Digital BW, The Print

dfaprinting wrote:

> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Danny
> Culbertson" <danculb@b...> wrote:
> > 12 heads can't be far away...
>
> Roland, and maybe a Mimaki or two (older), and I believe there were
> using the same heads as the Epson 9500 (could be wrong), just had
> four sets. There was an early Colorspan that used 12 HP/Encad type
> heads that had hardware configuration for the colors, so you didn't
> need a horribly expensive RIP to drive it.
>
> Now how many shades of black do we really need?


Well, think about it. For example, think how BO works. For black, you 
get full coverage (that is, the ink dots overlap) of the substrate. As 
the image tones get lighter, you get less coverage (the ink dots spread 
out) so the tone is a mix of the color of the substrate ("paper-white") 
and the black ink. As the tones continue to lighten, you get more 
spacing between the ink dots and thus more paper-white and less ink 
coverage. As some point the spacing between the ink dots becomes visible 
to the naked eye and the tone becomes "grainy." Finally you get to the 
point where there is little to no ink (white).

If you now try two inks, you get something different. The dark ink goes 
from full coverage to partial coverage, but not to zero coverage. The 
ink dots are closer together and there is less paper-white showing 
through. The ink dots are not spaced as far apart as with BO because at 
some point in the tonality, there is a cross over and the lighter ink 
takes over. The key here is, at this cross over point, is that for the 
same tone, the dark ink has less coverage and the lighter ink has more. 
That is, you see less paper-white showing through, and the average 
distance between ink dots becomes smaller because you are now using two 
inks..

As you go up in the number of inks you use, you successively increase 
the amount of ink coverage for any given tone, and decrease the amount 
of paper-white showing through, because you are decreasing the average 
distance between ink dots.

Two effects. First, your print becomes smoother due to the decrease in 
the distance between the ink dots. Second, the overall tone of the print 
becomes more consistent because there is greater ink coverage and less 
paper-white showing through.

So, how many shades of black do we really need? It's really a question 
of print quality - how smooth do you need your print, and how consistent 
in color?

All other things being equal, I suspect you can make an acceptable B&W 
print from three dilutions of black ink. I think that four inks will 
show an improvement over three. Many people have experimented with six 
or seven inks and found an improvement over quadtones. Indeed, Cone is 
starting to roll out a new heptone inkset. Where is the point of 
diminishing returns? I have no idea. Maybe someone will take one of 
these 12 channel Rolands and experiment for a while and find out...
--
Bruce Watson