Add premultiplied alpha

Former-commit-id: 346fe4d5a27014ff153447113eee4406c9b9d07e
Former-commit-id: fd5c29c65e88e8ba292879950f70ea072848753a
Former-commit-id: 8c2da3d64065b5884117016885a26c5913b932de

README.md

@@ -2,7 +2,7 @@
 
 **This branch contains the new cross platform version of ImageProcessor**.
 
-This is a complete rewrite from the ground up to allow the processing of images without the use of `System.Drawing` using a portable class library (PCL). It's still in early stages but progress has been pretty quick.
+This is a complete rewrite from the ground up to allow the processing of images without the use of `System.Drawing` using a cross-platform class library. It's still in early stages but progress has been pretty quick.
 
 ###Why am I writing this?
 

src/ImageProcessor/Colors/Color.cs

@@ -10,7 +10,8 @@ namespace ImageProcessor
     using System.Numerics;
 
     /// <summary>
-    /// Represents a four-component color using red, green, blue, and alpha data.
+    /// Represents a four-component color using red, green, blue, and alpha data. 
+    /// Each component is stored in premultiplied format multiplied by the alpha component.
     /// </summary>
     /// <remarks>
     /// This struct is fully mutable. This is done (against the guidelines) for the sake of performance,
@@ -470,7 +471,8 @@ namespace ImageProcessor
         {
             amount = amount.Clamp(0f, 1f);
 
-            return (from * (1 - amount)) + (to * amount);
+            //return (from * (1 - amount)) + (to * amount);
+            return (from * (1 - amount)) + to ;
         }
 
         /// <summary>
@@ -478,7 +480,7 @@ namespace ImageProcessor
         /// <see href="http://www.4p8.com/eric.brasseur/gamma.html#formulas"/>
         /// <see href="http://entropymine.com/imageworsener/srgbformula/"/>
         /// </summary>
-        /// <param name="linear">The <see cref="Color"/> whos signal to compress.</param>
+        /// <param name="linear">The <see cref="Color"/> whose signal to compress.</param>
         /// <returns>The <see cref="Color"/>.</returns>
         public static Color Compand(Color linear)
         {
@@ -495,7 +497,7 @@ namespace ImageProcessor
         /// <see href="http://www.4p8.com/eric.brasseur/gamma.html#formulas"/>
         /// <see href="http://entropymine.com/imageworsener/srgbformula/"/>
         /// </summary>
-        /// <param name="gamma">The <see cref="Color"/> whos signal to expand.</param>
+        /// <param name="gamma">The <see cref="Color"/> whose signal to expand.</param>
         /// <returns>The <see cref="Color"/>.</returns>
         public static Color InverseCompand(Color gamma)
         {
@@ -511,33 +513,29 @@ namespace ImageProcessor
         /// Converts a non-premultipled alpha <see cref="Color"/> to a <see cref="Color"/>
         /// that contains premultiplied alpha.
         /// </summary>
-        /// <param name="r">The red component of this <see cref="Color"/>.</param>
-        /// <param name="g">The green component of this <see cref="Color"/>.</param>
-        /// <param name="b">The blue component of this <see cref="Color"/>.</param>
-        /// <param name="a">The alpha component of this <see cref="Color"/>.</param>
+        /// <param name="color">The <see cref="Color"/> to convert.</param>
         /// <returns>The <see cref="Color"/>.</returns>
-        public static Color FromNonPremultiplied(float r, float g, float b, float a)
+        public static Color FromNonPremultiplied(Color color)
         {
-            return new Color(r * a, g * a, b * a, a);
+            float a = color.A;
+            return new Color(color.R * a, color.G * a, color.B * a, a);
         }
 
         /// <summary>
         /// Converts a premultipled alpha <see cref="Color"/> to a <see cref="Color"/>
         /// that contains non-premultiplied alpha.
         /// </summary>
-        /// <param name="r">The red component of this <see cref="Color"/>.</param>
-        /// <param name="g">The green component of this <see cref="Color"/>.</param>
-        /// <param name="b">The blue component of this <see cref="Color"/>.</param>
-        /// <param name="a">The alpha component of this <see cref="Color"/>.</param>
+        /// <param name="color">The <see cref="Color"/> to convert.</param>
         /// <returns>The <see cref="Color"/>.</returns>
-        public static Color ToNonPremultiplied(float r, float g, float b, float a)
+        public static Color ToNonPremultiplied(Color color)
         {
+            float a = color.A;
             if (Math.Abs(a) < Epsilon)
             {
-                return new Color(r, g, b, a);
+                return new Color(color.R, color.G, color.B, a);
             }
 
-            return new Color(r / a, g / a, b / a, a);
+            return new Color(color.R / a, color.G / a, color.B / a, a);
         }
 
         /// <summary>

src/ImageProcessor/Filters/BackgroundColor.cs

@@ -0,0 +1,61 @@
+// <copyright file="Blend.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessor.Filters
+{
+    using System.Threading.Tasks;
+
+    /// <summary>
+    /// Sets the background color of the image.
+    /// </summary>
+    public class BackgroundColor : ParallelImageProcessor
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Blend"/> class.
+        /// </summary>
+        /// <param name="color">The <see cref="Color"/> to set the background color to.</param>
+        public BackgroundColor(Color color)
+        {
+            this.Value = Color.FromNonPremultiplied(color);
+        }
+
+        /// <summary>
+        /// Gets the background color value.
+        /// </summary>
+        public Color Value { get; }
+
+        /// <inheritdoc/>
+        protected override void Apply(ImageBase target, ImageBase source, Rectangle targetRectangle, Rectangle sourceRectangle, int startY, int endY)
+        {
+            int sourceY = sourceRectangle.Y;
+            int sourceBottom = sourceRectangle.Bottom;
+            int startX = sourceRectangle.X;
+            int endX = sourceRectangle.Right;
+            Color backgroundColor = this.Value;
+
+            Parallel.For(
+                startY,
+                endY,
+                y =>
+                {
+                    if (y >= sourceY && y < sourceBottom)
+                    {
+                        for (int x = startX; x < endX; x++)
+                        {
+                            Color color = source[x, y];
+
+                            // TODO: Fix this nonesense.
+                            if (color.A < .9)
+                            {
+                                color = Color.Lerp(color, backgroundColor, .5f);
+                            }
+
+                            target[x, y] = color;
+                        }
+                    }
+                });
+        }
+    }
+}

src/ImageProcessor/Filters/ImageFilterExtensions.cs

@@ -35,6 +35,18 @@ namespace ImageProcessor.Filters
             return source.Process(rectangle, new Alpha(percent));
         }
 
+        /// <summary>
+        /// Combines the given image together with the current one by blending their pixels.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="image">The image to blend with the currently processing image.</param>
+        /// <param name="percent">The opacity of the image image to blend. Must be between 0 and 100.</param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image BackgroundColor(this Image source, Color color)
+        {
+            return source.Process(source.Bounds, new BackgroundColor(color));
+        }
+
         /// <summary>
         /// Combines the given image together with the current one by blending their pixels.
         /// </summary>

src/ImageProcessor/Formats/Gif/GifDecoderCore.cs

@@ -354,6 +354,8 @@ namespace ImageProcessor.Formats
                     {
                         // We divide by 255 as we will store the colors in our floating point format.
                         // Stored in r-> g-> b-> a order.
+                        // Gifs don't store alpha transparency so we don't need to convert to
+                        // premultiplied.
                         int indexOffset = index * 3;
                         this.currentFrame[offset + 0] = colorTable[indexOffset] / 255f; // r
                         this.currentFrame[offset + 1] = colorTable[indexOffset + 1] / 255f; // g

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

@@ -79,7 +79,7 @@ namespace ImageProcessor.Formats
                 for (int x = 0; x < width; x++)
                 {
                     // Now I have the pixel, call the FirstPassQuantize function...
-                    this.InitialQuantizePixel(source[x, y]);
+                    this.InitialQuantizePixel(Color.ToNonPremultiplied(source[x, y]));
                 }
             }
         }
@@ -107,7 +107,7 @@ namespace ImageProcessor.Formats
                 for (int x = 0; x < width; x++)
                 {
                     // Implicit cast here from Color.
-                    Bgra32 sourcePixel = source[x, y];
+                    Bgra32 sourcePixel = Color.ToNonPremultiplied(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.

src/ImageProcessor/Formats/Jpg/JpegEncoder.cs

@@ -105,9 +105,17 @@ namespace ImageProcessor.Formats
                             int start = x * 3;
                             int source = ((y * pixelWidth) + x) * 4;
 
-                            samples[start] = (byte)(sourcePixels[source].Clamp(0, 1) * 255);
-                            samples[start + 1] = (byte)(sourcePixels[source + 1].Clamp(0, 1) * 255);
-                            samples[start + 2] = (byte)(sourcePixels[source + 2].Clamp(0, 1) * 255);
+                            // Convert to non-premultiplied color.
+                            float r = sourcePixels[source];
+                            float g = sourcePixels[source + 1];
+                            float b = sourcePixels[source + 2];
+                            float a = sourcePixels[source + 3];
+
+                            Bgra32 color = Color.ToNonPremultiplied(new Color(r, g, b, a));
+
+                            samples[start] = color.R;
+                            samples[start + 1] = color.G;
+                            samples[start + 2] = color.B;
                         }
 
                         rows[y] = new SampleRow(samples, pixelWidth, 8, 3);

src/ImageProcessor/Formats/Png/GrayscaleReader.cs

@@ -47,10 +47,18 @@ namespace ImageProcessor.Formats
                 {
                     offset = ((this.row * header.Width) + x) * 4;
 
-                    pixels[offset] = newScanline[x * 2] / 255f;
-                    pixels[offset + 1] = newScanline[x * 2] / 255f;
-                    pixels[offset + 2] = newScanline[x * 2] / 255f;
-                    pixels[offset + 3] = newScanline[(x * 2) + 1] / 255f;
+                    // We want to convert to premultiplied alpha here.
+                    float r = newScanline[x * 2] / 255f;
+                    float g = newScanline[x * 2] / 255f;
+                    float b = newScanline[x * 2] / 255f;
+                    float a = newScanline[(x * 2) + 1] / 255f;
+
+                    Color premultiplied = Color.FromNonPremultiplied(new Color(r, g, b, a));
+
+                    pixels[offset] = premultiplied.R;
+                    pixels[offset + 1] = premultiplied.G;
+                    pixels[offset + 2] = premultiplied.B;
+                    pixels[offset + 3] = premultiplied.A;
                 }
             }
             else

src/ImageProcessor/Formats/Png/PaletteIndexReader.cs

@@ -55,13 +55,25 @@ namespace ImageProcessor.Formats
 
                     offset = ((this.row * header.Width) + i) * 4;
                     int pixelOffset = index * 3;
+                    
+                    float r = newScanline[pixelOffset] / 255f;
+                    float g = newScanline[pixelOffset + 1] / 255f;
+                    float b = newScanline[pixelOffset + 2] / 255f;
+                    float a = this.paletteAlpha.Length > index
+                                            ? this.paletteAlpha[index] / 255f
+                                            : 1;
 
-                    pixels[offset] = this.palette[pixelOffset] / 255f;
-                    pixels[offset + 1] = this.palette[pixelOffset + 1] / 255f;
-                    pixels[offset + 2] = this.palette[pixelOffset + 2] / 255f;
-                    pixels[offset + 3] = this.paletteAlpha.Length > index
-                                                ? this.paletteAlpha[index] / 255f
-                                                : 1;
+                    Color color = new Color(r, g, b, a);
+                    if (color.A < 1)
+                    {
+                        // We want to convert to premultiplied alpha here.
+                        color = Color.FromNonPremultiplied(color);
+                    }
+                    
+                    pixels[offset] = color.R;
+                    pixels[offset + 1] = color.G;
+                    pixels[offset + 2] = color.B;
+                    pixels[offset + 3] = color.A;
                 }
             }
             else

src/ImageProcessor/Formats/Png/PngEncoder.cs

@@ -46,7 +46,9 @@ namespace ImageProcessor.Formats
         /// <c>true</c> if the image should be written uncompressed to
         /// the stream; otherwise, <c>false</c>.
         /// </value>
-        public bool IsWritingUncompressed { get; set; }
+        // TODO: We can't quickly return a color to non-premultiplied with this method.
+        // Should we remove?
+        //public bool IsWritingUncompressed { get; set; }
 
         /// <summary>
         /// Gets or sets a value indicating whether this instance is writing
@@ -113,14 +115,14 @@ namespace ImageProcessor.Formats
             this.WritePhysicalChunk(stream, image);
             this.WriteGammaChunk(stream);
 
-            if (this.IsWritingUncompressed)
-            {
-                this.WriteDataChunksFast(stream, image);
-            }
-            else
-            {
-                this.WriteDataChunks(stream, image);
-            }
+            //if (this.IsWritingUncompressed)
+            //{
+            //    this.WriteDataChunksFast(stream, image);
+            //}
+            //else
+            //{
+            this.WriteDataChunks(stream, image);
+            //}
 
             this.WriteEndChunk(stream);
             stream.Flush();
@@ -318,19 +320,34 @@ namespace ImageProcessor.Formats
                     // Calculate the offset for the original pixel array.
                     int pixelOffset = ((y * imageBase.Width) + x) * 4;
 
-                    data[dataOffset] = (byte)(pixels[pixelOffset].Clamp(0, 1) * 255);
-                    data[dataOffset + 1] = (byte)(pixels[pixelOffset + 1].Clamp(0, 1) * 255);
-                    data[dataOffset + 2] = (byte)(pixels[pixelOffset + 2].Clamp(0, 1) * 255);
-                    data[dataOffset + 3] = (byte)(pixels[pixelOffset + 3].Clamp(0, 1) * 255);
+                    // Convert to non-premultiplied color.
+                    float r = pixels[pixelOffset];
+                    float g = pixels[pixelOffset + 1];
+                    float b = pixels[pixelOffset + 2];
+                    float a = pixels[pixelOffset + 3];
+
+                    Bgra32 color = Color.ToNonPremultiplied(new Color(r, g, b, a));
+
+                    data[dataOffset] = color.R;
+                    data[dataOffset + 1] = color.G;
+                    data[dataOffset + 2] = color.B;
+                    data[dataOffset + 3] = color.A;
 
                     if (y > 0)
                     {
                         int lastOffset = (((y - 1) * imageBase.Width) + x) * 4;
 
-                        data[dataOffset] -= (byte)(pixels[lastOffset].Clamp(0, 1) * 255);
-                        data[dataOffset + 1] -= (byte)(pixels[lastOffset + 1].Clamp(0, 1) * 255);
-                        data[dataOffset + 2] -= (byte)(pixels[lastOffset + 2].Clamp(0, 1) * 255);
-                        data[dataOffset + 3] -= (byte)(pixels[lastOffset + 3].Clamp(0, 1) * 255);
+                        r = pixels[lastOffset];
+                        g = pixels[lastOffset + 1];
+                        b = pixels[lastOffset + 2];
+                        a = pixels[lastOffset + 3];
+
+                        color = Color.ToNonPremultiplied(new Color(r, g, b, a));
+
+                        data[dataOffset] -= color.R;
+                        data[dataOffset + 1] -= color.G;
+                        data[dataOffset + 2] -= color.B;
+                        data[dataOffset + 3] -= color.A;
                     }
                 }
             }

src/ImageProcessor/Formats/Png/TrueColorReader.cs

@@ -44,10 +44,18 @@ namespace ImageProcessor.Formats
                 {
                     offset = ((this.row * header.Width) + (x >> 2)) * 4;
 
-                    pixels[offset + 0] = newScanline[x] / 255f;
-                    pixels[offset + 1] = newScanline[x + 1] / 255f;
-                    pixels[offset + 2] = newScanline[x + 2] / 255f;
-                    pixels[offset + 3] = newScanline[x + 3] / 255f;
+                    // We want to convert to premultiplied alpha here.
+                    float r = newScanline[x] / 255f;
+                    float g = newScanline[x + 1] / 255f;
+                    float b = newScanline[x + 2] / 255f;
+                    float a = newScanline[x + 3] / 255f;
+
+                    Color premultiplied = Color.FromNonPremultiplied(new Color(r, g, b, a));
+
+                    pixels[offset] = premultiplied.R;
+                    pixels[offset + 1] = premultiplied.G;
+                    pixels[offset + 2] = premultiplied.B;
+                    pixels[offset + 3] = premultiplied.A;
                 }
             }
             else
@@ -57,7 +65,7 @@ namespace ImageProcessor.Formats
                     offset = ((this.row * header.Width) + x) * 4;
                     int pixelOffset = x * 3;
 
-                    pixels[offset + 0] = newScanline[pixelOffset] / 255f;
+                    pixels[offset] = newScanline[pixelOffset] / 255f;
                     pixels[offset + 1] = newScanline[pixelOffset + 1] / 255f;
                     pixels[offset + 2] = newScanline[pixelOffset + 2] / 255f;
                     pixels[offset + 3] = 1;

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

@@ -46,9 +46,9 @@ namespace ImageProcessor.Tests
         [MemberData("Filters")]
         public void FilterImage(string name, IImageProcessor processor)
         {
-            if (!Directory.Exists("Filtered"))
+            if (!Directory.Exists("TestOutput/Filtered"))
             {
-                Directory.CreateDirectory("Filtered");
+                Directory.CreateDirectory("TestOutput/Filtered");
             }
 
             foreach (string file in Files)
@@ -58,7 +58,7 @@ namespace ImageProcessor.Tests
                     Stopwatch watch = Stopwatch.StartNew();
                     Image image = new Image(stream);
                     string filename = Path.GetFileNameWithoutExtension(file) + "-" + name + Path.GetExtension(file);
-                    using (FileStream output = File.OpenWrite($"Filtered/{ Path.GetFileName(filename) }"))
+                    using (FileStream output = File.OpenWrite($"TestOutput/Filtered/{ Path.GetFileName(filename) }"))
                     {
                         image.Process(processor).Save(output);
                     }

tests/ImageProcessor.Tests/Processors/ProcessorTestBase.cs

@@ -30,6 +30,7 @@ namespace ImageProcessor.Tests
             //"TestImages/Formats/Jpg/greyscale.jpg",
             //"TestImages/Formats/Bmp/Car.bmp",
             "TestImages/Formats/Png/cballs.png",
+            "TestImages/Formats/Png/blur.png",
             //"TestImages/Formats/Png/cmyk.png",
             //"TestImages/Formats/Png/gamma-1.0-or-2.2.png",
             "TestImages/Formats/Png/splash.png",

tests/ImageProcessor.Tests/Processors/Samplers/SamplerTests.cs

@@ -4,6 +4,7 @@ namespace ImageProcessor.Tests
     using System.Diagnostics;
     using System.IO;
 
+    using ImageProcessor.Filters;
     using ImageProcessor.Samplers;
 
     using Xunit;

tests/ImageProcessor.Tests/TestImages/Formats/Png/blur.png.REMOVED.git-id

@@ -0,0 +1 @@
+8b5342317c64603069b6b7227edeb96f6acf6c29