QTR-Quadtone RIP

Hi Eric,

Don't worry -- it takes a while to grasp it all.

On Tuesday, September 27, 2005, at 01:39  PM, Eric Ashworth wrote:

> Thanks Roy & Olivier,
>
> Little by little I think I'm getting this and am close to grasping the  
> big picture.
>
> Roy, I read through the entire thread that you had linked to and it  
> cleared up quite a bit for me. However, I'm hoping you can answer a  
> couple questions, as I'm still a little fuzzy on a few details. If I  
> understand clearly what I've read, then there have been two main  
> workflows ending with QTR.
>
> The first (and apparently outdated?) process, completely bypassed any  
> color management system and sent the file straight to QTR sans  
> conversion, as per the printing instructions in the tutorial. So, the  
> calibration & characterization/profiling of any ink/paper set were  
> being combined in the QTR curves. And, any particular bumps in the  
> output were taken care of by further manipulating the curves or  
> through correction layers or some similar tactic.

The original was pretty good -- linearization fixes bumps and  
weirdnesses.  The screen wouldn't exactly match but with
some practice you could get-it-right on the screen and then have a  
fairly dependable set of tweaks to get-it-right on the print.

>
> Now however, it appears that the linearization is only meant to  
> calibrate the output and any characterization/profiling is being done  
> via QTR-Create-ICC, essentially leading to the same type of process as  
> a color managed workflow.

Yes.

>
> While I can't find the quote, I recently read something regarding  
> color management that stated, ideally calibration and linearization  
> would be all that was needed to color manage a device, but since there  
> are still irregularities in the output, profiling is necessary.

It's not so much correcting irregularities as it's getting the color  
management system involved.  Without the CMS 50% gray has
a different meaning whether you are in GG 1.8, GG 2.2, Adobe RGB, sRGB  
...   Every possible imbedded profile gives a
different meaning for all the values.

>
> If the above statement is true, then am I right in coming to the  
> conclusion that using profiles in addition to the QTR curves is  
> optional, as long as one is willing to tweak their linearization  
> curves or use corrective layers in order to get their desired output?

It possible to pick ONE profile space and tweak the curves so that  
profile space prints correctly.  This is how most workflows
actually work.  E.g Roark's curves, the old Piezo plugin all are good  
systems as long as you are careful to use exactly the
correct work spaces everywhere.  The QTR linearizing without ICC  
profiles is probably more accurate than most print drivers
without profiles.  But the profiles -- even just the generic Gray Matte  
Paper -- are very helpful in matching the image's embedded
profiles.

>
> Also, if working with profiles, since the calibration is largely  
> dependent on the particular paper being used, would one have to create  
> a set of QTR curves for each paper as well as create a profile or in  
> the case of differing tonal output, multiple profiles per paper?

Ideally you ought to have a profile for each particular setup you are  
going to use.  Potentially there are an awful lot of curves
and profiles.  But I think one should narrow it down to a few that you  
like the best and stick to them and become familiar
with nuances that are only visible with real prints under real viewing  
conditions.  CMS is not a substitute for critical viewing
and critical image editing.

>
> What exactly is the target performance that is desired, when  
> linearizing your output, re: the "ideal" densities? Am I correct in  
> assuming that the densities are meant to correspond to the human  
> visual response to changes in value, or are they more an arbitrary  
> division of densities based on mathematical/mechanical efficiency?

The "ideal" densities are straight lines if you convert to Lab  
Luminosity units.  If you go from L=16 to L=96 the steps
are supposed to in a straight line.  Lab units correspond to human  
vision so they make a lot of sense for getting
good tonal separation throughout the scale.  In a sense this is the  
tonal description of the QTR ICC profile.  But
none of the idealized grayspaces correspond to this so leaving the  
conversion to the CMS using Perceptual Intent
makes the most sense.

Roy

>
> Thanks again in advance,
>
> Eric
> www.ericashworth.net
>
>
>
> On Sep 26, 2005, at 7:56 PM, Roy Harrington wrote:
>
> --- In QuadtoneRIP@yahoogroups.com, Roy Harrington <roy@h...> wrote:
> > On another group I wrote a fair amount about the linearization, icc
> > profiling, etc.
> > I'm not sure I addressed all you questions but I think it will help a
> > lot.
> >
> > See:
> >  
> http://groups.yahoo.com/group/DigitalBlackandWhiteThePrint/message/ 
> 68052
> >
> > Roy
> >
>
> I decided to load the info into the Files section of this group.
>
> See:   ICC Info.txt
>
> Roy
>
>
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-
Roy Harrington
roy@harrington.com
Black & White Photo Gallery
http://www.harrington.com