Adobe [are] offering new reasons to get DNG religion, writes Stephen Shankland in this fine review of the new options for working with DNG in Lightroom 4 beta and Photoshop CS6. One option is fast load data, which helps Develop kick into gear faster each time you take a picture into it, and the much more controversial possibility to create lossy DNGs :

Lossy DNGs… throw away data to produce a file size something like a quarter the size of a regular lossless DNG. To do that, Adobe demosaics the raw data so that strictly speaking it’s not raw anymore. More alarming to some, the original 12-,14-, or 16-bit raw data has been boiled down with the JPEG algorithm to 8 bits, meaning that there aren’t as many gradations of color values.

But Adobe didn’t just make an ordinary JPEG. First of all, the eight bits of data are carefully distributed according to each image with a “stretched” tone curve, Chan said in a forum post. Second, Adobe “dithers,” which means it carefully adds a little noise when moving to 8-bit values, which can actually improve the appearance.

And unlike JPEGs, the lossy DNGs preserve much of the flexibility of raw, such as the ability to change white balance, keep a wide color gamut, and recover overexposed highlights, Chan said.

But while Adobe likes the lossy DNG option and believes some will enjoy its more economical storage demand, it doesn’t suffer the illusion that it’s for everybody. “It’s not a default nor an option for everyone,” Hogarty said. “However, I know that a number of photographers shooting time lapses in a raw format or looking to archive outtakes in a more compact format will appreciate the flexibility.” And some could use it as an archival format for second-tier photos.

I’ve no problem with fast load data, even if I can’t detect any speed difference on my own computer, but you need to be very careful to distinguish between lossy DNGs and full-blooded ones. If not, it would be very easy to create lossy DNGs for some reason like taking on the road or saving disc space by compressing frames shot for timelapses, and then confuse them with the real negatives, even overwrite non-lossy DNGs.

A couple of features in Lightroom 4 are helpful. Library’s filter panel’s File Type now distinguishes between the different types of DNG, and you can examine individual images in the Metadata panel’s DNG view.

But outside Lightroom, you may not be able to see lossy DNGs at all until other software catches up, and in Explorer / Finder the only indications that you’ve got a lossy DNG may be its file size and that the thumbnail doesn’t resolve (at least until an OS update).

I have no real reason to create lossy DNGs from my full-blooded ones. My own preference is to keep all panorama or timelapse frames in their original formats (DNGs with the NEFs archived) and I would have preferred a rather different solution. There will be some who care to compress 8Gb to 1Gb and save increasingly-inexpensive disc space, but when you are still left with x hundred individual files cluttering up your system. That management problem was what I wish Adobe had solved, maybe with a mechanism to store all these “component” frames in a single zip or package file, a kind of multi-image DNG. So in helping us overcome the problems of multi-frame techniques, I’ve got to feel that lossy DNG is hitting the wrong target.

But let’s say I did decide to save these files in this lossy format, in that case one thing I would certainly be doing is taking extra steps to prevent the resulting confusion – probably adding a filename suffix to every lossy DNG. Whatever app I am using, I would then be able to readily distinguish the full blooded DNG “120210_0123 Blea Tarn.dng” from its lossy counterpart “120210_0123 Blea Tarn LSS.dng”. In fact, I have also tried baking my own file extension and using DNGL or DNL – but I know that going my own way is not a good idea!

These changes are positive and progressive, and I am already taking advantage of the lossy format by saving the small number of JPEGs that I shoot with my iPad as  sensibly-sized DNGs rather than being 16 bit mini-monsters.

But I do feel we should not dive blindly into these waters. Lossy DNG offers new capabilities and potential workflows, but it also opens up risks to the integrity of our picture collections. Where we are now, are those risks outweighed by tangible workflow benefits? For me, no, not yet…. You?

Here you see how easily lossy and full-blooded DNGs can be confused - especially if you don't do something like add a suffix to the filename. I might even start adding a coloured label as an extra way to distinguish them.