From 9a80514f2c5bc248ef73498cf9453bb16ce0c38e Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Thu, 21 Jun 2018 14:11:05 +1000
Subject: [PATCH] Faster 32-64 bit conversion, update references, and cleanup.

---
 src/ImageSharp/PixelFormats/Argb32.cs         | 23 +++++++---
 src/ImageSharp/PixelFormats/Bgr24.cs          | 29 +++++++-----
 src/ImageSharp/PixelFormats/Bgra32.cs         | 29 +++++++-----
 src/ImageSharp/PixelFormats/Byte4.cs          |  2 +-
 src/ImageSharp/PixelFormats/Rgb24.cs          | 31 +++++++------
 src/ImageSharp/PixelFormats/Rgb48.cs          | 41 ++++++++---------
 src/ImageSharp/PixelFormats/Rgba32.cs         | 24 +++++++---
 src/ImageSharp/PixelFormats/Rgba64.cs         | 44 +++++++++----------
 src/ImageSharp/PixelFormats/Short4.cs         |  3 +-
 .../ImageComparison/TolerantImageComparer.cs  | 17 ++++---
 .../ReferenceCodecs/SystemDrawingBridge.cs    |  3 +-
 .../TestUtilities/TestEnvironment.cs          |  2 +-
 tests/Images/External                         |  2 +-
 13 files changed, 145 insertions(+), 105 deletions(-)

diff --git a/src/ImageSharp/PixelFormats/Argb32.cs b/src/ImageSharp/PixelFormats/Argb32.cs
index bd4c93d28b..ccb17a2a5e 100644
--- a/src/ImageSharp/PixelFormats/Argb32.cs
+++ b/src/ImageSharp/PixelFormats/Argb32.cs
@@ -63,7 +63,7 @@ namespace SixLabors.ImageSharp.PixelFormats
             this.R = r;
             this.G = g;
             this.B = b;
-            this.A = 255;
+            this.A = byte.MaxValue;
         }
 
         /// <summary>
@@ -312,7 +312,13 @@ namespace SixLabors.ImageSharp.PixelFormats
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void PackFromRgb48(Rgb48 source) => this.PackFromScaledVector4(source.ToScaledVector4());
+        public void PackFromRgb48(Rgb48 source)
+        {
+            this.R = (byte)(((source.R * 255) + 32895) >> 16);
+            this.G = (byte)(((source.G * 255) + 32895) >> 16);
+            this.B = (byte)(((source.B * 255) + 32895) >> 16);
+            this.A = byte.MaxValue;
+        }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -320,7 +326,13 @@ namespace SixLabors.ImageSharp.PixelFormats
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void PackFromRgba64(Rgba64 source) => this.PackFromScaledVector4(source.ToScaledVector4());
+        public void PackFromRgba64(Rgba64 source)
+        {
+            this.R = (byte)(((source.R * 255) + 32895) >> 16);
+            this.G = (byte)(((source.G * 255) + 32895) >> 16);
+            this.B = (byte)(((source.B * 255) + 32895) >> 16);
+            this.A = (byte)(((source.A * 255) + 32895) >> 16);
+        }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -352,8 +364,9 @@ namespace SixLabors.ImageSharp.PixelFormats
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public override int GetHashCode()
         {
-            // ReSharper disable once NonReadonlyMemberInGetHashCode
-            return this.Argb.GetHashCode();
+            int hash = HashHelpers.Combine(this.R.GetHashCode(), this.G.GetHashCode());
+            hash = HashHelpers.Combine(hash, this.B.GetHashCode());
+            return HashHelpers.Combine(hash, this.A.GetHashCode());
         }
 
         /// <summary>
diff --git a/src/ImageSharp/PixelFormats/Bgr24.cs b/src/ImageSharp/PixelFormats/Bgr24.cs
index 13673aa472..8655210844 100644
--- a/src/ImageSharp/PixelFormats/Bgr24.cs
+++ b/src/ImageSharp/PixelFormats/Bgr24.cs
@@ -69,13 +69,8 @@ namespace SixLabors.ImageSharp.PixelFormats
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public override int GetHashCode()
         {
-            unchecked
-            {
-                int hashCode = this.B;
-                hashCode = (hashCode * 397) ^ this.G;
-                hashCode = (hashCode * 397) ^ this.R;
-                return hashCode;
-            }
+            int hash = HashHelpers.Combine(this.R.GetHashCode(), this.G.GetHashCode());
+            return HashHelpers.Combine(hash, this.B.GetHashCode());
         }
 
         /// <inheritdoc/>
@@ -149,7 +144,7 @@ namespace SixLabors.ImageSharp.PixelFormats
             dest.R = this.R;
             dest.G = this.G;
             dest.B = this.B;
-            dest.A = 255;
+            dest.A = byte.MaxValue;
         }
 
         /// <inheritdoc/>
@@ -159,7 +154,7 @@ namespace SixLabors.ImageSharp.PixelFormats
             dest.R = this.R;
             dest.G = this.G;
             dest.B = this.B;
-            dest.A = 255;
+            dest.A = byte.MaxValue;
         }
 
         /// <inheritdoc/>
@@ -174,12 +169,17 @@ namespace SixLabors.ImageSharp.PixelFormats
             dest.R = this.R;
             dest.G = this.G;
             dest.B = this.B;
-            dest.A = 255;
+            dest.A = byte.MaxValue;
         }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void PackFromRgb48(Rgb48 source) => this.PackFromScaledVector4(source.ToScaledVector4());
+        public void PackFromRgb48(Rgb48 source)
+        {
+            this.R = (byte)(((source.R * 255) + 32895) >> 16);
+            this.G = (byte)(((source.G * 255) + 32895) >> 16);
+            this.B = (byte)(((source.B * 255) + 32895) >> 16);
+        }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -187,7 +187,12 @@ namespace SixLabors.ImageSharp.PixelFormats
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void PackFromRgba64(Rgba64 source) => this.PackFromScaledVector4(source.ToScaledVector4());
+        public void PackFromRgba64(Rgba64 source)
+        {
+            this.R = (byte)(((source.R * 255) + 32895) >> 16);
+            this.G = (byte)(((source.G * 255) + 32895) >> 16);
+            this.B = (byte)(((source.B * 255) + 32895) >> 16);
+        }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
diff --git a/src/ImageSharp/PixelFormats/Bgra32.cs b/src/ImageSharp/PixelFormats/Bgra32.cs
index 86a141bc52..f951be8811 100644
--- a/src/ImageSharp/PixelFormats/Bgra32.cs
+++ b/src/ImageSharp/PixelFormats/Bgra32.cs
@@ -60,7 +60,7 @@ namespace SixLabors.ImageSharp.PixelFormats
             this.R = r;
             this.G = g;
             this.B = b;
-            this.A = 255;
+            this.A = byte.MaxValue;
         }
 
         /// <summary>
@@ -113,14 +113,9 @@ namespace SixLabors.ImageSharp.PixelFormats
         /// <inheritdoc/>
         public override int GetHashCode()
         {
-            unchecked
-            {
-                int hashCode = this.B;
-                hashCode = (hashCode * 397) ^ this.G;
-                hashCode = (hashCode * 397) ^ this.R;
-                hashCode = (hashCode * 397) ^ this.A;
-                return hashCode;
-            }
+            int hash = HashHelpers.Combine(this.R.GetHashCode(), this.G.GetHashCode());
+            hash = HashHelpers.Combine(hash, this.B.GetHashCode());
+            return HashHelpers.Combine(hash, this.A.GetHashCode());
         }
 
         /// <summary>
@@ -248,7 +243,13 @@ namespace SixLabors.ImageSharp.PixelFormats
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void PackFromRgb48(Rgb48 source) => this.PackFromScaledVector4(source.ToScaledVector4());
+        public void PackFromRgb48(Rgb48 source)
+        {
+            this.R = (byte)(((source.R * 255) + 32895) >> 16);
+            this.G = (byte)(((source.G * 255) + 32895) >> 16);
+            this.B = (byte)(((source.B * 255) + 32895) >> 16);
+            this.A = byte.MaxValue;
+        }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -256,7 +257,13 @@ namespace SixLabors.ImageSharp.PixelFormats
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void PackFromRgba64(Rgba64 source) => this.PackFromScaledVector4(source.ToScaledVector4());
+        public void PackFromRgba64(Rgba64 source)
+        {
+            this.R = (byte)(((source.R * 255) + 32895) >> 16);
+            this.G = (byte)(((source.G * 255) + 32895) >> 16);
+            this.B = (byte)(((source.B * 255) + 32895) >> 16);
+            this.A = (byte)(((source.A * 255) + 32895) >> 16);
+        }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
diff --git a/src/ImageSharp/PixelFormats/Byte4.cs b/src/ImageSharp/PixelFormats/Byte4.cs
index 48430d17a3..4269557270 100644
--- a/src/ImageSharp/PixelFormats/Byte4.cs
+++ b/src/ImageSharp/PixelFormats/Byte4.cs
@@ -198,7 +198,7 @@ namespace SixLabors.ImageSharp.PixelFormats
         /// <inheritdoc />
         public override bool Equals(object obj)
         {
-            return (obj is Byte4) && this.Equals((Byte4)obj);
+            return obj is Byte4 byte4 && this.Equals(byte4);
         }
 
         /// <inheritdoc />
diff --git a/src/ImageSharp/PixelFormats/Rgb24.cs b/src/ImageSharp/PixelFormats/Rgb24.cs
index c3ad827558..4c7ad5909a 100644
--- a/src/ImageSharp/PixelFormats/Rgb24.cs
+++ b/src/ImageSharp/PixelFormats/Rgb24.cs
@@ -70,13 +70,8 @@ namespace SixLabors.ImageSharp.PixelFormats
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public override int GetHashCode()
         {
-            unchecked
-            {
-                int hashCode = this.R;
-                hashCode = (hashCode * 397) ^ this.G;
-                hashCode = (hashCode * 397) ^ this.B;
-                return hashCode;
-            }
+            int hash = HashHelpers.Combine(this.R.GetHashCode(), this.G.GetHashCode());
+            return HashHelpers.Combine(hash, this.B.GetHashCode());
         }
 
         /// <inheritdoc/>
@@ -131,7 +126,7 @@ namespace SixLabors.ImageSharp.PixelFormats
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public Vector4 ToVector4()
         {
-            return new Rgba32(this.R, this.G, this.B, 255).ToVector4();
+            return new Rgba32(this.R, this.G, this.B, byte.MaxValue).ToVector4();
         }
 
         /// <inheritdoc/>
@@ -142,7 +137,7 @@ namespace SixLabors.ImageSharp.PixelFormats
         public void ToRgba32(ref Rgba32 dest)
         {
             dest.Rgb = this;
-            dest.A = 255;
+            dest.A = byte.MaxValue;
         }
 
         /// <inheritdoc/>
@@ -151,7 +146,7 @@ namespace SixLabors.ImageSharp.PixelFormats
             dest.R = this.R;
             dest.G = this.G;
             dest.B = this.B;
-            dest.A = 255;
+            dest.A = byte.MaxValue;
         }
 
         /// <inheritdoc/>
@@ -168,12 +163,17 @@ namespace SixLabors.ImageSharp.PixelFormats
             dest.R = this.R;
             dest.G = this.G;
             dest.B = this.B;
-            dest.A = 255;
+            dest.A = byte.MaxValue;
         }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void PackFromRgb48(Rgb48 source) => this.PackFromScaledVector4(source.ToScaledVector4());
+        public void PackFromRgb48(Rgb48 source)
+        {
+            this.R = (byte)(((source.R * 255) + 32895) >> 16);
+            this.G = (byte)(((source.G * 255) + 32895) >> 16);
+            this.B = (byte)(((source.B * 255) + 32895) >> 16);
+        }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -181,7 +181,12 @@ namespace SixLabors.ImageSharp.PixelFormats
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void PackFromRgba64(Rgba64 source) => this.PackFromScaledVector4(source.ToScaledVector4());
+        public void PackFromRgba64(Rgba64 source)
+        {
+            this.R = (byte)(((source.R * 255) + 32895) >> 16);
+            this.G = (byte)(((source.G * 255) + 32895) >> 16);
+            this.B = (byte)(((source.B * 255) + 32895) >> 16);
+        }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
diff --git a/src/ImageSharp/PixelFormats/Rgb48.cs b/src/ImageSharp/PixelFormats/Rgb48.cs
index 8340060118..2d92b0e4e3 100644
--- a/src/ImageSharp/PixelFormats/Rgb48.cs
+++ b/src/ImageSharp/PixelFormats/Rgb48.cs
@@ -166,53 +166,48 @@ namespace SixLabors.ImageSharp.PixelFormats
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ToRgb24(ref Rgb24 dest)
         {
-            Vector4 vector = this.ToVector4() * 255F;
-            dest.R = (byte)MathF.Round(vector.X);
-            dest.G = (byte)MathF.Round(vector.Y);
-            dest.B = (byte)MathF.Round(vector.Z);
+            dest.R = (byte)(((this.R * 255) + 32895) >> 16);
+            dest.G = (byte)(((this.G * 255) + 32895) >> 16);
+            dest.B = (byte)(((this.B * 255) + 32895) >> 16);
         }
 
         /// <inheritdoc />
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ToRgba32(ref Rgba32 dest)
         {
-            Vector4 vector = this.ToVector4() * 255F;
-            dest.R = (byte)MathF.Round(vector.X);
-            dest.G = (byte)MathF.Round(vector.Y);
-            dest.B = (byte)MathF.Round(vector.Z);
-            dest.A = (byte)MathF.Round(vector.W);
+            dest.R = (byte)(((this.R * 255) + 32895) >> 16);
+            dest.G = (byte)(((this.G * 255) + 32895) >> 16);
+            dest.B = (byte)(((this.B * 255) + 32895) >> 16);
+            dest.A = 255;
         }
 
         /// <inheritdoc />
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ToArgb32(ref Argb32 dest)
         {
-            Vector4 vector = this.ToVector4() * 255F;
-            dest.R = (byte)MathF.Round(vector.X);
-            dest.G = (byte)MathF.Round(vector.Y);
-            dest.B = (byte)MathF.Round(vector.Z);
-            dest.A = (byte)MathF.Round(vector.W);
+            dest.R = (byte)(((this.R * 255) + 32895) >> 16);
+            dest.G = (byte)(((this.G * 255) + 32895) >> 16);
+            dest.B = (byte)(((this.B * 255) + 32895) >> 16);
+            dest.A = 255;
         }
 
         /// <inheritdoc />
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ToBgr24(ref Bgr24 dest)
         {
-            Vector4 vector = this.ToVector4() * 255F;
-            dest.R = (byte)MathF.Round(vector.X);
-            dest.G = (byte)MathF.Round(vector.Y);
-            dest.B = (byte)MathF.Round(vector.Z);
+            dest.R = (byte)(((this.R * 255) + 32895) >> 16);
+            dest.G = (byte)(((this.G * 255) + 32895) >> 16);
+            dest.B = (byte)(((this.B * 255) + 32895) >> 16);
         }
 
         /// <inheritdoc />
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ToBgra32(ref Bgra32 dest)
         {
-            Vector4 vector = this.ToVector4() * 255F;
-            dest.R = (byte)MathF.Round(vector.X);
-            dest.G = (byte)MathF.Round(vector.Y);
-            dest.B = (byte)MathF.Round(vector.Z);
-            dest.A = (byte)MathF.Round(vector.W);
+            dest.R = (byte)(((this.R * 255) + 32895) >> 16);
+            dest.G = (byte)(((this.G * 255) + 32895) >> 16);
+            dest.B = (byte)(((this.B * 255) + 32895) >> 16);
+            dest.A = 255;
         }
 
         /// <inheritdoc/>
diff --git a/src/ImageSharp/PixelFormats/Rgba32.cs b/src/ImageSharp/PixelFormats/Rgba32.cs
index c585dbfda8..79794ee462 100644
--- a/src/ImageSharp/PixelFormats/Rgba32.cs
+++ b/src/ImageSharp/PixelFormats/Rgba32.cs
@@ -83,7 +83,7 @@ namespace SixLabors.ImageSharp.PixelFormats
             this.R = r;
             this.G = g;
             this.B = b;
-            this.A = 255;
+            this.A = byte.MaxValue;
         }
 
         /// <summary>
@@ -389,7 +389,13 @@ namespace SixLabors.ImageSharp.PixelFormats
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void PackFromRgb48(Rgb48 source) => this.PackFromScaledVector4(source.ToScaledVector4());
+        public void PackFromRgb48(Rgb48 source)
+        {
+            this.R = (byte)(((source.R * 255) + 32895) >> 16);
+            this.G = (byte)(((source.G * 255) + 32895) >> 16);
+            this.B = (byte)(((source.B * 255) + 32895) >> 16);
+            this.A = byte.MaxValue;
+        }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -397,7 +403,14 @@ namespace SixLabors.ImageSharp.PixelFormats
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void PackFromRgba64(Rgba64 source) => this.PackFromScaledVector4(source.ToScaledVector4());
+        public void PackFromRgba64(Rgba64 source)
+        {
+            // Taken from libpng pngtran.c line: 2419
+            this.R = (byte)(((source.R * 255) + 32895) >> 16);
+            this.G = (byte)(((source.G * 255) + 32895) >> 16);
+            this.B = (byte)(((source.B * 255) + 32895) >> 16);
+            this.A = (byte)(((source.A * 255) + 32895) >> 16);
+        }
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -426,8 +439,9 @@ namespace SixLabors.ImageSharp.PixelFormats
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public override int GetHashCode()
         {
-            // ReSharper disable once NonReadonlyMemberInGetHashCode
-            return this.Rgba.GetHashCode();
+            int hash = HashHelpers.Combine(this.R.GetHashCode(), this.G.GetHashCode());
+            hash = HashHelpers.Combine(hash, this.B.GetHashCode());
+            return HashHelpers.Combine(hash, this.A.GetHashCode());
         }
 
         /// <summary>
diff --git a/src/ImageSharp/PixelFormats/Rgba64.cs b/src/ImageSharp/PixelFormats/Rgba64.cs
index ad7d2dc9dd..b0aeab92ea 100644
--- a/src/ImageSharp/PixelFormats/Rgba64.cs
+++ b/src/ImageSharp/PixelFormats/Rgba64.cs
@@ -170,7 +170,7 @@ namespace SixLabors.ImageSharp.PixelFormats
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public Vector4 ToVector4()
         {
-            return new Vector4(this.R / Max, this.G / Max, this.B / Max, this.A / Max);
+            return new Vector4(this.R, this.G, this.B, this.A) / Max;
         }
 
         /// <inheritdoc />
@@ -213,21 +213,20 @@ namespace SixLabors.ImageSharp.PixelFormats
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ToRgb24(ref Rgb24 dest)
         {
-            Vector4 vector = this.ToVector4() * 255F;
-            dest.R = (byte)MathF.Round(vector.X);
-            dest.G = (byte)MathF.Round(vector.Y);
-            dest.B = (byte)MathF.Round(vector.Z);
+            dest.R = (byte)(((this.R * 255) + 32895) >> 16);
+            dest.G = (byte)(((this.G * 255) + 32895) >> 16);
+            dest.B = (byte)(((this.B * 255) + 32895) >> 16);
         }
 
         /// <inheritdoc />
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ToRgba32(ref Rgba32 dest)
         {
-            Vector4 vector = this.ToVector4() * 255F;
-            dest.R = (byte)MathF.Round(vector.X);
-            dest.G = (byte)MathF.Round(vector.Y);
-            dest.B = (byte)MathF.Round(vector.Z);
-            dest.A = (byte)MathF.Round(vector.W);
+            // Taken from libpng pngtran.c line: 2419
+            dest.R = (byte)(((this.R * 255) + 32895) >> 16);
+            dest.G = (byte)(((this.G * 255) + 32895) >> 16);
+            dest.B = (byte)(((this.B * 255) + 32895) >> 16);
+            dest.A = (byte)(((this.A * 255) + 32895) >> 16);
         }
 
         /// <inheritdoc/>
@@ -250,32 +249,29 @@ namespace SixLabors.ImageSharp.PixelFormats
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ToArgb32(ref Argb32 dest)
         {
-            Vector4 vector = this.ToVector4() * 255F;
-            dest.R = (byte)MathF.Round(vector.X);
-            dest.G = (byte)MathF.Round(vector.Y);
-            dest.B = (byte)MathF.Round(vector.Z);
-            dest.A = (byte)MathF.Round(vector.W);
+            dest.R = (byte)(((this.R * 255) + 32895) >> 16);
+            dest.G = (byte)(((this.G * 255) + 32895) >> 16);
+            dest.B = (byte)(((this.B * 255) + 32895) >> 16);
+            dest.A = (byte)(((this.A * 255) + 32895) >> 16);
         }
 
         /// <inheritdoc />
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ToBgr24(ref Bgr24 dest)
         {
-            Vector4 vector = this.ToVector4() * 255F;
-            dest.R = (byte)MathF.Round(vector.X);
-            dest.G = (byte)MathF.Round(vector.Y);
-            dest.B = (byte)MathF.Round(vector.Z);
+            dest.R = (byte)(((this.R * 255) + 32895) >> 16);
+            dest.G = (byte)(((this.G * 255) + 32895) >> 16);
+            dest.B = (byte)(((this.B * 255) + 32895) >> 16);
         }
 
         /// <inheritdoc />
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ToBgra32(ref Bgra32 dest)
         {
-            Vector4 vector = this.ToVector4() * 255F;
-            dest.R = (byte)MathF.Round(vector.X);
-            dest.G = (byte)MathF.Round(vector.Y);
-            dest.B = (byte)MathF.Round(vector.Z);
-            dest.A = (byte)MathF.Round(vector.W);
+            dest.R = (byte)(((this.R * 255) + 32895) >> 16);
+            dest.G = (byte)(((this.G * 255) + 32895) >> 16);
+            dest.B = (byte)(((this.B * 255) + 32895) >> 16);
+            dest.A = (byte)(((this.A * 255) + 32895) >> 16);
         }
 
         /// <inheritdoc />
diff --git a/src/ImageSharp/PixelFormats/Short4.cs b/src/ImageSharp/PixelFormats/Short4.cs
index 41371362e1..5683ffceea 100644
--- a/src/ImageSharp/PixelFormats/Short4.cs
+++ b/src/ImageSharp/PixelFormats/Short4.cs
@@ -295,8 +295,7 @@ namespace SixLabors.ImageSharp.PixelFormats
             vector *= 255;
             vector += Half;
             vector += Round;
-            vector = Vector4.Clamp(vector, Vector4.Zero, MaxBytes);
-            return vector;
+            return Vector4.Clamp(vector, Vector4.Zero, MaxBytes);
         }
     }
 }
\ No newline at end of file
diff --git a/tests/ImageSharp.Tests/TestUtilities/ImageComparison/TolerantImageComparer.cs b/tests/ImageSharp.Tests/TestUtilities/ImageComparison/TolerantImageComparer.cs
index ccc5094707..674603380f 100644
--- a/tests/ImageSharp.Tests/TestUtilities/ImageComparison/TolerantImageComparer.cs
+++ b/tests/ImageSharp.Tests/TestUtilities/ImageComparison/TolerantImageComparer.cs
@@ -18,6 +18,8 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison
         /// <summary>
         /// Individual manhattan pixel difference is only added to total image difference when the individual difference is over 'perPixelManhattanThreshold'.
         /// </summary>
+        /// <param name="imageThreshold">The maximal tolerated difference represented by a value between 0.0 and 1.0 scaled to 0 and 65535.</param>
+        /// <param name="perPixelManhattanThreshold">Gets the threshold of the individual pixels before they acumulate towards the overall difference.</param>
         public TolerantImageComparer(float imageThreshold, int perPixelManhattanThreshold = 0)
         {
             Guard.MustBeGreaterThanOrEqualTo(imageThreshold, 0, nameof(imageThreshold));
@@ -27,24 +29,27 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison
         }
 
         /// <summary>
-        /// The maximal tolerated difference represented by a value between 0.0 and 1.0.
+        /// <para>
+        /// Gets the maximal tolerated difference represented by a value between 0.0 and 1.0 scaled to 0 and 65535.
         /// Examples of percentage differences on a single pixel:
         /// 1. PixelA = (65535,65535,65535,0) PixelB =(0,0,0,65535) leads to 100% difference on a single pixel
         /// 2. PixelA = (65535,65535,65535,0) PixelB =(65535,65535,65535,65535) leads to 25% difference on a single pixel
-        /// 3. PixelA = (65535,65535,65535,0) PixelB =(128,128,128,128) leads to 50% difference on a single pixel
-        /// 
+        /// 3. PixelA = (65535,65535,65535,0) PixelB =(32767,32767,32767,32767) leads to 50% difference on a single pixel
+        /// </para>
+        /// <para>
         /// The total differences is the sum of all pixel differences normalized by image dimensions!
         /// The individual distances are calculated using the Manhattan function:
         /// <see>
         ///     <cref>https://en.wikipedia.org/wiki/Taxicab_geometry</cref>
         /// </see>
-        /// ImageThresholdInPercents = 1.0/65535 means that we allow one unit difference per channel on a 1x1 image
-        /// ImageThresholdInPercents = 1.0/(100*100*65535) means that we allow only one unit difference per channel on a 100x100 image
+        /// ImageThresholdInPercents = 1/255 =  257/65535 means that we allow one unit difference per channel on a 1x1 image
+        /// ImageThresholdInPercents = 1/(100*100*255) = 257/(100*100*65535) means that we allow only one unit difference per channel on a 100x100 image
+        /// </para>
         /// </summary>
         public float ImageThreshold { get; }
 
         /// <summary>
-        /// The threshold of the individual pixels before they acumulate towards the overall difference.
+        /// Gets the threshold of the individual pixels before they acumulate towards the overall difference.
         /// For an individual <see cref="Rgba64"/> pixel pair the value is the Manhattan distance of pixels:
         /// <see>
         ///     <cref>https://en.wikipedia.org/wiki/Taxicab_geometry</cref>
diff --git a/tests/ImageSharp.Tests/TestUtilities/ReferenceCodecs/SystemDrawingBridge.cs b/tests/ImageSharp.Tests/TestUtilities/ReferenceCodecs/SystemDrawingBridge.cs
index c281b50c38..f0daa0abb4 100644
--- a/tests/ImageSharp.Tests/TestUtilities/ReferenceCodecs/SystemDrawingBridge.cs
+++ b/tests/ImageSharp.Tests/TestUtilities/ReferenceCodecs/SystemDrawingBridge.cs
@@ -19,6 +19,7 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs
         /// <summary>
         /// Returns an image from the given System.Drawing bitmap.
         /// </summary>
+        /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="bmp">The input bitmap.</param>
         /// <exception cref="ArgumentException">Thrown if the image pixel format is not of type <see cref="PixelFormat.Format32bppArgb"/></exception>
         internal static unsafe Image<TPixel> From32bppArgbSystemDrawingBitmap<TPixel>(Bitmap bmp)
@@ -64,6 +65,7 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs
         /// <summary>
         /// Returns an image from the given System.Drawing bitmap.
         /// </summary>
+        /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="bmp">The input bitmap.</param>
         /// <exception cref="ArgumentException">Thrown if the image pixel format is not of type <see cref="PixelFormat.Format24bppRgb"/></exception>
         internal static unsafe Image<TPixel> From24bppRgbSystemDrawingBitmap<TPixel>(Bitmap bmp)
@@ -124,7 +126,6 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs
             {
                 fixed (Bgra32* sourcePtr = &workBuffer.GetReference())
                 {
-
                     for (int y = 0; y < h; y++)
                     {
                         Span<TPixel> row = image.Frames.RootFrame.GetPixelRowSpan(y);
diff --git a/tests/ImageSharp.Tests/TestUtilities/TestEnvironment.cs b/tests/ImageSharp.Tests/TestUtilities/TestEnvironment.cs
index 4cee650e8a..d766378863 100644
--- a/tests/ImageSharp.Tests/TestUtilities/TestEnvironment.cs
+++ b/tests/ImageSharp.Tests/TestUtilities/TestEnvironment.cs
@@ -27,7 +27,7 @@ namespace SixLabors.ImageSharp.Tests
             () =>
                 {
                     bool isCi;
-                    return Boolean.TryParse(Environment.GetEnvironmentVariable("CI"), out isCi) && isCi;
+                    return bool.TryParse(Environment.GetEnvironmentVariable("CI"), out isCi) && isCi;
                 });
 
         // ReSharper disable once InconsistentNaming
diff --git a/tests/Images/External b/tests/Images/External
index 1473062944..94cc43a65e 160000
--- a/tests/Images/External
+++ b/tests/Images/External
@@ -1 +1 @@
-Subproject commit 147306294437dc03f6e640f5db2dcd496a43ced7
+Subproject commit 94cc43a65e304aa312bea9d098206086095e6dff