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Adobe DNG Converter

Adobe DNG Converter is a handy standalone application that converts camera vendors' proprietary raw images to Adobe's new DNG format. It's entirely up to you whether or not you choose to use it—Camera Raw, Bridge, and Photoshop are equally happy with proprietary raw files or DNGs—but the following discussion may help you decide. My personal bias is that the advantages of DNG outweigh any disadvantages, and using DNG sends camera vendors an important message about the future of digital photography, but it is a bias. The choice is really up to you.

To DNG or Not to DNG

Adobe developed the DNG format in response to a very real concern over the longevity of digital raw captures. One of the major problems with camera vendors' proprietary raw formats is that they're undocumented—only the camera vendor knows for sure what they contain. I bear no ill will to any camera vendor, and I hope that they'll all be around for decades to come, stimulating competition and innovation, but it's not beyond the bounds of possibility that one of today's vendors may not be around five, ten, or fifty years hence. The question then becomes, what happens to all the images locked up in a defunct vendor's proprietary raw format?

Archival format

A kindly third-party vendor may decide to take on the work of reverse-engineering the format to continue support (and let's all give a huge vote of thanks to Thomas Knoll for the enormous amount of work he's already done in decoding all those proprietary raw formats), but absent that, you'll be stuck with old, non-upgradable software at best, and gigabytes of unreadable data at worst.

The DNG format provides insurance against obsolescence because unlike proprietary raw formats, it's an open, documented format whose file spec is readily available, so any reasonably talented programmer can build a converter that reads DNG files without any reverse engineering, even if Adobe should, perish the thought, no longer be in business. So unlike the proprietary raw formats, DNG can fairly lay claim to being an archival format.

The first release of Adobe DNG Converter had one potential flaw—it stripped any private metadata that it couldn't understand. While the only things that could possibly use this metadata were the vendors' proprietary raw converters, few of us like the idea of losing something in the translation. Subsequent releases of Adobe DNG Converter address this problem by letting you embed a bit-for-bit copy of the proprietary raw file that can be extracted at any time, at the cost of a somewhat larger file size.

Metadata friendly

A related issue is that, because proprietary raw files are undocumented, Adobe treats them as read-only files, since writing to them runs the risk of overwriting potentially useful data. So when you add metadata to an image, it gets stored in either a sidecar .xmp file or in one or another application's database.

In contrast, since DNG is a documented file format that's designed to hold metadata, it's safe to write metadata directly into the DNG file, eliminating the need for sidecar files and thus simplifying the workflow. As with proprietary raw formats, the actual image data in the DNG never gets changed. If you work for a client who demands that you submit raw files (as does National Geographic, for example), it's safer to hand off a DNG file with all metadata embedded than it is to submit a proprietary raw along with a sidecar file that may get discarded.

Third party support

As an open format, DNG is much easier for third parties to support than are the proprietary raw formats. Asset managers and cataloging applications that support DNG automatically gain support for every camera supported by Camera Raw. Thumbnails and previews can be stored directly in the image file so applications don't have to spend time building their own, and there's no possibility of the image losing its metadata because the metadata is right in the image file.

More specialized applications are also beginning to support DNG. For example, DxO Labs' DxO Optics Pro, which provides sophisticated corrections for distortions introduced by many common lenses, now offers the ability to write the corrected images as DNG files, so you can apply lens corrections, write them to DNG files, then process the images in Camera Raw.

Ultimately, the proliferation of proprietary raw formats serves no one's interest, not even that of the camera vendors (although at the time of writing, many of them still seem to need convincing on this point). The DNG spec is flexible enough to let those vendors who insist on doing so put private, secret metadata tags into their images, while ensuring that those images will still be readable by any DNG-compliant converter.


The major disadvantage to using DNG is that DNG files will likely not be readable by your camera vendor's proprietary converter. If you typically use Camera Raw on some images and a proprietary converter on others, it's fairly inconvenient to extract the proprietary raws from the DNG file, so you'll want to either keep versions of the images in both formats, or forego the advantages of DNG. If you don't use the camera vendor's software, this disadvantage doesn't apply.

The second disadvantage is that when you choose the "bulletproof" option that embeds the entire proprietary raw file in the DNG, your files will be somewhat larger than the original proprietary raws.

My own solution has been to archive one copy of each image as DNG-with-raw-embedded to long-term storage, while using the smaller, losslessly compressed DNG option for my working files. An equally viable option is to archive a copy of the original raws (bearing in mind that they'll only be readable as long as the camera vendor chooses to support them) while using DNG for working files.

Using Adobe DNG Converter

Adobe DNG Converter is a very simple application. It's not the only way to convert proprietary raws to DNG—you can save DNGs right out of Camera Raw—but it's a very convenient way to process large numbers of images into DNG format. See Figure 3-3.


Figure 3-3 Adobe DNG Converter

The main screen lets you set the following options:

  • You can choose a source folder full of raw images for conversion, and optionally include subfolders.
  • You can choose a destination, either in the same location as the source raw files or in a new folder, with the option to preserve the subfolder organization.
  • You can rename the converted images with the same options as the Batch Rename command in Photoshop and Bridge.
  • If you have previously saved DNG files with the original raw file embedded, you can extract the original raw file.

To change the conversion options, click the Preferences button to open the Preferences screen—see Figure 3-4.


Figure 3-4 Adobe DNG Converter Preferences

The conversion options are likewise very straightforward.

  • Compression (lossless) applies lossless conversion. Unless you own stock in a hard drive vendor, I can't think of a reason to turn this off.
  • Preserve Raw Image preserves the raw pixel data in its original mosaic format. Use this option if you want to be able to take advantage of all Camera Raw's features. You can convert a DNG saved this way to a linear DNG, but not vice versa.
  • Convert to Linear Image saves a demosaiced version of the image. This option is mostly useful if you want to use a DNG-compliant raw converter other than Camera Raw on images from a camera with a mosaic pattern that isn't supported by the raw converter. Linear DNGs are much larger than mosaic-format ones, so if you're thinking you can save processing time by converting to linear DNG, think again—any savings in processing time are offset by the extra time needed to read the data.
  • Embed Original Raw File embeds a bit-for-bit copy of the original raw file in the DNG, from which it can be extracted at any time. I use this option for my archived images just in case I need to retrieve the original raw files at some future date, but I turn it off for my working files to save space, because embedding the original raw file increases the file size considerably.

When you click Convert, Adobe DNG Converter goes to work converting the selected raw files to DNG format using the options specified in Preferences, and displays a status window that shows the progress of the conversions—see Figure 3-5.


Figure 3-5 Adobe DNG Converter status window

To extract the original raw files from DNGs with the original raw embedded, click Extract, which opens the Extract Originals dialog box. Here you can specify source and destination folders for the extraction. When you click Extract, Adobe DNG Converter extracts the original raw files from the DNGs. See Figure 3-6.


Figure 3-6 Extract Originals

At the time of writing, the main benefit offered by DNG is the elimination of sidecar files, and it's entirely up to you whether or not you want to use it, though it's very easy to do so. There's no particular urgency to adopting DNG, but if you care about the longevity of your images, I do recommend archiving at least one copy of each image in DNG format, and if you want to be able to retrieve the original raw files, embed the original raw in the DNG. That way, you've preserved the raw image in a format that's documented and hence is likely to readable as long as humans can still read.

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