Re: rafe b-generations inks

[Dan Culbertson <danculb@concentric.net>]

Michael Greer wrote:
>But Jerry, that still doesn't answer why this is occuring. Jim said he gets a
>very black black at 95, but not at 100. I understand that the orginal black is
>very dark charcoal gray. Therefore, the 100% black not being really black
>makes
>sense. But why is a very black black being realized at 95% with the same ink
>set? Does the mixing of some of the CYM inks at 95% make the result a blacker
>black than the 100% black?

In a 255/255/255 to 0/0/0 RGB gradient (or 100/100/100 to 0/0/0 in the RGB
percentage range) the Epson driver starts to replace black ink with CMY
blends at about 96% or so and by 80 % to 70% (depending on the chosen media
selection) there is no little, if any, black ink in the blend.  Makes for
nice smooth (but distincly not neutral) light tonal areas in the print.  If
the black is significantly weaker than the Epson black this CMY undercolor
addition will indeed make a darker black in the lighter dark tones.  This
explains Rafe's problem with the RGB driver and the only solution I can see
is the blacker black ink substitution or adjusting the overall RGB curve at
print time to try and defeat it (a rather difficult prospect since it is
somewhat of a blind operation even with a good RGB profile viewer).

This doesn't, however,  explain why Jim is getting lighter K in 100%
patches of a CMYK file where the K is specified to the printer free of CMY
undercolors.  I have seen this phenomenum on some gelatin papers where the
heavier ink amounts excessively wet the gelatin and are fully absorbed
beneath it while the lighter inks seem to stay closer to the top (or at
least that is my guess as what is happening).  The cure for that problem
(which may be mostly a CMYK/RIP problem, and especially a PressReady
unlimited black ink curve problem) seems to be simply limiting the inks to
the amount the paper can hold.  But with a weak K ink you may still need to
manually add CMY undercolors to pick up the dark tones and that may send
you back the too much ink problem .

Another problem (seen mostly on films like Konica QP) is that heavy ink
coverage in dark areas creates a metalic blush which visually destroys the
appearance of a deep black when seen at certain angles (though they may
actually measure blacker).  Never found a solution for that one other than
to avoid Konica QP for dark prints.  Best bet is get a paper/ink/driver
combination that work well together and that may take some experimenting.

Dan Culbertson




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