[Openicc] Fwd: A New Topic!.. printer calibration

[Jan-Peter Homann]

Hello list, hello Edmund and roland
The G7 calibration method, I have discussed in earlier mails in the 
oppenICC list is exactly targeting the needs of a defined gradation and 
CMY-gray balance for calibration. G7 could be implemented into GutenPrint.

Another possibility would be to use the iterative optimization from 
Argyll to create a 4D calibration. Such strategies are used mainly in 
High-End Proofing solutions from e.g. CGS, GMG, ColorGATE 5 and others.
The idea is, that sending CMYK-values to the output device will lead 
exactly to defined L*a*b* values for the paper/ink combination.

Normaly such L*a*b* target values are created after basic Inklimit and 
linearization for the paper/ink combination.
In the colormanagement chain, we would have
- Input-profile
- destination-profile
- calibration devicelink

Regards
Jan-Peter




edmund ronald wrote:
> 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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