Digital BW, The Print

On Tuesday, January 7, 2003, at 06:08 PM, Austin Franklin wrote:

> Hi Kevin,
>
>> Thanks for the detailed answer.  I'm not sure if you are agreeing or
>> disagreeing though :)
>
> Agree in conclusion, but I think you were missing some details there 
> as to
> how things work.

Yes.  My conclusion seemed counterintuitive.  Your answer helped fill 
in some of the 'gaps'.

>
>> After reading your response I think I can still say development times
>> are 'mostly irrelevant'
>
> Hum.  If you use N+- exposure to compress/expand the scene density 
> onto the
> film, you have to use N+- development...
>
>>  From a purist perspective getting the largest density range on the 
>> film
>> is best because your scanner produces more discernible data.
>
> Correct.
>
>>>> By setting the black point, setting the
>>>> white point and scanning the negative am I not mapping the entire
>>>> density range of the image to a numerical range of 0-256 or 0-64k?
>>>
>>> Not quite.  The setpoints have not a thing to do with the scan.  They
>>> are
>>> applied to the scanned data AFTER the scan occurs.  I believe that's
>>> actually not the right question.
>>
>> OK, it makes sense that the set-points are applied after the scan.
>
> That is true of the consumer scanners you and I use.  There are some
> scanners, and I've designed one, that have analog gain control between 
> the
> CCD and the A/D, and has, basically, hardware setpoints.


That would be add a whole new meaning to the auto-exposure function!!

>
>> Cool, thanks for the primer.  Wouldn't the software use some algorithm
>> to interpolate values for the gaps instead of leaving them empty?
>
> That is a good guess, but no...remember, every pixel has a value 
> associated
> with it.  What are you going to interpolate?  If you did somehow
> interpolate, you are giving data that was the same, different values, 
> or
> creating NEW data that didn't exist before...  The gaps really don't 
> mean
> anything, as you are taking the N bit data and converting it to 
> CONTINUOUS 8
> bit data...in other words, when you go to print, you DO have every data
> value from 0-255 (or most every one).
>
>>>> This mapping would take place independent of the absolute density 
>>>> any
>>>> particular zone.
>>>
>>> That is true.  There is no directly calibrated correlation between
>>> scene
>>> density, film density and scanner value....unless you went out of 
>>> your
>>> way
>>> to calibrate it...which is really unnecessary, as doing so won't get
>>> you
>>> better scans.
>>
>> Agreed.  So can't I conclude that the value of the slope of the
>> exposure density curve is (ignoring the number of gaps) irrelevant to
>> the scan?
>
> If I understand you correctly, the answer is yes, it is irrelevant, as 
> long
> as you have enough data there...as the slope approaches 90, you have 
> less
> data points per delta.
>
>> OK, the greater the density range of the film the more discernible
>> data.
>
> Correct.
>
>> So couldn't I just settle on an N+1 time or N+2 time as long as
>> the resultant film density doesn't exceed the optical density range
>> of my scanner I should be OK. Yes?
>
> I am confused as to why you think you always would use +
> exposure/development.  + is for expansion of low contrast scenes (small
> density range) into the higher density range of the film...and - is for
> contraction of a high contrast scene (large scene density range) into 
> the
> smaller density range of the film.  There are circumstances in the real
> world where you would use either.

Yes I understand classic zone methodology.

Just let me make sure I have understood what you are saying and that we 
do in fact agree.  In the same hypothetical the N-1 development 
(density range of .7), the N development (density range of 1) and the 
N+1 development( density range of 1.5) all produce virtually the same 
scan after set points are applied.

  With an extremely shallow exposure/density curve you may have too few 
discernible points from the scanner to fill the 256 data points 
(assuming 8bit).  As a principle more data points (ie maximum density 
range) is better.  Except in situations with an extreme brightness 
range adding development time to your 'normal' time (or the 
manufacturers recommended time if you haven't done any testing at all) 
will increase the density range. And be a good thing.

>
> Regards,
>
> Austin
>
>
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