DNG Benefits?


Today’s Question: I am a wedding photographer and, along with my other photographers, sometimes take as many as 2000 pictures at a wedding. Of course, I upload these into Lightroom as soon as I get back to the studio (along with backing them up on two external hard drives). Downloading 2000 RAW picture into Lightroom takes a long time, but if I also convert them to DNGs, it takes a very long time. I realize that DNGs are smaller files and will save me space but is there any advantage or disadvantage to working with camera RAW images versus working on DNG images? I am tempted to just upload the camera RAW images and not convert them to DNGs to save time.

Tim’s Quick Answer: Personally, I would favor the use of the original RAW captures rather than converting to Adobe DNG, especially in a situation where you need to be able to work as quickly as possible.

More Detail: To be sure, as a general rule you can expect a RAW capture converted to an Adobe DNG file to have a file size that is around 20% smaller than the original RAW file. Your specific results may vary, but in general the DNG file will be smaller than the original RAW capture due to compression. And it should be noted that the compression used for those DNG images does not degrade image quality in any way.

It should be noted that there is not an issue with processing DNG versus RAW captures in the Develop module in Lightroom (or in Adobe Camera Raw). Overall image quality will be preserved with the conversion from a proprietary RAW capture to the Adobe DNG format.

Of course, as noted in today’s question, additional time is required to create a DNG image based on each original RAW capture, which adds additional time to your overall workflow. That additional time can be significant, especially when you are trying to hurry to get photos to clients.

There is another reason that I prefer to retain the original RAW captures rather than convert to DNG, related to how metadata is stored. I prefer to turn on the option on the Metadata tab in the Catalog Settings dialog in Lightroom to “Automatically write changes into XMP”. This causes key metadata values (such as star ratings and keywords) to be saved out to the original image file, or to an XMP “sidecar” file in the case of proprietary RAW captures.

Some photographers prefer to convert their RAW captures to the DNG file format for exactly this reason. They prefer not to have an XMP “sidecar” file for every RAW capture for which they’ve applied any standard metadata updates. With a DNG image, the metadata updates are added to the actual DNG file, without the need for a sidecar file.

My issue with this relates to my use of a synchronization-based backup solution. In short, each time I backup my photos I’m really just updating the existing backup based on which files have changed. In the case of a metadata update, the updated XMP file will be significantly smaller than the updated DNG file. So by not converting to DNG I’m also saving time with my backup workflow.

There are certainly some advantages to the Adobe DNG format as compared to proprietary RAW capture formats. But on balance my preference is to retain the original RAW captures, and to not convert my captures to DNG.