For YCbCr Tiff's with Jpeg compression explicitly assume RGB color space

src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanScanDecoder.cs

@@ -67,7 +67,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
         private readonly SpectralConverter spectralConverter;
 
-        private CancellationToken cancellationToken;
+        private readonly CancellationToken cancellationToken;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="HuffmanScanDecoder"/> class.

src/ImageSharp/Formats/Jpeg/Components/Decoder/SpectralConverter.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters;
+
 namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 {
     /// <summary>
@@ -30,5 +32,13 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// Actual stride height depends on the subsampling factor of the given component.
         /// </remarks>
         public abstract void ConvertStrideBaseline();
+
+        /// <summary>
+        /// Gets the color converter.
+        /// </summary>
+        /// <param name="frame">The jpeg frame with the color space to convert to.</param>
+        /// <param name="jpegData">The raw JPEG data.</param>
+        /// <returns>The color converter.</returns>
+        public abstract JpegColorConverter GetConverter(JpegFrame frame, IRawJpegData jpegData);
     }
 }

src/ImageSharp/Formats/Jpeg/Components/Decoder/SpectralConverter{TPixel}.cs

@@ -11,12 +11,12 @@ using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 {
-    internal sealed class SpectralConverter<TPixel> : SpectralConverter, IDisposable
+    internal class SpectralConverter<TPixel> : SpectralConverter, IDisposable
         where TPixel : unmanaged, IPixel<TPixel>
     {
         private readonly Configuration configuration;
 
-        private CancellationToken cancellationToken;
+        private readonly CancellationToken cancellationToken;
 
         private JpegComponentPostProcessor[] componentProcessors;
 
@@ -59,6 +59,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             }
         }
 
+        /// <inheritdoc/>
         public override void InjectFrameData(JpegFrame frame, IRawJpegData jpegData)
         {
             MemoryAllocator allocator = this.configuration.MemoryAllocator;
@@ -85,9 +86,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             this.rgbaBuffer = allocator.Allocate<Vector4>(frame.PixelWidth);
 
             // color converter from Rgba32 to TPixel
-            this.colorConverter = JpegColorConverter.GetConverter(jpegData.ColorSpace, frame.Precision);
+            this.colorConverter = this.GetConverter(frame, jpegData);
         }
 
+        /// <inheritdoc/>
         public override void ConvertStrideBaseline()
         {
             // Convert next pixel stride using single spectral `stride'
@@ -103,6 +105,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             }
         }
 
+        /// <inheritdoc/>
+        public override JpegColorConverter GetConverter(JpegFrame frame, IRawJpegData jpegData) => JpegColorConverter.GetConverter(jpegData.ColorSpace, frame.Precision);
+
         public void Dispose()
         {
             if (this.componentProcessors != null)

src/ImageSharp/Formats/Tiff/Compression/Decompressors/JpegTiffCompression.cs

@@ -23,6 +23,8 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Decompressors
 
         private readonly byte[] jpegTables;
 
+        private readonly TiffPhotometricInterpretation photometricInterpretation;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="JpegTiffCompression"/> class.
         /// </summary>
@@ -31,12 +33,19 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Decompressors
         /// <param name="width">The image width.</param>
         /// <param name="bitsPerPixel">The bits per pixel.</param>
         /// <param name="jpegTables">The JPEG tables containing the quantization and/or Huffman tables.</param>
-        /// <param name="predictor">The predictor.</param>
+        /// <param name="photometricInterpretation">The photometric interpretation.</param>
-        public JpegTiffCompression(Configuration configuration, MemoryAllocator memoryAllocator, int width, int bitsPerPixel, byte[] jpegTables, TiffPredictor predictor = TiffPredictor.None)
+        public JpegTiffCompression(
-            : base(memoryAllocator, width, bitsPerPixel, predictor)
+            Configuration configuration,
+            MemoryAllocator memoryAllocator,
+            int width,
+            int bitsPerPixel,
+            byte[] jpegTables,
+            TiffPhotometricInterpretation photometricInterpretation)
+            : base(memoryAllocator, width, bitsPerPixel)
         {
             this.configuration = configuration;
             this.jpegTables = jpegTables;
+            this.photometricInterpretation = photometricInterpretation;
         }
 
         /// <inheritdoc/>
@@ -47,8 +56,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Decompressors
             {
                 var jpegDecoder = new JpegDecoderCore(this.configuration, new JpegDecoder());
 
-                // Should we pass through the CancellationToken from the tiff decoder?
+                // TODO: Should we pass through the CancellationToken from the tiff decoder?
-                using var spectralConverter = new SpectralConverter<Rgb24>(this.configuration, CancellationToken.None);
+                // If the PhotometricInterpretation is YCbCr we explicitly assume the JPEG data is in RGB color space.
+                // There seems no other way to determine that the JPEG data is RGB colorspace (no APP14 marker, componentId's are not RGB).
+                using SpectralConverter<Rgb24> spectralConverter = this.photometricInterpretation == TiffPhotometricInterpretation.YCbCr ?
+                    new RgbJpegSpectralConverter<Rgb24>(this.configuration, CancellationToken.None) : new SpectralConverter<Rgb24>(this.configuration, CancellationToken.None);
                 var scanDecoder = new HuffmanScanDecoder(stream, spectralConverter, CancellationToken.None);
                 jpegDecoder.LoadTables(this.jpegTables, scanDecoder);
                 scanDecoder.ResetInterval = 0;

src/ImageSharp/Formats/Tiff/Compression/Decompressors/RgbJpegSpectralConverter.cs

@@ -0,0 +1,33 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.Threading;
+using SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder;
+using SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Decompressors
+{
+    /// <summary>
+    /// Spectral converter for YCbCr TIFF's which use the JPEG compression.
+    /// The jpeg data should be always treated as RGB color space.
+    /// </summary>
+    /// <typeparam name="TPixel">The type of the pixel.</typeparam>
+    internal sealed class RgbJpegSpectralConverter<TPixel> : SpectralConverter<TPixel>
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="RgbJpegSpectralConverter{TPixel}"/> class.
+        /// This Spectral converter will always convert the pixel data to RGB color.
+        /// </summary>
+        /// <param name="configuration">The configuration.</param>
+        /// <param name="cancellationToken">The cancellation token.</param>
+        public RgbJpegSpectralConverter(Configuration configuration, CancellationToken cancellationToken)
+            : base(configuration, cancellationToken)
+        {
+        }
+
+        /// <inheritdoc/>
+        public override JpegColorConverter GetConverter(JpegFrame frame, IRawJpegData jpegData) => JpegColorConverter.GetConverter(JpegColorSpace.RGB, frame.Precision);
+    }
+}

src/ImageSharp/Formats/Tiff/Compression/TiffDecompressorsFactory.cs

@@ -54,7 +54,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression
 
                 case TiffDecoderCompressionType.Jpeg:
                     DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
-                    return new JpegTiffCompression(configuration, allocator, width, bitsPerPixel, jpegTables);
+                    return new JpegTiffCompression(configuration, allocator, width, bitsPerPixel, jpegTables, photometricInterpretation);
 
                 default:
                     throw TiffThrowHelper.NotSupportedDecompressor(nameof(method));

tests/ImageSharp.Tests/Formats/Jpg/SpectralJpegTests.cs

@@ -7,6 +7,7 @@ using System.Linq;
 using SixLabors.ImageSharp.Formats.Jpeg;
 using SixLabors.ImageSharp.Formats.Jpeg.Components;
 using SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder;
+using SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters;
 using SixLabors.ImageSharp.IO;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
@@ -200,6 +201,8 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
 
                 this.spectralData = new LibJpegTools.SpectralData(spectralComponents);
             }
+
+            public override JpegColorConverter GetConverter(JpegFrame frame, IRawJpegData jpegData) => JpegColorConverter.GetConverter(jpegData.ColorSpace, frame.Precision);
         }
     }
 }

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

@@ -290,8 +290,8 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
 
         [Theory]
         [WithFile(Calliphora_RgbUncompressed, PixelTypes.Rgba32)]
-        public void TiffEncoder_EncodeRgb_WithjpegCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
+        public void TiffEncoder_EncodeRgb_WithJpegCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
-            where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Bit24, TiffPhotometricInterpretation.Rgb, TiffCompression.Jpeg);
+            where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Bit24, TiffPhotometricInterpretation.Rgb, TiffCompression.Jpeg, useExactComparer: false, compareTolerance: 0.012f);
 
         [Theory]
         [WithFile(Calliphora_GrayscaleUncompressed, PixelTypes.Rgba32)]