[argyllcms] Re: Accounting for dot gain in press simulation
- From: "Alastair M. Robinson" <profiling@xxxxxxxxxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 02 Mar 2011 09:31:24 +0000
Hi :)
On 02/03/11 05:19, Craig Ringer wrote:
Just prior to getting a half-decent profile from them I'd successfully
convinced them to run some swatch sheets off for me. I produced a very
rough profile from those using Argyll, but it had some weird abberations
and wasn't usable in production. I suspect the problem was that the
output was so far from what Argyll had expected that I had to turn the
spot read tolerance way up, so I probably also got bad reads accepted as
valid as a results.
Could also be that their duct settings were wacky, leading to
inconsistencies between columns of the test chart.
In any case, it seems they're not using sensor-feedback controlled ink
flow. They apparently prime the press setup with CIP3 data from the RIP,
but they play with the ink flow by hand as the press runs, using a
combination of manual solid colour densitometer (not spectro) readings
and "by eye" judgement.
That's what I wondered, and it's why I suggested putting photos on the
target sheet - old-school press operators will confer way more respect
upon a job that contains something they recognise as a real image, not
least because lousy looking photos are a tell-tale sign that they did a
poor job! They won't bother to tweak their duct settings if all that's
on the sheet is a mass of coloured squares, because no-one can tell by
eye how good a job they did!
By the way, a 60-70% tint of each colour in a band all the way across
the sheet (perpendicular to the sheet's direction of travel in the
press) is another useful trick - an uneven screen is another immediately
visible sign that duct settings were uneven. (I wouldn't be surprised
if a profiling chart "tracked" through a screen to some extent, though,
since the total ink coverage over the length of the sheet can change
abruptly from column to column.)
I'm trying to convince them to use greybar / colour bar
measurement-driven press control for our jobs now, but I'm not sure they
even have the sensors and software to do it.
It sounds to me as though you'll get better results with these guys
doing well what they know, rather than doing badly what's correct! The
hard part is getting them to devote the same time and effort to getting
the ink even on a profiling run as they do on production.
All the best
--
Alastair M. Robinson
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