pef vs dng

Godfrey DiGiorgi gdigiorgi at gmail.com
Wed Oct 7 15:59:45 EDT 2009


On Tue, Oct 6, 2009 at 7:53 PM, Doug Franklin <jehosephat at mindspring.com> wrote:
>> PEF files are always atomic ... one single file ... but if you use
>> Bridge+Camera Raw or Lightroom to add IPTC metadata and perform your
>> adjustments, and write the adjustments out (rather than keeping them
>> hidden in a centralized database), the applications will create .XMP
>> sidecar files for each PEF file.
>
> Hmmm, I must be missing something here.  Both PEF and DNG are atomic, in the
> sense that they're comprehensive and without need of any sort of "sidecar"
> file, in terms of the photographic data and metadata itself. I think/suspect
> the .XMP "sidecar" files are more in the nature of the processing
> instructions you indicated while in Lightroom than anything /necessary/ for
> the realization of the image captured in the PEF or DNG file.  At least,
> that's been my experience with other programs, though I haven't used
> Lightroom.

Camera native RAW format files have no way to store IPTC data
internally (keywords and all the other bits of information that the
International Press Telecommunications Council defined as part of the
standard. This metadata must be stored external to a PEF file. The
only metadata stored in native RAW files are what the camera
manufacturer embedded into them as part of their creation in the
camera.

DNG files were designed as container files, with a well known
structure for appending this information as well as information about
their rendering (the Camera Raw and Lightroom instructions), as well
as any other data that might seem appropriate.

As a demonstration, I opened an old folder of K10D RAW image files.
Some were in DNG format, others in PEF format:

http://homepage.mac.com/godders/before–IPTC-metadata-save.jpg

I imported them into a Lightroom catalog. No image editing was done,
the only operation was to add a keyword, "testing", and my standard
IPTC data (my copyright info, name, address, web address). The exact
same data was added to every image. I used the function
("Metadata->Save metadata to file...") to save this IPTC metadata to
the files. Note what the state of the files is now:

http://homepage.mac.com/godders/after–IPTC-metadata-save.jpg

Lightroom embeds the IPTC data into the .DNG files, but writes the
same data to .XMP sidecar files for native RAW PEF files. This is
because there's no standard facility to store IPTC data into .PEF
files ... it must be saved elsewhere.

-- 
Godfrey
  godfreydigiorgi.posterous.com




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