Fix transparency issues caused by rounding.

Former-commit-id: 54a03e11c23470c8f6f195c5b403eff2b7b6bf42
Former-commit-id: bed20d51eb17f0855cc1c122af34af1226f3b1f1
Former-commit-id: f04832c77a4b550059acfd716f766be278bf510a

src/ImageProcessor/Formats/Gif/GifEncoder.cs

@@ -57,7 +57,7 @@ namespace ImageProcessor.Formats
 
             // Write the LSD and check to see if we need a global color table.
             // Always true just now.
-            bool globalColor = this.WriteGlobalLogicalScreenDescriptor(image, stream, bitDepth);
+            this.WriteGlobalLogicalScreenDescriptor(image, stream, bitDepth);
             QuantizedImage quantized = this.WriteColorTable(imageBase, stream, quality, bitDepth);
 
             this.WriteGraphicalControlExtension(imageBase, stream);

src/ImageProcessor/Formats/Gif/Quantizer/OctreeQuantizer.cs

@@ -8,6 +8,8 @@ namespace ImageProcessor.Formats
     using System;
     using System.Collections.Generic;
 
+    using ImageProcessor.Common.Extensions;
+
     /// <summary>
     /// Encapsulates methods to calculate the colour palette if an image using an Octree pattern.
     /// <see href="http://msdn.microsoft.com/en-us/library/aa479306.aspx"/>
@@ -60,6 +62,11 @@ namespace ImageProcessor.Formats
             this.maxColors = maxColors;
         }
 
+        /// <summary>
+        /// Gets or sets the transparency threshold.
+        /// </summary>
+        public byte Threshold { get; set; } = 128;
+
         /// <summary>
         /// Process the pixel in the first pass of the algorithm
         /// </summary>
@@ -90,8 +97,8 @@ namespace ImageProcessor.Formats
             // The color at [maxColors] is set to transparent
             byte paletteIndex = (byte)this.maxColors;
 
-            // Get the palette index if this non-transparent
-            if (pixel.A > 0)
+            // Get the palette index if it's transparency meets criterea.
+            if (pixel.A >= this.Threshold)
             {
                 paletteIndex = (byte)this.octree.GetPaletteIndex(pixel);
             }
@@ -110,7 +117,6 @@ namespace ImageProcessor.Formats
             // First off convert the Octree to maxColors colors
             List<Bgra32> palette = this.octree.Palletize(Math.Max(this.maxColors - 1, 1));
 
-            // Add empty color for transparency
             palette.Add(Bgra32.Empty);
 
             return palette;
@@ -175,7 +181,7 @@ namespace ImageProcessor.Formats
             /// <summary>
             /// Gets or sets the number of leaves in the tree
             /// </summary>
-            private int Leaves
+            public int Leaves
             {
                 get { return this.leafCount; }
                 set { this.leafCount = value; }

tests/ImageProcessor.Tests/Processors/Filters/FilterTests.cs

@@ -13,31 +13,31 @@ namespace ImageProcessor.Tests
     {
         public static readonly TheoryData<string, IImageProcessor> Filters = new TheoryData<string, IImageProcessor>
         {
-            //{ "Brightness-50", new Brightness(50) },
-            //{ "Brightness--50", new Brightness(-50) },
-            //{ "Contrast-50", new Contrast(50) },
-            //{ "Contrast--50", new Contrast(-50) },
-            //{ "Blend", new Blend(new Image(File.OpenRead("../../TestImages/Formats/Bmp/Car.bmp")),15)},
-            //{ "Saturation-50", new Saturation(50) },
-            //{ "Saturation--50", new Saturation(-50) },
-            //{ "Alpha--50", new Alpha(50) },
-            //{ "Invert", new Invert() },
-            //{ "Sepia", new Sepia() },
-            //{ "BlackWhite", new BlackWhite() },
-            //{ "Lomograph", new Lomograph() },
-            //{ "Polaroid", new Polaroid() },
-            //{ "Kodachrome", new Kodachrome() },
-            //{ "GreyscaleBt709", new GreyscaleBt709() },
-            //{ "GreyscaleBt601", new GreyscaleBt601() },
-            //{ "Kayyali", new Kayyali() },
-            //{ "Kirsch", new Kirsch() },
-            //{ "Laplacian3X3", new Laplacian3X3() },
-            //{ "Laplacian5X5", new Laplacian5X5() },
-            //{ "LaplacianOfGaussian", new LaplacianOfGaussian() },
-            //{ "Prewitt", new Prewitt() },
-            //{ "RobertsCross", new RobertsCross() },
-            //{ "Scharr", new Scharr() },
-            //{ "Sobel", new Sobel() },
+            { "Brightness-50", new Brightness(50) },
+            { "Brightness--50", new Brightness(-50) },
+            { "Contrast-50", new Contrast(50) },
+            { "Contrast--50", new Contrast(-50) },
+            { "Blend", new Blend(new Image(File.OpenRead("../../TestImages/Formats/Bmp/Car.bmp")),15)},
+            { "Saturation-50", new Saturation(50) },
+            { "Saturation--50", new Saturation(-50) },
+            { "Alpha--50", new Alpha(50) },
+            { "Invert", new Invert() },
+            { "Sepia", new Sepia() },
+            { "BlackWhite", new BlackWhite() },
+            { "Lomograph", new Lomograph() },
+            { "Polaroid", new Polaroid() },
+            { "Kodachrome", new Kodachrome() },
+            { "GreyscaleBt709", new GreyscaleBt709() },
+            { "GreyscaleBt601", new GreyscaleBt601() },
+            { "Kayyali", new Kayyali() },
+            { "Kirsch", new Kirsch() },
+            { "Laplacian3X3", new Laplacian3X3() },
+            { "Laplacian5X5", new Laplacian5X5() },
+            { "LaplacianOfGaussian", new LaplacianOfGaussian() },
+            { "Prewitt", new Prewitt() },
+            { "RobertsCross", new RobertsCross() },
+            { "Scharr", new Scharr() },
+            { "Sobel", new Sobel() },
             { "GuassianBlur", new GuassianBlur(10) },
             { "GuassianSharpen", new GuassianSharpen(10) }
         };