Start work on jpeg 12 bit support

src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

@@ -33,7 +33,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// <summary>
         /// The only supported precision
         /// </summary>
-        public const int SupportedPrecision = 8;
+        public readonly int[] SupportedPrecisions = { 8, 12 };
 
         /// <summary>
         /// The global configuration
@@ -137,7 +137,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// <summary>
         /// Gets the color depth, in number of bits per pixel.
         /// </summary>
-        public int BitsPerPixel => this.ComponentCount * SupportedPrecision;
+        public int BitsPerPixel => this.ComponentCount * this.Frame.Precision;
 
         /// <summary>
         /// Gets the input stream.
@@ -720,10 +720,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
 
             this.InputStream.Read(this.temp, 0, remaining);
 
-            // We only support 8-bit precision.
+            // We only support 8-bit and 12-bit precision.
-            if (this.temp[0] != SupportedPrecision)
+            if (!SupportedPrecisions.Contains(this.temp[0]))
             {
-                throw new ImageFormatException("Only 8-Bit precision supported.");
+                throw new ImageFormatException("Only 8-Bit and 12-Bit precision supported.");
             }
 
             this.Frame = new JpegFrame

tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.Images.cs

@@ -28,7 +28,10 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
                 TestImages.Jpeg.Issues.ExifResizeOutOfRange696,
                 TestImages.Jpeg.Issues.InvalidAPP0721,
                 TestImages.Jpeg.Issues.ExifGetString750Load,
-                TestImages.Jpeg.Issues.ExifGetString750Transform
+                TestImages.Jpeg.Issues.ExifGetString750Transform,
+
+                // High depth images
+                TestImages.Jpeg.Baseline.Testorig12bit,
             };
 
         public static string[] ProgressiveTestJpegs =

tests/ImageSharp.Tests/TestImages.cs

@@ -135,12 +135,14 @@ namespace SixLabors.ImageSharp.Tests
                 public const string Testorig420 = "Jpg/baseline/testorig.jpg";
                 public const string MultiScanBaselineCMYK = "Jpg/baseline/MultiScanBaselineCMYK.jpg";
                 public const string Ratio1x1 = "Jpg/baseline/ratio-1x1.jpg";
+                public const string Testorig12bit = "Jpg/baseline/testorig12.jpg";
 
                 public static readonly string[] All =
                 {
                     Cmyk, Ycck, Exif, Floorplan,
                     Calliphora, Turtle, GammaDalaiLamaGray,
-                    Hiyamugi, Jpeg400, Jpeg420Exif, Jpeg444, Ratio1x1
+                    Hiyamugi, Jpeg400, Jpeg420Exif, Jpeg444,
+                    Ratio1x1, Testorig12bit
                 };
             }