diff --git a/src/ImageProcessorCore/Formats/Gif/GifEncoder.cs b/src/ImageProcessorCore/Formats/Gif/GifEncoder.cs
index 5fb3e4b8e9..4dd43f30f7 100644
--- a/src/ImageProcessorCore/Formats/Gif/GifEncoder.cs
+++ b/src/ImageProcessorCore/Formats/Gif/GifEncoder.cs
@@ -23,10 +23,15 @@ namespace ImageProcessorCore.Formats
         /// <remarks>For gifs the value ranges from 1 to 256.</remarks>
         public int Quality { get; set; }
 
+        /// <summary>
+        /// Gets or sets the transparency threshold.
+        /// </summary>
+        public byte Threshold { get; set; } = 128;
+
         /// <summary>
         /// The quantizer for reducing the color count.
         /// </summary>
-        public IQuantizer Quantizer { get; set; } = new OctreeQuantizer();
+        public IQuantizer Quantizer { get; set; }
 
         /// <inheritdoc/>
         public string Extension => "gif";
@@ -51,6 +56,11 @@ namespace ImageProcessorCore.Formats
 
             Image image = (Image)imageBase;
 
+            if (this.Quantizer == null)
+            {
+                this.Quantizer = new OctreeQuantizer { Threshold = this.Threshold };
+            }
+
             // Write the header.
             // File Header signature and version.
             this.WriteString(stream, GifConstants.FileType);
diff --git a/src/ImageProcessorCore/Quantizers/IQuantizer.cs b/src/ImageProcessorCore/Quantizers/IQuantizer.cs
index 68f7554dab..3196ebf9f1 100644
--- a/src/ImageProcessorCore/Quantizers/IQuantizer.cs
+++ b/src/ImageProcessorCore/Quantizers/IQuantizer.cs
@@ -10,6 +10,11 @@ namespace ImageProcessorCore.Quantizers
     /// </summary>
     public interface IQuantizer
     {
+        /// <summary>
+        /// Gets or sets the transparency threshold.
+        /// </summary>
+        byte Threshold { get; set; }
+
         /// <summary>
         /// Quantize an image and return the resulting output pixels.
         /// </summary>
diff --git a/src/ImageProcessorCore/Quantizers/Octree/OctreeQuantizer.cs b/src/ImageProcessorCore/Quantizers/Octree/OctreeQuantizer.cs
index 1ef4cd541c..c0c900145b 100644
--- a/src/ImageProcessorCore/Quantizers/Octree/OctreeQuantizer.cs
+++ b/src/ImageProcessorCore/Quantizers/Octree/OctreeQuantizer.cs
@@ -36,11 +36,6 @@ namespace ImageProcessorCore.Quantizers
         {
         }
 
-        /// <summary>
-        /// Gets or sets the transparency threshold.
-        /// </summary>
-        public byte Threshold { get; set; } = 128;
-
         /// <inheritdoc/>
         public override QuantizedImage Quantize(ImageBase image, int maxColors)
         {
diff --git a/src/ImageProcessorCore/Quantizers/Octree/Quantizer.cs b/src/ImageProcessorCore/Quantizers/Octree/Quantizer.cs
index 3c66cc944c..0db212da57 100644
--- a/src/ImageProcessorCore/Quantizers/Octree/Quantizer.cs
+++ b/src/ImageProcessorCore/Quantizers/Octree/Quantizer.cs
@@ -7,6 +7,7 @@ namespace ImageProcessorCore.Quantizers
 {
     using System;
     using System.Collections.Generic;
+    using System.Threading.Tasks;
 
     /// <summary>
     /// Encapsulates methods to calculate the color palette of an image.
@@ -39,6 +40,9 @@ namespace ImageProcessorCore.Quantizers
         /// </summary>
         public int TransparentIndex { get; protected set; } = -1;
 
+        /// <inheritdoc/>
+        public byte Threshold { get; set; }
+
         /// <inheritdoc/>
         public virtual QuantizedImage Quantize(ImageBase image, int maxColors)
         {
@@ -95,35 +99,17 @@ namespace ImageProcessorCore.Quantizers
         /// <param name="height">The height in pixels of the image</param>
         protected virtual void SecondPass(ImageBase source, byte[] output, int width, int height)
         {
-            int i = 0;
-
-            // Convert the first pixel, so that I have values going into the loop.
-            // Implicit cast here from Color.
-            Bgra32 previousPixel = source[0, 0];
-            byte pixelValue = this.QuantizePixel(previousPixel);
-
-            output[0] = pixelValue;
-
-            for (int y = 0; y < height; y++)
-            {
-                for (int x = 0; x < width; x++)
-                {
-                    Bgra32 sourcePixel = source[x, y];
-
-                    // Check if this is the same as the last pixel. If so use that value
-                    // rather than calculating it again. This is an inexpensive optimization.
-                    if (sourcePixel != previousPixel)
+            Parallel.For(
+                0,
+                source.Height,
+                y =>
                     {
-                        // Quantize the pixel
-                        pixelValue = this.QuantizePixel(sourcePixel);
-
-                        // And setup the previous pointer
-                        previousPixel = sourcePixel;
-                    }
-
-                    output[i++] = pixelValue;
-                }
-            }
+                        for (int x = 0; x < source.Width; x++)
+                        {
+                            Bgra32 sourcePixel = source[x, y];
+                            output[(y * source.Width) + x] = this.QuantizePixel(sourcePixel);
+                        }
+                    });
         }
 
         /// <summary>
diff --git a/src/ImageProcessorCore/Quantizers/Palette/PaletteQuantizer.cs b/src/ImageProcessorCore/Quantizers/Palette/PaletteQuantizer.cs
index 74f192834d..47f77a8777 100644
--- a/src/ImageProcessorCore/Quantizers/Palette/PaletteQuantizer.cs
+++ b/src/ImageProcessorCore/Quantizers/Palette/PaletteQuantizer.cs
@@ -35,9 +35,16 @@ namespace ImageProcessorCore.Quantizers
         public PaletteQuantizer(Color[] palette = null)
             : base(true)
         {
-            this.colors = palette == null
-                ? ColorConstants.WebSafeColors.Select(c => (Bgra32)c).ToArray()
-                : palette.Select(c => (Bgra32)c).ToArray();
+            if (palette == null)
+            {
+                List<Bgra32> safe = ColorConstants.WebSafeColors.Select(c => (Bgra32)c).ToList();
+                safe.Insert(0, Bgra32.Empty);
+                this.colors = safe.ToArray();
+            }
+            else
+            {
+                this.colors = palette.Select(c => (Bgra32)c).ToArray();
+            }
         }
 
         /// <inheritdoc/>
@@ -61,8 +68,8 @@ namespace ImageProcessorCore.Quantizers
             else
             {
                 // Not found - loop through the palette and find the nearest match.
-                // Firstly check the alpha value - if 0, lookup the transparent color
-                if (pixel.A == 0)
+                // Firstly check the alpha value - if less than the threshold, lookup the transparent color
+                if (!(pixel.A > this.Threshold))
                 {
                     // Transparent. Lookup the first color with an alpha value of 0
                     for (int index = 0; index < this.colors.Length; index++)
@@ -91,7 +98,7 @@ namespace ImageProcessorCore.Quantizers
                         int redDistance = paletteColor.R - red;
                         int greenDistance = paletteColor.G - green;
                         int blueDistance = paletteColor.B - blue;
-                        
+
                         int distance = (redDistance * redDistance) +
                                        (greenDistance * greenDistance) +
                                        (blueDistance * blueDistance);
@@ -111,7 +118,7 @@ namespace ImageProcessorCore.Quantizers
                 }
 
                 // Now I have the color, pop it into the cache for next time
-                this.colorMap.Add(colorHash, colorIndex);
+                this.colorMap[colorHash] = colorIndex;
             }
 
             return colorIndex;
diff --git a/src/ImageProcessorCore/Quantizers/Wu/WuQuantizer.cs b/src/ImageProcessorCore/Quantizers/Wu/WuQuantizer.cs
index 9bb4e5f842..55e0bdcc99 100644
--- a/src/ImageProcessorCore/Quantizers/Wu/WuQuantizer.cs
+++ b/src/ImageProcessorCore/Quantizers/Wu/WuQuantizer.cs
@@ -7,6 +7,7 @@ namespace ImageProcessorCore.Quantizers
 {
     using System;
     using System.Collections.Generic;
+    using System.Threading.Tasks;
 
     /// <summary>
     /// An implementation of Wu's color quantizer with alpha channel.
@@ -110,6 +111,9 @@ namespace ImageProcessorCore.Quantizers
             this.tag = new byte[TableLength];
         }
 
+        /// <inheritdoc/>
+        public byte Threshold { get; set; }
+
         /// <inheritdoc/>
         public QuantizedImage Quantize(ImageBase image, int maxColors)
         {
@@ -730,7 +734,7 @@ namespace ImageProcessorCore.Quantizers
                     byte b = (byte)(Volume(cube[k], this.vmb) / weight);
                     byte a = (byte)(Volume(cube[k], this.vma) / weight);
 
-                    var color = new Bgra32(b, g, r, a);
+                    Bgra32 color = new Bgra32(b, g, r, a);
 
                     if (color == Bgra32.Empty)
                     {
@@ -746,22 +750,29 @@ namespace ImageProcessorCore.Quantizers
                 }
             }
 
-            // TODO: Optimize here.
-            int i = 0;
-            for (int y = 0; y < image.Height; y++)
-            {
-                for (int x = 0; x < image.Width; x++)
-                {
-                    Bgra32 color = image[x, y];
-                    int a = color.A >> (8 - IndexAlphaBits);
-                    int r = color.R >> (8 - IndexBits);
-                    int g = color.G >> (8 - IndexBits);
-                    int b = color.B >> (8 - IndexBits);
-
-                    int ind = GetPaletteIndex(r + 1, g + 1, b + 1, a + 1);
-                    pixels[i++] = this.tag[ind];
-                }
-            }
+            Parallel.For(
+                0,
+                image.Height,
+                y =>
+                    {
+                        for (int x = 0; x < image.Width; x++)
+                        {
+                            Bgra32 color = image[x, y];
+                            int a = color.A >> (8 - IndexAlphaBits);
+                            int r = color.R >> (8 - IndexBits);
+                            int g = color.G >> (8 - IndexBits);
+                            int b = color.B >> (8 - IndexBits);
+
+                            if (transparentIndex > -1 && color.A <= this.Threshold)
+                            {
+                                pixels[(y * image.Width) + x] = (byte)transparentIndex;
+                                continue;
+                            }
+
+                            int ind = GetPaletteIndex(r + 1, g + 1, b + 1, a + 1);
+                            pixels[(y * image.Width) + x] = this.tag[ind];
+                        }
+                    });
 
             return new QuantizedImage(image.Width, image.Height, pallette.ToArray(), pixels, transparentIndex);
         }
diff --git a/tests/ImageProcessorCore.Tests/Processors/Formats/EncoderDecoderTests.cs b/tests/ImageProcessorCore.Tests/Processors/Formats/EncoderDecoderTests.cs
index c5eea6ba05..33df554423 100644
--- a/tests/ImageProcessorCore.Tests/Processors/Formats/EncoderDecoderTests.cs
+++ b/tests/ImageProcessorCore.Tests/Processors/Formats/EncoderDecoderTests.cs
@@ -62,7 +62,7 @@
 
                     using (FileStream output = File.OpenWrite($"TestOutput/Quantize/{Path.GetFileName(file)}"))
                     {
-                        quantizedImage.ToImage().Save(output);
+                        quantizedImage.ToImage().Save(output, image.CurrentImageFormat);
                     }
                 }
             }