Sunday, 3 August 2008

More about RAW and DNG

Maruhan dropped by for a read and made the following points:

DNG is an attempt by Adobe to create an open / standardised RAW format for digital image files...

(Wikipedia)

It is an attempt and a serious one. But, like Microsoft's .NET, Sun's Java and even the ubiquitous Adobe Acrobat it does not appear to be fully in the public domain.  See my earlier post: Adobe DNG is not RAW. DNG is also not a superset - and as long as the camera makers don't all come onboard, there will be RAW metadata attributes that are not mapped to DNG metadata.

Pentax has offered the choice of DNG or Pentax RAW .NEF in their newer DSLRs - the K10D, the K200D and the K20D.

In a related RAW topic of discussion, some DSLR models - the Nikon D3, D700, D300, Canon 40D and the Pentax K20D are saving 14bit RAW files.

The digital range for 12bit RAW is 4096 values, for 14bit RAW this is 16,384 values. What does that mean, other than my RAW is bigger than your RAW?

  • It's a case of the bottleneck in an image processing system limiting the number of values in digital processing. The sensor and electronics itself might be processing 16bits of data, converting to the final RAW format at the end. So certainly, as electronics follows Moore's law and gets better and faster every year, there is less need to downsample due to the current cost / state of the art of the electronics. A larger number of bits will allow more fineness in digital processing. Whether this translates to visual tones within the extremes, is another thing. One thing that the experts seem to agree on, is that shadows and noise may improve.
  • Image Dynamic Range may improve. How much depends on whether the 12bit RAW already handle the captured DR - if 12bit RAW is not the bottleneck but the sensor is, then 14bit RAW is unused headroom.
  • More bits means a larger data volume during in-camera processing and a larger datafile. That affects file save times to media cards.
  • Remember, the output JPEG, the bitmap language of the Web remains resolutely 8 bit.

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