DNG is a trademark of Adobe

Using DNG for archiving?

What is DNG?

DNG (digital negative) is a file format that allows storing RAW images. The file format was developed by Adobe and is supported in most RAW development software products. Unlike proprietary RAW file formats like CR2 (Canon) or NEF (Nikon) the definition of the DNG file format is openly documented and available.

Adobe recommends the conversion of RAW images to DNG for the workflow in Lightroom.

Advantages of DNG

DNG has many advantages against proprietary RAW file formats:

  • Meta data and development settings are stored within the DNG file. There is no need for a side by side XMP file that has to be stored and kept next to the RAW file.
  • Data is compressed losslessly. The need of storage is reduced by about 20% in case of CR2 files (Canon). This reduction can be relevant when working with SSDs that usually have limited memory. Also loading files from slow drives is sped up if files are smaller.
  • The file format is open documented. That means that even in a houndred years it will be at least possible to write a converter for reading old files. Proprietary RAW formats are usually closed. There are already RAW files that cannon be read anymore in any available software product.
  • When you buy a new camery there is no need to update the RAW development software. It's sufficient to update the DNG converter.

Disadvantages of DNG

Can there really be disadvantages? Yes, and it's a substantial one that can easily be overseen - as happend to me. Many photography contests (e.g. GDT) require proof of originality of all awarded images so they can see if there were forbidden manipulations applied. And by 'original image' they mean exactly that. A image that was converted to DNG is not accepted.

I had a correspondence on the topic with the persons in charge of the GDT contest. His explanations horrified me, really. And it strengthened my impression that there are many bad people out there. At GDT the check every awarded image bitwise, looking for patterns of digital manipulation. Because DNG by definition has been digitaly manipulated there is no way to guarantee its originality and compliance with the terms. This is why DNGs are not accepted. I'm dreadfully sorry with the guys of the jury who have to do such criminalistic work just to allow a fair contest.

Conclusion

I was thinking of DNG being the non-plus-ultra for a long time. The advantages are convin­cing. Now I changed my workflow again and don't convert my RAW images to DNG any­more.