Every camera manufacturer has its own way of storing the raw data that comes from the sensor. Several manufacturers even develop different formats for different cameras (or create a new format and abandon an older one). It sometimes seems that each new model introduces some wrinkle into the manufacturer's raw format. We see the effect of this in a lag between the release of a new camera and Lightroom's ability to interpret and render images from these new raw formats. While Adobe is rather good at deciphering new raw formats and providing support in a timely manner, they saw room for a new and open standard to store raw data. Enter the DNG, or Digital Negative, raw format.
Some may argue that DNG in not an open standard since it is controlled by Adobe. However, the standard is fully documented and has been submitted for consideration as the open standard for raw data. Several manufacturers are now offering DNG as the native format on their cameras. Adobe offers several ways to make the conversion of your proprietary raw formats to DNG. In fact, Adobe provides a free DNG converter. The free DNG Converter is available for both Windows and Mac OSX.
There are several excellent sources to learn about what DNG is and why it is a great addition to your workflow. dpBestflow.org (an absolutely indispensable resource for photographers in this digital age) has several articles on DNG. DNG is the recommended format for archival use and for PIE application such as Lightroom. (PIE - Parametric Image Editing) Richard Anderson's article is a great place to start. Julieanne Kost also has an excellent episode on Adobe TV that explains the DNG format.
So what are some of the advantages to converting your proprietary raw format files into DNG format? There are several:
- DNG is an openly documented format, allowing more and more developers and camera manufacturers to create compatible software and hardware.
- No information is lost in the conversion to DNG
- DNG files are, with few exceptions, smaller than their proprietary raw counterparts.
- DNG does away with the need to create, update, and keep track of XMP sidecar files. All information in XMP files can be written to the DNG file directly.
- DNG files have MD5 hashes built in that can detect corruption in the original image data or the entire DNG file.
Lightroom offers several ways to convert to DNG. The first is available when you import our images into the catalog. Look at the top of the import dialog and you will see several options.
If you choose Copy as DNG then Lightroom will read the file, make the conversion to DNG, and then add the DNG files to your catalog. This method will take time and make your import process longer. I've used this method on smaller imports but I don't recommend it for extensive shoots. I prefer to review the shots first, weed out those I won't keep, and then convert the winners to DNG.
The method I prefer is to convert to DNG after the images are in the catalog. Lightroom does this quite nicely and even removes the old raw image from the catalog and replaces it with the DNG version for you. Select the images you want to convert in the grid.
Here we can see three different proprietary raw files. (Thanks to X-Rite ColorChecker Passport for the NEF file!) Select the files and go to the Library menu and choose Convert Photos to DNG...
This will bring up a dialog where you have a few choices to make.
Let's examine each of these options. In the Source Files section there are two checkboxes. Only convert Raw files, when checked, tells Lightroom to ignore files that are not raw formats when doing the conversion. (Yes. Lightroom does allow you to convert files like TIFF and JPEG to DNG but the reason for this is a different subject for another article). I recommend you check this.
The next option, Delete originals after successful conversion, instructs Lightroom to delete your original files once they are converted. Personally, I prefer to archive the proprietary raw files so I leave this unchecked. Lightroom will still swap the DNG files for the original raw files in your catalog but with this option unchecked it leaves the original files on your hard drive.
The DNG Creation section's first option simply let's you decide whether the file extension will be dng or DNG. You can choose your compatibility level in the next option. If you are using an earlier version of Photoshop or Camera Raw this becomes important. The next option is where you will choose the size of the JPEG preview that is stored in the DNG file. The larger the preview the less space you'll save.
The last option, Embed Original Raw File, may seem like a good idea but be warned. Embedding the entire original raw file will double your file sizes. I prefer to archive the originals as another form of backup allowing me to save some space after the conversion.
Once you are done click OK and Lightroom will begin converting the files. If you are doing a large number of files it is best to let this run overnight. When you are done the grid looks the same but now you will see that all the files are DNG files.
The last method we'll cover is converting to DNG on export. Choose your files as before and then click export to bring up the export dialog. You will see a preset called Export to DNG.
There are more choices here that allow you to add the DNG files to the catalog and stack them (or not) with the original raw files. You can rename them if you like. The File Settings section compares to the DNG Creation section from the previous dialog we covered. The Image Sizing, Output Sharpening, and Watermarking sections are shown but they have no selectable options since nothing here applies to DNG files. Since keywords are included inside DNG files you do have the option of having them written in Lightroom Hierarchy. Click Export when you are done and Lightroom will perform the conversion and complete the export.
Stacked together in the Grid we can see no appreciable difference between the proprietary formats and the DNG from in catalog conversions or export conversions.
So experiment with DNG. Read the background articles. Watch Julieanne Kosts's episode. Have fun. I really recommend the DNG format. Some of you will disagree but that's what makes Lightroom great - flexibility of workflow!