QTR-Quadtone RIP

I've done a little testing in Qimage to see how using its CMS compared
to converting first in PS to my newly created custom (rgb) profile,
and then printing via Qimage with CM off.  Results (PS histograms of
Qimage print-to-files) are:


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

There's certainly something very strange going on in Qimage if you
convert to a QTR profile with BPC on.  BPC OFF looks better, but not
perfect.  

@Ernst: is this what you were seeing?  Is it worth provoking the
Qimage list again?  It almost looks like it's not a perceptual
conversion (which it was definitely specified as).

@Roy:  In message 5728 you said that you had included the Adobe BPC in
the QTR-Create-ICC profiles.  For the CMS-challenged among us, what
are the implications of including (or not including) BPC in
QTR-Create-ICC profiles?  Does this mean that we should specify BPC in
profile conversions, or does it mean that we do not need to?

F_P
 

--- In QuadtoneRIP@yahoogroups.com, "Roy Harrington" <roy@...> wrote:
>
> Mike,
> 
> Just in general the issue seems especially strange to me.  Originally
> my profiles
> used the TRC curves and black point mapping was particularly
important.  But
> now all the custom profiles from QTR-Create-ICC (and RGB) use A2B
and B2A
> curves that explicitly map Lab(0,0,0) to pure black (K=100 or
R=G=B=0) for all
> the intents.  So how and why any CMS would not honor that seems to
me to be
> wrong.  But they all do different things depending on intent and bpc
settings.
> I'm not a color management expert by a long shot so I really can't say
> who's wrong.
> But as a B&W printer it's imperative that you take advantage of the
best dMax
> that the paper/ink can achieve.  So far trial and error is what I've
used to see
> what happens for particular setup.   If you or anyone has advice or
even just
> ideas of how to best guarantee getting black I'm open to it.
> 
> The trouble with finding a lot of this stuff out is that just about
> everyone knows
> color and assumes B&W should be the same but it rarely is.
> 
> Thanks,
> Roy
> 
> On 6/19/07, mchaney1234567890 <mchaney@...> wrote:
> > As Roy indicated, BPC is not part of the ICC spec at all: it is an
> > Adobe abomination, one of which (as is often the case with Adobe) is
> > not completely specified for third parties to be able to reproduce.
> > There are additional limitations with BPC for ICC v4 profiles as BPC
> > really makes no sense for perceptual intent in v4 profiles.
> > Perceptual intent for v4 profiles runs on its own PCS and is
> > inherently different than RC and other intents making BPC undefinable
> > by the spec.  There are other issues as well, for example, when a
> > profile uses a black point tag and that tag doesn't agree with the
> > data in the look up tables.  On top of that is the fact that black
> > point for perceptual intent in v4 profiles should be a fixed value.
> > There's also color "noise" to deal with and the fact that you have to
> > deal with near-black.  All software will handle that a bit
> > differently.  When using v4 profiles, many times the profiles
> > themselves are not truly v4 as I've seen many that are a mix between
> > v2 and v4 and don't have all the required v4 tags.  Hard to tell which
> > of these factors is causing the problem, but I've been over BPC with
> > Marti Maria many times and am satisfied that it is working properly in
> > Qimage/LCMS.  PhotoShop also tends to "prune" profiles and do things
> > without telling you so in cases like this, the answer could be as
> > simple as PhotoShop ignoring BPC under these conditions while Qimage
> > still tries to do something with it.  Maybe the best thing in cases
> > like this is to turn off BPC when using perceptual intent with v4
> > profiles as BPC really makes no sense in those cases anyway.
> >
> > Mike
> >
> > > Roy Harrington wrote:
> > > > Ernst,
> > > >
> > > > When I first tried Qimage with QTR ICCs back over a year ago there
> > were some
> > > > issues.  The issue was a combination of both Qimage and Little CMS
> > which is the
> > > > internal color management of Qimage.  At the time we got things to
> > work just
> > > > like they do Photoshop.  I guess it's possible that it has
been broken
> > > > in a later
> > > > version -- (I don't use Qimage on any regular basis so I
wouldn't find
> > > > out about it).
> > > >
> > > > The whole BPC issue is a problem in general.  It is not
addressed in
> > > > the ICC standard
> > > > at all -- neither v2 or v4.  To quote the website it's "under
active
> > > > consideration".
> > > > Adobe is the one who initiated the concept and wrote the
> > "standard" for it.
> > > > Another issue is that rendering intents are also up to
implementers --
> > > > the idea is
> > > > specified in ICC but the exact math involved is not.
> > > >
> > > > It's easy to see what your particular setup does.  Instead of
printing
> > > > the output of
> > > > Qimage (or any other program) send the output to a tiff file and
> > open it up back
> > > > in Photoshop to see what's been done to it.  Use a 21 stepwedge
> > and look at the
> > > > histogram before and after -- or even just a 100% black box.
> > > >
> > > > Roy
> > >
> > > Roy,
> > >
> > >
> > > There's an older Qimage mailing list comment by Mike on BPC
> > > where he writes that BPC is not needed in perceptual
> > > rendering as the last already compresses the total within
> > > the printer's gamut. So he advises to keep BPC on in both
> > > perceptual (not doing harm) and relative colormetric (needed
> > > there for good shadow rendering). True if it works correctly
> > > but I see differences in Photoshop Perceptual rendering with
> > > and without BPC. In Qimage it certainly isn't inactive in
> > > the case I sketched.
> > >
> > > I rather print samples to really see and measure what I get
> > > than check it in PS that needs to be treated carefully  as
> > > CM is almost never really suppressed in that program.
> > > Picture Window Pro's CM can be switched off totally, on the
> > > other hand that application has a quirky CM when switched on :-)
> > > I have been testing all the applications on QTR ICC
> > > compatibility probably two or three years ago and PWP made a
> > > mess of it then and now, Qimage is back to an old problem it
> > > seems but worse now as I want to print gloss with the higher
> > > Dmax.
> > >
> > > I'm going to measure the targets I got and select the method
> > > with the tone range that comes near the ideal curve for that
> > > Dmax. If the HP ABW sans application CM isn't too bad I
> > > might use that with Qimage for the time being, the QTR
> > > profile did correct the tone range though but I do not want
> > > to print from PS.
> > >
> > >
> > > Met vriendelijke groeten,  Ernst
> > >
> > >
> > > |  Dinkla Grafische Techniek  |
> > > |     www.pigment-print.com    |
> > > |             ( unvollendet )            |
> > >
> >
> >
> >
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
>