Use correct parallel options

src/ImageSharp/Image/PixelAccessor{TColor}.cs

@@ -9,6 +9,7 @@ namespace ImageSharp
     using System.Diagnostics;
     using System.Runtime.CompilerServices;
     using System.Runtime.InteropServices;
+    using System.Threading.Tasks;
 
     /// <summary>
     /// Provides per-pixel access to generic <see cref="Image{TColor}"/> pixels.
@@ -60,6 +61,7 @@ namespace ImageSharp
             this.pixelsBase = (byte*)this.dataPointer.ToPointer();
             this.PixelSize = Unsafe.SizeOf<TColor>();
             this.RowStride = this.Width * this.PixelSize;
+            this.ParallelOptions = image.Bootstrapper.ParallelOptions;
         }
 
         /// <summary>
@@ -86,6 +88,7 @@ namespace ImageSharp
             this.pixelsBase = (byte*)this.dataPointer.ToPointer();
             this.PixelSize = Unsafe.SizeOf<TColor>();
             this.RowStride = this.Width * this.PixelSize;
+            this.ParallelOptions = Bootstrapper.Default.ParallelOptions;
         }
 
         /// <summary>
@@ -121,6 +124,11 @@ namespace ImageSharp
         /// </summary>
         public int Height { get; }
 
+        /// <summary>
+        /// Gets the global parallel options for processing tasks in parallel.
+        /// </summary>
+        public ParallelOptions ParallelOptions { get; }
+
         /// <summary>
         /// Gets or sets the pixel at the specified position.
         /// </summary>

src/ImageSharp/Quantizers/Quantize.cs

@@ -6,6 +6,7 @@
 namespace ImageSharp
 {
     using System;
+    using System.Threading.Tasks;
 
     using ImageSharp.Quantizers;
 
@@ -55,9 +56,24 @@ namespace ImageSharp
         public static Image<TColor> Quantize<TColor>(this Image<TColor> source, IQuantizer<TColor> quantizer, int maxColors)
             where TColor : struct, IPackedPixel, IEquatable<TColor>
         {
-            QuantizedImage<TColor> quantizedImage = quantizer.Quantize(source, maxColors);
-            source.SetPixels(source.Width, source.Height, quantizedImage.ToImage().Pixels);
+            QuantizedImage<TColor> quantized = quantizer.Quantize(source, maxColors);
+
+            int pixelCount = quantized.Pixels.Length;
+            int palleteCount = quantized.Palette.Length - 1;
+            TColor[] pixels = new TColor[pixelCount];
+
+            Parallel.For(
+                0,
+                pixelCount,
+                source.Bootstrapper.ParallelOptions,
+                i =>
+                {
+                    TColor color = quantized.Palette[Math.Min(palleteCount, quantized.Pixels[i])];
+                    pixels[i] = color;
+                });
+
+            source.SetPixels(source.Width, source.Height, pixels);
             return source;
         }
     }
-}
+}

src/ImageSharp/Quantizers/QuantizedImage.cs

@@ -59,33 +59,5 @@ namespace ImageSharp.Quantizers
         /// Gets the pixels of this <see cref="T:QuantizedImage"/>.
         /// </summary>
         public byte[] Pixels { get; }
-
-        /// <summary>
-        /// Converts this quantized image to a normal image.
-        /// </summary>
-        /// <returns>
-        /// The <see cref="Image"/>
-        /// </returns>
-        public Image<TColor> ToImage()
-        {
-            Image<TColor> image = new Image<TColor>(this.Width, this.Height);
-
-            int pixelCount = this.Pixels.Length;
-            int palleteCount = this.Palette.Length - 1;
-            TColor[] pixels = new TColor[pixelCount];
-
-            Parallel.For(
-                0,
-                pixelCount,
-                image.Bootstrapper.ParallelOptions,
-                i =>
-                    {
-                        TColor color = this.Palette[Math.Min(palleteCount, this.Pixels[i])];
-                        pixels[i] = color;
-                    });
-
-            image.SetPixels(this.Width, this.Height, pixels);
-            return image;
-        }
     }
 }

src/ImageSharp/Quantizers/Wu/WuQuantizer.cs

@@ -773,7 +773,7 @@ namespace ImageSharp.Quantizers
             Parallel.For(
                 0,
                 height,
-                Bootstrapper.Default.ParallelOptions,
+                imagePixels.ParallelOptions,
                 y =>
                 {
                     byte[] rgba = ArrayPool<byte>.Shared.Rent(4);