[filmscanners] RE: Dynamic range

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

> > You can't really base dynamic range specifications on the
> numbers, because
> > there's no guarantee that the numbers bear any particular relationship
> > (linear, log, gamma) to the light power. Dynamic range really should be
> > measured as the (log of) the ratio between the strongest light
> power that
> > the scanner can read without clipping, and the weak light power that is
> > equivalent to the electrical noise in the sensor and subsequent
> electronics.
> >
> > If you then took the log of the signal level, and converted that to a
> > digital value, the number of bits you have would no longer have any
> > relationship to the dynamic range, only to the resolution. That
> is, if the
> > electrical noise corresponds to a light level that's one
> millionth of the
> > light level that clips the sensor and converter, you've got
> 60db of dynamic
> > range, regardless of whether you use eight bits (60/256 db per step) or
> > sixteen bits (60/65536 db per step).
> >
> > All the stuff about rulers is meaningless, because dynamic range is only
> > meaningful when measuring the ratio of power levels, not linear
> quantities
> > like length.
> >
> > --
> >
> > Ciao,               Paul D. DeRocco
> > Paul                mailto:pderocco@ix.netcom.com
>
> Thanks, Paul.  "Ratio of power levels" is what it's all about --
> whether its light power levels or sound power levels.
>
> Roy

So what, Roy?  How does that at all have anything to do with your claims?

As I gave you the benefit of the doubt you would understand, that the ruler
examples were merely SIMPLE examples for some people to try to understand
this concept using something they are familiar with.  Apparently that
simplicity evaded you.

Digital numbers are used to REPRESENT that ratio, and as such, you REQUIRE
so many bits to "contain" the all the possible values across the entire
range.  That's just a fact, that is just SO WELL DOCUMENTED that it boggles
the mind that you want to somehow argue against it.

I thought you weren't going to say another word on this?  Eh?

Austin

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