors">The maximum number of colors to hold in the color palette</param>
+        public OctreeQuantizer(int maxColors)
+            : this(GetDiffuser(true), maxColors)
         {
         }
 
@@ -27,40 +36,34 @@ namespace SixLabors.ImageSharp.Processing.Quantization
         /// </summary>
         /// <param name="dither">Whether to apply dithering to the output image</param>
         public OctreeQuantizer(bool dither)
-            : this(dither, DiffuseMode.FloydSteinberg, 255)
+            : this(GetDiffuser(dither), 255)
         {
         }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="OctreeQuantizer"/> class.
         /// </summary>
-        /// <param name="maxColors">The maximum number of colors to hold in the color palette</param>
-        public OctreeQuantizer(int maxColors)
-            : this(true, DiffuseMode.FloydSteinberg, maxColors)
+        /// <param name="diffuser">The error diffusion algorithm, if any, to apply to the output image</param>
+        public OctreeQuantizer(IErrorDiffuser diffuser)
+             : this(diffuser, 255)
         {
         }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="OctreeQuantizer"/> class.
         /// </summary>
-        /// <param name="dither">Whether to apply dithering to the output image</param>
-        /// <param name="ditherType">The dithering algorithm to apply to the output image</param>
+        /// <param name="diffuser">The error diffusion algorithm, if any, to apply to the output image</param>
         /// <param name="maxColors">The maximum number of colors to hold in the color palette</param>
-        public OctreeQuantizer(bool dither, IErrorDiffuser ditherType, int maxColors)
+        public OctreeQuantizer(IErrorDiffuser diffuser, int maxColors)
         {
-            Guard.NotNull(ditherType, nameof(ditherType));
             Guard.MustBeBetweenOrEqualTo(maxColors, 1, 255, nameof(maxColors));
 
-            this.Dither = dither;
-            this.DitherType = ditherType;
+            this.Diffuser = diffuser;
             this.MaxColors = maxColors;
         }
 
         /// <inheritdoc />
-        public bool Dither { get; }
-
-        /// <inheritdoc />
-        public IErrorDiffuser DitherType { get; }
+        public IErrorDiffuser Diffuser { get; }
 
         /// <summary>
         /// Gets the maximum number of colors to hold in the color palette.
@@ -71,5 +74,7 @@ namespace SixLabors.ImageSharp.Processing.Quantization
         public IFrameQuantizer<TPixel> CreateFrameQuantizer<TPixel>()
             where TPixel : struct, IPixel<TPixel>
             => new OctreeFrameQuantizer<TPixel>(this);
+
+        private static IErrorDiffuser GetDiffuser(bool dither) => dither ? DiffuseMode.FloydSteinberg : null;
     }
 }

src/ImageSharp/Processing/Quantization/PaletteQuantizer.cs

@@ -19,7 +19,7 @@ namespace SixLabors.ImageSharp.Processing.Quantization
         /// Initializes a new instance of the <see cref="PaletteQuantizer"/> class.
         /// </summary>
         public PaletteQuantizer()
-            : this(true, DiffuseMode.FloydSteinberg)
+             : this(true)
         {
         }
 
@@ -28,28 +28,21 @@ namespace SixLabors.ImageSharp.Processing.Quantization
         /// </summary>
         /// <param name="dither">Whether to apply dithering to the output image</param>
         public PaletteQuantizer(bool dither)
-            : this(dither, DiffuseMode.FloydSteinberg)
+            : this(GetDiffuser(dither))
         {
         }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="PaletteQuantizer"/> class.
         /// </summary>
-        /// <param name="dither">Whether to apply dithering to the output image</param>
-        /// <param name="ditherType">The dithering algorithm to apply to the output image</param>
-        public PaletteQuantizer(bool dither, IErrorDiffuser ditherType)
+        /// <param name="diffuser">The error diffusion algorithm, if any, to apply to the output image</param>
+        public PaletteQuantizer(IErrorDiffuser diffuser)
         {
-            Guard.NotNull(ditherType, nameof(ditherType));
-
-            this.Dither = dither;
-            this.DitherType = ditherType;
+            this.Diffuser = diffuser;
         }
 
         /// <inheritdoc />
-        public bool Dither { get; }
-
-        /// <inheritdoc />
-        public IErrorDiffuser DitherType { get; }
+        public IErrorDiffuser Diffuser { get; }
 
         /// <summary>
         /// Gets the palette to use to quantize the image.
@@ -64,5 +57,7 @@ namespace SixLabors.ImageSharp.Processing.Quantization
         public IFrameQuantizer<TPixel> CreateFrameQuantizer<TPixel>()
             where TPixel : struct, IPixel<TPixel>
             => new PaletteFrameQuantizer<TPixel>(this);
+
+        private static IErrorDiffuser GetDiffuser(bool dither) => dither ? DiffuseMode.FloydSteinberg : null;
     }
 }

src/ImageSharp/Processing/Quantization/WuQuantizer.cs

@@ -18,7 +18,16 @@ namespace SixLabors.ImageSharp.Processing.Quantization
         /// Initializes a new instance of the <see cref="WuQuantizer"/> class.
         /// </summary>
         public WuQuantizer()
-            : this(255)
+            : this(true)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="WuQuantizer"/> class.
+        /// </summary>
+        /// <param name="maxColors">The maximum number of colors to hold in the color palette</param>
+        public WuQuantizer(int maxColors)
+            : this(GetDiffuser(true), maxColors)
         {
         }
 
@@ -27,40 +36,34 @@ namespace SixLabors.ImageSharp.Processing.Quantization
         /// </summary>
         /// <param name="dither">Whether to apply dithering to the output image</param>
         public WuQuantizer(bool dither)
-            : this(dither, DiffuseMode.FloydSteinberg, 255)
+            : this(GetDiffuser(dither), 255)
         {
         }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="WuQuantizer"/> class.
         /// </summary>
-        /// <param name="maxColors">The maximum number of colors to hold in the color palette</param>
-        public WuQuantizer(int maxColors)
-            : this(true, DiffuseMode.FloydSteinberg, maxColors)
+        /// <param name="diffuser">The error diffusion algorithm, if any, to apply to the output image</param>
+        public WuQuantizer(IErrorDiffuser diffuser)
+            : this(diffuser, 255)
         {
         }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="WuQuantizer"/> class.
         /// </summary>
-        /// <param name="dither">Whether to apply dithering to the output image</param>
-        /// <param name="ditherType">The dithering algorithm to apply to the output image</param>
+        /// <param name="diffuser">The error diffusion algorithm, if any, to apply to the output image</param>
         /// <param name="maxColors">The maximum number of colors to hold in the color palette</param>
-        public WuQuantizer(bool dither, IErrorDiffuser ditherType, int maxColors)
+        public WuQuantizer(IErrorDiffuser diffuser, int maxColors)
         {
-            Guard.NotNull(ditherType, nameof(ditherType));
             Guard.MustBeBetweenOrEqualTo(maxColors, 1, 255, nameof(maxColors));
 
-            this.Dither = dither;
-            this.DitherType = ditherType;
+            this.Diffuser = diffuser;
             this.MaxColors = maxColors;
         }
 
         /// <inheritdoc />
-        public bool Dither { get; }
-
-        /// <inheritdoc />
-        public IErrorDiffuser DitherType { get; }
+        public IErrorDiffuser Diffuser { get; }
 
         /// <summary>
         /// Gets the maximum number of colors to hold in the color palette.
@@ -71,5 +74,7 @@ namespace SixLabors.ImageSharp.Processing.Quantization
         public IFrameQuantizer<TPixel> CreateFrameQuantizer<TPixel>()
             where TPixel : struct, IPixel<TPixel>
             => new WuFrameQuantizer<TPixel>(this);
+
+        private static IErrorDiffuser GetDiffuser(bool dither) => dither ? DiffuseMode.FloydSteinberg : null;
     }
 }

tests/ImageSharp.Tests/Quantization/QuantizedImageTests.cs

@@ -14,9 +14,13 @@
             var octree = new OctreeQuantizer();
             var wu = new WuQuantizer();
 
-            Assert.True(palette.Dither);
-            Assert.True(octree.Dither);
-            Assert.True(wu.Dither);
+            Assert.NotNull(palette.Diffuser);
+            Assert.NotNull(octree.Diffuser);
+            Assert.NotNull(wu.Diffuser);
+
+            Assert.True(palette.CreateFrameQuantizer<Rgba32>().Dither);
+            Assert.True(octree.CreateFrameQuantizer<Rgba32>().Dither);
+            Assert.True(wu.CreateFrameQuantizer<Rgba32>().Dither);
         }
 
         [Theory]