To convert a DNG file without the embedded original RAW format back to the
original RAW format file runs counter to the purpose of creating a standard
format that contains RAW file data. It could be done, I'm sure, if it were
deemed important ... after all, the DNG Converter had to have the specific
knowledge of all those RAW file formats to create the DNG file. Of course,
you'd be throwing away some of the additional metadata added later in the
process. Why is it necessary to be guaranteed that this is possible? Is it
desirable for some practical reason?
It is only desireable from an archival standpoint. A one-way
transformation is not "lossless," therefore one never has the original
file. As you say, it may be a limitation of the software that can only
deal with PEF files. That may be true, but still... if the DNG cannot be
undone, then it's a lossy process.
In my (relatively unique) situation, DNG is much less useful. I
can use standard TIFF libraries to deal with PEF files. I have no
conversion utilities at my disposal to convert between the two formats
either way. With numerous open-source parsing utilities for the PEF
(TIFF) format, I feel as though it is more open for me under linux. If
there were an open-source (bi-directional) conversion utility to convert
between the two, I would likely use DNG format to save space. As it is
now, I losslessly compress them using bzip2 and get most of the benefit
with none of the risk.
Again... to each their own. Whatever floats your 'scope.
-Cory
--
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* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
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