Merge pull request #446 from SixLabors/js/premultiply

Premultiply to prevent transparent pixel bleed

src/ImageSharp/Common/Extensions/Vector4Extensions.cs

@@ -12,6 +12,34 @@ namespace SixLabors.ImageSharp
     /// </summary>
     internal static class Vector4Extensions
     {
+        /// <summary>
+        /// Pre-multiplies the "x", "y", "z" components of a vector by its "w" component leaving the "w" component intact.
+        /// </summary>
+        /// <param name="source">The <see cref="Vector4"/> to premultiply</param>
+        /// <returns>The <see cref="Vector4"/></returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector4 Premultiply(this Vector4 source)
+        {
+            float w = source.W;
+            Vector4 premultiplied = source * w;
+            premultiplied.W = w;
+            return premultiplied;
+        }
+
+        /// <summary>
+        /// Reverses the result of premultiplying a vector via <see cref="Premultiply(Vector4)"/>.
+        /// </summary>
+        /// <param name="source">The <see cref="Vector4"/> to premultiply</param>
+        /// <returns>The <see cref="Vector4"/></returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector4 UnPremultiply(this Vector4 source)
+        {
+            float w = source.W;
+            Vector4 unpremultiplied = source / w;
+            unpremultiplied.W = w;
+            return unpremultiplied;
+        }
+
         /// <summary>
         /// Compresses a linear color signal to its sRGB equivalent.
         /// <see href="http://www.4p8.com/eric.brasseur/gamma.html#formulas"/>

src/ImageSharp/Processing/Processors/Convolution/Convolution2DProcessor.cs

@@ -93,7 +93,7 @@ namespace SixLabors.ImageSharp.Processing.Processors
                                     int offsetX = x + fxr;
 
                                     offsetX = offsetX.Clamp(0, maxX);
-                                    var currentColor = sourceOffsetRow[offsetX].ToVector4();
+                                    Vector4 currentColor = sourceOffsetRow[offsetX].ToVector4().Premultiply();
 
                                     if (fy < kernelXHeight)
                                     {
@@ -118,7 +118,7 @@ namespace SixLabors.ImageSharp.Processing.Processors
                             float blue = MathF.Sqrt((bX * bX) + (bY * bY));
 
                             ref TPixel pixel = ref targetRow[x];
-                            pixel.PackFromVector4(new Vector4(red, green, blue, sourceRow[x].ToVector4().W));
+                            pixel.PackFromVector4(new Vector4(red, green, blue, sourceRow[x].ToVector4().W).UnPremultiply());
                         }
                     });
 

src/ImageSharp/Processing/Processors/Convolution/Convolution2PassProcessor.cs

@@ -113,13 +113,13 @@ namespace SixLabors.ImageSharp.Processing.Processors
 
                                 offsetX = offsetX.Clamp(0, maxX);
 
-                                var currentColor = row[offsetX].ToVector4();
+                                Vector4 currentColor = row[offsetX].ToVector4().Premultiply();
                                 destination += kernel[fy, fx] * currentColor;
                             }
                         }
 
                         ref TPixel pixel = ref targetRow[x];
-                        pixel.PackFromVector4(destination);
+                        pixel.PackFromVector4(destination.UnPremultiply());
                     }
                 });
         }

src/ImageSharp/Processing/Processors/Convolution/ConvolutionProcessor.cs

@@ -80,7 +80,7 @@ namespace SixLabors.ImageSharp.Processing.Processors
 
                                  offsetX = offsetX.Clamp(0, maxX);
 
-                                 var currentColor = sourceOffsetRow[offsetX].ToVector4();
+                                 Vector4 currentColor = sourceOffsetRow[offsetX].ToVector4().Premultiply();
                                  currentColor *= this.KernelXY[fy, fx];
 
                                  red += currentColor.X;
@@ -90,7 +90,7 @@ namespace SixLabors.ImageSharp.Processing.Processors
                          }
 
                          ref TPixel pixel = ref targetRow[x];
-                         pixel.PackFromVector4(new Vector4(red, green, blue, sourceRow[x].ToVector4().W));
+                         pixel.PackFromVector4(new Vector4(red, green, blue, sourceRow[x].ToVector4().W).UnPremultiply());
                      }
                  });
 

src/ImageSharp/Processing/Processors/Transforms/AffineTransformProcessor.cs

@@ -204,7 +204,7 @@ namespace SixLabors.ImageSharp.Processing.Processors
                                         var vector = source[i, j].ToVector4();
 
                                         // Values are first premultiplied to prevent darkening of edge pixels
-                                        var mupltiplied = new Vector4(new Vector3(vector.X, vector.Y, vector.Z) * vector.W, vector.W);
+                                        Vector4 mupltiplied = vector.Premultiply();
                                         sum += mupltiplied * xWeight * yWeight;
                                     }
                                 }
@@ -212,7 +212,7 @@ namespace SixLabors.ImageSharp.Processing.Processors
                                 ref TPixel dest = ref destRow[x];
 
                                 // Reverse the premultiplication
-                                dest.PackFromVector4(new Vector4(new Vector3(sum.X, sum.Y, sum.Z) / sum.W, sum.W));
+                                dest.PackFromVector4(sum.UnPremultiply());
                             }
                         });
             }

src/ImageSharp/Processing/Processors/Transforms/ProjectiveTransformProcessor.cs

@@ -199,7 +199,7 @@ namespace SixLabors.ImageSharp.Processing.Processors
                                     var vector = source[i, j].ToVector4();
 
                                     // Values are first premultiplied to prevent darkening of edge pixels
-                                    var mupltiplied = new Vector4(new Vector3(vector.X, vector.Y, vector.Z) * vector.W, vector.W);
+                                    Vector4 mupltiplied = vector.Premultiply();
                                     sum += mupltiplied * xWeight * yWeight;
                                 }
                             }
@@ -207,7 +207,7 @@ namespace SixLabors.ImageSharp.Processing.Processors
                             ref TPixel dest = ref destRow[x];
 
                             // Reverse the premultiplication
-                            dest.PackFromVector4(new Vector4(new Vector3(sum.X, sum.Y, sum.Z) / sum.W, sum.W));
+                            dest.PackFromVector4(sum.UnPremultiply());
                         }
                     });
             }

src/ImageSharp/Processing/Processors/Transforms/WeightsWindow.cs

@@ -87,7 +87,7 @@ namespace SixLabors.ImageSharp.Processing.Processors
             {
                 float weight = Unsafe.Add(ref horizontalValues, i);
                 Vector4 v = Unsafe.Add(ref vecPtr, i);
-                result += v * weight;
+                result += v.Premultiply() * weight;
             }
 
             return result;
@@ -114,10 +114,10 @@ namespace SixLabors.ImageSharp.Processing.Processors
             {
                 float weight = Unsafe.Add(ref horizontalValues, i);
                 Vector4 v = Unsafe.Add(ref vecPtr, i);
-                result += v.Expand() * weight;
+                result += v.Premultiply().Expand() * weight;
             }
 
-            return result;
+            return result.UnPremultiply();
         }
 
         /// <summary>
@@ -144,7 +144,7 @@ namespace SixLabors.ImageSharp.Processing.Processors
                 result += firstPassPixels[x, index] * yw;
             }
 
-            return result;
+            return result.UnPremultiply();
         }
     }
 }

tests/ImageSharp.Tests/Processing/Processors/Convolution/DetectEdgesTest.cs

@@ -3,7 +3,6 @@
 
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing;
-using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
 
 using SixLabors.Primitives;
 using Xunit;
@@ -14,7 +13,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Convolution
     public class DetectEdgesTest : FileTestBase
     {
         public static readonly string[] CommonTestImages = { TestImages.Png.Bike };
-        
+
         public static readonly TheoryData<EdgeDetection> DetectEdgesFilters = new TheoryData<EdgeDetection>
         {
             EdgeDetection.Kayyali,
@@ -39,9 +38,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Convolution
             {
                 image.Mutate(x => x.DetectEdges(detector));
                 image.DebugSave(provider, detector.ToString());
-
-                // TODO: Enable once we have updated the images
-                // image.CompareToReferenceOutput(provider, detector.ToString());
+                image.CompareToReferenceOutput(provider, detector.ToString());
             }
         }
 
@@ -54,9 +51,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Convolution
             {
                 image.Mutate(x => x.DetectEdges());
                 image.DebugSave(provider);
-
-                // TODO: Enable once we have updated the images
-                // image.CompareToReferenceOutput(provider);
+                image.CompareToReferenceOutput(provider);
             }
         }
 
@@ -83,12 +78,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Convolution
 
                 image.Mutate(x => x.DetectEdges(bounds));
                 image.DebugSave(provider);
-
-                // TODO: Enable once we have updated the images
-                //image.CompareToReferenceOutput(provider);
-
-                // TODO: We don't need this any longer after switching to ReferenceImages
-                //ImageComparer.Tolerant().EnsureProcessorChangesAreConstrained(source, image, bounds);
+                image.CompareToReferenceOutput(provider);
             }
         }
     }

tests/ImageSharp.Tests/Processing/Processors/Transforms/ResizeTests.cs

@@ -82,6 +82,19 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
             }
         }
 
+        [Theory]
+        [WithFile(TestImages.Png.Kaboom, DefaultPixelType)]
+        public void Resize_DoesNotBleedAlphaPixels<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            using (Image<TPixel> image = provider.GetImage())
+            {
+                image.Mutate(x => x.Resize(image.Width / 2, image.Height / 2));
+                image.DebugSave(provider);
+                image.CompareToReferenceOutput(provider);
+            }
+        }
+
         [Theory]
         [WithFile(TestImages.Gif.Giphy, DefaultPixelType)]
         public void Resize_IsAppliedToAllFrames<TPixel>(TestImageProvider<TPixel> provider)
@@ -89,7 +102,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
         {
             using (Image<TPixel> image = provider.GetImage())
             {
-                image.Mutate(x => x.Resize(image.Width / 2, image.Height / 2, true));
+                image.Mutate(x => x.Resize(image.Width / 2, image.Height / 2, KnownResamplers.NearestNeighbor));
 
                 // Comparer fights decoder with gif-s. Could not use CompareToReferenceOutput here :(
                 image.DebugSave(provider, extension: Extensions.Gif);

tests/ImageSharp.Tests/TestImages.cs

@@ -35,6 +35,7 @@ namespace SixLabors.ImageSharp.Tests
             public const string Rgb48BppInterlaced = "Png/rgb-48bpp-interlaced.png";
             public const string SnakeGame = "Png/SnakeGame.png";
             public const string Icon = "Png/icon.png";
+            public const string Kaboom = "Png/kaboom.png";
 
             // Filtered test images from http://www.schaik.com/pngsuite/pngsuite_fil_png.html
             public const string Filter0 = "Png/filter0.png";

tests/Images/External

@@ -1 +1 @@
-Subproject commit ddc4045926bb0331be8c1785d9adf5f76dc4e52e
+Subproject commit 376605e05bb704d425b2d17bf5b310f5376da22e