Fix transparency allocation

Former-commit-id: 85c4d5c0ccd92dce6265040068aeffe851604045
Former-commit-id: 5b59aa6bb210dcc113cee26d2986c172170a9d8e
Former-commit-id: a048ee2bfc5bf0bdbdcbdd709c485ccb6c50d90d

src/ImageProcessorCore/Formats/Gif/GifEncoder.cs

@@ -131,7 +131,7 @@ namespace ImageProcessorCore.Formats
         private QuantizedImage WriteColorTable(ImageBase image, Stream stream, int quality, int bitDepth)
         {
             // Quantize the image returning a palette.
-            QuantizedImage quantizedImage = this.Quantizer.Quantize(image, quality.Clamp(1, 255));
+            QuantizedImage quantizedImage = this.Quantizer.Quantize(image, quality);
 
             // Grab the palette and write it to the stream.
             Bgra32[] palette = quantizedImage.Palette;
@@ -162,6 +162,7 @@ namespace ImageProcessorCore.Formats
         /// </summary>
         /// <param name="image">The <see cref="ImageBase"/> to encode.</param>
         /// <param name="stream">The stream to write to.</param>
+        /// <param name="transparencyIndex">The index of the color in the color palette to make transparent.</param>
         private void WriteGraphicalControlExtension(ImageBase image, Stream stream, int transparencyIndex)
         {
             // TODO: Check transparency logic.
@@ -189,7 +190,7 @@ namespace ImageProcessorCore.Formats
 
             this.WriteByte(stream, packed);
             this.WriteShort(stream, extension.DelayTime);
-            this.WriteByte(stream, extension.TransparencyIndex);
+            this.WriteByte(stream, extension.TransparencyIndex == -1 ? 255 : extension.TransparencyIndex);
             this.WriteByte(stream, GifConstants.Terminator);
         }
 

src/ImageProcessorCore/Quantizers/Octree/Quantizer.cs

@@ -37,7 +37,7 @@ namespace ImageProcessorCore.Quantizers
         /// <summary>
         /// Gets or sets the transparency index.
         /// </summary>
-        public int TransparentIndex { get; protected set; }
+        public int TransparentIndex { get; protected set; } = -1;
 
         /// <inheritdoc/>
         public virtual QuantizedImage Quantize(ImageBase image, int maxColors)

src/ImageProcessorCore/Quantizers/Wu/WuQuantizer.cs

@@ -715,7 +715,7 @@ namespace ImageProcessorCore.Quantizers
         {
             List<Bgra32> pallette = new List<Bgra32>();
             byte[] pixels = new byte[image.Width * image.Height];
-            int transparentIndex = 0;
+            int transparentIndex = -1;
 
             for (int k = 0; k < colorCount; k++)
             {