[filmscanners] RE: Density vs Dynamic range

["Austin Franklin" <darkroom@ix.netcom.com>]

> ... I'd like to follow this through to a definitive source.
> >
>
> The proposed ISO standard on "Photography - Electronic scanners for
> photographic images - Dynamic range measurements" (WD 21550.3 (42N 4909))
> states that the dynamic range is calculated by:
>
> DR = Dmax - Dmin
> DR = Scanner dynamic range
> Dmax = Density where the signal to noise ratio is 1
> Dmin - Minimum density where the output signal of the luminance OECF
> (opto-electronic conversion function) appears to be unclipped

Hi Dean,

Interesting, but if that's what it says, it's simply wrong...in just about
every statement!  I'll have to get a hold of the spec and see what it is
trying to say before commenting much on it.

A couple of notes on your "snips" from it.  DR typically means Density
Range...in the imaging world.  DENSITY RANGE does equal dMax - dMin.

The statement about "dMax = Density where the signal to noise ration is 1"
is also simply wrong.  Because dMin has nothing to do with slipping, simply
noise...and dMax relates to clipping.

Now, if you simply mixed their definition of dMin and dMax that's a
different story...which it appears you have.  But I'll wait to see what you
say about that...the equation above, because it's in dB, CAN be made to be
exactly the same equation I've given, simply because it is already in log
notation, with some assumptions.

Austin

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