A few years ago the debate over RAW vs DNG looked to be leaning in towards the DNG file format as the way to go. Recently that debate has been revisited by a number of people and the pendulum is swinging back towards RAW as the file format of choice. This article will explore the pros and cons of each format.
First we have to understand what is RAW? A RAW file is the unprocessed data coming directly from the camera sensor; and “raw” truly means what it says—without any processing or manipulation what so ever. You might have noticed that when you take a photo and then bring in the RAW file that doesn’t look like the image that you saw on the back of your camera. That’s because that image on your camera is a jpeg and has been processed using the settings you have in your camera at the time. If you tell your camera you want to shoot in B&W, it will show you a B&W image on the back of your camera, but if you are shooting RAW and then bring it into your processing software—like Lightroom—you will notice it starts out B&W and then changes to color? Why? Because it displays the raw data—as in everything the camera sensor saw, and it saw the image as color. RAW files preserve the most amount of information about an image and generally contain more colors and dynamic range than other formats. When you edit a RAW file you aren’t actually changing that file; a side-car file called an XMP file is created to hold all of your scripted changes—think of this a layer that has your changes on it, while the base layer, the RAW file, is untouched.
Every manufacturer has their own RAW format which is why some people like the idea converting their RAW files over to DNG (Digital NeGative) files—an Adobe open source format at was created specifically to eliminate the anxiety of multiple camera manufactures proprietary formats and to “future-proof” your files. According to Adobe DNG files are RAW files, but are 10-15% smaller than your original RAW files and do not have the need for a XMP file; all the changes are stored within the DNG file—making backups take longer, but makes file handling much easier—especially if you want to move your files around. The DNG format has checksum information that is used to scan and prevent file corruption. This is a feature not available if you are using RAW files. The metadata can be written directly to the DNG file meaning that when using image management software such as Lightroom, you do not need to export the file with a separate sidecar file in order to maintain the metadata. Just in case you want to do both, keep your RAW file and go DNG there is a way to imbed your RAW file into your DNG file—though you lose the space savings by doing so, generally doubling the finished file size-before you begin to do the conversion.
Sounds like DNG is a great alternative to RAW—no one wants to be left out in the cold when their file format is deemed too old to be backwards compatible. The question is why aren’t more people flocking to this open format? The answer maybe be for two basic reasons—(1) Time: When you do a DNG conversion the time it takes to convert from DNG to RAW, especially with large imports of data, can be irritating, and when you to backup up your database it takes more time as it has to as it has to rewrite the entire file not just the XMP every time you make a change; (2) Compatibility: The adoption by other software manufacturers, such as your favorite plug-in or third-party software, hasn’t really taken off. Add to that if you enter photo contests for which DNG files are not generally excepted, even with the RAW files embedded (which may not be able to read by the recipient), and you may find that the advantages in converting to DNG diminishing.
What are some of the other reasons for not going with DNG? Once you convert to DNG and wipe out your original RAW files, you are at a point of no return – there is no way to convert a DNG file back to the original RAW file, even if you embed the RAW file into your DNG. Also when you bring your RAW files into a RAW converter like Lightroom, LR shows you your files with the camera profile of Adobe Standard. This may not be the best representation of your image—you might want to explore another camera profile such as: portrait, landscape, standard, or faithful. Possibly the best reason not to ditch your RAW files in favor of DNG is that in the conversion from RAW to DNG the camera profile will be baked in to Adobe Standard. This may not be the best way to display your image and if you convert and ditch, you don’t have a way to go back. Another point to note that nobody really knows how to interpret a manufacture’s RAW image. It’s just a guess, so the “RAW” file that Adobe can imbed into your DNG file isn’t really the RAW file that you started with; if it could be pulled out you would find that the manufacture’s software would no longer be able to read that file—hence it’s not really the RAW file that is being embedded.
When the debate first came up I took a wait and see attitude, not wanting to spend the time to convert my Terabyte+ library of photos to a new format. In revisiting this issue now years later, where professional photographers are now returning to RAW, I’m glad I didn’t