Fix issue with 24 bits per channel

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/Rgba24242424TiffColor{TPixel}.cs

@@ -58,7 +58,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                         ulong a = TiffUtils.ConvertToUIntBigEndian(buffer);
                         offset += 3;
 
-                        pixelRow[x] = TiffUtils.ColorScaleTo32Bit(r, g, b, a, color);
+                        pixelRow[x] = TiffUtils.ColorScaleTo24Bit(r, g, b, a, color);
                     }
                 }
                 else
@@ -81,7 +81,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                         ulong a = TiffUtils.ConvertToUIntLittleEndian(buffer);
                         offset += 3;
 
-                        pixelRow[x] = TiffUtils.ColorScaleTo32Bit(r, g, b, a, color);
+                        pixelRow[x] = TiffUtils.ColorScaleTo24Bit(r, g, b, a, color);
                     }
                 }
             }

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/Rgba24PlanarTiffColor{TPixel}.cs

@@ -58,7 +58,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
 
                         offset += 3;
 
-                        pixelRow[x] = TiffUtils.ColorScaleTo32Bit(r, g, b, a, color);
+                        pixelRow[x] = TiffUtils.ColorScaleTo24Bit(r, g, b, a, color);
                     }
                 }
                 else
@@ -76,7 +76,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
 
                         offset += 3;
 
-                        pixelRow[x] = TiffUtils.ColorScaleTo32Bit(r, g, b, a, color);
+                        pixelRow[x] = TiffUtils.ColorScaleTo24Bit(r, g, b, a, color);
                     }
                 }
             }

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

@@ -72,6 +72,15 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Utils
             return color;
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        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);
+            color.FromVector4(colorVector);
+            return color;
+        }
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static TPixel ColorScaleTo32Bit<TPixel>(ulong r, ulong g, ulong b, TPixel color)
             where TPixel : unmanaged, IPixel<TPixel>
@@ -85,7 +94,7 @@ 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);
+            var colorVector = new Vector4(r * Scale32Bit, g * Scale32Bit, b * Scale32Bit, a * Scale32Bit);
             color.FromVector4(colorVector);
             return color;
         }