What's a DNG?
For those of you not familiar with Adobe's DNG image format (short for Digital Negative), it was introduced back during the Photoshop CS era, as a means of standardizing and simplifying the process of editing raw picture data. The need for this format stems from the fact that -to this day- camera manufacturers have eschewed a standardized raw file format, in favor of proprietary formats like NEF and CR2.
The problem with these formats is that over time, as the camera makers' software evolves, they sometimes "orphan" support for files created by older cameras. Unlike a real film negative which can be scanned at any time, a proprietary raw file, absent some 3rd party solution like Lightroom or ACR, can be made obsolete at the whim of the company. You might stand to lose a large segment of your photo library in that case, were you to rely solely on the manufacturer's format. DNG helps to ensure that if you convert your raw files from today's cameras, those same files will be accessible and editable for you, years down the road. There are of course other dynamics involved in this equation, but this is the core of the matter -- making sure your raw picture data lasts as long as you need it to.
Lightroom has always supported DNG, and with the release of Lightroom 4, its status as a first-class DNG citizen has been reinforced.
New DNG Options in Lightroom 4
Typically there are two ways to convert your raw files to DNG format. You can either use a special, freely downloadable utility from Adobe called the DNG Converter, and follow its instructions for batch-conversion. Or within Lightroom, you can export raw files as DNG files. If you choose a series of files in your Library module and click the Export button (bottom-left portion of the window), you'll be greeted with the Export dialog. Within that there is a "File Settings" group that looks like this:
Within these settings you have an Image Format menu, and the DNG format is included as one of the options. What's new in Lightroom 4 is that while DNG is traditionally a lossless format (and therefore tends to generate larger file sizes for the same reason raw files do), you now have the option to create a "Lossy DNG" file on export. This will significantly reduce the size of the DNG files, while having only a slight impact on quality in most cases, as compared to the original raw file. You can expect that a Lossy DNG will typically produce file quality on par with a max quality JPEG, but which stands up to further post-export editing better than a JPEG file. (Thank you to Lightroom Queen Victoria Bampton for her expertise on file conversions and quality settings in this area... she helped yours truly -a "raw purist"- to see the light, if you'll pardon the pun.)
You also have the option to embed the original raw file into the DNG, in case you need to extract it later. This will greatly increase the file size for obvious reasons, but it's worth discussing. There are a number of reasons why you might do this, but one of the more common reasons is that some photographers prefer to have a single archival file for each shot, that they can then back up in multiple places. Rather than throw the original raw file away, some find it useful to keep a copy of the raw data inside the DNG file, which can later be extracted with the DNG converter, if necessary (for example if you wanted to try new conversion settings with the original data). The DNG Converter window is shown below, along with the Raw File Extractor dialog. As you can see this process looks and works a lot like the Photoshop Image Processor; it's very simple to set up.
(Just click the "Extract" button to get the dialog box below and choose your target and destination folders. Simple!)
Managing DNGs with Smart Collections
Another new DNG feature in Lightroom 4 is that you can use Smart Collections to keep track of which of your DNGs were created using the Lossy compression scheme, and which are Lossless. This can be very important over time, as it's not always easy to remember how different batches of files were converted. And depending on how you converted them, you will want to optimize (and possibly limit the extent of) your edits, based on that information. To create a Smart Collection that tracks the DNG files in your Catalog, click the pop-out menu on the Collections panel and choose Create Smart Collection.
Next give your collection a name and then choose File Type, Is, "Digital Negative / Lossy Compressed". Add other criteria if necessary and then click "Create". When you're done you should have a collection in the panel that automatically detects the Lossy DNG file type, so that you can make your edits in a targeted way when the time comes. Hopefully you'll find that it's worth experimenting with the DNG format, as a way of protecting your archives for future use! To learn more about the new features available in Lightroom 4, you can visit Colortrails.com.