The DNG Trap
A friend contacted me this weekend. Back when it was time to choose a Digital Asset Manager (DAM), he weighed back & forth with Aperture and Lightroom, ultimately going with the latter. Recently, he came to the conclusion that Aperture would be more to his liking. Then, a funny thing happened – except that it wasn't really funny. He couldn't import his files into Aperture.
It turns out that he was converting his Canon sRaw files to Adobe DNG. Aperture supports DNG, but it seems that not all DNG is equal. That's kind of ironic, because incompatibility between RAW files and software is exactly the problem Adobe claimed it was trying to prevent with the DNG (Digital Negative) file format.
The logic from Adobe sounds rational. RAW files from various vendors are proprietary, and some programs may not support all file formats. The DNG specification was supposed to be a public archival format for digital camera RAW files. What could go wrong?
Apparently, not all RAW file formats get converted to the same DNG format, and that's what bit my friend in the ass. His Canon sRaw files were converted into something called Linear DNG. It's the first I've heard of it, but my research shows this problem has bitten people for a few years now when they tried to switch from one DAM to another. If you're using DNG, which kind do you have? The difference seems to depend upon the type of sensor in your digital camera.
- Raw DNG or CFA DNG (colored Filtered Array): contains raw image data + added meta data and is not demosaiced. This Raw format is (usually) 4 channels coded with 12 bits (sometimes 14 bits) color depth.
- Linear DNG: contains RGB image data and is demosaiced. Linear DNG format is 3 (or more) channels coded with 16 bit color depth. Due to the bit depth coding, the size of a linear DNG is larger and much more important than a Raw DNG.
The good news for my friend is that his version Of DNG has more color depth than the other. The bad news is that he's stuck in Lightroom. You see, this isn't merely an issue of Aperture not supporting all aspects of DNG. DxO users have also discovered that their DNG files aren't quite on par with Adobe's results.
How universal is a file specification if a number of programs don't support it, or only partially support it? On the other hand, what incentive does a software vendor have to remove RAW file support that it's already implemented? The theory of DNG is that we can't trust camera vendors to be around to support their own file formats in 50 years or so.
- Nikon was founded in 1917.
- Canon was founded in 1937.
They're still supporting their RAW files. Adobe fails to mention the different DNG file formats on its DNG page. Of the choices before me, I think I'll stick with the original RAW files. They seem to have better support than their supposed universal replacement.
Since my friend didn't keep his RAW files after conversion to DNG (why would he?), he's pretty much left to export as TIFF or PSD conversions if he wants to move to Aperture. More likely, his old images will stay trapped in Lightroom and he can start working with his new images in Aperture using the original RAW format. At least that way, he has a better chance of migrating later if he feels the need.