DNG (Does Not Go)

I shoot almost all my photos in RAW format, which means that my important originals are in a variety of different formats: some Nikon, some Canon, some Panasonic. All of these are proprietary formats (though they’ve generally been reverse-engineered), and so not really ideal for long-term archiving.

It was for this reason that Adobe, some time ago, came up with the DNG — Digital Negative — format: an open standard intended for things like archiving. There are tools for converting most things into DNG, and the idea is that you’ll always be able to get your images out. Some cameras even save DNG as their native format. It’s a very good idea.

In theory.

The problem is that almost none of the tools I use support it. Adobe Lightroom does, of course, and makes it nice and easy to convert images automatically as you import them from your camera. But, once I have my image as a DNG, I find I can’t open it in Aperture, Preview, Acorn or even Photoshop CS3. I don’t get thumbnails in the Finder. I tried reverting to earlier, less efficient versions of the DNG format with fewer fancy options but it still didn’t help, unless you go back to really early variants, which can multiply the file size by three.

I could, of course, view my DNG files in Photoshop if I adopted the standard Adobe solution: pay hundreds of pounds to upgrade a product I paid hundreds of pounds for a little while ago. But I have the latest versions of other software products and none of them can open recent DNGs. Some of it may boil down to insufficient support in Apple’s underlying libraries. Whatever the reason, everything can open the closed, proprietary formats, whereas even Adobe’s DNG Converter can only convert to other forms of DNG. A few special tools like RPP can convert them to TIFFs, as long as you’re not using the latest DNG variants.

I’ve written about this before, but I repeat the experiment periodically to see if things have improved, because I really like the idea of storing things in an open raw format. But, sadly, at present, putting your files into DNG seems to imply locking yourself into expensive Adobe upgrades.

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Sounds like you are better off archiving in native RAW format – at least the open source reverse engineered tools to read them will always be around. Thank you for running the experiments for us showing that DNG continues to be nice in theory.

Would TIFF not be a better choice? I vaguely remember it supports high bit depth and no compression. It is usable in Photoshop and almost certainly GIMP.
Lead Tools may also be useful for file conversion.

Yes, Tim, that seems to be my experience. One possibility for archiving is to create a DNG with the native RAW embedded in it – you can then extract the latter if you ever need to. But that’s only useful if you don’t care about (at least) doubling your file size. And I’d only really use it for archiving, since non-DNG formats seem to be more manageable for day-to-day use.

Mike –

TIFFs are good in that they’re lossless, but bad in that they contain less information than comes off the original camera sensor, and they take a great deal of space. I think I’m right in saying that by the time something becomes a TIFF, various decisions about things like white balance have already been applied to the raw data, so you’ve thrown some stuff away.

You’re right, however, that pretty much everything can read and write them, and they can include layers etc, so they are a flexible format and often used in professional work for final delivery to the clients, when you’ve done the post-processing, and are only delivering a few images.

For my own use, though, if I wanted a non-RAW format, I’d probably just use JPEG at highest quality.

I am surprised that I am not having the same problem as you.

I convert all my Nikon (NEF) and Canon (CR2) files to DNG on import to Lightrooom. When I look at them in the Finder I see thumbnails, Quicklook works, and I can open them in Preview. Preview reports them as being DNG version 1.3, which appears from Wikipedia to the the latest version. My conversion settings in Lightroom are: ‘Camera Raw 7.1 and later’ compatibility, medium size JPEG preview, embed fast load data, and both lossy compression and embed original raw file are off.

I don’t think I am only seeing the JPEG preview in Preview as it is reporting the full resolution. Preview has no problem exporting the image as a TIFF.

Presumably I am missing some subtlety of your problem. I wonder what?


Paul Kelly

Please forgive my photography naivete, but wouldn’t bitmap be the raw file? I realize that bitmaps are huge, but storage is cheap. Of course, all of the discussion about file formats assumes that the future will be fairly similar to what we have today, as opposed to http://en.wikipedia.org/wiki/Lytro or holographic pictures.

David – good question, but there are two real considerations here.

The first is whether things are compressed in a way that loses any information. JPEG does this – it reduces the number of bits per colour and it discards information that the human visual system would not normally be able to see. How drastically it does this is the ‘quality’ setting… below a certain level, the human visual system *can* see it! And you’re right, that bitmaps don’t suffer from this, as long as they keep enough bits in each position in the ‘map’! In fact TIFF is essentially a bitmap format, but with extra facilities/complexities. Bitmap just really means raw data stored without loss in a per-pixel way… the Windows BMP format is a special case of a way to describe this in a file format, and so is similar to TIFF.

The second issue is *what* information is actually being stored. The key thing about RAW formats in the photographic sense is that they are designed to store what the camera captures, rather than things like JPEG which are tailored to what the user can see. It’s a bit like the difference between negatives and prints. At a later date, you can go back to the raw sensor data with a better algorithm for mapping those voltages into coloured pixels, with a different white balance, etc, and get a whole new view of your image without any loss in quality. You’re relying on the computer to do more of what a point-and-shoot camera does internally, which means you can change things after the event. (In some cameras, the RAW format even takes into account geometry distortions in the design of the optics and so the images actually need to be warped to produce a picture.)

This is why RAW formats are a bit of a pain for software writers, and why Apple includes support for so many as part of the OS – it’s like printer drivers: you don’t want every app to have to handle all of them.

But it’s also why photographers love them. And it’s why the DNG *idea* is a very good one.

Paul –

That’s very interesting – thanks. Do you have a recent Photoshop/Bridge installed? I wonder if Adobe installs extra drivers if you do? My Photoshop is fairly elderly now… and I don’t seem to get these facilities from Lightroom…


I have Photoshop Elements 9, but not Bridge.


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