Having used Photoshop CS3 for some time, I have been shooting RAW with my digital camera, and loading them into Camera Raw for modification. But it’s a somewhat complicated subject.

Most, if not all, consumer level cameras shoot JPG only, meaning they throw away extra information about an image when it is compressed (JPG is a lossy format, after all) so as to reduce file size. Higher level cameras, such as my Nikon D50 and other Digital SLRs, also offer the option of using RAW to capture images.

What is RAW?

RAW isn’t so much a file format as it is an idea. The idea being that we should try to retain as much data as possible when taking pictures. So a RAW file contains much more information, and is consequently larger in file size, than an equivalent JPG, even if taken with the same camera.

The RAW version of a photo is much larger, because it contains so much more information, which allows you more creative control of the image in post-production. For instance, you can open a RAW image in a photo editing package, such as Photoshop, and adjust various properties of the image such as aperture, lighting, brightness, and saturation, to name a few. This is easy to do with RAW, but not so much so with JPG, since JPG is a single compressed piece of information, where RAW is essentially many layers of information, all for the same image.

RAW is widely used among higher level cameras, yet it isn’t really a standard. Different manufacturers have their own proprietary RAW formats for their own cameras, but the idea remains the same: easier post-production photo adjustment. Nikon uses their NEF format, whereas Canon has it’s own formats, CRW and CR2, and so on and so forth. This is why I consider RAW to be more of an idea than a file format.

This difference in proprietary – and possibly conflicting – RAW formats can cause difficulties in using software to manage and manipulate photos from different cameras. Not every photo editor out there would be able to handle photo formats from all major camera manufacturers.

What is DNG?

DNG stands for Digital NeGative, and is an open RAW format proposed by Adobe. It is not an official standard at this point, but the general impression of other photographers seems to indicate they wish it were so.

What’s the Difference?

A standard DNG format has several advantages over proprietary RAW formats…

  • DNG is a proposed standard, meaning, if it was adopted by camera manufacturers (Nikon, Canon, et al), photos produced by cameras from those manufacturers would adhere to the standard. This would make photo editing and management via software much easier, as there would only be one standard format to deal with.
  • When you make adjustments to RAW files, the changes are stored in a file separate from the image. This is known as a “sidecar” file, and has an XMP extension. You are able to view it using a text editor; it appears to be in an XML format. This is a bit of an annoyance, because it means each modified image would have an accompanying file to go with it, and they must be kept together, or the changes made to the image will “disappear”, as the change information is stored in the sidecar file. DNG resolves this annoyance by storing the change information within the image file itself.
  • Because it is a proposed standard, it would be hardware and software independent. There would be no requirement to use a specific camera or software package. For this reason, some people are touting DNG as a future-proof image format. Imagine a newer version of Photoshop would not work with RAW files from older cameras…That’s the DNG advantage, in that the format would stay the same, and would always be supported.
  • If you want to retain your digital “negatives”, you can convert your camera-produced RAW files to DNG. DNG has the advantage here since it compresses the data without loss, resulting in smaller file sizes. You could then throw away your RAW files and retain the DNG versions.

So what’s the Bad News?

There are some downsides to DNG at this point…

  • DNG is not yet an official standard, and is not widely used by camera manufacturers in their cameras at this point.
  • Certain software packages do not yet support the proposed DNG standard.
  • I mentioned above the ability to convert RAW images to DNG, then throw away the RAW versions, resulting in reduced file size. This however comes at the price of not having your absolutely original camera-generated RAW images on hand. This could be important if you later wanted to convert a RAW image – which you would no longer have – into a different format, such as TIFF. The general view seems to be that the RAW files right from your camera are you actual “digital negatives”. And as some have said, “you wouldn’t throw away your negatives, would you?”
    • As a sub-point, you do have the ability to wrap the original RAW image into a DNG file, but with no real advantages. There would be no file size advantage, as all the original RAW data is within the DNG wrapper (this is different from converting a RAW file completely to a DNG). Also, you would still have the issue of hardware/software dependence…Again, it’s just the original RAW data in a DNG wrapper, so you would need specific software to handle the proprietary RAW format. This is an issue with Nikon at least, which has been encrypting certain bits of information within RAW files produced by some of their DSLRs, including my D50. And Canon apparently has a habit of changing their RAW formats every few generations. And it seems that once you convert a RAW image into a DNG, it is not possible to extract just the RAW data again. Although if you embed the RAW into a DNG, it is possible to extract the RAW data.

Conclusion

It is a known fact that camera manufacturers have undocumented RAW formats for their cameras, which makes managing and editing images from said cameras harder. Because software vendors would have a hard time supporting so many different proprietary formats out there. There is a proposed standard – DNG – for the formatting and data storage for RAW photos. If DNG were adopted by camera manufacturers, and the manufacturers stuck to that standard, software developers would much more easily be able to support photos created in the standard format.

DNG has several advantages, such as smaller file size and hardware/software independence, but it also has some shortcomings. The most immediate one being that while it is a proposed standard, it is not yet officially used by camera manufacturers. There is also the fact that a DNG file converted from a RAW file is not equal to that RAW file; it is not possible to convert a DNG back to RAW.

For the purpose of archiving and future-proofing photos, DNG sounds ideal. But the shortcomings are enough to give me pause in all out converting my RAW images to DNG, and discarding the RAW files.

The idea of DNG is a good one, to be sure, but I believe it would be best to just monitor the situation for the time being. By the time I start looking at replacing my D50 (not for a few years at the least), there may well be a newer model from Nikon that outputs directly to DNG, thereby resolving the issue of losing data to DNG from RAW.

Bottom line: I will be sticking with RAW for the time being.

Extra Reading

Here’s a few links to other sites discussing the same subject, they are good reads if you want to know more about the pros/cons of RAW versus DNG. There are many more such discussions out there, but these few sum things up pretty well.