Fix To() Method to allow vector scaling.

src/ImageSharp/Image/Image.cs

@@ -10,6 +10,7 @@ namespace ImageSharp
     using System.Diagnostics;
     using System.IO;
     using System.Linq;
+    using System.Numerics;
     using System.Text;
     using System.Threading.Tasks;
 
@@ -260,14 +261,25 @@ namespace ImageSharp
 
         /// <summary>
         /// Returns a copy of the image in the given pixel format.
+        /// <remarks>
+        /// Most color formats when converted to vectors have a range of <value>0</value> to <value>1</value>. Some however, <see cref="NormalizedByte4"/>, for example scale between
+        /// <value>-1</value> to <value>1</value>. This requires additional computation to convert between the formats. 
+        /// For example, if I wanted to convert from <see cref="Color"/> to <see cref="NormalizedByte4"/> the following function would be required. <example>v => (2F * v) - Vector4.One</example>
+        /// </remarks>
         /// </summary>
+        /// <param name="scaleFunc">A function that allows for the correction of vector scaling between color formats.</param>
         /// <typeparam name="TColor2">The pixel format.</typeparam>
         /// <typeparam name="TPacked2">The packed format. <example>uint, long, float.</example></typeparam>
         /// <returns>The <see cref="Image{TColor2, TPacked2}"/></returns>
-        public Image<TColor2, TPacked2> To<TColor2, TPacked2>()
+        public Image<TColor2, TPacked2> To<TColor2, TPacked2>(Func<Vector4, Vector4> scaleFunc = null)
             where TColor2 : struct, IPackedPixel<TPacked2>
             where TPacked2 : struct
         {
+            if (scaleFunc == null)
+            {
+                scaleFunc = v => v;
+            }
+
             Image<TColor2, TPacked2> target = new Image<TColor2, TPacked2>(this.Width, this.Height)
             {
                 Quality = this.Quality,
@@ -290,7 +302,7 @@ namespace ImageSharp
                             for (int x = 0; x < target.Width; x++)
                             {
                                 TColor2 color = default(TColor2);
-                                color.PackFromVector4(pixels[x, y].ToVector4());
+                                color.PackFromVector4(scaleFunc(pixels[x, y].ToVector4()));
                                 targetPixels[x, y] = color;
                             }
                         });

src/ImageSharp/Image/ImageFrame.cs

@@ -5,6 +5,8 @@
 
 namespace ImageSharp
 {
+    using System;
+    using System.Numerics;
     using System.Threading.Tasks;
 
     /// <summary>
@@ -40,14 +42,25 @@ namespace ImageSharp
 
         /// <summary>
         /// Returns a copy of the image frame in the given pixel format.
+        /// <remarks>
+        /// Most color formats when converted to vectors have a range of <value>0</value> to <value>1</value>. Some however, <see cref="NormalizedByte4"/>, for example scale between
+        /// <value>-1</value> to <value>1</value>. This requires additional computation to convert between the formats. 
+        /// For example, if I wanted to convert from <see cref="Color"/> to <see cref="NormalizedByte4"/> the following function would be required. <example>v => (2F * v) - Vector4.One</example>
+        /// </remarks>
         /// </summary>
+        /// <param name="scaleFunc">A function that allows for the correction of vector scaling between color formats.</param>
         /// <typeparam name="TColor2">The pixel format.</typeparam>
         /// <typeparam name="TPacked2">The packed format. <example>uint, long, float.</example></typeparam>
         /// <returns>The <see cref="ImageFrame{TColor2, TPacked2}"/></returns>
-        public ImageFrame<TColor2, TPacked2> To<TColor2, TPacked2>()
+        public ImageFrame<TColor2, TPacked2> To<TColor2, TPacked2>(Func<Vector4, Vector4> scaleFunc = null)
             where TColor2 : struct, IPackedPixel<TPacked2>
             where TPacked2 : struct
         {
+            if (scaleFunc == null)
+            {
+                scaleFunc = v => v;
+            }
+
             ImageFrame<TColor2, TPacked2> target = new ImageFrame<TColor2, TPacked2>
             {
                 Quality = this.Quality,
@@ -68,7 +81,7 @@ namespace ImageSharp
                         for (int x = 0; x < target.Width; x++)
                         {
                             TColor2 color = default(TColor2);
-                            color.PackFromVector4(pixels[x, y].ToVector4());
+                            color.PackFromVector4(scaleFunc(pixels[x, y].ToVector4()));
                             targetPixels[x, y] = color;
                         }
                     });

tests/ImageSharp.Tests/Formats/GeneralFormatTests.cs

@@ -7,6 +7,7 @@ namespace ImageSharp.Tests
 {
     using System;
     using System.IO;
+    using System.Numerics;
 
     using Xunit;
 
@@ -62,8 +63,8 @@ namespace ImageSharp.Tests
                 // Image<HalfVector4, ulong> image = file.CreateImage().To<HalfVector4, ulong>();
                 // Image<NormalizedByte2, ushort> image = file.CreateImage().To<NormalizedByte2, ushort>();
 
-                // TODO: Conversion between types who's vector ranges are different are not possible.
-                // Image<NormalizedByte4, uint> image = file.CreateImage().To<NormalizedByte4, uint>();
+                // TODO: Conversion between types who's vector ranges are different are not possible without scaling function, Make static version of known ones.
+                // Image<NormalizedByte4, uint> image = file.CreateImage().To<NormalizedByte4, uint>(v => (2F * v) - Vector4.One);
 
                 using (FileStream output = File.OpenWrite($"{path}/{file.FileName}"))
                 {