NEF --- DNG Conversion: Is it lossy or lossless?

Question

I was recently reading on a Nikon Forum where a writer stated that some data is lost when converting to DNG in Lightroom. His comments follow.
I'd appreciate if some of the seasoned experts here would offer an opinion, and hopefully, a rebuttal. Thanks for any information you can share on this subject
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Every compression algorith is flawed if a single bit is lost and the original can not be recreated. Since the DNG converter must know about your camera model and it actually converts the NEF into an image before compressing the image, AND you can not, after converting to DNG convert back to original NEF, it is to me obvious that it is indeed a lossy compression, not just 'simple' data compression like zip, tar or whatever other type of data compression you want to compare with, which is truly lossless.
The Nikon lossless compression works entirely on data compression principle, preserving every bit and recreating every bit of data when you edit the raw image, and that can not be done once the image is converted to DNG. That is why many people, who use DNG, also preserve the original NEF, which in my opinion, is a totally pointless work flow. The only reason I can see to use DNG is the ability to share the image with somebody else who is not able to edit NEF, but I might as well use TIFF in that case.
The DNG converter must have knowledge of the camera model concerned, and be able to process the source raw image file, including key metadata to be able to convert and compress. A real lossless compression algorithm NEVER looks at the contents of the data because it is totally irrelevant for the converter to know what type of data you convert and try to compress, since it is based on mathematical patterns and statistics only.
I look at DNG like I look at PDF. A Word document, especially with photographs in it, can be converted to PDF and it may look like you have not lost anything, but yes, you have lost a lot actually and you can never ever recreate the original Word document with the same quality like you have had in your original.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Answer 1

727737757 wrote:
The only reason why I convert NEF to DNG is that I like *not* having sidecar files.
A perfectly valid reason to convert to DNG, in my opinion.
And if you are using in Adobe software, you will notice no ill side-effects (e.g. no data loss) whatsoever, so I think you can have full confidence..
But to offer a little more explanation:
The DNG converter needs to know the camera model because it's doing a lot more than "zipping" up the raw data. e.g. it's also creating a camera profile, and interpreting white balance..
Obviously, lossy compression is, well, lossy - I was talking about the lossless compression of raw data, which is 100% perfectly lossless (not a single bit is dropped..).
But if you open a NEF in Aperture, you can see the focus point. If you open the converted DNG, you can't. Not because the focus point information is not in the DNG file, but because it's not in a prescribed place where Aperture can find it - so you could say it's "lost" for practical purposes, although that's not how I think of it.
Cheers,
Rob