New Topic
New Topic
- Subject: New Topic
- From: "Mark Rice" <email@hidden>
- Date: Thu, 7 Feb 2008 13:27:23 -0500
To create a neutral gray on an inkjet printer, one would have to choose the
correct UCR or GCR specs before linearization takes place - and that is what
I am advocating. Most RIP manufacturers leave the separation choice to the
last step - creating an ICC profile. If one made the choice early in the
process, it would account for crosstalk between the inks, and be much more
likely to provide a neutral gray scale. In addition, most RIP makers simply
linearize the individual colors up to an arbitrarily determined ink
limitation, thus ensuring that the darker portions of the grayscale will not
be neutral. I believe that linearization should account for the full
grayscale, not just the linearization of each color indepentenly. Inkjets do
not have to have a green cast in the shadows -it simply occurs because of
the hokey method the RIP makers have used for linearization.
Mark
-----Original Message-----
From: Lorenzo Ridolfi [mailto:email@hidden]
Sent: Wednesday, February 06, 2008 4:54 PM
To: Mark Rice
Subject: Re: A New Topic!
Hi Mark,
Ok. I'm not familiar with Lambda or Lightjet but did you look at G7
calibration method (www.gracol.com) ? Is a method to calibrate the gray
scale of an CMYK offset printer and it can be used in other
technologies, too. I'm starting to use it in inkjets. The challenge in
inkjets are a (known) green cast in CMY colors and a big color cast in
the black ink, too.
Best regards,
Lorenzo
Mark Rice wrote:
> Not iterative linearization. The RIP for Lambda or Lightjet can produce a
> grayscale that is targeted at specific density aim points, so the aim
points
> on one machine are identical to the aim points on another machine.
Besides,
> the GMG price is astronomical. There is not reason Onyx or SAI couldn't
> emulate Lamda Dice RIP. I tried to get the coder for the Lambda RIP to
> produce something for inkjet, but no luck.
>
> Mark
>
> -----Original Message-----
> From: Lorenzo Ridolfi [mailto:email@hidden]
> Sent: Wednesday, February 06, 2008 3:44 PM
> To: Mark Rice
> Subject: Re: A New Topic!
>
> Hi Mark,
> Did you try GMG? It has iterative features ...
>
> Best regards,
> Lorenzo
>
> Mark Rice wrote:
>
>> 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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