Move indexing to method.

src/ImageSharp/Dithering/Ordered/OrderedDitherBase.cs

@@ -1,13 +1,14 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Dithering.Base
 {
     /// <summary>
-    /// The base class for performing ordered ditheroing using a 4x4 matrix.
+    /// The base class for performing ordered dithering using a 4x4 matrix.
     /// </summary>
     public abstract class OrderedDitherBase : IOrderedDither
     {
@@ -30,7 +31,23 @@ namespace SixLabors.ImageSharp.Dithering.Base
             where TPixel : struct, IPixel<TPixel>
         {
             source.ToRgba32(ref rgba);
-            image[x, y] = this.matrix[y % 3, x % 3] >= rgba[index] ? lower : upper;
+            switch (index)
+            {
+                case 0:
+                    image[x, y] = this.matrix[y % 3, x % 3] >= rgba.R ? lower : upper;
+                    return;
+                case 1:
+                    image[x, y] = this.matrix[y % 3, x % 3] >= rgba.G ? lower : upper;
+                    return;
+                case 2:
+                    image[x, y] = this.matrix[y % 3, x % 3] >= rgba.B ? lower : upper;
+                    return;
+                case 3:
+                    image[x, y] = this.matrix[y % 3, x % 3] >= rgba.A ? lower : upper;
+                    return;
+            }
+
+            throw new ArgumentOutOfRangeException(nameof(index), "Index should be between 0 and 3 inclusive.");
         }
     }
 }

src/ImageSharp/PixelFormats/Rgba32.cs

@@ -220,32 +220,6 @@ namespace SixLabors.ImageSharp
             set => this.Rgba = value;
         }
 
-        /// <summary>
-        /// Gets the component value at the given index
-        /// </summary>
-        /// <param name="index">The component index</param>
-        /// <returns>The <see cref="byte"/></returns>
-        public byte this[int index]
-        {
-            [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            get
-            {
-                DebugGuard.MustBeGreaterThanOrEqualTo(index, 0, nameof(index));
-                DebugGuard.MustBeLessThanOrEqualTo(index, 3, nameof(index));
-                switch (index)
-                {
-                    case 0:
-                        return this.R;
-                    case 1:
-                        return this.G;
-                    case 2:
-                        return this.B;
-                    default:
-                        return this.A;
-                }
-            }
-        }
-
         /// <summary>
         /// Compares two <see cref="Rgba32"/> objects for equality.
         /// </summary>