The Lure of DNG

DNG, Digital NeGative, is Adobe's attempt at a unified RAW file format for all cameras world wide. Some people are all worked up about this and list numerous advantages.

I am not one of them.

There is nothing wrong with dng, it just so happens that it is not much better than other things either. Some people duly convert all their Nikon nef files to dng, but that may be a waste of time and a loss of some data.

However, if your camera produces dng files, by all means, keep them. They are not worse than other raw formats.

Let's look at some of the alleged benefits.

Archiving is one of the often quoted arguments for dng. As dng is supposed to be a universal standard, it seems reasonable to assume that support for it will be around for ever, right?

The answer is perhaps. A standard does not become a standard by someone calling it a standard. The internationally defined format for writing dates is year-month-day, like 080619 for today. However, apart from Finland and Sweden hardly any country uses that date format in daily life.

Adobe supports dng, and a few camera makers support it, but most camera makers do not see much advantage. The by far biggest SLR camera makers, Nikon and Canon, do not support it. That means that most raw pictures that are taken today use other formats than dng.

It is very possible that there will be dng readers in 50 years time, but it is equally likely that there will be readers for Nikon's nef files and Canon's cr2 files.


And it seems reasonable to assume that a program that can read one dng can read all, right?

But that is not the case. Just like for tiff or psd files, there are many flavours and extensions. If a program cannot read the native raw file from a particular camera, it is quite possible that the program cannot read dng files from that camera either. It is also possible that it can read some files but not all, depending on the lens used.

In some ways, a dng is simply a wrapper around some other file format. A dng can even embed the full original of another raw file. If the program cannot read the original, it cannot read the dng.


One claimed benefit for dng is the file size. The story is that raw files for early cameras were only lightly compressed. The nef file of a Nikon D1X from 2001, for example, weighed in 7.8 Megabyte, while an equivalent dng file only was 4.8 Megabyte. A Canon 300D from 2003 had a crw file of 6.0 Megabyte, while the equivalent dng was just 4.2 Megabyte.

However, there is nothing inherently large with Nikon or Canon files. The companies can modify the formats, and they compress them more and more. A lossless compressed 14 bit nef of 14.4 MB from a new Nikon D300, for example, is converted into a 13.3 MB lossless compressed dng file, which hardly is any significant gain. A non-compressed dng with embedded jpeg preview turns out to be 25.4 MB - much bigger than the original.

There are still cameras that have huge raw files, and in these cases a conversion to dng has a certain sense. However, often it may be as useful to convert the raw to tiff or even jpeg - formats that are easier to manipulate for other purposes.

If you convert a raw file to dng, you may not lose any information - at least not unless you use the "Linear Image" option. However, there may be camera specific information in the raw file, like the Picture Control data in a NEF file, that no program can interpret correctly when it hides in a dng. The information is definitely there, but it may in practice be impossible to actually use it.


But then, as said before, there is nothing wrong with a dng. If you see any use for dng, by all means use it. I for example convert my nef files from my D300 to dng in order to open them in Photoshop CS2. It is either that or upgrade to Photoshop CS3 or use Aperture. Most often I actually use Aperture, as I prefer to work on the original file.