On May 1, 2006, at 9:07 AM, Cory Papenfuss wrote:
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.
I think you're playing semantics with the definition of "lossless".
If you apply a transformation to data, the transformation is
considered lossless if none of the data is lost. A transformation
from PEF to DNG format preserves all of the data and is lossless. A
DNG file is just as "archival" as a PEF file because both contain the
same data, represented in different structures.
The transformation from DNG to PEF is certainly possible, it just
hasn't been done because it isn't something which a high value
priority. If it were, a utility to do it could be constructed.
There's nothing lossy about it, unless you consider the loss of
metadata added to the DNG file which has no possibility of
representation in the PEF file.
In my (relatively unique) situation, DNG is much less useful. ...
That much we agree upon.
(BTW: DNG files are yet another specialization of TIFF in structure,
so the same utilities that work on PEF files as specialized TIFFs
would also work on DNG files.)
Godfrey
