Digital BW, The Print

Hi Austin,

Thanks for the detailed answer.  I'm not sure if you are agreeing or 
disagreeing though :)

After reading your response I think I can still say development times 
are 'mostly irrelevant', but with   low contrast scenes there will/may 
be more gaps in the output data  and these may become apparent with 
subsequent modest or extreme  adjustments.

 From a purist perspective getting the largest density range on the film 
is best because your scanner produces more discernible data.  See 
comments below.

On Tuesday, January 7, 2003, at 04:38 PM, Austin Franklin wrote:

> Hi Kevin,
>
>> Is zone system development time manipulation irrelevant when scanning
>> film as opposed to traditional printing?
>
> An excellent question.  It is ABSOLUTELY relevant.  What you are doing 
> by
> using the Zone system is placing as wide a tonal range as you can on 
> your
> film, period.  In order to do that, you use exposure compensation and
> development compensation.
>
>> Since I am not doing wet prints but am scanning the negatives, it 
>> seems
>> to me that the N- or N+ development dependent on the scene brightness
>> range is, mostly, irrelevant.
>
> Well, no...see above.
>
>> 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.

> The question should be how to get the
> highest density range on the film THEN how to take advantage of that.
>
> I'll explain the scanning process as it related to setpoints.  The 
> scanner
> scans the film, and place the density range of the film in an N bit 
> space.
> The density occupies only a portion of that N bit space, and how much 
> of
> that it occupies is up to the density range of the film.
>
> You can verify this by doing a raw scan, and looking at the data from 
> that
> scan with the histogram tool.  It will only occupy a small portion of 
> the
> overall range.
>
> What you do when setpoint is "mark" the endpoints of the actual image 
> data
> within the overall N bits the scanner scanned at.  Example, your 
> scanner is
> 12 bits, that gives you a range of 2**12 or 0-4095.  You scan.  The 
> actual
> image data occupies data values from 200-766 in the raw scan.  When you
> setpoint this data, it takes the 567 values of image data, and spreads 
> them
> out over either 8 bits (some get combined when going to an 8 bit 
> space), or
> over 16 bits (where they get spread out).
>
> If the number of data values is less than the space you are mapping it 
> into
> (577 values into 16 bits) then there will be "equal" (not necessarily
> perfectly equal, but as close as can be done) gaps between the data 
> values.
> A simple example of that...you have a 4 bit scanner (0-15) and the data
> occupies 3-10.  You want 4 bit data out of the scanner, so you set 
> your low
> setpoint at 3, and the high one at 10 and the data gets remapped as 
> follows:
>
> Original image values 3-10 get mapped to 0-15 as follows:
>
> 3 -> 0
> 4 -> 2
> 5 -> 4
> 6 -> 6
> 7 -> 8
> 8 -> 10
> 9 -> 12
> 10-> 14
>
> note gaps in the data.  This is no big deal as far as real image data 
> goes
> (meaning 12 bit scanned data, mapped to 8 bit data to the printer or
> screen).
>
Cool, thanks for the primer.  Wouldn't the software use some algorithm 
to interpolate values for the gaps instead of leaving them empty?
> Map that same 3->10 into a 2 bit space:
>
> 3 -> 0
> 4 -> 1
> 5 -> 1
> 6 -> 1
> 7 -> 2
> 8 -> 2
> 9 -> 3
> 10-> 3
>
>> 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?

>> As a hypothetical example lets assume a scene contains a 8 stop range
>> of brightness.  Three images are similarly exposed to capture that
>> brightnesses range. The three images are given different development
>> times and produce density ranges of  (1.0-0.3=.7), (1.4-0.4=1.0) and
>> (2.0-.5=1.5).  When the images are scanned each one will produce a 
>> full
>> histogram from 0 to 255
>
> Only after setpointing the scanned data into an 8 bit space.
Agreed.
>
>> and a scene brightness at the 6th of the eight
>> stops will show up at the same place in each of the histograms.
>
> Possibly...
Agreed.
>
>> Soooo, can't I simplify the zone mantra to "expose for the shadows and
>> let the highlights fall where they may with normal development".
>
> No, because you can expose to get a higher scene density range onto the
> film.  The actual density range of the film is irrelevant to how much 
> scene
> density range you can record on the film.  BUT...the wider the film 
> density
> range, the more discernable data your scanner will record, because of 
> how
> the scanner works.

OK, the greater the density range of the film the more discernible 
data.  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?

>
>> Also,
>> wouldn't it be better to generally use N+1 development times
>
> It depends on if it's a high or low contrast scene.  Plus
> exposure/development is EXPANDING the scene range into the film range, 
> for
> use with LOW contrast images.  Negative exposure/development is 
> CONTRACTING
> the scene range into the film range for use with HIGH contrast images.
>
Comment just above applies I think.
>> so that
>> the numbers from the raw scan occupied more of the scanner's range?
>
> Yes, exactly.  You want to contract/expand the SCENE range into the 
> film
> range, therefore giving you more scene tones on the film and therefore 
> more
> discerned scanned values.
>
> If you already knew the answer, why get me to go through the whole 
> process
> ;-)
>
> I think I said all that correctly.  I'm sure I'll get a lashing if I 
> typo'd
> or missed something...
>
> Regards,
>
> Austin
>
>
>
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