Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Roger 
<user1@...> wrote:
>
> Paul,
> 
> I'm new to this users list, so here's a couple questions:
> 
> 1. What is BO printing?

"Black ink only" printing; some Epson drivers have this option, and 
some people printed B&W that way.  I use medium format Technical Pan 
film to get the very smoothest images, so that workflow never 
appealed to me -- until I found the small 1.5 picoliter drop of the 
R1800 could, if used in 3 channels, produce a very smooth print.  
Some still call that "BO" printing, although it's very different than 
how the term has usually been used.  The Eboni-6 approach is even 
further away from "BO" in that it uses dilute inks as well as the 
standard Eboni matte black.


> 2. On your chart, is the Y axis something like a difference from 
> expected value in db, or some other unit?

The Y axis shows the Lab A and B units.  Positive Lab A values 
indicate red (more of a magenta-red to me), and negative Lab A values 
indicate green.  Positive Lab B values are yellow, negative blue.

Someone with more color expertise than I will have to explain how the 
units were derived, but suffice it to say that the higher the 
absolute values, the stronger the color.  

At Lab A and B = 0, the print is technially neutral.  Visually and 
perceptually, I think that is usually true also.  However, I think we 
usually want a positive Lab A to avoid a greenish look.  I'm not sure 
why we prefer that, but a slightly elevated Lab A was typical of the 
selenium toned silver prints many of us favored.  Note that the paper 
manufacturers also seem to have opted for a slightly positive Lab A 
value.

Paul
www.PaulRoark.com


> pr_roark wrote:
> > 
> > 
> > 
> > I thought some might like to see a graph of the Lab A & B values 
that
> > I'm getting from a 21-step test strip printed with an R220 and the
> > Eboni-6 inkset on Premier Art Smooth BW paper. I've posted a Jpeg 
of
> > the Lab A & B graph, as well as small samples from 1600 dpi scans 
to
> > compare smoothness.
> > 
> > See http://www.paulroark.com/BW-Info/220-Eb6-PA-BW-Lab.jpg 
> > <http://www.paulroark.com/BW-Info/220-Eb6-PA-BW-Lab.jpg>
> > <http://www.paulroark.com/BW-Info/220-Eb6-PA-BW-Lab.jpg 
> > <http://www.paulroark.com/BW-Info/220-Eb6-PA-BW-Lab.jpg>>
> > 
> > The base for dilution here was 35% glycerin, 55% distilled water 
and 10%
> > Kodak Photo Flo.
> > 
> > Home darkroom work might take an interesting twist here. Just 
like the
> > developer days, different mixes cause different reactions to the 
tone of
> > the print -- with pure carbon and just these safe, readily 
available
> > substances. One tradeoff is also smoothness v. tone. There are
> > interesing variables here that allow the tuning of a 100% carbon 
inkset
> > to a particular paper for a particular tone and printer.
> > 
> > Paul
> > 
> > www.PaulRoark.com <http://www.PaulRoark.com 
<http://www.PaulRoark.com>>
> > 
> > [Non-text portions of this message have been removed]
> > 
> >
>