Tuesday, June 22nd 2010

Converting to DNG

After having thought about it loosely for ages, I decided to finally convert all my raw (CR2) files into the open DNG (digital negative) file format. But before I did so I sat down and did plenty of internet research to make sure I wasn’t doing something stupid.

If you didn’t know, DNG is Adobe’s attempt to create a universal and openly documented raw image file format. The (perhaps optimistic) idea being that camera makers will start using it instead of their proprietary raw formats (*cough* nikoncanon *splutter*). Whether or not this will ever become true remains to be seen.

Thankfully all photographers that want to can make use of DNG and its benefits regardless of which camera make they have, thanks to Adobe’s free DNG Converter.

Here are the factors that made me convert …

Future proof

Imagine the following scenario. Canon make a few bad decisions on their camera line-up. Nikon make a few really good ones. Nikon gains loads and loads of market share, making Canon a minor player. Canon is bought by Sony or Nikon, who proceed to terminate Canon’s own camera production. (Nikon users: Imagine the opposite.)

That could all happen in say five–ten years in a worst case scenario.

Then, in 2019, it is time to buy a new computer. And with a new computer comes a new operating system. Then, it turns out, there is no software for Windows 10 that reads CR2 files from a Canon EOS 30D. Dead end? Well, probably not, but there would be a lot of hassle for sure.

Actually, even if Canon are still around in 2019 it is quite possible that they won’t release software to cater for the oldest camera models and their raw files.

With DNG files the chance of there not being compatible software is much smaller since the specification is entirely open. (Read it here if you like.) Even if Adobe were to be blasted off the face of the earth, the DNG specification would live on. And someone in the intersection between photography geeks and computer geeks would most certainly write a program that can read DNGs.

Granted, you could argue that as long as Adobe’s DNG Converter is around there is no need to rush. And there isn’t really, but there are a few more pros that made me do the switch now. Read on.

Previews and metadata

DNGs will contain a preview JPEG (tiny, medium or full size) and all the metadata of the original raw file, plus any metadata you want to add such as keywords, titles, captions or develop settings. For anyone using Adobe Lightroom, Bridge or Camera Raw this means that you’ll have one DNG file instead of a CR2/NEF image file and an XMP metadata file next to it.

Also, when you’ve changed the appearance of a photo you can render a new preview JPEG and embed it in the DNG. (In Lightroom: Right click and choose Metadata -> Update DNG Preview & Metadata.) I don’t know how NEFs work, but with CR2 files there is definitely no way of updating the embedded JPEG.

File size

DNG files are often smaller then the camera’s raw file. This is thanks to better compression, but also thanks to the possibility to use a smaller size JPEG than in the original.

I chose the medium JPEG size (1024 pixels I think) and the DNG files are on average 19 percent smaller than the CR2s from my Canon EOS 50D. My thinking here is that I don’t really need a full size preview in the raw file once I have it on the computer. In the camera it’s a different matter – there I need the full size preview to be able to check focus. And even if I do choose to embed a full size JPEG the DNG ends up ~10% smaller.

It will be a while though before I will actually see the benefit of the smaller file size, because right now I’m keeping my CR2 files in parallel with the DNGs. I also have them backed up to our two external drives (one off location) as well as on DVDs. So I have essentially doubled my storage needs.

In a few weeks though I’ll probably feel 100% comfortable with the conversion, and then I’ll delete the CR2s from my working folders and only have the three backup copies.

No negatives?

Considering that DNGs are just that, negatives, there are very few drawbacks. The only one, as I see it, is that I won’t be able to go back and use Canon’s own raw converters Raw Image Task or Digital Photo Professional. This is a rather academic point though, since I have never wanted to use either of them since moving to Lightroom. The only reason I might want to do that in the future would be to see how much better raw image processing has become since I bought my camera. So I might make such a comparison before I actually chuck the CR2 files.


Being a Lightroom user, the DNG format is very useful. I’m not sure if DNG is quite as sweet a deal if you’re using some other raw converter though, and DNG isn’t necessarily for everyone. But for me it definitely is a great step up from the CR2 format. So far I haven’t had any second thoughts at all, and I doubt I will have any later on either.

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