Add support decoding for 12 bits per channel tiff's

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

@@ -97,6 +97,16 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                     DebugGuard.IsTrue(colorMap == null, "colorMap");
                     return new RgbTiffColor<TPixel>(bitsPerSample);
 
+                case TiffColorType.Rgb121212:
+                    DebugGuard.IsTrue(
+                        bitsPerSample.Length == 3
+                        && bitsPerSample[2] == 12
+                        && bitsPerSample[1] == 12
+                        && bitsPerSample[0] == 12,
+                        "bitsPerSample");
+                    DebugGuard.IsTrue(colorMap == null, "colorMap");
+                    return new RgbTiffColor<TPixel>(bitsPerSample);
+
                 case TiffColorType.Rgb141414:
                     DebugGuard.IsTrue(
                         bitsPerSample.Length == 3

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

@@ -78,6 +78,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
         /// </summary>
         Rgb101010,
 
+        /// <summary>
+        /// RGB color image with 12 bits for each channel.
+        /// </summary>
+        Rgb121212,
+
         /// <summary>
         /// RGB color image with 14 bits for each channel.
         /// </summary>

src/ImageSharp/Formats/Tiff/TiffBitsPerPixel.cs

@@ -70,6 +70,13 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// </summary>
         Bit30 = 30,
 
+        /// <summary>
+        /// 36 bits per pixel. 12 bit for each color channel.
+        ///
+        /// Note: The TiffEncoder does not yet support 12 bits per color channel and will default to 24 bits per pixel instead.
+        /// </summary>
+        Bit36 = 36,
+
         /// <summary>
         /// 42 bits per pixel. 14 bit for each color channel.
         ///

src/ImageSharp/Formats/Tiff/TiffDecoderOptionsParser.cs

@@ -189,6 +189,10 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                                 options.ColorType = TiffColorType.Rgb141414;
                                 break;
 
+                            case 12:
+                                options.ColorType = TiffColorType.Rgb121212;
+                                break;
+
                             case 10:
                                 options.ColorType = TiffColorType.Rgb101010;
                                 break;

src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs

@@ -325,6 +325,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                     case TiffBitsPerPixel.Bit14:
                     case TiffBitsPerPixel.Bit16:
                     case TiffBitsPerPixel.Bit30:
+                    case TiffBitsPerPixel.Bit36:
                     case TiffBitsPerPixel.Bit42:
                         // Encoding not yet supported bits per pixel will default to 24 bits.
                         this.SetEncoderOptions(TiffBitsPerPixel.Bit24, TiffPhotometricInterpretation.Rgb, compression, TiffPredictor.None);

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

@@ -149,6 +149,11 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         public void TiffDecoder_CanDecode_30Bit<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> => TestTiffDecoder(provider);
 
+        [Theory]
+        [WithFile(FlowerRgb121212Contiguous, PixelTypes.Rgba32)]
+        public void TiffDecoder_CanDecode_36Bit<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel> => TestTiffDecoder(provider);
+
         [Theory]
         [WithFile(FlowerRgb141414Contiguous, PixelTypes.Rgba32)]
         [WithFile(FlowerRgb141414Planar, PixelTypes.Rgba32)]

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

@@ -79,6 +79,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
 
         [Theory]
         [InlineData(TiffBitsPerPixel.Bit42)]
+        [InlineData(TiffBitsPerPixel.Bit36)]
         [InlineData(TiffBitsPerPixel.Bit30)]
         [InlineData(TiffBitsPerPixel.Bit12)]
         [InlineData(TiffBitsPerPixel.Bit10)]

tests/ImageSharp.Tests/TestImages.cs

@@ -564,6 +564,7 @@ namespace SixLabors.ImageSharp.Tests
             public const string FlowerRgb141414Planar = "Tiff/flower-rgb-planar-14.tiff";
             public const string FlowerRgb101010Contiguous = "Tiff/flower-rgb-contig-10.tiff";
             public const string FlowerRgb101010Planar = "Tiff/flower-rgb-planar-10.tiff";
+            public const string FlowerRgb121212Contiguous = "Tiff/flower-rgb-contig-12.tiff";
             public const string FlowerRgb444Contiguous = "Tiff/flower-rgb-contig-04.tiff";
             public const string FlowerRgb444Planar = "Tiff/flower-rgb-planar-04.tiff";
             public const string FlowerRgb222Contiguous = "Tiff/flower-rgb-contig-02.tiff";

tests/Images/Input/Tiff/flower-rgb-contig-12.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:5f7a63eb8636e2b1ee39dfda4d0bddfc98bdc9eb94bea2dd657619331fa38b5b
+size 14483