Fix Saturation, tweak Polaroid.

Former-commit-id: dc91b2297f19411f822db6e460cda7588dba2f98
Former-commit-id: 1edc310dfa1a7293564500e90a1b0b72061edcad
Former-commit-id: 7e12412768a1ff6ad545e77a3b7d5d61f9dea3d7

src/ImageProcessor/Filters/ColorMatrix/ColorMatrixFilter.cs

@@ -13,6 +13,13 @@ namespace ImageProcessor.Filters
     /// </summary>
     public class ColorMatrixFilter : ParallelImageProcessor
     {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ColorMatrixFilter"/> class.
+        /// </summary>
+        public ColorMatrixFilter()
+        {
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="ColorMatrixFilter"/> class.
         /// </summary>
@@ -23,9 +30,9 @@ namespace ImageProcessor.Filters
         }
 
         /// <summary>
-        /// Gets the matrix value.
+        /// Gets or sets the matrix value.
         /// </summary>
-        public Matrix4x4 Value { get; }
+        public Matrix4x4 Value { get; set; }
 
         /// <inheritdoc/>
         protected override void Apply(ImageBase target, ImageBase source, Rectangle targetRectangle, Rectangle sourceRectangle, int startY, int endY)

src/ImageProcessor/Filters/ColorMatrix/Polaroid.cs

@@ -24,7 +24,7 @@ namespace ImageProcessor.Filters
             M21 = -0.022f,
             M22 = 1.578f,
             M23 = -0.022f,
-            M31 = .616f,
+            M31 = .216f,
             M32 = -.16f,
             M33 = 1.5831f,
             M41 = 0.02f,

src/ImageProcessor/Filters/ColorMatrix/Saturation.cs

@@ -0,0 +1,56 @@
+// <copyright file="Saturation.cs" company="James South">
+// Copyright (c) James South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessor.Filters
+{
+    using System;
+    using System.Numerics;
+
+    /// <summary>
+    /// An <see cref="IImageProcessor"/> to change the saturation of an <see cref="Image"/>.
+    /// </summary>
+    public class Saturation : ColorMatrixFilter
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Saturation"/> class.
+        /// </summary>
+        /// <param name="saturation">The new saturation of the image. Must be between -100 and 100.</param>
+        /// <exception cref="ArgumentException">
+        /// <paramref name="saturation"/> is less than -100 or is greater than 100.
+        /// </exception>
+        public Saturation(int saturation)
+        {
+            Guard.MustBeBetweenOrEqualTo(saturation, -100, 100, nameof(saturation));
+            float saturationFactor = saturation / 100f;
+
+            // Stop at -1 to prevent inversion.
+            saturationFactor++;
+
+            // The matrix is set up to "shear" the colour space using the following set of values.
+            // Note that each colour component has an effective luminance which contributes to the
+            // overall brightness of the pixel.
+            // See http://graficaobscura.com/matrix/index.html
+            float saturationComplement = 1.0f - saturationFactor;
+            float saturationComplementR = 0.3086f * saturationComplement;
+            float saturationComplementG = 0.6094f * saturationComplement;
+            float saturationComplementB = 0.0820f * saturationComplement;
+
+            Matrix4x4 matrix = new Matrix4x4()
+            {
+                M11 = saturationComplementR + saturationFactor,
+                M12 = saturationComplementR,
+                M13 = saturationComplementR,
+                M21 = saturationComplementG,
+                M22 = saturationComplementG + saturationFactor,
+                M23 = saturationComplementG,
+                M31 = saturationComplementB,
+                M32 = saturationComplementB,
+                M33 = saturationComplementB + saturationFactor,
+            };
+
+            this.Value = matrix;
+        }
+    }
+}

src/ImageProcessor/Filters/Saturation.cs

@@ -1,78 +0,0 @@
-// <copyright file="Saturation.cs" company="James South">
-// Copyright (c) James South and contributors.
-// Licensed under the Apache License, Version 2.0.
-// </copyright>
-
-namespace ImageProcessor.Filters
-{
-    using System;
-    using System.Numerics;
-    using System.Threading.Tasks;
-
-    /// <summary>
-    /// An <see cref="IImageProcessor"/> to change the saturation of an <see cref="Image"/>.
-    /// </summary>
-    public class Saturation : ParallelImageProcessor
-    {
-        /// <summary>
-        /// Initializes a new instance of the <see cref="Saturation"/> class.
-        /// </summary>
-        /// <param name="saturation">The new saturation of the image. Must be between -100 and 100.</param>
-        /// <exception cref="ArgumentException">
-        /// <paramref name="saturation"/> is less than -100 or is greater than 100.
-        /// </exception>
-        public Saturation(int saturation)
-        {
-            Guard.MustBeBetweenOrEqualTo(saturation, -100, 100, nameof(saturation));
-            this.Value = saturation;
-        }
-
-        /// <summary>
-        /// Gets the saturation value.
-        /// </summary>
-        public int Value { get; }
-
-        /// <inheritdoc/>
-        protected override void Apply(ImageBase target, ImageBase source, Rectangle targetRectangle, Rectangle sourceRectangle, int startY, int endY)
-        {
-            float saturation = this.Value / 100f;
-            int sourceY = sourceRectangle.Y;
-            int sourceBottom = sourceRectangle.Bottom;
-            int startX = sourceRectangle.X;
-            int endX = sourceRectangle.Right;
-
-            Parallel.For(
-                startY,
-                endY,
-                y =>
-                    {
-                        if (y >= sourceY && y < sourceBottom)
-                        {
-                            for (int x = startX; x < endX; x++)
-                            {
-                                target[x, y] = AdjustSaturation(source[x, y], saturation);
-                            }
-                        }
-                    });
-        }
-
-        /// <summary>
-        /// Returns a <see cref="Color"/> with the saturation adjusted.
-        /// </summary>
-        /// <param name="color">The source color.</param>
-        /// <param name="saturation">The saturation adjustment factor.</param>
-        /// <returns>
-        /// The <see cref="Color"/>.
-        /// </returns>
-        private static Color AdjustSaturation(Color color, float saturation)
-        {
-            //color = PixelOperations.ToLinear(color);
-
-            // TODO: This can be done with a matrix. But why can I not get conversion to work?
-            Hsv hsv = color;
-            return new Hsv(hsv.H, saturation, hsv.V);
-
-            //return PixelOperations.ToSrgb(newHsv);
-        }
-    }
-}

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

@@ -16,15 +16,15 @@ namespace ImageProcessor.Tests
             //{ "Brightness--50", new Brightness(-50) },
             //{ "Contrast-50", new Contrast(50) },
             //{ "Contrast--50", new Contrast(-50) },
-            //{ "Saturation-100", new Saturation(100) },
+            { "Saturation-50", new Saturation(50) },
-            //{ "Saturation--0", new Saturation(0) },
+            { "Saturation--50", new Saturation(-50) },
             //{ "Alpha--50", new Alpha(50) },
             //{ "Invert", new Invert() },
             //{ "Sepia", new Sepia() },
             //{ "BlackWhite", new BlackWhite() },
             //{ "Lomograph", new Lomograph() },
             //{ "Polaroid", new Polaroid() },
-            { "Brownie", new Kodachrome() },
+            //{ "Kodachrome", new Kodachrome() },
             //{ "GreyscaleBt709", new GreyscaleBt709() },
             //{ "GreyscaleBt601", new GreyscaleBt601() },
         };