On May 1, 2006, at 6:10 AM, Cory Papenfuss wrote:
First off, the original capture file is the source ... How could
you "extract more metadata in the process" of converting from PEF
to DNG?
I'm referring to the closed-nature of some of the metadata in the
EXIF of the RAW file. Of course there's no "more" data (other than
whatever the DNG conversion might want to record about itself).
What it *might* allow is open-access to some of the unknown data.
I've tried to contact Pentax to get more information on the
"VendorTAG"-type EXIF tags, with little success. If one
proprietary company (Adobe) manages to beg/borrw/steal/reverse-
engineer/buy the ability to read this stuff and put it in an open-
format like DNG, I consider that more data.
'Maker notes' in the EXIF data are not easily decipherable because
the EXIF specification left too much ambiguous and up to the whim of
the manufacturers. Same reason there two different ways to represent
both aperture and shutter speed in the EXIF spec. Adobe's other
initiative, the Extensible Metadata Protocol format (XMP) is a much
much more sensible metadata specification that I'm hoping becomes a
standard for all application utilities.
This has little to do with DNG format. DNG conversion simply puts the
EXIF data into the converted file in a standardized format, with
appropriate sections for tags whose structure is unknown/
unpredictable. All the same data is there.
The way I understood it (which could be way off since I've never
even played with it since I cannot), was one could a) convert to
DNG, or b) throw the original RAW file in as well. If I was
guaranteed I could always reverse the process through an open-
source means, option a) would be a viable archival method to get
the compression and pseudo-application-agnostic qualities. Option
b) seems like a silly idea for archival since it takes up even more
space than the original file.
It's not a mutually exclusive "A or B" choice. One can convert to DNG
and bring all the data from the RAW file into the container format.
Optionally, one can also embed the original RAW file into the
container, whole, for those who want to be able to extract the
original RAW file again, for whatever reason, at some future date.
I also find this a relatively useless option ... I haven't found
anything I couldn't do with DNG files compared to PEF, ORF, SR2, SRF,
CRW, RAW and MRF format files, and the DNG files are smaller, contain
more metadata after I've added my IPTC and Camera Raw parameters. The
only reason that I can see for wanting an original RAW file format is
to take advantage of some special software that can only operate on
the original RAW format data ... To my mind, that's a deficiency of
the software, not the DNG file format, because all the original data
is there in the DNG already. I haven't found anything like that worth
being interested in so far either.
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?
Godfrey
