Digital BW, The Print

"craig_spaulding" <craig_spaulding@...> writes:

> Jeff,
> 
> I have several questions re your transfer curves technique:
> 
> 1) Can the black and white points be set in Photoshop instead of the 
> scanner after the step-edge has been scanned? I work with a digital 
> camera and my scanner is marginal and I don't think the black and 
> white points can be set in the software.

Are you suggesting taking a digital photo of the step wedge instead of
using the scanner?  In theory this should work okay.  The one obvious
way to ruin it is to have the lighting uneven (since the point of the
scan/image of the step wedge is to quantify the brightness
differences). 

> 2) Is this a technique for making a transfer curve or a curve that 
> is to be applied in an adjustment layer? Once the curve is made, can 
> it be applied either place?

I've used it only as a transfer curve.  The units are different in
transfer curves and adjustment curves, so they're not *directly*
interchangeable.  

The point of the Nevins method is to be able to edit "by eye" until it
looks good, and then use the transfer curve to bring the paper into
line with what's on the screen, so I haven't experimented with making
the paper-specific adjustments visibly on screen.

> 3) Is there a good method for going about modifying an existing 
> curve (like the Woolf)? Do you click on the appropriate step in the 
> step-wedge to find out where it is on the curve that step is, then 
> use the up/down arrow or change the numbers in the dialog box? If 
> so, is there a rhyme or reason for how much to change it to equally 
> space out the peaks, or, is it all trial and error. Or, do you just 
> focus on changing the general shape of the curve to space out the 
> peaks?

What I do is scan the most-recent-generation step wedge and measure
each patch using the histogram tool (constrained by a rectangular
marquee), and write down all the numbers.  Then I calculate what each
number *should* have been (starting with the 0% and 100% numbers being
inherently correct).  Then I calculate the adjustment for each
intermediate step.  Then I go apply those adjustments to the transfer
curve, and save it.  Then I print a new step wedge and start over.

Depending on the ink/paper combination you use, it may be crucial to
let the step wedge dry before scanning it.
-- 
David Dyer-Bennet, dd-b@...  /  Ghugle: the Fannish Ghod of Queries
 John Dyer-Bennet 1915-2002 Memorial Site http://john.dyer-bennet.net
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