how to convert png to tff

[moonfanslyj]

im trying to use imagesharp to do convert from png to tiff， its work but tiff Transparent channels are missing
code like:
using (var image = SixLabors.ImageSharp.Image.Load(tmppath))
{
image.SaveAsTiff(outputTiffPath, new TiffEncoder() {
Compression = SixLabors.ImageSharp.Formats.Tiff.Constants.TiffCompression.Lzw,
CompressionLevel = SixLabors.ImageSharp.Compression.Zlib.DeflateCompressionLevel.BestCompression });
}
How can I use it?

Thanks and best regards,

[moonfanslyj]

finally...problem is EXTRASAMPLES