[Openicc] ALL YOU NEED IS A PROFILE, THE MYTH... linearization / G7

[Hal V. Engel]

On Thursday 17 January 2008 11:23:43 Jan-Peter Homann wrote:
> hello list,
> I agree with edmund, that good linearization is the most important basis
> for good results in printing.
> As in a former mail, i strongly recommend to look at G7-process from
> IDEAlliance / GRACoL as target values and method for linearization. 

I had a quick look at this after Jan-Peter's last email.  It was interesting 
and they actually have a manual method using graph paper and a set of 
measurements of their calibration target taken with a spectrophotometer for 
calculating a set of linearization corrections.  Documentation of the method 
this including the linearization target and the graph paper tempates can be 
downloaded for free (see http://www.gracol.org/resources/).  They also have 
an application that takes these measurements and does all of the calculations 
and spits out the results for a either a specific RIP or generic curve 
corrections.  You have to be a member to download the software so it is not 
free and I suspect it only runs on Windows and/or the Mac in anycase.  

I suspect that it would be possible to figure out the algorithms they are 
using by digging into the materials needed for the manual method and that 
this could be used as a basis for writing an open source application that has 
the same functionality as their members only app.  In addition I think it 
would be possible to directly integrate this into the GutenPrint back end to 
make all of this accessable to GutenPrint users with a spectrophotometer as 
well as the GutenPrint developers. 


> This 
> will lead to a gradation and gray balance which is very similar to SWOP
> TR001, GRACoL2006coated and ISOcoated_v2/FOGRA39 the worldwide most
> important standards for CMYK-data.
>
> for sRGB-data standard settings, it would be possible to use a
> standard-conversion sRGB->SWOPTR001 or littlebit better
> sRGB->GRACoLcoated without the need for individual printer profiles

This would take care of the "I just want it to work" users.

>
> For the  CMYK-data standard-settings it would be possible to deliver a
> standard conversion e.g. SWOP->SWOP_GCR only for applying GCR and
> Inklimit without changing the color appearance.
>
> Combined with tools for optimal (re)-linearization based on G7, we could
> handle the most important steps for predictable color in printing
> without the need of dozens of profiles for differnt papers. Tools for
> (re)-linearization should also include procedures for checking the
> actual linerization (by comparison to a printers sample or masuring with
> a i1 spectrophotometer)

I would say any spectrophotometer that is supported by open source libraries.  
This gives users more options for what device they use.  In addition the 
number of patches that need to be measured for this process is fairly small 
so even a spot reading device would work for this process.

>
> ON TOP of (re)-linearized system we can talk about standard printer
> profiles for different types of paper and the possibility to integrate
> individual printer profiles.

This would be OK for most users and most printers.  Looking at their specs it 
calls for a minimum L* of 15 to 18.97 depending on paper type for the K 
channel.  For many printers this is fine but for some printers like the Epson 
R2400 values as low as 3 are possible and even the current default setup for 
GutenPrint gets a min K channel of around 12 on glossy paper.  In other words 
some of our printers can have significantly more dynamic range than this 
standard calls for.  This means that the generic process would need to be 
augmented for some very high performance printers.  I don't see any issues 
doing this as long as this is taken into account when something like this is 
implemented.

Hal

>
> Regards
> Jan-Peter
>
> edmund ronald wrote:
> > I think I need to put out a new topic explaining why PROFILES COME LAST.
> >
> > Profiles allow softproofing on screen. They allow simulation. They
> > allow gamut mapping. BUT THEY COME LAST.
> >
> > The inkjet industry has been exposing "visible" profiles because they
> > allow the above (softproofing, simulation, gamut mapping) when used
> > with Photoshop. However in practice, the profile will only get decent
> > results if the press or inkjet driver are already pretty well tuned to
> > put down the right amount of ink on paper.
> >
> > The inkjet native drivers do this, in a "secret" way. Which is why
> > using third party papers or inks is complicated. No surprise here,
> > inkjet manufacturers make their profit from paper and ink sales.
> >
> > What the inkjet guys and RIP resellers really guarantee in exchange of
> > their excessive profits is perfect stability. A print run today and in
> > one year with new inks, a new batch of paper,  and maybe with a
> > different OS and maybe with a PC instead of a Mac, and maybe even a
> > new printer of the same brand and model etc etc will usually still
> > yield results that are usably close. This is why canned profiles are
> > useful, why third party profiling makes sense, and why end-users don't
> > need spectros.
> >
> > Before open-source people start to worry their heads about profiles
> > they should first turn their attention to obtaing the same degree of
> > cross-platform cross-application and time-invariant stability
> > guaranteed by the native printer drivers.
> >
> > PROFILES COME LAST, folks, really..Just like Gutenprint is already
> > pretty useful, Argyll is also very good; Lots of people own spectros,
> > and they're getting cheaper. Profiles themselves are easy to make.
> > Creyating the preconditions for a good profile is hard.
> >
> > 1. If your printer drivers have a block the shadows or have an
> > insufficient gamut because of bad linearisation, color consultants
> > will advise users to use native drivers because  it's very hard to
> > compensate for bad linearisation.
> >
> > 2. If your system keeps varying its output each time you update then
> > your end-users will get VERY unhappy and will ditch your apps presto.
> >
> > In summary: Profiles are the last link in the printing chain, and
> > probably the most trivial step for well-equipped domain experts to
> > achieve, even if this appears counter-intuitive to programmers.
> >
> > Edmund
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