Re: New Topic
Re: New Topic
- Subject: Re: New Topic
- From: Dan Reid <email@hidden>
- Date: Thu, 07 Feb 2008 17:41:48 -0700
- Thread-topic: New Topic
on 2/7/08 11:27 AM, Mark Rice at email@hidden wrote:
> 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.
>
Hi Mark,
There are many ways to achieve this with current RIP products. I have
been teaching this type of grayscale (lin) balancing for years. It's
possible, I do it all the time. Yes some RIP manufacturers are more clueless
than others in how to do this with their products, but that's why I get paid
the big bucks. ;-)
I teach graybalance lin using ColorPort and ColorShop X ( or ColorThink
). It's really not that difficult once you understand how each RIP product
behaves with the lin. You shouldn't be too concerned with shadows (darker
than 3/4 tones) as the eye is not sensitive to this area of the tonal scale.
You can successful graybalance down to the 3/4 tones without much
difficulty, but figuring how to do it with your RIP (which RIP are you
using?) is key as each have a different method of implementation. Obviously
some easier/better than others.
In terms of relin, yeah most RIPs are not very good at hitting the same
targets time and time again. Only a few can do it in the proofing world with
measurable success. BUT, if you have automated spectro it ain't that big of
deal to make a new profile if you are really SEEING a difference. Remember
trust your eyes. . . . . . .
BTW, density and D/Max is so 20th century thinking and totally
inappropriate for inkjets. And if you are going to talk about density at
least clarify by stating Status A (photo), Status E (Europe), of Status T
(US).
Step into the 21st century of the LAB color model (D50 2degree) ;-)
PS, Onyx has a graybalance feature built into their linearization process. .
....
--
Dan B. Reid
RPimaging, INC
Color Management Products and Training for Print, Internet, and Motion
Graphics
http://www.rpimaging.com | Toll Free: (866) RGB-CMYK
>
> -----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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