Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Loris Medici"
<lorism@t...> wrote:
SNIP
> 2) Low CYAN usage [It seems that the Randall curves/Epson driver
> combination substites CYAN with BLACK and this makes a negative
> influence on hue/chromacity I think]
SNIP

Jeff Randall wrote:

>  Yes, the black kicks in soon after the cyan position ink
>(dark gray) starts. This is driven by the reflective density on the
>paper of the cyan position ink and the Epson driver controlling the
>black ink.  ...

The Epson driver looks at the three RGB curves and starts the black when the
three of them together add up to some combined volume of ink.  To avoid the
black ink from coming in too soon, some prefer to use the lightest gray
(usually blue curve, yellow position ink) as an indirect switch for the
black ink.  For this approach, the blue curve is pulled down sharply in the
highlights, as usual.  However, once the darker gray inks are flowing the
blue curve is pulled back up.  So, there is a reverse curve for a while.
Some curves pull the blue curve almost to the top of the graph.  You
ultimately have to pull the blue curve back down to "turn on" the black ink.
The curve ends up looking like a radical roller coaster.

The same can be done with the magenta to a lesser extent, although the need
for this is questionable.

What this roller-coaster blue curve allows is the cyan ink to be virtually
full-on before the black ink is needed.  This usually hides the dots better
and keeps the tone of the cyan ink predominant through the entire midtone
section of the print.

The bad news of this approach is that the more radical curves are, I
believe, more sensitive to printer variations.

At any rate, how the curves are drawn significantly affects when the black
ink will be pulled into the mix.

Paul
http://www.PaulRoark.com