Fix cross-format quantization

Png can now store more transparent pixels when indexed and work with all
quantizers.


Former-commit-id: 6a4724535829d2c73024b6b1f0235e94e25ccad1
Former-commit-id: 24e4cfff4583c97caef30369302340a3a75ea57a
Former-commit-id: 56ff119c5a2a2506f06b59a23e5e13ec0c3a4688

src/ImageProcessorCore/Formats/Gif/GifEncoderCore.cs

@@ -55,7 +55,7 @@ namespace ImageProcessorCore.Formats
 
             if (this.Quantizer == null)
             {
-                this.Quantizer = new OctreeQuantizer<TColor, TPacked> { Threshold = this.Threshold };
+                this.Quantizer = new OctreeQuantizer<TColor, TPacked>();
             }
 
             // Do not use IDisposable pattern here as we want to preserve the stream. 
@@ -71,14 +71,16 @@ namespace ImageProcessorCore.Formats
             // Quantize the image returning a palette.
             QuantizedImage<TColor, TPacked> quantized = ((IQuantizer<TColor, TPacked>)this.Quantizer).Quantize(image, this.Quality);
 
+            int index = GetTransparentIndex(quantized);
+
             // Write the header.
             this.WriteHeader(writer);
 
             // Write the LSD. We'll use local color tables for now.
-            this.WriteLogicalScreenDescriptor(image, writer, quantized.TransparentIndex);
+            this.WriteLogicalScreenDescriptor(image, writer, index);
 
             // Write the first frame.
-            this.WriteGraphicalControlExtension(image, writer, quantized.TransparentIndex);
+            this.WriteGraphicalControlExtension(image, writer, index);
             this.WriteImageDescriptor(image, writer);
             this.WriteColorTable(quantized, writer);
             this.WriteImageData(quantized, writer);
@@ -90,7 +92,8 @@ namespace ImageProcessorCore.Formats
                 foreach (ImageFrame<TColor, TPacked> frame in image.Frames)
                 {
                     QuantizedImage<TColor, TPacked> quantizedFrame = ((IQuantizer<TColor, TPacked>)this.Quantizer).Quantize(frame, this.Quality);
-                    this.WriteGraphicalControlExtension(frame, writer, quantizedFrame.TransparentIndex);
+                    
+                    this.WriteGraphicalControlExtension(frame, writer, GetTransparentIndex(quantizedFrame));
                     this.WriteImageDescriptor(frame, writer);
                     this.WriteColorTable(quantizedFrame, writer);
                     this.WriteImageData(quantizedFrame, writer);
@@ -101,6 +104,37 @@ namespace ImageProcessorCore.Formats
             writer.Write(GifConstants.EndIntroducer);
         }
 
+        /// <summary>
+        /// Returns the index of the most transparent color in the palette.
+        /// </summary>
+        /// <param name="quantized">
+        /// The quantized.
+        /// </param>
+        /// <typeparam name="TColor">The pixel format.</typeparam>
+        /// <typeparam name="TPacked">The packed format. <example>uint, long, float.</example></typeparam>
+        /// <returns>
+        /// The <see cref="int"/>.
+        /// </returns>
+        private static int GetTransparentIndex<TColor, TPacked>(QuantizedImage<TColor, TPacked> quantized)
+            where TColor : IPackedVector<TPacked>
+            where TPacked : struct
+        {
+            // Find the lowest alpha value and make it the transparent index.
+            int index = 255;
+            float alpha = 1;
+            for (int i = 0; i < quantized.Palette.Length; i++)
+            {
+                float a = quantized.Palette[i].ToVector4().W;
+                if (a < alpha)
+                {
+                    alpha = a;
+                    index = i;
+                }
+            }
+
+            return index;
+        }
+
         /// <summary>
         /// Writes the file header signature and version to the stream.
         /// </summary>

src/ImageProcessorCore/Formats/Png/PngEncoder.cs

@@ -32,7 +32,7 @@ namespace ImageProcessorCore.Formats
         public string Extension => "png";
 
         /// <summary>
-        /// The compression level 1-9. 
+        /// Gets or sets the compression level 1-9. 
         /// <remarks>Defaults to 6.</remarks>
         /// </summary>
         public int CompressionLevel { get; set; } = 6;
@@ -46,14 +46,14 @@ namespace ImageProcessorCore.Formats
         public float Gamma { get; set; } = 2.2F;
 
         /// <summary>
-        /// The quantizer for reducing the color count.
+        /// Gets or sets quantizer for reducing the color count.
         /// </summary>
         public IQuantizer Quantizer { get; set; }
 
         /// <summary>
         /// Gets or sets the transparency threshold.
         /// </summary>
-        public byte Threshold { get; set; } = 128;
+        public byte Threshold { get; set; } = 0;
 
         /// <summary>
         /// Gets or sets a value indicating whether this instance should write
@@ -81,7 +81,7 @@ namespace ImageProcessorCore.Formats
                 CompressionLevel = this.CompressionLevel,
                 Gamma = this.Gamma,
                 Quality = this.Quality,
-                PngColorType = PngColorType,
+                PngColorType = this.PngColorType,
                 Quantizer = this.Quantizer,
                 WriteGamma = this.WriteGamma,
                 Threshold = this.Threshold

src/ImageProcessorCore/Formats/Png/PngEncoderCore.cs

@@ -8,6 +8,7 @@ namespace ImageProcessorCore.Formats
     using System;
     using System.Collections.Generic;
     using System.IO;
+    using System.Linq;
     using System.Threading.Tasks;
 
     using Quantizers;
@@ -86,7 +87,7 @@ namespace ImageProcessorCore.Formats
         /// <summary>
         /// Gets or sets the transparency threshold.
         /// </summary>
-        public byte Threshold { get; set; } = 128;
+        public byte Threshold { get; set; }
 
         /// <summary>
         /// Encodes the image to the specified stream from the <see cref="ImageBase{TColor, TPacked}"/>.
@@ -492,7 +493,7 @@ namespace ImageProcessorCore.Formats
 
             if (this.Quantizer == null)
             {
-                this.Quantizer = new WuQuantizer<TColor, TPacked> { Threshold = this.Threshold };
+                this.Quantizer = new WuQuantizer<TColor, TPacked>();
             }
 
             // Quantize the image returning a palette. This boxing is icky.
@@ -501,7 +502,7 @@ namespace ImageProcessorCore.Formats
             // Grab the palette and write it to the stream.
             TColor[] palette = quantized.Palette;
             int pixelCount = palette.Length;
-
+            List<byte> transparentPixels = new List<byte>();
             // Get max colors for bit depth.
             int colorTableLength = (int)Math.Pow(2, header.BitDepth) * 3;
             byte[] colorTable = new byte[colorTableLength];
@@ -517,14 +518,19 @@ namespace ImageProcessorCore.Formats
                     colorTable[offset] = color.R;
                     colorTable[offset + 1] = color.G;
                     colorTable[offset + 2] = color.B;
+
+                    if (color.A <= this.Threshold)
+                    {
+                        transparentPixels.Add((byte)offset);
+                    }
                 });
 
             this.WriteChunk(stream, PngChunkTypes.Palette, colorTable);
 
             // Write the transparency data
-            if (quantized.TransparentIndex > -1)
+            if (transparentPixels.Any())
             {
-                this.WriteChunk(stream, PngChunkTypes.PaletteAlpha, new[] { (byte)quantized.TransparentIndex });
+                this.WriteChunk(stream, PngChunkTypes.PaletteAlpha, transparentPixels.ToArray());
             }
 
             return quantized;

src/ImageProcessorCore/Quantizers/IQuantizer.cs

@@ -30,9 +30,5 @@ namespace ImageProcessorCore.Quantizers
     /// </summary>
     public interface IQuantizer
     {
-        /// <summary>
-        /// Gets or sets the transparency threshold.
-        /// </summary>
-        byte Threshold { get; set; }
     }
 }

src/ImageProcessorCore/Quantizers/Octree/OctreeQuantizer.cs

@@ -7,7 +7,6 @@ namespace ImageProcessorCore.Quantizers
 {
     using System;
     using System.Collections.Generic;
-    using System.Linq;
 
     /// <summary>
     /// Encapsulates methods to calculate the colour palette if an image using an Octree pattern.
@@ -44,7 +43,7 @@ namespace ImageProcessorCore.Quantizers
         /// <inheritdoc/>
         public override QuantizedImage<TColor, TPacked> Quantize(ImageBase<TColor, TPacked> image, int maxColors)
         {
-            this.colors = maxColors.Clamp(1, 255);
+            this.colors = maxColors.Clamp(1, 256);
 
             if (this.octree == null)
             {
@@ -80,16 +79,7 @@ namespace ImageProcessorCore.Quantizers
         /// </returns>
         protected override byte QuantizePixel(TColor pixel)
         {
-            // The color at [maxColors] is set to transparent
-            byte paletteIndex = (byte)this.colors;
-
-            // Get the palette index if it's transparency meets criterea.
-            if (new Color(pixel.ToVector4()).A > this.Threshold)
-            {
-                paletteIndex = (byte)this.octree.GetPaletteIndex(pixel);
-            }
-
-            return paletteIndex;
+            return (byte)this.octree.GetPaletteIndex(pixel);
         }
 
         /// <summary>
@@ -100,17 +90,18 @@ namespace ImageProcessorCore.Quantizers
         /// </returns>
         protected override List<TColor> GetPalette()
         {
+            return this.octree.Palletize(Math.Max(this.colors, 1));
+
             // First off convert the Octree to maxColors colors
-            List<TColor> palette = this.octree.Palletize(Math.Max(this.colors, 1));
+            //List<TColor> palette = this.octree.Palletize(Math.Max(this.colors, 1));
 
-            int diff = this.colors - palette.Count;
-            if (diff > 0)
-            {
-                palette.AddRange(Enumerable.Repeat(default(TColor), diff));
-            }
-            this.TransparentIndex = this.colors;
+            //int diff = this.colors - palette.Count;
+            //if (diff > 0)
+            //{
+            //    palette.AddRange(Enumerable.Repeat(default(TColor), diff));
+            //}
 
-            return palette;
+            //return palette;
         }
 
         /// <summary>
@@ -134,7 +125,7 @@ namespace ImageProcessorCore.Quantizers
             /// <summary>
             /// Mask used when getting the appropriate pixels for a given node
             /// </summary>
-            private static readonly int[] Mask = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
+            private static readonly int[] Mask = { 0x100, 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
 
             /// <summary>
             /// The root of the Octree
@@ -196,6 +187,7 @@ namespace ImageProcessorCore.Quantizers
             public void AddColor(TColor pixel)
             {
                 TPacked packed = pixel.PackedValue;
+
                 // Check if this request is for the same color as the last
                 if (this.previousColor.Equals(packed))
                 {
@@ -324,6 +316,11 @@ namespace ImageProcessorCore.Quantizers
                 /// </summary>
                 private int blue;
 
+                /// <summary>
+                /// Alpha component
+                /// </summary>
+                private int alpha;
+
                 /// <summary>
                 /// The index of this node in the palette
                 /// </summary>
@@ -346,7 +343,7 @@ namespace ImageProcessorCore.Quantizers
                     // Construct the new node
                     this.leaf = level == colorBits;
 
-                    this.red = this.green = this.blue = 0;
+                    this.red = this.green = this.blue = this.alpha = 0;
                     this.pixelCount = 0;
 
                     // If a leaf, increment the leaf count
@@ -392,9 +389,10 @@ namespace ImageProcessorCore.Quantizers
                         // Go to the next level down in the tree
                         int shift = 7 - level;
                         Color color = new Color(pixel.ToVector4());
-                        int index = ((color.B & Mask[level]) >> (shift - 2)) |
-                                    ((color.G & Mask[level]) >> (shift - 1)) |
-                                    ((color.R & Mask[level]) >> shift);
+                        int index = ((color.A & Mask[0]) >> (shift - 3)) |
+                                    ((color.B & Mask[level + 1]) >> (shift - 2)) |
+                                    ((color.G & Mask[level + 1]) >> (shift - 1)) |
+                                    ((color.R & Mask[level + 1]) >> shift);
 
                         OctreeNode child = this.children[index];
 
@@ -416,7 +414,7 @@ namespace ImageProcessorCore.Quantizers
                 /// <returns>The number of leaves removed</returns>
                 public int Reduce()
                 {
-                    this.red = this.green = this.blue = 0;
+                    this.red = this.green = this.blue = this.alpha = 0;
                     int childNodes = 0;
 
                     // Loop through all children and add their information to this node
@@ -427,6 +425,7 @@ namespace ImageProcessorCore.Quantizers
                             this.red += this.children[index].red;
                             this.green += this.children[index].green;
                             this.blue += this.children[index].blue;
+                            this.alpha += this.children[index].alpha;
                             this.pixelCount += this.children[index].pixelCount;
                             ++childNodes;
                             this.children[index] = null;
@@ -455,10 +454,11 @@ namespace ImageProcessorCore.Quantizers
                         byte r = (this.red / this.pixelCount).ToByte();
                         byte g = (this.green / this.pixelCount).ToByte();
                         byte b = (this.blue / this.pixelCount).ToByte();
+                        byte a = (this.alpha / this.pixelCount).ToByte();
 
                         // And set the color of the palette entry
                         TColor pixel = default(TColor);
-                        pixel.PackFromVector4(new Color(r, g, b).ToVector4());
+                        pixel.PackFromVector4(new Color(r, g, b, a).ToVector4());
                         palette.Add(pixel);
                     }
                     else
@@ -490,9 +490,10 @@ namespace ImageProcessorCore.Quantizers
                     {
                         int shift = 7 - level;
                         Color color = new Color(pixel.ToVector4());
-                        int pixelIndex = ((color.B & Mask[level]) >> (shift - 2)) |
-                                         ((color.G & Mask[level]) >> (shift - 1)) |
-                                         ((color.R & Mask[level]) >> shift);
+                        int pixelIndex = ((color.A & Mask[0]) >> (shift - 3)) |
+                                         ((color.B & Mask[level + 1]) >> (shift - 2)) |
+                                         ((color.G & Mask[level + 1]) >> (shift - 1)) |
+                                         ((color.R & Mask[level + 1]) >> shift);
 
                         if (this.children[pixelIndex] != null)
                         {
@@ -520,6 +521,7 @@ namespace ImageProcessorCore.Quantizers
                     this.red += color.R;
                     this.green += color.G;
                     this.blue += color.B;
+                    this.alpha += color.A;
                 }
             }
         }

src/ImageProcessorCore/Quantizers/Octree/Quantizer.cs

@@ -38,14 +38,6 @@ namespace ImageProcessorCore.Quantizers
             this.singlePass = singlePass;
         }
 
-        /// <summary>
-        /// Gets or sets the transparency index.
-        /// </summary>
-        public int TransparentIndex { get; protected set; } = -1;
-
-        /// <inheritdoc/>
-        public byte Threshold { get; set; }
-
         /// <inheritdoc/>
         public virtual QuantizedImage<TColor, TPacked> Quantize(ImageBase<TColor, TPacked> image, int maxColors)
         {
@@ -73,7 +65,7 @@ namespace ImageProcessorCore.Quantizers
                 this.SecondPass(pixels, quantizedPixels, width, height);
             }
 
-            return new QuantizedImage<TColor, TPacked>(width, height, palette.ToArray(), quantizedPixels, this.TransparentIndex);
+            return new QuantizedImage<TColor, TPacked>(width, height, palette.ToArray(), quantizedPixels);
         }
 
         /// <summary>

src/ImageProcessorCore/Quantizers/Palette/PaletteQuantizer.cs

@@ -80,51 +80,36 @@ namespace ImageProcessorCore.Quantizers
             else
             {
                 // Not found - loop through the palette and find the nearest match.
-                // Firstly check the alpha value - if less than the threshold, lookup the transparent color
-                Color color =new Color(pixel.ToVector4());
-                if (!(color.A > this.Threshold))
-                {
-                    // Transparent. Lookup the first color with an alpha value of 0
-                    for (int index = 0; index < this.colors.Length; index++)
-                    {
-                        if (new Color(this.colors[index].ToVector4()).A == 0)
-                        {
-                            colorIndex = (byte)index;
-                            this.TransparentIndex = colorIndex;
-                            break;
-                        }
-                    }
-                }
-                else
+                Color color = new Color(pixel.ToVector4());
+
+                int leastDistance = int.MaxValue;
+                int red = color.R;
+                int green = color.G;
+                int blue = color.B;
+                int alpha = color.A;
+
+                for (int index = 0; index < this.colors.Length; index++)
                 {
-                    // Not transparent...
-                    int leastDistance = int.MaxValue;
-                    int red = color.R;
-                    int green = color.G;
-                    int blue = color.B;
-
-                    // Loop through the entire palette, looking for the closest color match
-                    for (int index = 0; index < this.colors.Length; index++)
-                    {
-                        Color paletteColor = new Color(this.colors[index].ToVector4());
-                        int redDistance = paletteColor.R - red;
-                        int greenDistance = paletteColor.G - green;
-                        int blueDistance = paletteColor.B - blue;
+                    Color paletteColor = new Color(this.colors[index].ToVector4());
+                    int redDistance = paletteColor.R - red;
+                    int greenDistance = paletteColor.G - green;
+                    int blueDistance = paletteColor.B - blue;
+                    int alphaDistance = paletteColor.A - alpha;
 
-                        int distance = (redDistance * redDistance) +
-                                       (greenDistance * greenDistance) +
-                                       (blueDistance * blueDistance);
+                    int distance = (redDistance * redDistance) +
+                                   (greenDistance * greenDistance) +
+                                   (blueDistance * blueDistance) +
+                                   (alphaDistance * alphaDistance);
 
-                        if (distance < leastDistance)
+                    if (distance < leastDistance)
+                    {
+                        colorIndex = (byte)index;
+                        leastDistance = distance;
+
+                        // And if it's an exact match, exit the loop
+                        if (distance == 0)
                         {
-                            colorIndex = (byte)index;
-                            leastDistance = distance;
-
-                            // And if it's an exact match, exit the loop
-                            if (distance == 0)
-                            {
-                                break;
-                            }
+                            break;
                         }
                     }
                 }
@@ -142,4 +127,4 @@ namespace ImageProcessorCore.Quantizers
             return this.colors.ToList();
         }
     }
-}
+}

src/ImageProcessorCore/Quantizers/QuantizedImage.cs

@@ -24,8 +24,7 @@ namespace ImageProcessorCore.Quantizers
         /// <param name="height">The image height.</param>
         /// <param name="palette">The color palette.</param>
         /// <param name="pixels">The quantized pixels.</param>
-        /// <param name="transparentIndex">The transparency index.</param>
-        public QuantizedImage(int width, int height, TColor[] palette, byte[] pixels, int transparentIndex = -1)
+        public QuantizedImage(int width, int height, TColor[] palette, byte[] pixels)
         {
             Guard.MustBeGreaterThan(width, 0, nameof(width));
             Guard.MustBeGreaterThan(height, 0, nameof(height));
@@ -42,7 +41,6 @@ namespace ImageProcessorCore.Quantizers
             this.Height = height;
             this.Palette = palette;
             this.Pixels = pixels;
-            this.TransparentIndex = transparentIndex;
         }
 
         /// <summary>
@@ -65,11 +63,6 @@ namespace ImageProcessorCore.Quantizers
         /// </summary>
         public byte[] Pixels { get; }
 
-        /// <summary>
-        /// Gets the transparent index
-        /// </summary>
-        public int TransparentIndex { get; }
-
         /// <summary>
         /// Converts this quantized image to a normal image.
         /// </summary>
@@ -98,4 +91,4 @@ namespace ImageProcessorCore.Quantizers
             return image;
         }
     }
-}
+}

src/ImageProcessorCore/Quantizers/Wu/WuQuantizer.cs

@@ -117,9 +117,6 @@ namespace ImageProcessorCore.Quantizers
             this.tag = new byte[TableLength];
         }
 
-        /// <inheritdoc/>
-        public byte Threshold { get; set; }
-
         /// <inheritdoc/>
         public QuantizedImage<TColor, TPacked> Quantize(ImageBase<TColor, TPacked> image, int maxColors)
         {
@@ -334,7 +331,7 @@ namespace ImageProcessorCore.Quantizers
                 for (int x = 0; x < pixels.Width; x++)
                 {
                     // Colors are expected in r->g->b->a format
-                   Color color = new Color(pixels[x, y].ToVector4());
+                    Color color = new Color(pixels[x, y].ToVector4());
 
                     byte r = color.R;
                     byte g = color.G;
@@ -729,7 +726,6 @@ namespace ImageProcessorCore.Quantizers
         {
             List<TColor> pallette = new List<TColor>();
             byte[] pixels = new byte[imagePixels.Width * imagePixels.Height];
-            int transparentIndex = -1;
             int width = imagePixels.Width;
             int height = imagePixels.Height;
 
@@ -741,25 +737,18 @@ namespace ImageProcessorCore.Quantizers
 
                 if (Math.Abs(weight) > Epsilon)
                 {
-                    byte r = (byte)(Volume(cube[k], this.vmr) / weight);
-                    byte g = (byte)(Volume(cube[k], this.vmg) / weight);
-                    byte b = (byte)(Volume(cube[k], this.vmb) / weight);
-                    byte a = (byte)(Volume(cube[k], this.vma) / weight);
+                    float r = (float)(Volume(cube[k], this.vmr) / weight);
+                    float g = (float)(Volume(cube[k], this.vmg) / weight);
+                    float b = (float)(Volume(cube[k], this.vmb) / weight);
+                    float a = (float)(Volume(cube[k], this.vma) / weight);
 
                     TColor color = default(TColor);
                     color.PackFromVector4(new Vector4(r, g, b, a) / 255F);
-
-                    if (color.Equals(default(TColor)))
-                    {
-                        transparentIndex = k;
-                    }
-
                     pallette.Add(color);
                 }
                 else
                 {
                     pallette.Add(default(TColor));
-                    transparentIndex = k;
                 }
             }
 
@@ -778,18 +767,12 @@ namespace ImageProcessorCore.Quantizers
                             int b = color.B >> (8 - IndexBits);
                             int a = color.A >> (8 - IndexAlphaBits);
 
-                            if (transparentIndex > -1 && color.A <= this.Threshold)
-                            {
-                                pixels[(y * width) + x] = (byte)transparentIndex;
-                                continue;
-                            }
-
                             int ind = GetPaletteIndex(r + 1, g + 1, b + 1, a + 1);
                             pixels[(y * width) + x] = this.tag[ind];
                         }
                     });
 
-            return new QuantizedImage<TColor, TPacked>(width, height, pallette.ToArray(), pixels, transparentIndex);
+            return new QuantizedImage<TColor, TPacked>(width, height, pallette.ToArray(), pixels);
         }
     }
 }