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Revamped DNG format shows new Lightroom possibilities

Adobe's updated raw-image format now handles stitched panoramas and HDR photos, part of a plan to attract more photographers and allies. Adobe hopes to see the features used -- but isn't promising anything.

Stephen Shankland principal writer
Stephen Shankland has been a reporter at CNET since 1998 and writes about processors, digital photography, AI, quantum computing, computer science, materials science, supercomputers, drones, browsers, 3D printing, USB, and new computing technology in general. He has a soft spot in his heart for standards groups and I/O interfaces. His first big scoop was about radioactive cat poop.
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Stephen Shankland
9 min read
Adobe's DNG 1.4 image file format now accommodates transparent pixels, shown here with the checkerboard pattern, a key move in enabling stitched panoramic images. The company hopes to see software supporting panoramic DNGs, though the maker of the highest-profile image-editing software on the market isn't itself committing to do so. Adobe Systems

Adobe Systems isn't making any promises, but an update to company's Digital Negative (DNG) image format paves the way for two important features in Lightroom: panoramas and high-dynamic range photography.

Lightroom is for editing, cataloging, and publishing photos, especially those shot in higher-end cameras' raw formats. Raw photos consist of data captured directly from the image sensor without in-camera processing into a JPEG. Although raw photos offer better quality and flexibility, they're also much less convenient than JPEGs.

One aspect of their inconvenience is that raw photos usually arrive in proprietary formats from camera makers. Adobe has been trying for years to ease some of the difficulties with its own DNG format, which the company has openly documented and is trying to standardize. Only a relatively small number of cameras can record photos directly in DNG format, but Adobe offers conversion tools in Lightroom and Photoshop.

Adobe has just extended DNG a major step beyond its original scope, though. It began as a way to repackage the original raw data from the camera's image sensor, but increasingly it can handle some kinds of processed images, too. It's what Tom Hogarty, Adobe's group product manager for Lightroom and DNG, calls a "derivative DNG."

That at least in principle means photographers could preserve higher image quality and better flexibility farther through their workflow.

Two of these areas are creating panoramas by stitching multiple photos together and creating high dynamic range (HDR) images by layering multiple photos that collectively span a greater range between bright and dark. The new DNG 1.4 specification (PDF) describes how: in the first area, by accommodating transparent pixels that often are produced when multiple photos are stitched into panoramas, and in the second area, by accommodating floating-point numbers whose format can span a much greater range of exposure values.

Adobe has said built-in panorama and HDR support are within Lightroom's scope but hasn't promised support beyond today's ability to hand off groups of photos to Photoshop's HDR and and panorama tools. With the new DNG, Adobe is sounding more hopeful, though.

"There's nothing committed at this time, but as the DNG product matures, I sure hope software manufacturers will take advantage of these features," Hogarty said.

The DNG 1.4 specification also better matches what cameras can do today and potentially can do tomorrow. Sweep panoramas and HDR are both increasingly common features built into higher-end cameras and smartphones.

Updating DNG is important for Adobe's ultimate ambition. to make it "as simple to work with raw files as it is to work with JPEGs," Hogarty said.

One factor to bear in mind, though: Adobe expects these situations to use DNGs that have been processed so they're a step removed from the original sensor data. That step is the conversion from the "mosaic" data almost all cameras use initially, in which a pixel records only red, green, or blue, into the "demosaic" data where image-processing algorithms give each pixel a combination of all three colors.

DNG perks
Adobe added a number of other features to DNG 1.4 and started using them in Lightroom 4, released earlier this year. Those new DNG features included a smaller file size option and faster image-loading performance.

The panorama support is helped by the addition of transparency to DNG, which provides a mechanism for image data that's not merely some particular color but that's got no color at all. That'll be useful for cameras that can stitch images together into panoramic sweeps -- a process that often leaves empty patches around the edges.

"There's a fundamental flaw in the current panorama stitching experience where you have to capture each raw image and merge those together. The resulting output loses the flexibility of the of original raws," Hogarty said. "Having the ability to stitch together the raws into a derivative DNG file that still retains the flexibility of the initial capture is a pretty big opportunity."

Adobe Systems' DNG logo

Second is floating-point data. Instead of storing pixels' color values with integers, using floating-point numerals means a vastly wider range of data can be stored. That's not useful for most photos, but it is when it's time for high-dynamic range (HDR) images that need more elbow room to capture both extremely dark areas of an image and extremely bright areas.

HDR can lead to an eerie, surreal style of photography that some people love and others loathe, but it also can can be used with more conventional styles to do things like show both the shadowed regions and the bright windows of a cathedral.

"Through the eyes of someone (who) works (for a) software manufacturer, I see an opportunity to align and merge images after capture and then create a higher bit depth DNG file," Hogarty said.

As with the transparency-enabled panorama feature, he sees HDR support as interesting for software makers that want to give photographers new possibilities through "derivative DNG" images after the photos were taken, but also potentially useful for camera makers as well.

And even if a camera doesn't go for combining multiple photos into an HDR image, floating-point data could be useful. Today's top-end SLRs record 14 bits of data per pixel, and medium-format cameras go a notch further with 16-bit data. Going beyond that, though, is complicated, since computers handle 16-bit data well but the next obvious jump up to 32 bits would mean much larger file sizes. Thus, if image sensors improve enough that they can capture more than 16-bit data, floating-point DNG files could be useful.

A third new feature that appeared with DNG 1.4 is the ability to retrieve pixels that were originally captured by the camera but that are hidden with camera-applied cropping. That doesn't just mean full images can be recovered when using crop modes like a 16:9 aspect ratio, but also sometimes that a few extra pixels around the edges that are cropped by cameras using their regular aspect ratios.

Using an Adobe plug-in on DNG 1.4 files in Lightroom 4, photographers can recover a fringe of pixels the camera crops away. It's not much extra, as shown in the comparison images at the bottom of this view, but it can help when a photographer needs more breathing room around a subject, as in the case of this photo of an Amsterdam building shot from a moving boat. Screenshot by Stephen Shankland/CNET

For example, a Canon 5D Mark III takes a 5,760x3,840 pixel photo, a 22.1-megapixel image. DNG 1.4 surfaces some hidden pixels to produce a 5,796x3,870, 22.4-megapixel image. Likewise, a Nikon D800's 7,360x4,912 pixel photo, a 36.2 megapixel image, can become a 7,378x4,924 pixel, or a 36.3-megapixel image.

Unlike the panorama and HDR features, people can make use of the ability to see the full recorded image area right now, because Adobe released a Lightroom plug-in to retrieve the bonus pixels. It's not a big increase in image size, and image quality typically is worst around the edges of an image given the constraints of lens design, but it can be a useful extra fringe in cases where subjects are uncomfortably close to the edge of a photo.

Note, though, that the pixels outside the crop area can't be retrieved in some cases, such as with Nikon and Panasonic cameras, when they're set to crop images. And you may not get the pixels back that you wanted: a shot I took with an Olympus OM-D E-M5 went from 4,608x3456 to 4640x3472 resolution, but all the new pixels were on the right and bottom sides of the image.

Catching camera makers
The full potential of Adobe's DNG format remains unmet. Only a few cameras, most notably those from Leica and Pentax, let photographers shoot DNG straight from the camera. That means most people who use DNG must convert raw photos on their own.

If Adobe is to woo more camera makers, it's got to match DNG better with what cameras and photographers can do today and will want to do tomorrow. In cameras, the utility of DNG is significantly reduced if it can store only some of photographer's shots.

The situation is reminiscent of DNG 1.2, when Adobe added camera profiles to try to match the colors in DNG files with the camera settings such as "natural" or "vivid." And in DNG 1.3, Adobe added "opcodes," which are instructions that can mathematically correct lens problems such as vignetting, chromatic aberration, and barrel distortion.

The earlier lack of opcode support is why Hasselblad backed off from its DNG support, and the company still hasn't come back into the DNG fold.

Thus, adding new incentives for DNG adoption makes sense to attract camera makers, sofware makers, and photographers. And the newly disclosed DNG 1.4 features aren't the only recent additions. Some others already are supported in Lightroom.

First is fast-load data, which builds in a small-scale image that can make Lightroom faster at switching among photos. Second is lossy DNG compression, which reduces file sizes significantly compared to ordinary raw or DNG files while retaining some of the raw-image flexibility that's lost in a conversion to something like JPEG or TIFF.

"A lossy compressed DNG file is much smaller but maintains the flexibility of raw data," Hogarty said in a blog post about DNG 1.4.

Lossy DNGs, supported in Adobe Lightroom since version 4 was released earlier this year and defined in the new DNG 1.4 spec, cuts the file size of regular DNG files significantly while preserving some of the image quality and flexibility of the original raw data. Note how the clouds aren't as washed out as in the JPEG image.
Lossy DNGs, supported in Adobe Lightroom since version 4 was released earlier this year and defined in the new DNG 1.4 spec, cuts the file size of regular DNG files significantly while preserving some of the image quality and flexibility of the original raw data. Note how the clouds aren't as washed out as in the JPEG image. Adobe Systems

DNG offers some other advantages, too, such as an ability to store lots of metadata -- not just the EXIF metadata such as exposure duration and camera model, but also captions, copyright notices, and geotags. DNG files can store editing instructions, too, so that photographers don't have to ensure they keep separate "sidecar" files to accompany raw photos or rely on separate image databases managed by software such as Lightroom, Aperture, or iPhoto.

Control vs. standardization
So if it's so great, why aren't more camera makers using it?

Likely in part because it's Adobe's in-house technology, and a company like Canon might reasonably be worried about using another company's technology.

"We're really trying to cajole the entire industry, but it's still an Adobe-controlled format. We're making changes at our pace and our prioritization," Hogarty said.

Thus, Adobe has been working to make DNG a formal international standard under the ISO's TIFF/EP format. "I can understand a camera manufacturer not trying to prioritize that support until it is a standard," Hogarty said.

That standardization effort has been under way for years without bearing fruit, but Adobe remains committed to it.

"We're still actively involved in pursuing standardization," Hogarty said, but said confidentiality restrictions forbid him to share further details.

Adobe hopes the most recent version of DNG will make the standards cut. "The latest submission is DNG 1.3, and we intend to submit DNG 1.4 now that it has been finalized," Hogarty said.

File formats take a long time to catch on, and once established, successful ones last a long time. By standardizing DNG and adding new abilities, Adobe hopes DNG will fit photographers' archival needs.

Cinema DNG on the back-burner
Less clear is Adobe's ambition for a related effort for using raw imagery in video through a project called Cinema DNG. Adobe announced Cinema DNG in 2008, and it's now arrived in the world with the Blackmagic Cinema Camera and several other videocameras. As with shooting still photos, using raw formats in video gives more control over tricky after-the-fact operations such as correcting colors or recovering blown-out highlights. CinemaDNG in cameras today simply is a sequence of frames consisting of DNG images.

Handling still images in raw formats is taxing to computers, and handling raw video is even more so. Although the right camera can produce impressive video with CinemaDNG, editing that video in Adobe's Premiere Pro is painful. Filmmaker Andrew Reid of EOSHD got CinemaDNG playback rates of only 1 frame per second, for example, and recommends using Adobe's After Effects to convert CinemaDNG to another format before editing.

Adobe evidently isn't happy either, because it has deep-sixed its prototype CinemaDNG plug-in for Premiere Pro. It explained the reasoning in a blog post in September:

One question that we've been seeing a lot -- especially since the recent announcements of a couple of cameras -- is why Premiere Pro doesn't import CinemaDNG files. The answer is simply that we have not been satisfied with the performance that we have been able to achieve with CinemaDNG files in Premiere Pro, in which real-time playback is crucial. If it's important to you that we add native import of CinemaDNG footage into Premiere Pro, please let us know with a feature request so that we can get a sense of whether this is an area where we need to put more effort.

And Karl Soule added, "During the CS6 [Creative Suite 6] development period, it was decided to not use engineering resources to make a new plug-in for CinemaDNG. The number of downloads of the CS5 and CS5.5 plug-in didn't justify it."

The Blackmagic camera, though, surprised Adobe; its engineers used the openly available CinemaDNG specifications but didn't work with Adobe. And the camera's $3,000 price tag gives it a broader appeal than many competing products. So presumably if demand picks up enough, Premiere Pro could see CinemaDNG support.

Supporting CinemaDNG in software is one thing. Developing the specification and technology is another. Hogarty had this to say about the matter:

Adobe is not currently doing additional development work on the format itself. Adobe has released the specs and examples to our various partners for them to continue work on the format and on support for it in various devices and applications. We'll be posting the specs and examples and such on a new DevNet page very soon.

In other words, Adobe looks like it's happy to let others carry the CinemaDNG water. Adobe's DNG enthusiasm evidently has its limits.