Add box blur. Fix #263

Former-commit-id: f8adc1e633f948b24cee0113681133b075603183
Former-commit-id: 1917069ba119db6ecddc34581c258e050ab40e3d
Former-commit-id: 4d1a9fefc9f2767a66fc236ddb25d14b3c600c9f

src/ImageProcessor/Filters/Convolution/BoxBlur.cs

@@ -0,0 +1,106 @@
+// <copyright file="BoxBlur.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessor.Filters
+{
+    /// <summary>
+    /// Applies a Box blur filter to the image.
+    /// </summary>
+    public class BoxBlur : Convolution2PassFilter
+    {
+        /// <summary>
+        /// The maximum size of the kernal in either direction.
+        /// </summary>
+        private readonly int kernelSize;
+
+        /// <summary>
+        /// The vertical kernel
+        /// </summary>
+        private float[,] kernelY;
+
+        /// <summary>
+        /// The horizontal kernel
+        /// </summary>
+        private float[,] kernelX;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="GuassianBlur"/> class.
+        /// </summary>
+        /// <param name="radius">
+        /// The 'radius' value representing the size of the area to sample.
+        /// </param>
+        public BoxBlur(int radius = 7)
+        {
+            this.kernelSize = (radius * 2) + 1;
+        }
+
+        /// <inheritdoc/>
+        public override float[,] KernelX => this.kernelX;
+
+        /// <inheritdoc/>
+        public override float[,] KernelY => this.kernelY;
+
+        /// <inheritdoc/>
+        public override int Parallelism => 1;
+
+        /// <inheritdoc/>
+        protected override void OnApply(ImageBase source, ImageBase target, Rectangle targetRectangle, Rectangle sourceRectangle)
+        {
+            if (this.kernelY == null)
+            {
+                this.kernelY = this.CreateBoxKernel(false);
+            }
+
+            if (this.kernelX == null)
+            {
+                this.kernelX = this.CreateBoxKernel(true);
+            }
+        }
+
+        /// <summary>
+        /// Create a 1 dimensional Box kernel.
+        /// </summary>
+        /// <param name="horizontal">Whether to calculate a horizontal kernel.</param>
+        /// <returns>The <see cref="T:float[,]"/></returns>
+        private float[,] CreateBoxKernel(bool horizontal)
+        {
+            int size = this.kernelSize;
+            float[,] kernel = horizontal ? new float[1, size] : new float[size, 1];
+            float sum = 0.0f;
+
+            for (int i = 0; i < size; i++)
+            {
+                float x = 1;
+                sum += x;
+                if (horizontal)
+                {
+                    kernel[0, i] = x;
+                }
+                else
+                {
+                    kernel[i, 0] = x;
+                }
+            }
+
+            // Normalise kernel so that the sum of all weights equals 1
+            if (horizontal)
+            {
+                for (int i = 0; i < size; i++)
+                {
+                    kernel[0, i] = kernel[0, i] / sum;
+                }
+            }
+            else
+            {
+                for (int i = 0; i < size; i++)
+                {
+                    kernel[i, 0] = kernel[i, 0] / sum;
+                }
+            }
+
+            return kernel;
+        }
+    }
+}

src/ImageProcessor/Filters/Convolution/GuassianBlur.cs

@@ -35,9 +35,7 @@ namespace ImageProcessor.Filters
         /// <summary>
         /// Initializes a new instance of the <see cref="GuassianBlur"/> class.
         /// </summary>
-        /// <param name="sigma">
+        /// <param name="sigma">The 'sigma' value representing the weight of the blur.</param>
-        /// The 'sigma' value representing the weight of the blur.
-        /// </param>
         public GuassianBlur(float sigma = 3f)
         {
             this.kernelSize = ((int)Math.Ceiling(sigma) * 2) + 1;

src/ImageProcessor/Filters/ImageFilterExtensions.cs

@@ -96,6 +96,31 @@ namespace ImageProcessor.Filters
             return source.Process(rectangle, new BlackWhite());
         }
 
+        /// <summary>
+        /// Applies a box blur to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="radius">The 'radius' value representing the size of the area to sample.</param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image BoxBlur(this Image source, int radius = 7)
+        {
+            return BoxBlur(source, radius, source.Bounds);
+        }
+
+        /// <summary>
+        /// Applies a box blur to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="radius">The 'radius' value representing the size of the area to sample.</param>
+        /// <param name="rectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to alter.
+        /// </param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image BoxBlur(this Image source, int radius, Rectangle rectangle)
+        {
+            return source.Process(rectangle, new BoxBlur(radius));
+        }
+
         /// <summary>
         /// Alters the brightness component of the image.
         /// </summary>
@@ -209,6 +234,56 @@ namespace ImageProcessor.Filters
                 : source.Process(rectangle, new GreyscaleBt601());
         }
 
+        /// <summary>
+        /// Applies a Guassian blur to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="sigma">The 'sigma' value representing the weight of the blur.</param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image GuassianBlur(this Image source, float sigma = 3f)
+        {
+            return GuassianBlur(source, sigma, source.Bounds);
+        }
+
+        /// <summary>
+        /// Applies a Guassian blur to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="sigma">The 'sigma' value representing the weight of the blur.</param>
+        /// <param name="rectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to alter.
+        /// </param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image GuassianBlur(this Image source, float sigma, Rectangle rectangle)
+        {
+            return source.Process(rectangle, new GuassianBlur(sigma));
+        }
+
+        /// <summary>
+        /// Applies a Guassian sharpening filter to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="sigma">The 'sigma' value representing the weight of the blur.</param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image GuassianSharpen(this Image source, float sigma = 3f)
+        {
+            return GuassianSharpen(source, sigma, source.Bounds);
+        }
+
+        /// <summary>
+        /// Applies a Guassian sharpening filter to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="sigma">The 'sigma' value representing the weight of the blur.</param>
+        /// <param name="rectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to alter.
+        /// </param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image GuassianSharpen(this Image source, float sigma, Rectangle rectangle)
+        {
+            return source.Process(rectangle, new GuassianSharpen(sigma));
+        }
+
         /// <summary>
         /// Alters the hue component of the image.
         /// </summary>

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

@@ -43,7 +43,8 @@ namespace ImageProcessor.Tests
             { "GuassianBlur", new GuassianBlur(10) },
             { "GuassianSharpen", new GuassianSharpen(10) },
             { "Hue-180", new Hue(180) },
-            { "Hue--180", new Hue(-180) }
+            { "Hue--180", new Hue(-180) },
+            { "BoxBlur", new BoxBlur(10) },
         };
 
         [Theory]