Use pre-existing pixel conversion methods

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/Rgba16161616TiffColor{TPixel}.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers;
 using System.Numerics;
 using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
@@ -50,7 +51,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
             bool hasAssociatedAlpha = this.extraSamplesType.HasValue && this.extraSamplesType == TiffExtraSampleType.AssociatedAlphaData;
             int offset = 0;
 
-            using System.Buffers.IMemoryOwner<Vector4> vectors = hasAssociatedAlpha ? this.memoryAllocator.Allocate<Vector4>(width) : null;
+            using IMemoryOwner<Vector4> vectors = hasAssociatedAlpha ? this.memoryAllocator.Allocate<Vector4>(width) : null;
             Span<Vector4> vectorsSpan = hasAssociatedAlpha ? vectors.GetSpan() : Span<Vector4>.Empty;
             for (int y = top; y < top + height; y++)
             {
@@ -86,7 +87,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                     if (hasAssociatedAlpha)
                     {
                         PixelOperations<TPixel>.Instance.ToVector4(this.configuration, pixelRow, vectorsSpan);
-                        TiffUtils.UnPremultiplyRow(vectorsSpan, pixelRow, color);
+                        PixelOperations<TPixel>.Instance.FromVector4Destructive(this.configuration, vectorsSpan, pixelRow, PixelConversionModifiers.Premultiply | PixelConversionModifiers.Scale);
                     }
 
                     offset += byteCount;

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/Rgba8888TiffColor{TPixel}.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers;
 using System.Numerics;
 using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
@@ -36,7 +37,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
 
             var color = default(TPixel);
             color.FromVector4(TiffUtils.Vector4Default);
-            using System.Buffers.IMemoryOwner<Vector4> vectors = hasAssociatedAlpha ? this.memoryAllocator.Allocate<Vector4>(width) : null;
+            using IMemoryOwner<Vector4> vectors = hasAssociatedAlpha ? this.memoryAllocator.Allocate<Vector4>(width) : null;
             Span<Vector4> vectorsSpan = hasAssociatedAlpha ? vectors.GetSpan() : Span<Vector4>.Empty;
             for (int y = top; y < top + height; y++)
             {
@@ -51,7 +52,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                 if (hasAssociatedAlpha)
                 {
                     PixelOperations<TPixel>.Instance.ToVector4(this.configuration, pixelRow, vectorsSpan);
-                    TiffUtils.UnPremultiplyRow(vectorsSpan, pixelRow, color);
+                    PixelOperations<TPixel>.Instance.FromVector4Destructive(this.configuration, vectorsSpan, pixelRow, PixelConversionModifiers.Premultiply | PixelConversionModifiers.Scale);
                 }
 
                 offset += byteCount;

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/RgbaPlanarTiffColor{TPixel}.cs

@@ -81,7 +81,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                     var vec = new Vector4(r, g, b, a);
                     if (hasAssociatedAlpha)
                     {
-                        color = TiffUtils.UnPremultiply(vec, color);
+                        color = TiffUtils.UnPremultiply(ref vec, color);
                     }
                     else
                     {

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/RgbaTiffColor{TPixel}.cs

@@ -70,7 +70,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                     var vec = new Vector4(r, g, b, a);
                     if (hasAssociatedAlpha)
                     {
-                        pixelRow[x] = TiffUtils.UnPremultiply(vec, color);
+                        pixelRow[x] = TiffUtils.UnPremultiply(ref vec, color);
                     }
                     else
                     {

src/ImageSharp/Formats/Tiff/Utils/TiffUtils.cs

@@ -69,7 +69,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Utils
         {
             rgba.PackedValue = r | (g << 16) | (b << 32) | (a << 48);
             var vec = rgba.ToVector4();
-            return UnPremultiply(vec, color);
+            return UnPremultiply(ref vec, color);
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -85,7 +85,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Utils
         public static TPixel ColorScaleTo24Bit<TPixel>(ulong r, ulong g, ulong b, ulong a, TPixel color)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            var colorVector = new Vector4(r * Scale24Bit, g * Scale24Bit, b * Scale24Bit, a * Scale24Bit);
+            Vector4 colorVector = new Vector4(r, g, b, a) * Scale24Bit;
             color.FromVector4(colorVector);
             return color;
         }
@@ -94,8 +94,8 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Utils
         public static TPixel ColorScaleTo24BitPremultiplied<TPixel>(ulong r, ulong g, ulong b, ulong a, TPixel color)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            var colorVector = new Vector4(r * Scale24Bit, g * Scale24Bit, b * Scale24Bit, a * Scale24Bit);
+            Vector4 colorVector = new Vector4(r, g, b, a) * Scale24Bit;
-            return UnPremultiply(colorVector, color);
+            return UnPremultiply(ref colorVector, color);
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -111,7 +111,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Utils
         public static TPixel ColorScaleTo32Bit<TPixel>(ulong r, ulong g, ulong b, ulong a, TPixel color)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            var colorVector = new Vector4(r * Scale32Bit, g * Scale32Bit, b * Scale32Bit, a * Scale32Bit);
+            Vector4 colorVector = new Vector4(r, g, b, a) * Scale32Bit;
             color.FromVector4(colorVector);
             return color;
         }
@@ -120,8 +120,8 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Utils
         public static TPixel ColorScaleTo32BitPremultiplied<TPixel>(ulong r, ulong g, ulong b, ulong a, TPixel color)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            var colorVector = new Vector4(r * Scale32Bit, g * Scale32Bit, b * Scale32Bit, a * Scale32Bit);
+            Vector4 colorVector = new Vector4(r, g, b, a) * Scale32Bit;
-            return UnPremultiply(colorVector, color);
+            return UnPremultiply(ref colorVector, color);
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -152,22 +152,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Utils
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void UnPremultiplyRow<TPixel>(Span<Vector4> vectors, Span<TPixel> pixelRow, TPixel color)
+        public static TPixel UnPremultiply<TPixel>(ref Vector4 vector, TPixel color)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            for (int x = 0; x < vectors.Length; x++)
+            Numerics.UnPremultiply(ref vector);
-            {
+            color.FromVector4(vector);
-                Vector4 vec = vectors[x];
-                pixelRow[x] = UnPremultiply(vec, color);
-            }
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static TPixel UnPremultiply<TPixel>(Vector4 vec, TPixel color)
-            where TPixel : unmanaged, IPixel<TPixel>
-        {
-            float invW = 1.0f / vec.W;
-            color.FromVector4(new Vector4(vec.X * invW, vec.Y * invW, vec.Z * invW, vec.W));
 
             return color;
         }

tests/ImageSharp.Tests/Formats/Tiff/TiffDecoderTests.cs

@@ -362,7 +362,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
             }
 
             // Note: Using tolerant comparer here, because there is a small difference to the reference decoder probably due to floating point rounding issues.
-            TestTiffDecoder(provider, useExactComparer: false);
+            TestTiffDecoder(provider, useExactComparer: false, compareTolerance: 0.004F);
         }
 
         [Theory]