Palette Quantizer is now threadsafe.

Former-commit-id: 7e9f0265dd832ab739a0579deabae792f351efda
Former-commit-id: 8d60a4d0e34f89e2ef638da8c7b1873ac77aee03
Former-commit-id: 7bc7b4acc76f558796b3cf580446d0f517bb15fa

src/ImageProcessorCore/Quantizers/Palette/PaletteQuantizer.cs

@@ -6,6 +6,7 @@
 namespace ImageProcessorCore.Quantizers
 {
     using System;
+    using System.Collections.Concurrent;
     using System.Collections.Generic;
     using System.Linq;
 
@@ -18,7 +19,7 @@ namespace ImageProcessorCore.Quantizers
         /// <summary>
         /// A lookup table for colors
         /// </summary>
-        private readonly Dictionary<int, byte> colorMap = new Dictionary<int, byte>();
+        private readonly ConcurrentDictionary<string, byte> colorMap = new ConcurrentDictionary<string, byte>();
 
         /// <summary>
         /// List of all colors in the palette
@@ -58,7 +59,7 @@ namespace ImageProcessorCore.Quantizers
         protected override byte QuantizePixel(Bgra32 pixel)
         {
             byte colorIndex = 0;
-            int colorHash = pixel.Bgra;
+            string colorHash = pixel.ToString();
 
             // Check if the color is in the lookup table
             if (this.colorMap.ContainsKey(colorHash))
@@ -118,7 +119,7 @@ namespace ImageProcessorCore.Quantizers
                 }
 
                 // Now I have the color, pop it into the cache for next time
-                this.colorMap[colorHash] = colorIndex;
+                this.colorMap.TryAdd(colorHash, colorIndex);
             }
 
             return colorIndex;

tests/ImageProcessorCore.Tests/Processors/Formats/EncoderDecoderTests.cs

@@ -57,10 +57,27 @@
                 using (FileStream stream = File.OpenRead(file))
                 {
                     Image image = new Image(stream);
-                    IQuantizer quantizer = new OctreeQuantizer();
+                    
+                    IQuantizer quantizer   = new OctreeQuantizer();
                     QuantizedImage quantizedImage = quantizer.Quantize(image, 256);
 
-                    using (FileStream output = File.OpenWrite($"TestOutput/Quantize/{Path.GetFileName(file)}"))
+                    using (FileStream output = File.OpenWrite($"TestOutput/Quantize/Octree-{Path.GetFileName(file)}"))
+                    {
+                        quantizedImage.ToImage().Save(output, image.CurrentImageFormat);
+                    }
+
+                    quantizer = new WuQuantizer();
+                    quantizedImage = quantizer.Quantize(image, 256);
+
+                    using (FileStream output = File.OpenWrite($"TestOutput/Quantize/Wu-{Path.GetFileName(file)}"))
+                    {
+                        quantizedImage.ToImage().Save(output, image.CurrentImageFormat);
+                    }
+
+                    quantizer = new PaletteQuantizer();
+                    quantizedImage = quantizer.Quantize(image, 256);
+
+                    using (FileStream output = File.OpenWrite($"TestOutput/Quantize/Palette-{Path.GetFileName(file)}"))
                     {
                         quantizedImage.ToImage().Save(output, image.CurrentImageFormat);
                     }
@@ -84,7 +101,7 @@
 
                     using (FileStream output = File.OpenWrite($"TestOutput/Indexed/{Path.GetFileNameWithoutExtension(file)}.png"))
                     {
-                        image.Quality = 255;
+                        image.Quality = 256;
                         image.Save(output, new PngFormat());
                     }
                 }