Set PhotometricInterpretation to RGB, let jpeg decoder handle color conversion

src/ImageSharp/Formats/Tiff/TiffDecoderOptionsParser.cs

@@ -478,8 +478,9 @@ internal static class TiffDecoderOptionsParser
             {
                 options.CompressionType = TiffDecoderCompressionType.OldJpeg;
 
-                // Like libtiff: always assume PhotometricInterpretation to be YCbCr, if the compression is old jpeg.
+                // Note: Setting PhotometricInterpretation and color type to RGB here, since the jpeg decoder will handle the conversion of the pixel data.
-                options.PhotometricInterpretation = TiffPhotometricInterpretation.YCbCr;
+                options.PhotometricInterpretation = TiffPhotometricInterpretation.Rgb;
+                options.ColorType = TiffColorType.Rgb;
 
                 if (!options.OldJpegCompressionStartOfImageMarker.HasValue)
                 {

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

@@ -666,6 +666,7 @@ public class TiffDecoderTests : TiffDecoderBaseTester
 
     [Theory]
     [WithFile(RgbOldJpegCompressed, PixelTypes.Rgba32)]
+    [WithFile(YCbCrOldJpegCompressed, PixelTypes.Rgba32)]
     public void TiffDecoder_CanDecode_OldJpegCompressed<TPixel>(TestImageProvider<TPixel> provider)
         where TPixel : unmanaged, IPixel<TPixel> => TestTiffDecoder(provider, useExactComparer: false);
 

tests/ImageSharp.Tests/TestImages.cs

@@ -796,6 +796,7 @@ public static class TestImages
         public const string RgbJpegCompressed = "Tiff/rgb_jpegcompression.tiff";
         public const string RgbJpegCompressed2 = "Tiff/twain-rgb-jpeg-with-bogus-ycbcr-subsampling.tiff";
         public const string RgbOldJpegCompressed = "Tiff/OldJpegCompression.tiff";
+        public const string YCbCrOldJpegCompressed = "Tiff/YCbCrOldJpegCompressed.tiff";
         public const string RgbWithStripsJpegCompressed = "Tiff/rgb_jpegcompressed_stripped.tiff";
         public const string RgbJpegCompressedNoJpegTable = "Tiff/rgb_jpegcompressed_nojpegtable.tiff";
         public const string RgbLzwPredictor = "Tiff/rgb_lzw_predictor.tiff";

tests/Images/Input/Tiff/YCbCrOldJpegCompressed.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:b6527e69a3cce3e6d425c35695319711ad36d939f934902faa47f6ee1f1c7e08
+size 10076700