Re: Final Thoughts on TAC/ ink limits
Re: Final Thoughts on TAC/ ink limits
- Subject: Re: Final Thoughts on TAC/ ink limits
- From: Steve Upton <email@hidden>
- Date: Mon, 8 Oct 2001 09:50:56 -0700
At 10:17 AM -0600 10/8/01, William Barrett wrote:
> The correct TAC/ink limit is usually 400%. The printer expects to receive
that much ink, and it's does it's own ink limiting function along with a
bunch of other stuff. The actual ink limit of color lasers is quite low,
I forget exactly what it is, but it's around 200%. Building a color laser
profile with a 200% TAC will result in a profile with substantially
inferior performance than a profile using 400%TAC.
I am going to politely disagree with you on this. Each manufacturer
has their own special way of limiting TAC via hardware; depending on
the data sent to the controller, the limiting feature may or may not
be invoked. If you don't know when or at what point this occurs,
it's impossible to build a profile that accurately portrays the
characteristics of the device.
I would agree that every manufacturer has its own controls over TAC
but in every xerographic device I have worked with do far, that is
handled in a way that is all but invisible to the user.
Just like in an inkjet RIP, if you do your limiting in the RIP you do
not want or need to do any limiting in the profile. You want the
profile to have access to the full 0-400% coverage available from the
device (from the RIP-external perspective) otherwise you stand to
reduce the gamut of your output unnecessarily.
So I would have to say that the responses you have received are on
the money. From the profiling perspective - ie, how to setup the
software when building a profile - you should treat it as a 400%
coverage device.
If you are limiting TAC via a profile or via hardware makes no
difference, as long as it's only done once.
Exactly!
TAC is irrelevent for this purpose. It won't matter if you build the
profile with 200% TAC or 400% TAC. The on-screen simulation using this
profile will be the same.
What then is the difference between a simulation profile create for
a laser printer and a simulation profile created for a printing
press?
You mean other than one simulates a laser printer and the other
simulates the press? <g>
Why would we throw out the TAC/limits for a laser printer and not
one for a press? I can't agree that the TAC limit for a laser
printer is irrelevant. If you are trying to simulate *any* output
device, correct TAC/ink limits are necessary.
They are not irrelevant for rendering in either case. BUT if you are
looking at the profile solely for proofing purposes then it is
(typically) irrelevant.
Try it yourself. Build 3 different profiles for the same printer with
the same dataset. Use 200%, 300% and 400% TAC for each profile. Then
compare the proofing capabilities of the profile in Photoshop by
viewing a CMYK file through a proof setup for each profile while
keeping the "preserve color numbers" box checked. You will see that
they are all the same.
When most profiling applications build profiles they alter TAC for
the rendering (Lab->device) transforms but are set to proof 0-400%
coverage for the proofing(device->Lab) side. This makes sense for
print shops as they may not know how the CMYK they received was
generated but they still want to proof it using their press or
proofer profile.
I didn't get any worthwhile answers on an easy way to determine
TAC/ink limits (thanks for those who responded) but if I come up
with something easy, I'll share it with the group.
TAC testing is not typically that tough. There are several TAC test
charts running around (the next version of our remote profiling kit
will have one in it), or you can just make one yourself. Make a
gradient in Photoshop that goes from say 250-400% coverage. Posterize
it into 20 or more bands and then print it. Viewing with your eye or
reading with an instrument should show you where your blacks stop
getting blacker or where your ink starts puddling or your toner stops
sticking. Then you just pick the level just below the problem and
you're off.
Regards,
Steve Upton
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o Steve Upton CHROMiX
www.chromix.com
o (hueman)
866.CHROMiX
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