Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Jeff Medkeff <medkeff@g...> 
wrote:
> 
> 
> Roy Harrington wrote:
> 
> 
> > E.G. with a 12 bit integer value the biggest ratio you can represent is 4096/1.
> > If you want a larger dynamic range ratio than 4096 you have to have more bits.
> 
> The biggest ADU *ratio* you can represent is 4096/1. But the actual 
> dynamic range this ratio represents depends on the number of electrons 
> per ADU.
> 
> For example, isn't ten electrons per ADU (=0 to 40,960 electrons) a 
> smaller dynamic range than 100 electrons per ADU (=0 to 409,600 electrons)?

No, they are the same.  Dynamic range is the ratio of the largest / smallest
distinguishable value.   So 40,960 / 10 = 409,600 / 100 = 4096.  It's
the linearity of the units (electrons, photons, millivolts) that allow to do the 
simple ratio.

> 
> Another way of saying this is at what electrical potential does the ADC 
> output 2048 ADUs? Would that be 10 millivolts? 50 millivolts? And how 
> much is the well potential amplified, anyway?

The actual millivolts don't matter -- its the ratio of the largest to the smallest.
The amplifier being linear makes no difference.

> 
> Without *also* having this data, you do not know how much dynamic range 
> is represented by a given ratio. I'm all for increasing the ratio. But 
> I'd like to see the dynamic range detectable by the sensors increase, too.

Basically you increase the sensor dynamic range by either: reducing the noise
at the low end and/or increasing the clip point at the high end.   The bits of
the A/D have to fine enough to take advantage of the reduced noise at the
low end and coarse enough to not get clipped at the high end.

Roy


> 
> --
> Jeff Medkeff
> Eagle River, Alaska