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[filmscanners] RE: color bit depth and digital cameras



I wonder if the confusion comes from the option for compressed NEF as the
raw format.  The D200 default is uncompressed & lossless but it's easy to
change to the just barely lossy compressed option.  Compressed in-camera
squeezes the 12 bit, 4096 native analog RAW value scale into 683 values,
~9.4 bits but differently allocated.  Nearly all the compression loss is in
more highly gradated high values.  In uncompressed RAW, the top 4 stops use
3840 (2048+1024+512+256) values of the 4096.  The remaining 256 values cover
the rest of the 8 bits.  Compressed NEF's allocate 251 values to the lower
256 (8 stops) and the remaining 432 to the top 4 stops (3860 raw values).
The result is just a little less recoverable highlight data -- on average
more values per f-stop than the lower range.  The loss seems to  empirically
provable but hardly ever meaningful in the image.  I still shoot
uncompressed NEFs just in case.  The D80, D70, D50 & D40 bodies only have
compressed NEF.

http://www.photography-forums.com/t80862-drawbacks-of-compressed-nef-in-d200
.html

Bob G
-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk] On Behalf Of Berry Ives
Sent: Saturday, July 14, 2007 8:05 AM
To: bobgeo@dgiinc.com
Subject: [filmscanners] Re: color bit depth and digital cameras

Dpreview.com's review indicates that it is a 12-bit raw format.
~Berry


On 7/13/07 11:27 PM, "David J. Littleboy" <davidjl@gol.com> wrote:

>
> From: <ppatton@bgnet.bgsu.edu>
>>>>>>>>>>>>
>
> I was just playing with my new Nikon D200 and discovered
> something that surprised me.  Unless there is some quality
> adjustment setting I missed, it's color bit depth apparently is
> only 8 bits in NEF Raw.  By comparison, my Polaroid SprintScan
> 4000 scanner has a color bit depth of 12 bits, and other scanners
> have much higher color bit depths than this.  While color bit
> depth is a commonly cited specification for scanners, I've seldom
> seen it cited for digital cameras.  Does the lower bit depth for
> the D200 imply lower quality color rendition than my 12 bit scanner?
> <<<<<<<<<<<<<<<<<<<<<<<<<<
>
> I suspect you've done something wrong. This reference
>
>
http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary/in
de
> x.html
>
> Shows the D200 doing very well indeed at ISO 100. I'm quite sure it uses a
> 12-bit A/D converter.
>
> Note that just because a camera or scanner has X bits in its A/D converter
> doesn't mean you have X bits of valid data in the output files.
>
> David J. Littleboy
> davidjl@gol.com
> Tokyo, Japan
>
>
>
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