Multiply by inv max value instead of dividing in GeneratePalette

Author: brianpopow

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

@@ -19,6 +19,8 @@ internal class PaletteTiffColor<TPixel> : TiffBaseColorDecoder<TPixel>
 
         private readonly TPixel[] palette;
 
+        private const float InvMax = 1.0f / 65535F;
+
         /// <param name="bitsPerSample">The number of bits per sample for each pixel.</param>
         /// <param name="colorMap">The RGB color lookup table to use for decoding the image.</param>
         public PaletteTiffColor(TiffBitsPerSample bitsPerSample, ushort[] colorMap)
@@ -56,9 +58,9 @@ private static TPixel[] GeneratePalette(ushort[] colorMap, int colorCount)
 
             for (int i = 0; i < palette.Length; i++)
             {
-                float r = colorMap[rOffset + i] / 65535F;
-                float g = colorMap[gOffset + i] / 65535F;
-                float b = colorMap[bOffset + i] / 65535F;
+                float r = colorMap[rOffset + i] * InvMax;
+                float g = colorMap[gOffset + i] * InvMax;
+                float b = colorMap[bOffset + i] * InvMax;
                 palette[i].FromScaledVector4(new Vector4(r, g, b, 1.0f));
             }
 

tests/ImageSharp.Tests/Formats/Tiff/PhotometricInterpretation/BlackIsZeroTiffColorTests.cs

@@ -13,14 +13,14 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff.PhotometricInterpretation
     [Trait("Format", "Tiff")]
     public class BlackIsZeroTiffColorTests : PhotometricInterpretationTestBase
     {
-        private static readonly Rgba32 Gray000 = new Rgba32(0, 0, 0, 255);
-        private static readonly Rgba32 Gray128 = new Rgba32(128, 128, 128, 255);
-        private static readonly Rgba32 Gray255 = new Rgba32(255, 255, 255, 255);
-        private static readonly Rgba32 Gray0 = new Rgba32(0, 0, 0, 255);
-        private static readonly Rgba32 Gray8 = new Rgba32(136, 136, 136, 255);
-        private static readonly Rgba32 GrayF = new Rgba32(255, 255, 255, 255);
-        private static readonly Rgba32 Bit0 = new Rgba32(0, 0, 0, 255);
-        private static readonly Rgba32 Bit1 = new Rgba32(255, 255, 255, 255);
+        private static readonly Rgba32 Gray000 = new(0, 0, 0, 255);
+        private static readonly Rgba32 Gray128 = new(128, 128, 128, 255);
+        private static readonly Rgba32 Gray255 = new(255, 255, 255, 255);
+        private static readonly Rgba32 Gray0 = new(0, 0, 0, 255);
+        private static readonly Rgba32 Gray8 = new(136, 136, 136, 255);
+        private static readonly Rgba32 GrayF = new(255, 255, 255, 255);
+        private static readonly Rgba32 Bit0 = new(0, 0, 0, 255);
+        private static readonly Rgba32 Bit1 = new(255, 255, 255, 255);
 
         private static readonly byte[] BilevelBytes4X4 =
         {
@@ -30,8 +30,7 @@ public class BlackIsZeroTiffColorTests : PhotometricInterpretationTestBase
             0b10010000
         };
 
-        private static readonly Rgba32[][] BilevelResult4X4 = new[]
-        {
+        private static readonly Rgba32[][] BilevelResult4X4 = {
             new[] { Bit0, Bit1, Bit0, Bit1 },
             new[] { Bit1, Bit1, Bit1, Bit1 },
             new[] { Bit0, Bit1, Bit1, Bit1 },