Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@y..., "Austin Franklin" <
darkroom@i...> wrote:
> > > I don't know quite what you mean here...we only measure
> > relative values, as
> > > in 2 times, 3 times, 4 times....1000 times...only integer ratio values.
> >
> > What he is saying is that the CCD's voltage is analog and therefore
> > infinite.
> 
> That's a misnomer.  Analog is not infinite.  It is limited by noise, and
> that is what dynamic range is...the largest signal over the noise.  If you
> have a maximum 6V signal, and your noise level is .003 volts, you have a
> dynamic range of 3.3.

okay, well why don't you make a CCD with more volts and less noise?
You can't put aside our theoretical arguments by saying a CCD has 
noise.

> > Why can't, using your above example, someone make a scanner using the
> > more sensitive 14bit A/D converter on the less sensitive CCD from the
> > 10bit scanner. (I assume you mean sensitive as in the ability of the
> > CCD to judge brighter or darker tones)  This should allow more tonal
> > information over the same Density Range.
> 
> Nope.  The values you get out of the CCD/AD are RELATIVE.  2 is twice as
> bright as 1, and 4 is twice as bright as 2, no matter what CCD or A/D you
> use.

Why does it have to be that way though?

> 
> You need to have a more sensitive CCD to give you less noise...hence the
> need for more bits to increase the dynamic range so you can read the smaller
> signals that are less than 10 bits can represent...which is why you get an
> increase in the shadow detail (for chromes).
> 
> Keep in mind, the analog output of the CCD, no matter what it's noise, is
> matched (voltage wise and/or current wise) to the input range of the A/D
> through analog circuitry.  The A/D (as in number of bits) is chosen (as well
> as the analog interface circuitry) to match the CCD...one typically doesn't
> use 24 bit A/Ds when the noise level is only good for 10 bits of that 24!
> Even if you did use a 24 bit A/D, only 10 bits of it would be "useful",
> because of the noise.

I guess this is why the older Scanmaker 5 always made very noisy scans.

-mikeH