Re: Dot Gain mathematical Formula
Re: Dot Gain mathematical Formula
- Subject: Re: Dot Gain mathematical Formula
- From: Terry Wyse <email@hidden>
- Date: Wed, 30 Mar 2005 16:50:14 -0500
Hi Steve,
As far as the formula for calculating dot gain, you simply need the
Murray-Davies formula. This will allow you to figure dot gain from
density. There's also a unique way to find approximate dot gain using
XYZ and Lab data. You can find all this at Bruce Lindbloom's web site
(http://www.brucelindbloom.com). Go to his MATH page and you'll find
everything you need.
But my guess is that you can already measure dot gain but that what
you're looking for is a method to arrive at a dot gain compensation
based on ACTUAL press behavior vs. some sort of target or desired
behavior. Most prepress systems have this capability already. For
example, Rampage uses these exact terms for press gain compensation;
Actual press behavior/dot gain and Desired dot gain. It will then do
the math and put the right dots on plates to achieve this. Your Xitron
RIP has the same thing using only slightly different terminology. Most
systems will either give you a two curve option (actual/desired) or
simply give you a single tone curve compensation that would amount to
+/- dot from a linear condition. Actually, your Xitron RIP has BOTH
options, your choice on which one to use.
The TRICK is knowing what the desired or target condition should be.
You could use "SWOP" or "GRACoL" as a guideline or something else. But
the catch is that most specs are only at the 50% dot and not for the
complete tone curve. To complicate matters, a press printing at the
"proper" dot gain spec will/should not have linear or balanced
behavior. By "balanced" I mean a certain amount of gain at the 50% with
equal but less gain at both the 25% and 75% aimpoints. No, a press
will/should have a bit more 1/4 tone gain relative to the 3/4 tone but
you won't find a specification for this anywhere AFAIK. For my own
press profiling work, I've analyzed typical press behavior and have my
own adjustments that I apply to 1/4, mid and 3/4 tones from which I
then derive a smooth curve. This is sort of the "magic decoder ring" if
you will. And even armed with this information, it still comes down to
charts and graphs to get from the press acutal to the desired behavior
if the RIP doesn't do this for you.
Cheers,
Terry
On Mar 28, 2005, at 2:42 PM, Steve Lehning wrote:
Does anyone out there know of the Dot Gain Mathmatical
Formula to figure out a Dot gain curve setting for
plates. I had someone tell me what it was at one time
and I lost the paper work when we recently moved to
our new facility. When you run out the linear plates
and take readings, there is a math forumula you
applied to it to give you your plate curves you plug
into your output device. Xitron and Trendsetter in our
case.
_____________________________
WyseConsul
Color Management Consulting
email@hidden
704.843.0858
http://www.colormanagementgroup.com
http://www.wyseconsul.com (coming soon)
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