Add check, if YcbcrSubSampling has a value

src/ImageSharp/Formats/Tiff/TiffDecoderOptionsParser.cs

@@ -633,21 +633,22 @@ internal static class TiffDecoderOptionsParser
             case TiffCompression.Jpeg:
             {
                 options.CompressionType = TiffDecoderCompressionType.Jpeg;
-                if (options.PhotometricInterpretation is TiffPhotometricInterpretation.YCbCr && options.JpegTables is null)
-                {
-                    // Note: Setting PhotometricInterpretation and color type to RGB here, since the jpeg decoder will handle the conversion of the pixel data.
-                    options.PhotometricInterpretation = TiffPhotometricInterpretation.Rgb;
-                    options.ColorType = TiffColorType.Rgb;
-                }
 
                 // Some tiff encoder set this to values different from [1, 1]. The jpeg decoder already handles this,
                 // so we set this always to [1, 1], see: https://github.com/SixLabors/ImageSharp/issues/2679
-                if (options.PhotometricInterpretation is TiffPhotometricInterpretation.YCbCr)
+                if (options.PhotometricInterpretation is TiffPhotometricInterpretation.YCbCr && options.YcbcrSubSampling != null)
                 {
                     options.YcbcrSubSampling[0] = 1;
                     options.YcbcrSubSampling[1] = 1;
                 }
 
+                if (options.PhotometricInterpretation is TiffPhotometricInterpretation.YCbCr && options.JpegTables is null)
+                {
+                    // Note: Setting PhotometricInterpretation and color type to RGB here, since the jpeg decoder will handle the conversion of the pixel data.
+                    options.PhotometricInterpretation = TiffPhotometricInterpretation.Rgb;
+                    options.ColorType = TiffColorType.Rgb;
+                }
+
                 break;
             }