Digital BW, The Print

Thanks, Tony,

I guess the upshot is I won't obsess over scanner specs. Also, I need to continue learning about VueScan. I didn't realize how or why it gives better shadow detail. 

One more question: what is ADC, as mentioned in your next-to-last paragraph?

Regards,

Paul

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Tony Sleep <TonySleep@...> wrote:
>
> On 18/11/2012 00:59, Paul wrote:
> > But scanner specs don't show that, they show Dmax in the negative. Like
> > you say, Dmax is Dmax. And so the scanner specs give me information on how
> > my highlights might look like in the print - and of course I'd like some
> > detail there too, I don't want them blown out. But it looks like typical
> > scanner specs can't help me with detail in the print's shadow areas.
> 
>   The DMax does, as you say, correspond to the darkest area within which 
> the scanner is able to capture tonal detail. This is highlights in 
> transmissive mode with negs, shadows in tranparencies, and shadows in 
> prints in reflective mode.
> 
> This limiting factor is very much complicated by sensor noise. Ability of 
> sensors to record detail at minimum signal is invariably compromised by 
> this - there will always be a shading of detail into noise which will 
> obliterate detail.
> 
> Stated DMax that is unaccompanied by a qualifying statement of the noise 
> level present (at the measured DMax) is meaningless, a bullsh*t marketing 
> claim. What matters here is signal to noise ratio. Manufacturers almost 
> never state this anywhere.
> 
> The same applies to ODR (optical density range), since it takes DMax as 
> its lower bound. Without qualification regarding noise level, it means 
> nothing.
> 
> There is no valid or useful way to compare scanner abilities from 
> published DMax or ODR, you can only tell by using them.
> 
> Optical system abilities are also never specified in any useful way, but 
> lens systems are as crucial as in enlarging. You just don't get excellent 
> lenses in cheap scanners, because a fine macro costs too much to manufacture.
> 
> There is also OE software to contend with - eg scanners with 10,12 or 14 
> bit ADC's with OE software that works at 8 bit throughout, then merely 
> upsamples to produce 16bit output if selected.
> 
> For years HP, Epson and Polaroid OE sofware was hobbled like this. This 
> has severe bad effects at the dark end where bit values are small and 
> rounding errors are very significant. End to end 16 bit working was one of 
> the great advantages of Vuescan, and the improvement in noise was 
> dramatic, on some models gaining almost a full stop more usable shadow detail.
> -- 
> Regards
> 
> Tony Sleep
> http://tonysleep.co.uk
>