From 250fc599e16d2258e2272ef51a8e4bfdaa681e0d Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Sat, 30 Jul 2016 19:37:39 +1000
Subject: [PATCH] Add Lanczos2 resampler

Former-commit-id: 7190b01b85ed5933e0f5dd276b3eb718a8d78e30
Former-commit-id: 56df11ca6ffb6d0075115dc3b2c714317a379ab8
Former-commit-id: becd320711a19b21267790300429105e071fc5de
---
 README.md                                     | 33 ++++--------------
 .../Samplers/Resamplers/Lanczos2Resampler.cs  | 34 +++++++++++++++++++
 2 files changed, 41 insertions(+), 26 deletions(-)
 create mode 100644 src/ImageProcessorCore/Samplers/Resamplers/Lanczos2Resampler.cs

diff --git a/README.md b/README.md
index 85edc99565..65168b6bde 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,4 @@
+
 # ImageProcessorCore
 
 <img src="build/icons/imageprocessor-logo-512.png" width="128" height="128"/>
@@ -74,6 +75,7 @@ git clone https://github.com/JimBobSquarePants/ImageProcessor
 - Resampling algorithms. (Optional gamma correction, resize modes, Performance improvements?)
  - [x] Box
  - [x] Bicubic
+ - [x] Lanczos2
  - [x] Lanczos3
  - [x] Lanczos5
  - [x] Lanczos8
@@ -81,7 +83,6 @@ git clone https://github.com/JimBobSquarePants/ImageProcessor
  - [x] Nearest Neighbour 
  - [x] Robidoux
  - [x] Robidoux Sharp
- - [x] Robidoux Soft
  - [x] Spline
  - [x] Triangle
  - [x] Welch
@@ -100,8 +101,8 @@ git clone https://github.com/JimBobSquarePants/ImageProcessor
  - [x] Skew by x/y angles and center point.
 - ColorMatrix operations (Uses Matrix4x4)
  - [x] BlackWhite
- - [x] Greyscale BT709
- - [x] Greyscale BT601
+ - [x] Grayscale BT709
+ - [x] Grayscale BT601
  - [x] Hue
  - [x] Saturation
  - [x] Lomograph
@@ -160,7 +161,7 @@ With this version the API will change dramatically. Without the constraints of `
 
 Image methods are also fluent which allow chaining much like the `ImageFactory` class in the Framework version.
 
-Here's an example of the code required to resize an image using the default Bicubic resampler then turn the colors into their greyscale equivalent using the BT709 standard matrix.
+Here's an example of the code required to resize an image using the default Bicubic resampler then turn the colors into their grayscale equivalent using the BT709 standard matrix.
 
 ```csharp
 using (FileStream stream = File.OpenRead("foo.jpg"))
@@ -168,32 +169,12 @@ using (FileStream output = File.OpenWrite("bar.jpg"))
 {
     Image image = new Image(stream);
     image.Resize(image.Width / 2, image.Height / 2)
-         .Greyscale()
+         .Grayscale()
          .Save(output);
 }
 ```
 
-It will also be possible to pass collections of processors as params to manipulate images. For example here I am applying a Gaussian blur with a sigma of 5 to an image, then detecting the edges using a Sobel operator working in greyscale mode.
-
-```csharp
-using (FileStream stream = File.OpenRead("foo.jpg"))
-using (FileStream output = File.OpenWrite("bar.jpg"))
-{
-    Image image = new Image(stream);
-    List<IImageProcessor> processors = new List<IImageProcessor>()
-    {
-        new GuassianBlur(5),
-        new Sobel { Greyscale = true }
-    };
-
-    foreach (IImageProcessor processor in processors){
-
-        image.Process(processor)
-             .Save(output);
-    }
-}
-```
-Individual processors can be initialised and apply processing against images. This allows nesting which will allow the powerful combination of processing methods:
+Individual processors can be initialised and apply processing against images. This allows nesting which brings the potential for powerful combinations of processing methods:
 
 ```csharp
 new Brightness(50).Apply(sourceImage, targetImage, sourceImage.Bounds);
diff --git a/src/ImageProcessorCore/Samplers/Resamplers/Lanczos2Resampler.cs b/src/ImageProcessorCore/Samplers/Resamplers/Lanczos2Resampler.cs
new file mode 100644
index 0000000000..ced92365b8
--- /dev/null
+++ b/src/ImageProcessorCore/Samplers/Resamplers/Lanczos2Resampler.cs
@@ -0,0 +1,34 @@
+// <copyright file="Lanczos2Resampler.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessorCore
+{
+    /// <summary>
+    /// The function implements the Lanczos kernel algorithm as described on
+    /// <see href="https://en.wikipedia.org/wiki/Lanczos_resampling#Algorithm">Wikipedia</see>
+    /// with a radius of 2 pixels.
+    /// </summary>
+    public class Lanczos2Resampler : IResampler
+    {
+        /// <inheritdoc/>
+        public float Radius => 2;
+
+        /// <inheritdoc/>
+        public float GetValue(float x)
+        {
+            if (x < 0F)
+            {
+                x = -x;
+            }
+
+            if (x < 2F)
+            {
+                return ImageMaths.SinC(x) * ImageMaths.SinC(x / 2F);
+            }
+
+            return 0F;
+        }
+    }
+}