Copyright Emilio Del Tessandoro 2017.


I’ve been shooting with a DLSR for almost 8 years now and I accumulated quite a lot of files on my hard drive. At the beginning I’ve been looking at DNG files mostly for space and archiving reasons.

In fact one of the main obvious advantages of DNG format is compression. Is quite obvious that the compression of a format designed for a portable device, that is the camera, can’t be extremely high. DNG supports both lossy and lossless compression with compression ratios much higher than raw files.

Comparing NEF files from Nikon D800 and D7000 I found that lossless DNG is around 2/3 of the size of a NEF file. And this is without loosing any bit of information 1.

If you are okay to go with lossy compression the savings are quite amazing, around 1/3 of the original NEF. That means that if you have 1Tb of original photos you could archive them it very high quality DNG using around 300Gb. Not bad at all. Another interesting feature is that lossy DNG can be smaller in resolution too. So if you are okay with archiving your 36 Megapixel (7360x4912) photos downsized down to say 4928x3264 (16 Megapixel) you basically save another 55%. A 1Tb collection could be archived in a 140Gb space, around one seventh of the original, with quality that is still reasonable.

The only problem here is that even if there is no visible difference in quality, there has to be some (pretty big) loss somewhere. The most obvious one is the bit depth reduction. Raw formats usually have 12 or 14 bits per color, while lossy DNG is 8 bits per channel. It’s also stated on the Photoshop DNG import dialog:

On the other hand there has to be some other optimization to preserve information in dark and bright areas. Usually detail in these areas are the first loss of information in algorithms like JPG, since it they are based on perceptual models (our eye it’s not particularly good in detecting contrast in almost black or almost white areas). But this doesn’t happen with DNG. So in this respect DNG is like a better version JPG with a lot of room for shadow and highlight recovery. Summarizing:

  NEF 36Mp Lossless DNG 36Mp Lossy DNG 36Mp Lossy DNG 16Mp
Depth 12 or 14 bits 8 bits 8 bits 8 bits
Size 100% ~70% ~33% ~15%

Another big problem of DNG in my opinion is that is not open source, so it’s not a widely adopted format yet. Capture One for example doesn’t like DNG files at the moment. I really hope Adobe will open source it or that other famous processing applications will start adopting this format in the near future. If this doesn’t happen soon I’m afraid the format is gonna die.

So all in all, I’ve considered the idea of converting my files to DNG for archiving reasons, but I’m not convinced enough for going through the effort. I think could be a good option though, if you are thinking to store your files on some cloud provider solution. If storage is expensive, like in the case of cloud storage, then it makes much more sense.

  1. Well, this is actually not true. I found out after writing this post that DNG always reduces the color depth to 8 bit, even when using lossless compression. In other words DNG doesn’t seem to use at all the original Bayer filter representation that instead is 12 or 14 bits per channel.