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Converting proprietary raw into DNG: how much do I lose?

 
 
JD
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      06-06-2005

Hi, when I convert a raw file from my Pentax *istDs with Adobe Raw
Converter, the original *.PEF file of 11030 Ko becomes a *.DNG file of 6394
Ko.

What am I losing? If I'm not losing anything, why does the *.PEF need to be
so big?

Which one should I keep both for archiving?

Regards,

Jean.


 
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Bill Hilton
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      06-06-2005
> Jean asks ...
>
>What am I losing? If I'm not losing anything, why does the *.PEF need to
>be so big?
>
>Which one should I keep both for archiving?


Here's a link to the best write-up I've seen on what you lose and why,
with a suggested workflow by well-known Photoshop guru Jeff Schewe ...

http://photoshopnews.com/2005/05/23/...rkflow-part-i/

Bill

 
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Barry Pearson
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      06-06-2005
JD wrote:
> Hi, when I convert a raw file from my Pentax *istDs with Adobe Raw
> Converter, the original *.PEF file of 11030 Ko becomes a *.DNG file
> of 6394 Ko.


I have a Pentax *istD, and that has PEF files of about 13MB, instead of
about 11MB for the *istDS. The DNGs are about 6MB.

> What am I losing? If I'm not losing anything, why does the *.PEF
> need to be so big?


The PEF from my *istD is probably not compressed at all. (If it holds
the 12-bit sensor data as 16-bit aligned, then a 6 megapixel sensor
will take about 12+MB). The PEF from your *istDS is probably (lossless)
compressed a bit in the camera. The DNG Converter optionally uses
LOSSLESS compression, based on a lossless-type of JPEG compression. It
doesn't lose anything by this compression.

Try an experiment. Use the "don't compress" option in the DNG Converter
when converting from PEF. I'll bet that the result is about 13MB, but I
don't know for sure. Or try running your DNGs through the DNG Converter
again, (it will happily convert them, of course), with compression
switched off. I'm sure the resultant DNGs will be about 13MB.

> Which one should I keep both for archiving?


Against the advice of Adobe and others, I only keep the DNGs. In fact,
I now convert straight from the card, so I never see the PEFs on my PC.
That is because I don't intend to use any Raw processor that doesn't
accept DNGs. (There is "secret" Pentax stuff in the PEF which Adobe
doesn't understand. The 3.1 DNG Converter stores it in the resultant
DNG, but doesn't use it. If you need it in future, it would be possible
for code to extract it, although there is no "off the shelf" code yet).

But "don't try this yourself" unless you are confident you know what
you are doing. If you will ever want to use a Raw processor that
doesn't accept DNG, either keep the original PEFs, or embed the PEFs in
the DNGs, (an option in the DNG Converter), so that you can extract
them later.

--
Barry Pearson
http://www.barry.pearson.name/photography/
http://www.birdsandanimals.info/

 
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