Re: New Topic
Re: New Topic
- Subject: Re: New Topic
- From: Chris Protopapas <email@hidden>
- Date: Thu, 7 Feb 2008 16:52:04 -0500
Having had some experience with LVTs and Lambdas myself, I can see
where you're coming from. On such a system, you live and die by your
linearization, because it's pretty much everything you've got, given
that profiling (if any) happens upstream.
My attitude towards CMYK inkjet RIPs is that they're something like
sausage factories -you don't really want to know what goes on in
them. From the point of view of an LVT veteran, it's not a pretty
picture. It's strictly geared towards getting an acceptable proof
that visually and/or colorimetrically matches SWOP or GRACol, or a
press condition. What goes on under the hood is best not examined too
closely. Those raw inks can be nasty...
Chris Protopapas
************
email@hidden
Fuel Digital Inc.
902 Broadway, 11th Floor
New York, NY 10010
P 212-564-4646 F 212-947-9984
www.fueldigitalinc.com
On Feb 7, 2008, at 3:03 PM, email@hidden
wrote:
From: "Mark Rice" <email@hidden>
Subject: Re: New Topic
To: <email@hidden>
Message-ID: <014001c869bb$23791dc0$6a6b5940$@net>
Content-Type: text/plain; charset="US-ASCII"
No, I am not having a laugh. I have used the LVT film recorder, the
Durst
Lambda, and the Oce Lightjet. All can deliver precisely calibrated
grayscales for months on end, even though the chemical developing
process
may drift. Each value of the gray scale has target densities in the
computer, and the output densities are extremely close to the target
densities.
The Onyx and SAI RIPS, the two most prevalent DO NOT even have any
target
densities. The curve shape is recalculated by some form of internal
algorithm (an unknown one that the manufacturers will not release),
and is
recalculated each time a re-linearization is done. What the the
calculation
based on? Simply ink density limitations, which are selected by eye, by
guess or by golly, by each user. This is the crudest possible process
I can
imagine.
To see what a "re-linearization" provides on the average RIP, try
this: take
an RGB grayscale and print it in the RIP after linearization has been
done,
but before the ICC profile is generated. Everyone I have seen is
ridiculously bad. The reason is the each channel is "linearized"
independently, based on ink limitations chosen via the crude method
shown
above. This process is NOT repeatable!
Martin, I did not copyright the process - I simply copyrighted the
article I
wrote.
Graeme - you raise some good points.
1. The process does not require inversion, even if the device
behavior is
complicated. It simply uses an algorithm that I will compare to herding
sheep - one creates a set of target aim densities, and the iterative
process
"herds" the device behavior in that direction. As I mentioned, the
iterative
process has to be changed as the targets are more closely approached,
or it
will overshoot the target.
2. Again, I have to mention that the starting point for calibration is
critical, and is done in a very haphazard fashion in most RIPS - the
"eyeball" choosing of ink limitations. There is not method of
determining
what set of ink limitations produces neutral values on paper.
My frustration is showing because of this problem - I get a
calibration that
is nearly neutral, and nearly color appropriate (I was going to say
"accurate", but I knew that would stir up another argument), and when
I try
to make it better, it is much more likely to get worse.
Mark
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