Backport v3 : Tiff decoder: Fix issue 2679

src/ImageSharp/Formats/Tiff/TiffDecoderOptionsParser.cs

@@ -637,6 +637,14 @@ private static void ParseCompression(this TiffDecoderCore options, TiffCompressi
             {
                 options.CompressionType = TiffDecoderCompressionType.Jpeg;
 
+                // 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 && 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.

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

@@ -705,6 +705,23 @@ public void TiffDecoder_CanDecode_TiledWithNonEqualWidthAndHeight<TPixel>(TestIm
     public void TiffDecoder_CanDecode_BiColorWithMissingBitsPerSample<TPixel>(TestImageProvider<TPixel> provider)
         where TPixel : unmanaged, IPixel<TPixel> => TestTiffDecoder(provider);
 
+    // https://github.com/SixLabors/ImageSharp/issues/2679
+    [Theory]
+    [WithFile(Issues2679, PixelTypes.Rgba32)]
+    public void TiffDecoder_CanDecode_JpegCompressedWithIssue2679<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(TiffDecoder.Instance);
+
+        // The image is handcrafted to simulate issue 2679. ImageMagick will throw an expection here and wont decode,
+        // so we compare to reference output instead.
+        image.DebugSave(provider);
+        image.CompareToReferenceOutput(
+            ImageComparer.Exact,
+            provider,
+            appendPixelTypeToFileName: false);
+    }
+
     [Theory]
     [WithFile(JpegCompressedGray0000539558, PixelTypes.Rgba32)]
     public void TiffDecoder_ThrowsException_WithCircular_IFD_Offsets<TPixel>(TestImageProvider<TPixel> provider)

tests/ImageSharp.Tests/TestImages.cs

@@ -1112,6 +1112,7 @@ public static class Tiff
         public const string Issues2255 = "Tiff/Issues/Issue2255.png";
         public const string Issues2435 = "Tiff/Issues/Issue2435.tiff";
         public const string Issues2587 = "Tiff/Issues/Issue2587.tiff";
+        public const string Issues2679 = "Tiff/Issues/Issue2679.tiff";
         public const string JpegCompressedGray0000539558 = "Tiff/Issues/JpegCompressedGray-0000539558.tiff";
         public const string Tiled0000023664 = "Tiff/Issues/tiled-0000023664.tiff";
         public const string ExtraSamplesUnspecified = "Tiff/Issues/ExtraSamplesUnspecified.tif";