Add nearest neighbour resampler #257

Former-commit-id: 8e6ac4bf4ee07615c7bb707aedc12afccd1647af
Former-commit-id: 40db8d0882d4974b675fd0cd7531eabb7c701210
Former-commit-id: 99fdd9fb8851e2e23510f3682f671acf06620a31

src/ImageProcessor/Samplers/ImageSampleExtensions.cs

@@ -105,11 +105,23 @@ namespace ImageProcessor.Samplers
         /// Rotates an image by the given angle in degrees.
         /// </summary>
         /// <param name="source">The image to resize.</param>
-        /// <param name="degrees">The angle in degrees to porform the rotation.</param>
+        /// <param name="degrees">The angle in degrees to perform the rotation.</param>
         /// <returns>The <see cref="Image"/></returns>
         public static Image Rotate(this Image source, float degrees)
         {
             return source.Process(source.Width, source.Height, source.Bounds, source.Bounds, new Resampler(new RobidouxResampler()) { Angle = degrees });
         }
+
+        /// <summary>
+        /// Rotates an image by the given angle in degrees.
+        /// </summary>
+        /// <param name="source">The image to resize.</param>
+        /// <param name="degrees">The angle in degrees to perform the rotation.</param>
+        /// <param name="sampler">The <see cref="IResampler"/> to perform the resampling.</param>
+        /// <returns>The <see cref="Image"/></returns>
+        public static Image Rotate(this Image source, float degrees, IResampler sampler)
+        {
+            return source.Process(source.Width, source.Height, source.Bounds, source.Bounds, new Resampler(sampler) { Angle = degrees });
+        }
     }
 }

src/ImageProcessor/Samplers/Resampler.cs

@@ -77,8 +77,11 @@ namespace ImageProcessor.Samplers
         /// <inheritdoc/>
         protected override void OnApply(ImageBase source, ImageBase target, Rectangle targetRectangle, Rectangle sourceRectangle)
         {
-            this.horizontalWeights = this.PrecomputeWeights(targetRectangle.Width, sourceRectangle.Width);
+            if (!(this.Sampler is NearestNeighborResampler))
-            this.verticalWeights = this.PrecomputeWeights(targetRectangle.Height, sourceRectangle.Height);
+            {
+                this.horizontalWeights = this.PrecomputeWeights(targetRectangle.Width, sourceRectangle.Width);
+                this.verticalWeights = this.PrecomputeWeights(targetRectangle.Height, sourceRectangle.Height);
+            }
         }
 
         /// <inheritdoc/>
@@ -126,6 +129,37 @@ namespace ImageProcessor.Samplers
             int startX = targetRectangle.X;
             int endX = targetRectangle.Right;
 
+            if (this.Sampler is NearestNeighborResampler)
+            {
+                // Scaling factors
+                float widthFactor = source.Width / (float)target.Width;
+                float heightFactor = source.Height / (float)target.Height;
+
+                Parallel.For(
+                    startY,
+                    endY,
+                    y =>
+                    {
+                        if (y >= targetY && y < targetBottom)
+                        {
+                            // Y coordinates of source points
+                            int originY = (int)((y - targetY) * heightFactor);
+
+                            for (int x = startX; x < endX; x++)
+                            {
+                                // X coordinates of source points
+                                int originX = (int)((x - startX) * widthFactor);
+
+                                target[x, y] = source[originX, originY];
+                            }
+                        }
+                    });
+
+                // Break out now.
+                return;
+            }
+
+            // Interpolate the image using the calculated weights.
             Parallel.For(
                 startY,
                 endY,
@@ -198,6 +232,45 @@ namespace ImageProcessor.Samplers
             float negativeAngle = -this.angle;
             Vector2 centre = Rectangle.Center(sourceRectangle);
 
+            if (this.Sampler is NearestNeighborResampler)
+            {
+                // Scaling factors
+                float widthFactor = source.Width / (float)target.Width;
+                float heightFactor = source.Height / (float)target.Height;
+
+                Parallel.For(
+                    startY,
+                    endY,
+                    y =>
+                    {
+                        if (y >= targetY && y < targetBottom)
+                        {
+                            // Y coordinates of source points
+                            int originY = (int)((y - targetY) * heightFactor);
+
+                            for (int x = startX; x < endX; x++)
+                            {
+                                // X coordinates of source points
+                                int originX = (int)((x - startX) * widthFactor);
+
+                                // Rotate at the centre point
+                                Vector2 rotated = ImageMaths.RotatePoint(new Vector2(originX, originY), centre, negativeAngle);
+                                int rotatedX = (int)rotated.X;
+                                int rotatedY = (int)rotated.Y;
+
+                                if (sourceRectangle.Contains(rotatedX, rotatedY))
+                                {
+                                    target[x, y] = source[rotatedX, rotatedY];
+                                }
+                            }
+                        }
+                    });
+
+                // Break out now.
+                return;
+            }
+
+            // Interpolate the image using the calculated weights.
             Parallel.For(
                 startY,
                 endY,
@@ -236,13 +309,6 @@ namespace ImageProcessor.Samplers
                                         destination.B += sourceColor.B * weight;
                                         destination.A += sourceColor.A * weight;
                                     }
-                                    else
-                                    {
-                                        // This is well hacky but clears up most of the 
-                                        // Alpha bleeding issues present in rotated images.
-                                        float weight = yw.Value * xw.Value;
-                                        destination.A += .9f * weight;
-                                    }
                                 }
                             }
 

src/ImageProcessor/Samplers/Resamplers/BicubicResampler.cs

@@ -8,6 +8,7 @@ namespace ImageProcessor.Samplers
     /// <summary>
     /// The function implements the bicubic kernel algorithm W(x) as described on
     /// <see href="https://en.wikipedia.org/wiki/Bicubic_interpolation#Bicubic_convolution_algorithm">Wikipedia</see>
+    /// A commonly used algorithm within imageprocessing that preserves sharpness better than triangle interpolation.
     /// </summary>
     public class BicubicResampler : IResampler
     {

src/ImageProcessor/Samplers/Resamplers/BoxResampler.cs

@@ -6,7 +6,8 @@
 namespace ImageProcessor.Samplers
 {
     /// <summary>
-    /// The function implements the box (nearest neighbour) algorithm.
+    /// The function implements the box algorithm. Similar to nearest neighbour when upscaling.
+    /// When downscaling the pixels will average, merging together.
     /// </summary>
     public class BoxResampler : IResampler
     {

src/ImageProcessor/Samplers/Resamplers/NearestNeighborResampler.cs

@@ -0,0 +1,23 @@
+// <copyright file="NearestNeighborResampler.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessor.Samplers
+{
+    /// <summary>
+    /// The function implements the nearest neighbour algorithm. This uses an unscaled filter
+    /// which will select the closest pixel to the new pixels position.
+    /// </summary>
+    public class NearestNeighborResampler : IResampler
+    {
+        /// <inheritdoc/>
+        public float Radius => 1;
+
+        /// <inheritdoc/>
+        public float GetValue(float x)
+        {
+            return x;
+        }
+    }
+}

src/ImageProcessor/Samplers/Resamplers/TriangleResampler.cs

@@ -7,6 +7,8 @@ namespace ImageProcessor.Samplers
 {
     /// <summary>
     /// The function implements the triangle (bilinear) algorithm.
+    /// Bilinear interpolation can be used where perfect image transformation with pixel matching is impossible, 
+    /// so that one can calculate and assign appropriate intensity values to pixels.   
     /// </summary>
     public class TriangleResampler : IResampler
     {

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

@@ -21,6 +21,7 @@ namespace ImageProcessor.Tests
                 { "Lanczos5", new Lanczos5Resampler() },
                 { "Lanczos8", new Lanczos8Resampler() },
                 { "MitchellNetravali", new MitchellNetravaliResampler() },
+                { "NearestNeighbor", new NearestNeighborResampler() },
                 { "Hermite", new HermiteResampler() },
                 { "Spline", new SplineResampler() },
                 { "Robidoux", new RobidouxResampler() },
@@ -33,9 +34,9 @@ namespace ImageProcessor.Tests
         [MemberData("Samplers")]
         public void ImageShouldResize(string name, IResampler sampler)
         {
-            if (!Directory.Exists("TestOutput/Resized"))
+            if (!Directory.Exists("TestOutput/Resize"))
             {
-                Directory.CreateDirectory("TestOutput/Resized");
+                Directory.CreateDirectory("TestOutput/Resize");
             }
 
             foreach (string file in Files)
@@ -45,7 +46,7 @@ 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($"TestOutput/Resized/{filename}"))
+                    using (FileStream output = File.OpenWrite($"TestOutput/Resize/{filename}"))
                     {
                         image.Resize(image.Width / 2, image.Height / 2, sampler)
                              .Save(output);
@@ -56,6 +57,33 @@ namespace ImageProcessor.Tests
             }
         }
 
+        [Theory]
+        [MemberData("Samplers")]
+        public void ImageShouldRotate(string name, IResampler sampler)
+        {
+            if (!Directory.Exists("TestOutput/Rotate"))
+            {
+                Directory.CreateDirectory("TestOutput/Rotate");
+            }
+
+            foreach (string file in Files)
+            {
+                using (FileStream stream = File.OpenRead(file))
+                {
+                    Stopwatch watch = Stopwatch.StartNew();
+                    Image image = new Image(stream);
+                    string filename = Path.GetFileNameWithoutExtension(file) + "-" + name + Path.GetExtension(file);
+                    using (FileStream output = File.OpenWrite($"TestOutput/Rotate/{filename}"))
+                    {
+                        image.Rotate(45, sampler)
+                             .Save(output);
+                    }
+
+                    Trace.WriteLine($"{name}: {watch.ElapsedMilliseconds}ms");
+                }
+            }
+        }
+
         [Fact]
         public void ImageShouldEntropyCrop()
         {
@@ -81,9 +109,9 @@ namespace ImageProcessor.Tests
         [Fact]
         public void ImageShouldCrop()
         {
-            if (!Directory.Exists("TestOutput/Cropped"))
+            if (!Directory.Exists("TestOutput/Crop"))
             {
-                Directory.CreateDirectory("TestOutput/Cropped");
+                Directory.CreateDirectory("TestOutput/Crop");
             }
 
             foreach (string file in Files)
@@ -91,8 +119,8 @@ namespace ImageProcessor.Tests
                 using (FileStream stream = File.OpenRead(file))
                 {
                     Image image = new Image(stream);
-                    string filename = Path.GetFileNameWithoutExtension(file) + "-Cropped" + Path.GetExtension(file);
+                    string filename = Path.GetFileNameWithoutExtension(file) + "-Crop" + Path.GetExtension(file);
-                    using (FileStream output = File.OpenWrite($"TestOutput/Cropped/{filename}"))
+                    using (FileStream output = File.OpenWrite($"TestOutput/Crop/{filename}"))
                     {
                         image.Crop(image.Width / 2, image.Height / 2).Save(output);
                     }