Add support decoding for 16 bits per channel tiff's

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

@@ -117,6 +117,16 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                     DebugGuard.IsTrue(colorMap == null, "colorMap");
                     return new RgbTiffColor<TPixel>(bitsPerSample);
 
+                case TiffColorType.Rgb161616:
+                    DebugGuard.IsTrue(
+                        bitsPerSample.Length == 3
+                        && bitsPerSample[2] == 16
+                        && bitsPerSample[1] == 16
+                        && bitsPerSample[0] == 16,
+                        "bitsPerSample");
+                    DebugGuard.IsTrue(colorMap == null, "colorMap");
+                    return new RgbTiffColor<TPixel>(bitsPerSample);
+
                 case TiffColorType.PaletteColor:
                     DebugGuard.NotNull(bitsPerSample, "bitsPerSample");
                     DebugGuard.NotNull(colorMap, "colorMap");

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/TiffColorType.cs

@@ -88,6 +88,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
         /// </summary>
         Rgb141414,
 
+        /// <summary>
+        /// RGB color image with 16 bits for each channel.
+        /// </summary>
+        Rgb161616,
+
         /// <summary>
         /// RGB Full Color. Planar configuration of data.
         /// </summary>

src/ImageSharp/Formats/Tiff/TiffBitsPerPixel.cs

@@ -83,5 +83,12 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// Note: The TiffEncoder does not yet support 14 bits per color channel and will default to 24 bits per pixel instead.
         /// </summary>
         Bit42 = 42,
+
+        /// <summary>
+        /// 48 bits per pixel. 16 bit for each color channel.
+        ///
+        /// Note: The TiffEncoder does not yet support 16 bits per color channel and will default to 24 bits per pixel instead.
+        /// </summary>
+        Bit48 = 48,
     }
 }

src/ImageSharp/Formats/Tiff/TiffDecoderOptionsParser.cs

@@ -185,6 +185,10 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                         ushort bitsPerChannel = options.BitsPerSample[0];
                         switch (bitsPerChannel)
                         {
+                            case 16:
+                                options.ColorType = TiffColorType.Rgb161616;
+                                break;
+
                             case 14:
                                 options.ColorType = TiffColorType.Rgb141414;
                                 break;

src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs

@@ -327,6 +327,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                     case TiffBitsPerPixel.Bit30:
                     case TiffBitsPerPixel.Bit36:
                     case TiffBitsPerPixel.Bit42:
+                    case TiffBitsPerPixel.Bit48:
                         // Encoding not yet supported bits per pixel will default to 24 bits.
                         this.SetEncoderOptions(TiffBitsPerPixel.Bit24, TiffPhotometricInterpretation.Rgb, compression, TiffPredictor.None);
                         break;

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

@@ -160,6 +160,12 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         public void TiffDecoder_CanDecode_42Bit<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> => TestTiffDecoder(provider);
 
+        [Theory]
+        [WithFile(FlowerRgb161616Contiguous, PixelTypes.Rgba32)]
+        [WithFile(FlowerRgb161616Planar, PixelTypes.Rgba32)]
+        public void TiffDecoder_CanDecode_48Bit<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel> => TestTiffDecoder(provider);
+
         [Theory]
         [WithFile(GrayscaleDeflateMultistrip, PixelTypes.Rgba32)]
         [WithFile(RgbDeflateMultistrip, PixelTypes.Rgba32)]

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

@@ -78,6 +78,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         }
 
         [Theory]
+        [InlineData(TiffBitsPerPixel.Bit48)]
         [InlineData(TiffBitsPerPixel.Bit42)]
         [InlineData(TiffBitsPerPixel.Bit36)]
         [InlineData(TiffBitsPerPixel.Bit30)]

tests/ImageSharp.Tests/TestImages.cs

@@ -560,6 +560,8 @@ namespace SixLabors.ImageSharp.Tests
             public const string RgbPaletteDeflate = "Tiff/rgb_palette_deflate.tiff";
             public const string Flower4BitPalette = "Tiff/flower-palette-04.tiff";
             public const string Flower4BitPaletteGray = "Tiff/flower-minisblack-04.tiff";
+            public const string FlowerRgb161616Contiguous = "Tiff/flower-rgb-contig-16.tiff";
+            public const string FlowerRgb161616Planar = "Tiff/flower-rgb-planar-16.tiff";
             public const string FlowerRgb141414Contiguous = "Tiff/flower-rgb-contig-14.tiff";
             public const string FlowerRgb141414Planar = "Tiff/flower-rgb-planar-14.tiff";
             public const string FlowerRgb101010Contiguous = "Tiff/flower-rgb-contig-10.tiff";

tests/Images/Input/Tiff/flower-rgb-contig-16.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:ab3d6b619a198ff2e5fdd8f9752bf43c5b03a782625b1f0e3f2cfe0f20c4b24a
+size 19177

tests/Images/Input/Tiff/flower-rgb-planar-16.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:0a143fb6c5792fa7755e06feb757c745ad68944336985dc5be8a0c37247fe36d
+size 19177