how to make the image phash value just 16bit

Question

I used https://github.com/pgrho/phash in c#. I want to get hash value like 51A70C737AD03A97 (16bit);

But it make phash value like : 7CFF35758E9E42009DA0839E955B465588816A709063336E8F81639A965D6381A784738995686189(80bit).

I use the code:

            var bitmap = (Bitmap)img;
            var hash = ImagePhash.ComputeDigest(bitmap.ToLuminanceImage());
            byte[] bytearr = hash.Coefficients;
            return byteToHexStr(bytearr);

Now, who knows how to make a hash value just 16bit, like 51A70C737AD03A97;