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Re: [OM] (IMG) Deep Purple

Subject: Re: [OM] (IMG) Deep Purple
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Sun, 7 Jun 2009 10:12:46 -0500
>
> No, there is in fact another reason --- I didn't understand the type of
> output file: a RAW in 8 bit / Ch IIRC ? Why not 16 ?
>

Well, in Irfanview or in Nikonscan, there is the scanning bitdepth and then
there is the file-save bitdepth. If a straight scan with minimal contrast or
color change is necessary, then a 8-bit per channel scan and save is
sufficient. However, if there is extensive curves, contrast or color change,
then a 16-bit per channel scan is preferred.

However,

Unlike a digital camera, a film negative or slide has substantial random
noise (grain) which will create the effect of greater bit-depth than is
actually there.  With a digital camera image, you will get "solarization" in
the image if you attempt too radical of a curves/contrast/color adjustment.
With a scan, you just increase the grain, but no solarization occurs.

Scanning at higher bit-depth in the Nikonscan software does have a nice
little side-benefit. The grain level is usually reduced some. If I scan at
16-bit (14-bit true in the Coolscan itself, the software expands it to
16-bit for file writing) and then post-process the image entirely within
Picture Window Pro or Photoshop in 16-bit mode, I see about an effective 50%
reduction in grain in a heavily processed image.  If I have no further
processing, the grain is about the same, with maybe a slight nod towards the
16-bit file, but usually not enough to worry about.

Sorry, Fernando, this has been a recent discovery.

AG
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