[Openicc] Fwd: A New Topic!

[edmund ronald]

I think this proposal is sufficiently interesting that some of the
members of *this* list might wish to contact the author.
Please forgive me for forwarding it here.

Edmund

---------- Forwarded message ----------
From: Mark Rice <markrice at comcast.net>
Date: Feb 6, 2008 9:22 PM
Subject: A New Topic!
To: colorsync-users at lists.apple.com


I am a fan of color management, but I have one major problem in dealing with
in the context of most inkjet printers: most inkjet RIPS are not consistent
or repeatable in calibration procedure. That flaw means that color
management is larger doomed on these RIPS for exacting users. My experience
came from the photographic digital imaging field, where extreme precision is
a must. All photographic photo printers and film recorders use "iterative
linearization" to obtain precisely controlled grayscales that match target
densities very precisely. I have been begging RIP makers Onyx and SAI to
produce such a RIP, but they don't really see the need for it. My problem is
that if one achieves a linearization that is close, but not dead on, one can
re-linearize, but it is just as likely to make the linearization worse as
better. And, of course, if the linearization changes, the ICC profiles
become nearly useless.
[>]
Here is my proposal for an Iterative Linearization RIP:

"Procedures for an Iterative Linearization RIP for Inkjet
        Copyright Mark Rice 2007
This is a theory derived from working with photo equipment such as the Kodak
LVT, Durst Lambda, and Oce Lightjet.
1. Print test chart similar to existing Ink Limit chart.
2. Measure each value densitometrically until D-Max is achieved in each
color. Or, D-Max may be limited arbitrarily to assure that a similar value
can be achieved under all conditions of humidity, temperature, etc.
Comparable to process deviation in photo equipment.
3. Build a series of aim points from D-min to D-max based on some form of
theory - photo devices usually use L-Star RGB or "equal brightness" RGB for
good viewing discrimination. Aim points should be in a text or XML file for
editability and should be high precision values-up to four decimal points of
density. D-Min and D-Max may need to be edited in particular for
repeatability, and that often entails adjusting nearby points for evenness.
4. Discuss what cross color ink limitations should be.
5. Print the 4 or 6 or N-color grayscale, all colors combined to include
crosstalk characteristics. Present software doesn't seem to adjust for
crosstalk, except for ICC profiling.
6. Read the resulting gray scale into appropriate software. Compare
Difference of read values with aim points. Use an algorithm to move toward
aim points. LVT and Lambda use a different algorithm for initial reading
than subsequent readings.
7. Perform step 6 again, but with a new grayscale incorporating the
adjustments from step seven. A new algorithm that steps more "lightly"
toward the aim points is needed to avoid overshooting and "chasing its
tail".
8. Repeat until a minimum established variance from Difference is achieved.
(It can't aim for dead on or it will keep trying forever.)
9. Prepare the ICC profile.

This procedure will produce highly repeatable results that also will match
one machine and RIP to another with great accuracy. Presently I have this
problem: I may get close to a good linearization, and attempt to improve it,
but it may get worse instead of better. There is no possibility of improving
on an old linearization. If a filter is used, all the value of an ICC
profile is lost.
It also potentially allows one manufacturer's RIP profiles to be converted
to another manufacturer's profiles, a big problem in the industry at this
time.
Mark Rice Wednesday, February 06, 2008"

Comments, please!

Mark Rice

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