QTR-Quadtone RIP

I regret to say that I seem to have been getting inconsistent results.
 I've double checked and rechecked them all and posted a revised
version of my histograms chart:

     http://www.ferdinand-paris.com/BPC-Qimage_V2.png

It seems that the only combination that causes a big dMax loss is the
one that you really want to work: Convert to custom in Qimage with BPC
(bottom left).

I fully appreciate that it is hard to find the problem when it only
happens when converting to a QTR custom profile in Qimage.  Is the
profile at fault or the Qimage CMS?  The fact that the Q-CMS handles
other profiles ok suggests the profile.  That PS handles the profile
ok suggests the Q-CMS.

I wish I could help.

F_P


--- In QuadtoneRIP@yahoogroups.com, "Roy Harrington" <roy@...> wrote:
>
> Thanks Ferdinand.  It's interesting to see how many different
> transformationsshow up.  Unfortunately solving it all seems to be
elusive.
>  The CMS of Qimage
> is done by yet another person, so it becomes very difficult to pin
down the
> problems.
> In fact even to agree on the existence of something wrong is hard.
> 
> The difference between my generic profiles and now custom profiles
is mostly
> an
> accident of the evolution of my understanding ICC profiles.  There
are two
> major formats
> for curves in ICCs -- one uses a "transfer function" and the other uses
> "lookup tables".
> The transfer functions are simpler and what I did first -- they have
one set
> of curve values
> and the same curve is used for both directions of a profile -- i.e.
K to L
> and L to K with the
> CMS doing the inversion.  I used this first and that's what the generics
> use.  Later on
> I used the lookup tables which allow lots of curves for different things
> ---each direction,
> each intent and full color as well.  This allowed softproofing with
the hue
> of the print.
> 
> So the custom ICCs use the tables and I have separate K to L curve
and L to
> K curve.
> L=0 in your file maps to K=100 to the driver, but in softproofing
K=100 maps
> back to L=dMax
> so you can see "Simulate Black Ink".  I think somehow the
softproofing curve
> is getting
> used during the print conversion but I haven't any idea where or
why. (maybe
> BPC isn't
> even the real issue).
> 
> You can actually see some of this and play with conversions using
Photoshop
> and softproofing.
> I think there are some free programs that you can download to graph the
> innards of ICC profiles.
> 
>    *  Ernst's point about the PS CM never being fully off is well taken,
>       but these are large changes.  All programs than can display the
>       histogram (e.g.  BreezeBrowser Pro), display the same dMax loss.
> I think you are safe if you look at histograms -- the info palette is ok
> ONLY for the native type
> of the file.  I.e. Don't look at RGB values for a grayscale, only
the K is
> valid for a grayscale.
> 
> Roy
> 
> On Dec 24, 2007 4:43 AM, ferdinand_paris <ferdinand_paris@...> wrote:
> 
> > CLARIFICATIONS:
> >
> > *  All conversions were perceptual (but see below).  CM_OFF was done
> > in PS.  Others were done in Qimage.
> > *  All conversions were to my newly created custom RGB profile.
> > *  Ernst's point about the PS CM never being fully off is well taken,
> > but these are large changes.  All programs than can display the
> > histogram (e.g.  BreezeBrowser Pro), display the same dMax loss.
> > *  I was using Qimage 2008.104 but have since upgraded to .109 (latest
> > - see below).
> > *  I tested Ernst's idea of using 8-bit input to Qimage to no avail -
> > same problem.
> > *  Since the initial QTR-related problems with the CMS in Qimage were
> > discovered in early 2006, I have generally followed Ernst's workflow:
> >  i.e. create a copy and do the CM in PS, and do all other printing
> > manipulations in Qimage with CM off.  But this partly defeats one
> > purpose in using Qimage, the ability to print from master files and
> > not have to create special versions just for printing.  It works for
> > colour, but not it seems for B&W.
> >
> > FURTHER RESULTS
> >
> > I upgraded to 2008.109 and one histogram changed.  The one with
> > profile conversion done in Qimage but no BPC ("CM On, BPC off in Q")
> > now looks exactly the same as the one done in Qimage *with* BPC ("CM
> > on, BPC on in Q").  Now in both cases the black point shifts from 1 to
> > 27 with an associated loss in dMax.
> >
> > This tests my sanity.  I am fairly sure that I used all perceptual
> > conversion when I produced those histograms.  But I can't now
> > replicate the middle histogram ("CM On, BPC off in Q") using *any* of
> > CM options in Qimage.  This suggests that something has change in
> > Qimage, but the revision log says nothing about any changes to the CM.
> >
> > I decided to push the tests a step further.  I also produced
> > histograms for conversions in Qimage to generic profiles.  Results
are at:
> >
> >  http://www.ferdinand-paris.com/BPC-Qimage_V2.png
> >
> > CONCLUSIONS
> >
> > *  BPC is not the problem per se when I convert to a QTR custom
> > profile, the reading of the custom profile by the whole Qimage CMS is.
> > *  There is something about the custom profiles that Qimage can't
> > handle, but can with the generic profiles.  I don't know if this has
> > been discovered and commented on before.
> >
> > @Roy:  I still don't understand the differing treatment of BPC between
> > custom profiles and the generic profiles that you mentioned in post
> > 5728.  What practical difference would I expect to see (other than the
> > fairly obvious ones in Qimage)?
> >
> > F_P
> >
> >
> 
> 
> [Non-text portions of this message have been removed]
>