Digital BW, The Print

Hi Steve,

Looks like you're getting different pieces of the puzzle from different people
here.  My contribution is inline below... 

Best regards,

-= mike =-

-----Original Message-----
From: Steve Kale
Sent: 23 November 2004 10:09
To: DigitalBlackandWhiteThePrint@yahoogroups.com
Subject: Re: [Digital BW] Tonal range recording


Ok so I must confess that this and the other responses blew straight over my
head, not being a zone guy and not understanding film shoulders and toes.
Can I ask some basic questions so that I can follow the discussion:

1)  You speak of 15 stops from colour negative film.  I have heard people
saying that Velvia slide film has just +/- 1 2/3 stops, or 3 1/3 stops, of
workable range.  Are these measurements of the same thing?  (What is the tonal
range of Provia?)

[Mike] Yes they are, so it's very hard to keep any detail in the shadows with
a super-contrasty film like Velvia if you expose correctly for the main parts
of a scene. There are very few colour transparency films with more than five
stops of dynamic range, none (that I'm aware of) with more than six. Provia is
less contrasty than Velvia, and Astia -- my own fave -- is somewhat less
contrasty still.

2) How does one convert stops to density? Loosely.  For example, if a scanner
has a rated dMax of 4.8 how does that relate to the tonal range in stops of
film that it is going to scan?

[Mike] Danger, danger! There is no direct relationship between the two, it
depends upon the characteristics of the film. In the case of colour neg, the
film has a very wide dynamic range (10+ stops as mentioned before) but the
resulting range of density on the film is quite narrow. Conversely,
transparency films can only handle a much narrower range of scene brightness
but the actual density range on the film is much higher, mainly because the
black areas are very dense compared to the densest areas of the highlights on
neg film.

3) Where does the "12 stop linear capability of some censors" come from?
What is the figure for the 1Ds MK II or 1Ds?

[Mike] If you have 12-bit converters in your camera, then that sets a
theoretical maximum of 12 stops of dynamic range, because the scale of f-stops
is also a 2x progression. However, note that at the dark end of the range, the
tonal separation is very coarse (whole stops only!) plus there will be noise
coming from the sensor anyway, so it would be more realistic to assume that
one or two bits get lost that way, and the real range would be nearer to 10
stops.

4) I think I understand the importance of linearity - kind-of-sort-of - from
printing.  Is this a similar concept? Ie evenly distributed tonal range?

[Mike] Hopefully Pieris's reply has helped you here.

5) At the end of the day we are severely constrained by the tonal range
capability of our printing.  Hogarth mentioned 8 stops for silver gelatin
paper.  How do I relate a linearised print of a step wedge on HPR with a paper
white dMin of .04 and a best black dMax of 1.68 to these figures?
(Wouldn't it be nice if they all used the same scale?)

[Mike] While echoing Pieris's comments, I'd add that for paper the same
relationship exist between dynamic range and density as it does for film (ref
my reply to point 2 above). Assume that the dMax and dMin are fixed for a
given type of paper, but you have several grades available. If you use a
harder grade, then a shorter range of values from the neg will map to that
range. If you use a softer paper, then more of the scale will fit. With
Photoshop we simply have much greater control over how we fit the values to
the available range, but in the end we are still limited by the output medium.

While the boundaries of the digital print are expanding, I guess we still need
to shoot by compressing the tonal range of the scene with ND filters (or
multiple exposures) so that it can be rendered well in the print - traditional
or inkjet.  I am trying to relate the two (and the steps that may be in
between eg scanning) so that when I get out my spot meter I am not only
thinking in terms of stops but also in terms of my printer's tonal range.
Sorry if these are basic questions but I think it will help a lot of people
tie all the talk of dMax back to the camera itself.

[Mike] Don't think in terms of your final print's tonal range, think in terms
of getting the best possible data in your capture. The principle is quite
similar to the approach you'd take using film, except you don't need to limit
yourself to only recording values on the neg that will be usefully printable.
Also, with neg film, you could theoretically use a really low-contrast
film/developer combination for absolutely everything you shoot, but then if
you decided you did want a nice contrasty print, you'd be trying to use very
hard paper to pull out tonal separations that are barely distinguishable on
the film. Therefore you might choose to develop for more contrast or use a
different film for a certain project. With digital the contrast ratio of the
sensor is fixed, so the best you can do is make sure you set the exposure so
that you use the full sensitivity that's available, and then use curves in
Photoshop to increase or reduce the contrast later. If you don't succeed in
using the full dynamic range (i.e., the histogram is bunched up down the
left-hand side) then if you choose to increase the shadow contrast you'll see
more noise than if you'd done a better job of the exposure.


<snip>

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