Digital BW, The Print

Cross-posted from the Piezo list:

Yesterday I had a chance to try Peter Baumbach's adjustment curve for 
PiezoTone Warm Neutral inks (original black), printing on Hahnemuhle 
Photo Rag and the Piezo 6 driver on an 1160 with a Nomorecarts CIS.

Along with Siobhan, we had both seen a tonal imbalance, with the 
lighter midtones (magenta position) poorly melding with the lower 
mids (cyan position). The problem was clearly visible on the 21 step 
ramp (as visible "steps" in the smooth ramp) and in images, where it 
is seen as a coarse graininess in the 80-50% range where the two inks 
presumably overlap. It was not responsive to gamma or ink density 
adjustments. My suspicion was that the the magenta position ink was 
too light and/or the cyan position ink was too dark. Ominously, this 
recalled the tonal shifts that plagued the original Piezo inks (the 
DDS, or "greenies" problems) in a less severe manner.

Peter's curves smoothed out the tonal transitions nicely, indicating 
that whether this is a bad profile problem or not, it can be 
addressed by adding a correction curve. In effect, Peter's adjustment 
lightens and increases the "slope" in the "cyan" portion of the curve 
(85-60%), and darkens the tones above 50%. There is a "kink" in the 
curve at around 50%.
In my set-up, I had to increase the severity of both displacements to 
get both local smoothness and overall light/dark balance to get a 
good match to the screen. While the curve corrects the tonal shift, 
the overlaid gray inks in the lower midtones still appear "dotty" or 
grainy.

My set-up may have needed the stronger correction because the inks 
were installed shortly before the concern for the warm-fade of the 
PiezoTone K ink. I have used it only for occasional proofing since, 
while waiting for the (still back-ordered) Museum Black. My concern 
is that there may be some "settling-out" of the gray tone pigments in 
the liquid if it stands for extended periods.

Although several have posted on the Piezolist, there has been no 
response from ConeTech/IJM that I am aware of. I have checked to see 
if there were newer profiles at the IJM website, but the Piezo update 
page link no longer works. I will print some tests and send them up 
to Vermont this weekend.

For the moment, I am swirling the bottles and printing purge patterns 
daily in hope of seeing improvement.

-Bruce



Peter wrote:

>Siobhan,
>
>I am not shure if we are talking about the same thing but I also notice an
>abrupt shift in the 50% to 80% tonal range with PiezoTone Warm Neutral inks.
>I noticed it especially with skin tones. The transitions from the lighter to
>the darker skin tones looked rather clumpsy. I would call it posterization.
>Some time ago I posted it here entitled "grain drives piezotone mad" because
>I first thought it was an interference effect between grainy negatives and
>the piezo driver. But meanwhile I am quite shure that the grain only
>pronounces the effect and that the piezo profiles may not be perfect for the
>new ink. I sent examples to Cone Tech support but do have a solution until
>now.
>
>In order to find a practical solution I printed the 21-step image, measured
>the densities of each step and calculated a correction curve that linearizes
>the output. I apply this correction curve in PS just before I print with
>Piezo and this way the bad looking effect is gone.
>
>Peter
>
>
>Siobhan wrote
>-----------------------------------------------
>Bruce,
>You have gotten way too technical for me but in reply to paragraph 1, I have
>been seeing "dots"  in the lower mid-tones.  The shift in the tonal range is
>more abrupt.  Awaiting the solution. Cheers.  Siobhan
>on 11/13/02 7:27 PM, Bruce Kinch at pvx@... wrote:
>


-- 
Bruce C. Kinch
Associate Professor of Photography
The Art Institute of Boston at Lesley University