Lossy DNG shows strong visible differences but JPG not, is this a bug?

Question

Hello,
I tried out the lossy DNG format with a lot of pictures.
For most pictures I can't find any visible differences.
But I found also some pictures with very noticible visible differences between lossless and lossy DNG.
It seems that the lossy DNG format has problems with dark pictures with small light sources for example
the stars in the dark sky or the red lights of an aeroplane in the dark sky.
I have an example where you can see red security lights of a great antenna on top of a mountain.
Surprisingly with this extreme example the JPG versions looks much better as the lossy DNG version of my source lossless DNG.
Here is the cropped JPG from the lossless DNG (file size 10877KB):
Between this JPG and the lossless DNG file is no visible difference.
And here a JPG from the lossy DNG (file size 13261KB):
Between this JPG and the source lossy DNG file is no visible difference.
The source of both DNG files was a NEF File from a Nikon D7100.
Also interessting is, that for this excample the file size of the lossy DNG is  greater than the lossless DNG. This seems crasy IMHO.
I was very surprised, that JPG result is is much better than the lossy DNG for this case.
Perhaps there is a hidden bug in the lossy DNG conversion process.
I hope Adobe can look in to this. If you need the original NEF file let me know.

Answer 1

JimHess wrote:
I thought about responding the other day, but decided my remarks wouldn't help you. And they still won't because I'm going to give you my personal opinion about lossy DNG. I don't think it is intended for your master "important" images. I watched a video on Adobe.tv about this, and the example that was given was, suppose you have taken pictures at a wedding. Perhaps you have 2000-3000 images, 500 of which are keepers that are really good. You don't want to get rid of the other bunch but want to save space. So those would be the images that you would convert to lossy DNG. I mean, let's be realistic about this. You can't throw away data and hope to still have full raw quality. That isn't the idea behind the format.
Personally, I think converting to DNG of any sort as a workflow routine is frivolous and unwise. I know a lot of people routinely download and convert, and then they don't have copies of their original raw images. Yes, I know, the DNG files contain all the original raw image data. But not all software will read those DNG files. For example, I use Nikon cameras. The cameras shipped with ViewNX 2. It's not a very useful program, but has a couple of features that I like to use once in a while. But it won't open the DNG files. And if I have converted and then discarded the original NEF files, I can't use the software. With my cameras there is only a 15-20% savings in space. The tutorial I watched indicated that the lossy DNG files would load in Lightroom up to 8 times faster. I haven't used a stopwatch, but if anything the DNG files take longer to load than the original NEF files.
The only benefit I see to converting to DNG is if I have a file from a camera for which I don't have native support because my software is older or not up-to-date. I know this hasn't helped you. But maybe it will stimulate some conversation and you'll get a more enlightening opinion from someone else.
First of all I want to use lossy DNG because I want save space.
Second, I have no extra XMP-File for every image.
If I can't see any visible difference between a  lossy DNG and a lossless DNG, then I have no problems with losing some data.