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Adobe expands DNG spec with lossy compression … and why it matters to you


October 7, 2012

Adobe has introduced lossy compression to the DNG specification because of the gulf between the size of RAW and JPEG files

Adobe has introduced lossy compression to the DNG specification because of the gulf between the size of RAW and JPEG files

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While the majority of people use their digital cameras to shoot JPEG files, serious photographers swear by RAW, which offers much increased possibilities in post processing. But while RAW images are of a higher quality than their JPEG counterparts, they also take up a lot more space and require more processing power to work with. That's why Adobe has included lossy compression in the recently announced 1.4 specification for its Digital Negative (DNG) RAW file format.

As digital cameras have seen improvements in things like their dynamic range and an increase in megapixels, the gulf between the quality of RAW and JPEG files has been getting bigger and bigger … unfortunately, so has the size difference. RAW files can often be seven or eight times the size of a JPEG, which can be a problem when it comes to processing images and, to a lesser extent, storing them.

Adobe is addressing this by including the option of a lossy compression format of its Digital Negative (DNG) RAW files. These new lossy DNGs, which are based on the same compression algorithm as JPEG, come in at about a third of the size of full RAW, but retain much of the flexibility to adjust things like White Balance while preserving detail. This means that they could come in handy if you realize you've underexposed a shot (just not by the six stops you might be able to recover in full RAW), or have a lot of batch processing to do.

Unless you have a Pentax, Leica or Hasselblad, the chances are that your camera doesn't allow you to shoot in DNG. However, because Digital Negative (DNG) is an open RAW format rather than the proprietary RAW your DSLR probably shoots, it is more future proof, and is slowly being added to more new cameras.

Because no-one knows what backwards compatibility there will be in software for proprietary RAW files in the future, many photographers also convert their RAW files to DNG for archiving. DNG files also open in most photo editing programs without the need for software updates every time a new camera is released.

Other updates to the 1.4 specification include the ability to apply an in-camera crop to an image (such as different aspect ratios) but then "un-crop" the image in post-production to see the entire sensor area, and combine data from multiple stitched files into a single DNG with "transparent" pixels allowing for undefined areas. New Floating Point (HDR) capabilities also mean DNG files can now retain a larger amount of dynamic range information from multiple RAW files.

Source: Adobe

About the Author
Simon Crisp Simon is a journalist and photographer who has spent the last ten years working for national UK newspapers - but has never hacked a mobile phone - and specializes in writing about weird products and photography technology. When not writing for Gizmag, Simon is often found playing with LEGO and drinking far too much coffee. All articles by Simon Crisp

In a world full of digital formats, which sane camera company would prefer to pay license frees to adobe for RAW formats they already own ?, especially as most already boast the ability to convert and store digital data from their cameras CCD into JPEG format already instead of RAW as a user option, and JPEG already compresses data with the option of lossless compression, for free.


It is a strange world when we are so used to TLAs, three-letter-acronyms, that when we encounter a three-letter word such as "raw" it is often assumed that it too is an acronym for something, in this case for yet another algorithm. Yet of course this time it is the common word "raw" meaning uncooked - as in "raw meat". This is because there has been no processing to the original image data coming directly from the imaging system. That is why the quality is the highest possible for any camera.


Well L1ma, JPG only supports 256 degrees of brightness per pixel, while RAW formats (including DNG) can have many more finer gradations, useful in bringing out detail in very dark or very bright pictures, details which are permanently lost when the raw data is saved as JPG. There's also the fact that RAW/DNG saves the data as it arrives from the sensor without any further processing, which is always necessary when saving to JPG. Lastly DNG is not proprietary, it's an open format. Says so right in the article.

Michael Grosberg

I buy more storage space instead


I don't see any difference in the examples.

Art Toegemann

I just got the new T4i. Will check to see about it. Exciting. @ Art toegemann-your not likely to see any difference in a web browser. They might have used a closeup. I'm heading over to DPreview right now to see they have on the subject. aloha, Uhane


In reply Michael Grosburg,

the majority of users will be the mid to low end of the SLR market who will be saving that data as a JPEG by choice. which gives 16777216 colour variations - enough most users which is why it is the format of choice. Even commercial vendors in the industry top out at 24 bit colour, outside scientific uses it is hard to see the use of uncompressed formats because at the point of processing the RAW image it has to lose data at some point, printing, editing and publishing all require only a tiny fraction of that data maxing out at 24 bit colour. For instance an epson R1900 printing a 20 by 10 inch 5760 x 1440 dpi image is 197.7 MB (1,658,880,000 bits) in BW -16 million colours is 3*256 times this file size without compression(158.8 GB). Rendering time becomes a very important factor for the photographer/editor. Not many of whom have 6 core 32 gigabyte ram solid state drive computers to process and edit high resolution RAW photographs in a decent time interval.

Adobe has not announced the DNG format as an open format in this article and that can mean many things with Adobe's business model - its website states "Digital Negative (DNG), a publicly available archival format for the raw files generated by digital cameras. By addressing the lack of an 'open standard' for the raw files created by individual camera models, DNG helps ensure that photographers will be able to access their files in the future."

i.e PDF from Adobe is also a publicly available archive format, you can publish to pdf and read and print one - but you pay at some point by proxy or purchasing the software directly from Adobe to edit and convert from one. Thats the Adobe model, it is more expensive than free, and there are not many photographers who need their cameras to read each others DNG formats and those that want to save their RAW files elsewhere to archive could ZIP them - but as an industry standard not an open standard it will be in everthing you buy anyway - displacing the open formats.

In truth what Adobe is doing will affect a very tiny number of users who want to get trapped into using a tied in Adobe format - all this is rather a non arguement but as I work for local government they still send each other PDF's to edit by return of email even though it is an Archive format and they all use office and write the originals as .doc.


L1ma, your numbers are wrong. It's not 3256 bigger, it's just 38 since it's 24 bits per pixel, not 768 bpp, so your memory requirements are completely wrong.

While 24 bits are enough for interchange of processed images, it's not good enough for capture and editing. It's very likely the dynamic range of your source exceeds what 24-bit can deliver, but it's vital to be able to preserve full resolution until rendering down to that range. As a simple example: a common operation after image capture is adjusting black and white points, resulting in scaling of the dynamic range to match what's available - but if you're scaling something less than 24 bits to 24 bits, you will have gaps and comb-filtering effects, so you need to start out with more bits than that. QED.

"Adobe has not announced the DNG format as an open format in this article" Why would they, given that it's been that way since it was launched in 2004? You're missing the point of DNG; raw formats are useless for interchange - they differ wildly across manufacturers (and even individual cameras) and are mostly proprietary, incompatible, undocumented and require additional software (often expensive, closed and proprietary itself) to even be viewed - so if a camera manufacturer disappears, you may find yourself cut off from your images. There are already over 200 different raw formats.

DNG avoids these issues by storing raw image data in a consistent format. The DNG format is freely licensed (in both senses), unencumbered by patents, documented, is based on other open specifications (such as TIFF and JPEG), and there is free source code available to use, so anybody can create software or hardware that both reads and writes DNG formats without paying Adobe anything. It's true that Adobe has good support for DNG in their own applications - but then they would be pretty stupid not to; if you were writing image processing software, would you prefer to support 200 random formats or one good one? The only alternative to date has been OpenRAW, which wasn't really an alternative (it just proposed documenting all those random formats, not establishing a new standard) and seems to have faded away.


Re Syncro;

I calculated as RGB (256 shades of grey per pixel) - i will not say I am right or wrong - however I will stick with what I say about Adobe, which is not a charity but a business.

Agreed If you want to keep a propriety raw format it is pointless, I did point out evey manufacturer has their own however but what about PNG and BItmap which are lossless compression formats.

Perhaps If you wanted a perfect medium you should have kept that 35 mm slide film camera.

As to storing your data as DNG that is up to you, but it is still an archive format. Please state the supporting packages which are able to edit DNG and their price - other than Adobe Photoshop that is.

There is nothing wrong in 200 formats as long as they can be converted, there is something wrong about a user who archives material without converting it to a current format in line with the product cycle. Todays SDcards are 2022's floppys, how many people copied their entire 1995 floppy collection onto a hard drive ?.

But I will stick with what I said - this will still be a problem for a tiny minority of people, professional photographers, engineers and scientists. Most other people will neither care or know and will be perfectly happy with JPEG.

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