on 8/28/02 9:45 AM, Paul D. DeRocco at pderocco@ix.netcom.com wrote:
...
>
>
> 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
Roy Harrington
roy@harrington.com
Black & White Photography Gallery
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