QTR-Quadtone RIP

Eric Neilsen wrote:
> Ernst (or anyone that recalls), Could you quickly go over those differences
> or give us a time frame to look at for info?

A message from June this year that sums it up best:

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 )            |
 > >



-- 
Met vriendelijke groeten,  Ernst


|  Dinkla Grafische Techniek  |
|     www.pigment-print.com    |
|             ( unvollendet )            |