RAW vs DNG image file formats



I have been approached by a few of our PMPE participants on why the colors of their pictures seem different went they used Lightroom or Photoshop. What they see from the LCD screen is so different especially when they shoot in RAW. This has got me to do some research on the difference of these two formats.

RAW files are usually proprietary formats by different camera manufacturers and they name it differently too. Nikon called their RAW format as NEF, Canon as CRW, Olympus as ORF, Sony  as SRF, etc…and the confusion goes on. These formats will work with the propriety software that comes with the camera, however, when they are post processed in Lightroom or Photoshop, all these RAW formats are converted into DNG format, the format used by Adobe.

This is where the fun starts. Most proprietary post processing software are limited in their functions and hence a serious photographer would either process the RAW images in Lightroom, Aperture or Photoshop (the grand daddy of image processing)

What is RAW?

RAW images, also known as “digital negatives” are truly “raw”, meaning they are almost unprocessed data coming directly from the camera sensor. Unlike JPEG files that can be easily opened, viewed and printed by most image-viewing/editing programs, RAW is a proprietary format that is tied to the camera manufacturer and sensor, and therefore is not supported by all software products. RAW files preserve the most amount of information about an image and generally contain more colors and dynamic range than other formats.

Advantages of RAW format

  1. .    RAW files contain full JPEG Previews that were processed by the camera, using the camera settings you chose when you shot the image.
  2. .    In addition to basic exposure information, RAW files also store other camera-specific data such as focus point, picture controls, etc.
  3. .    RAW files are fully supported by their manufacturers and therefore work with camera-specific software packages such as Nikon Capture NX.

Disadvantages of RAW format

  1. .    Not all software packages can open RAW files. If you have a brand new camera that just got released, you might need to wait for a while for software companies to catch up and update their software so that your RAW files could be opened and worked on, even on the most popular image-editing products such as Lightroom.
  2. .    Because RAW files cannot be modified by third party software, your settings will have to be stored in a separate sidecar (XMP) file, which means more storage and tougher file management.

What is DNG?

DNG is also considered to be a RAW image file. It is Adobe’s proprietary image standard that was created to store image data in a generic, highly-compatible format, unlike RAW files that have specific formats based on manufacturer and camera type. Although DNG was invented by Adobe and is supported in all Adobe applications, there are other companies like Leica, Pentax and Hasselblad that adopted this standard and use it in their cameras as their native RAW file format.

What are the advantages of DNG format?

  1. .    No need to be worried about proprietary camera RAW formats – once a RAW file in converted to DNG, it will work with any software that can read the DNG format.
  2. .    DNG files are generally smaller than RAW files and can be made even smaller if minimal or no JPEG Preview is stored within the file.
  3. .    Changes to images can be written directly into DNG files without having to create separate sidecar XMP files to store this data. This simplifies file management.
  4. .    DNG files are capable of storing full original RAW files and these RAW files can be later be manually extracted, if needed.
  5. .    Adobe provides many ways to automatically convert RAW images to DNG format in such programs as Lightroom.
  6. .    Adobe continues to work on the DNG format, enhancing it year after year and adding more functionality and features.

What are the disadvantages of DNG format?

  1. .    Conversion from RAW to DNG takes extra time during the import process.
  2. .    DNG does not work with all manufacturer image-processing programs. For example, it doesn’t work with Nikon’s Capture NX product.
  3. .    DNG strips out some of the unrecognized meta data (such as Active D-Lighting and Picture Control) from RAW files, making it impossible to retrieve this data from DNG in the future.
  4. .    Because all changes are written into the DNG file, you would have to back up the entire DNG file every time you make changes to it.

Should you use DNG or RAW?

I am using a Pentax that allows the use of their proprietary RAW format (PEF) or DNG format. Personally I prefer to use DNG for the following three reasons:

  1. .    Compatibility – it doesn’t matter what version of Lightroom or Photoshop I use today or tomorrow, my files are preserved in one highly-compatible format that is here to stay.
  2. .    Simplicity – all changes are written into the same file and I do not have to worry about having one separate file per image just to store my post-processing settings.
  3. .    Size – that 15-20% of extra space does make a difference when you have tens of thousands of pictures. With DNG format I can save this storage space. However, the cost of data storage is coming down and the speed of data access is also much faster and easier.

Most photographers pay little attention to what happens after they have taken their images, hence there will be endless discussions on which brand of cameras is better. Seldom would anyone bother about what happens to the image after they have captured it.


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