Digital BW, The Print

On 08/07/2011 04:42 PM, Paul wrote:

>
> The dogma is that the more channels of gray ink we have printing, the
> smoother the final print.  This dogma is probably a good starting
> point, but my experience is that not only is it characterized by
> decreasing marginal utility, but more may actually be worse in some
> situations.
>
> With the Epson 1800 and Eboni, in the experiments that ultimately
> lead to the "3-MK" workflow with 3 full strength Eboni channels, I
> tried all sorts of different numbers of channels of that ink.  For
> that printer and approach, the smoothest was about 3.5 channels.
> That is, while subsequent experience found that a minority of the
> 1800 printers needed 4 to be smooth, mine was about equal between 3
> and 4, and less smooth above that.  While the final decision to go
> with a 3-MK approach obviously was influenced by that number also
> allowing color to be installed, I found that more channels did not
> necessarily result in smoother prints, at least with that type of
> arrangement.

> Similarly, with a good 1400 and using a channel that does not band
> (not all channels are equal on mine), a single black only can be
> smoother than  the 1800 3-MK workflow.

At the time when BO printing was first discussed I mentioned the use of 
more channels for black ink to even out banding issues. There would be 
cons and pros I wrote then. With the same inks used over more channels 
the droplet size is forced to the minimum size and addressing of minimum 
droplet sizes usually is not as good as larger drop sizes. On the 
highest printer resolutions the minimum droplet size is already used but 
I still wonder about the black channel though, it is much more difficult 
to achieve a good Dmax with many minimum sized droplets than with fewer 
bigger droplets. The use of minimum droplet sizes may show small 
differences between head qualities faster. Then there is the dotgain 
that should be more inconsistent with smaller droplets compared to 
bigger ones (humidity, coating differences). Few manufacturer solutions 
use the same ink on two channels but on the Canon iPF500 (510,610 etc) 
model there are two MK channels used to get a higher density and the 
droplet size is the standard 4 picoliter of all the iPF models. In that 
case the droplet placement is still in Canon hands and could have been 
optimised for that combination. Which is a thing I mentioned in the 
past, is the weaving of a color printer optimal for a B&W printer?  Is 
noise created in a kind of aliasing of smaller droplets/dots to larger 
irregular dots as a result of unsuitable weaving, droplet addressing 
issues and more dotgain?

The question is whether the photo quality printers use more consistent 
heads than the workforce models starting from the same minimum droplet 
size. In most custom made solutions the highest resolution is used so 
the droplet variation does not come into use but I wonder if there is 
also a difference there too between the printer classes. In the Epson 
dry Minilab technology I recall a droplet variation of 5 or 6 droplet 
sizes and I can only guess that the minimum must be near 1 picoliter for 
a satisfying 4x6 quality. Single array heads that do not move and few 
choices of media so the platen gap/droplet addressing can be kept as 
optimal as possible. Maybe the droplets sizes are divided to two heads 
placed after another in the paper path.

> At least with the use of multiple high density inks, as in the 3-MK
> approach, it appears that once enough are employed to hide the
> banding, the use of more channels begins to increase the noise in
> (roughness of) the print.  With scanning and digital exposures I'm
> accustomed to thinking that random noise is averaged out with
> multiple sampling.  With printing at least with the 1800 3-MK setup,
> however, noise appears to be additive.

There is no averaging to a single value done of variable readings like 
in scanner multi sampling but a correct tone value is divided over 
several nozzles with different qualities and the uncertainties mentioned 
above start to play a role. Banding can be solved with more channels up 
to a point where irregular dot shapes, inconstant dot sizes become worse 
than nice big round dots placed precisely.

> Note that this issue is where multiple channels are firing at the
> same time, not where they are used in a serial partitioning profile.
> But it does raise the issue of whether, using multiple overlapping
> channels will always lead to a smoother result.

The pros and cons still apply there, banding can be reduced by overlaps 
and irregular/inconstant dots made with different ink dilutions will not 
be as visible but stretched too much give a similar noise experience.

> Overall, there seem to be a lot of different issues that affect our
> printing, but it may be that more inks firing at the same time is not
> necessarily a good thing.  Noise, including possibly not only the
> dots but the dithering patterns, in our printing systems may, at
> least in some respects, be additive.
>
> Paul www.PaulRoark.com

Which hints at and sums up what I tried to describe.

-- 
Met vriendelijke groeten,   Ernst

Try: http://tech.groups.yahoo.com/group/Wide_Inkjet_Printers/

|      Dinkla Grafische Techniek      |
|         www.pigment-print.com        |
|                 ( unvollendet )                 |