Digital BW, The Print

hi John -

Joe's "canned" curves are a good starting point, but you may need to
make significant changes. Here is a curve-editing procedure you may find
helpful.

1. Prepare a 26 step grayscale step wedge suitable for your
spectrophotometer. The Photoshop gray values of the patches should be
0%, 4%, 8%, and so on, up to 100% of black.

2. Print the step wedge through OPM using your starting "profile."

3. Measure the luminance (L*) of the patches, import the data into
Excel, graph the points, and compare the resulting curve to a luminance
target straight line from your maximum L* (paper white, at 0% K) to your
minimum L* (Dmax, at 100% K).

4. Adjust ink levels using "free edit" in IJC. Add ink where the L* plot
is above your luminance target line; remove ink where the L* plot is
below target. You'll need to study your curves to decide which ink to
vary in each part of your gray scale. Also, to get the best possible
Dmax (i.e., lowest minimum luminance), adjust the ink mixture at 100%
carefully. Save the adjusted ink curves as a new "profile."

5. Repeat steps 2 through 4 until you get the best result you can. When
you're very close, you can try using IJC's "Linearize" function to see
if it does any better than you can by hand.

I use an X-Rite DTP-41 strip-reading spectrophotometer for this kind of
work, and I have found working toward a linear gray ramp in L* space
works very well. 

If you don't have a spectro, you can work with a densitometer and
convert density readings to L*, or you can work with densities instead
of luminance, but in this case you should work toward a gamma curve
target, not a straight line. If you don't have a densitometer either,
you may be able to get decent results working with a scanner, but you'll
be at a disadvantage, I think.

I realize this may seem a bit sketchy. Expect a fairly steep learning
curve if this all seems new to you.

Richard Wolfson
Fine Art Photographer & Digital Imaging Consultant




> -----Original Message-----
> From: johndavidgill2003 [mailto:jdgill@...] 
> Sent: Wednesday, January 05, 2005 11:08 AM
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: [Digital BW] IJC/OPM - Creating Curves from scratch
> 
> Any pointers on how to do this?
> I have an Epson 1160 with VTBlax dedicated B&W inks. How does 
> one determine what the curves should look like for each of 
> the 4 inks (if indeed all inks should be on)? I know how to 
> set the ink limits but after that the ink shapes section is a 
> bit of a mystery. I tried using the Black ink, dark grey ink 
> etc sample curves and just got a very dark print.
> Is there a simple step by step way of doing this that would 
> at least get me to a reasonable starting point? 
> 
> I realise I might be missing something obvious (it has been 
> known) but all and any help would be appreciated.
>