QTR-Quadtone RIP

Ernst Dinkla wrote:
> Howard Shaw wrote:
> 
>> I'm none the wiser. I can see the profiling step described on that page 
>> (for use with Epson's ABW mode) but not a table of "perceptually correct 
>> density values". Could anyone explain further please or, better still, 
>> provide the table?
>>
>> Howard
> 
> Where would the same 21 steps of the wedge land in print
> density if that wedge goes through the profile first ?
> 
> There could be density tables made for several 
> Dmax-Paperwhite ranges that way. Maybe just down to earth 
> density ranges of certain papers and the Dmax possible on 
> them with a given inkset as obtained in practice but I'm 
> sure there are ways to create them more mathematically.
> 
> The linearised tables are nice for control when there's 
> control on printer linearisation or one has to find out what
> setup has the best linearised output if there's no control. 
> Good to have control at say 85% of the job to get a printer 
> in line but why not add what that last 15% does. I too have 
> some difficulty in the way that perceptual tone separation 
> is expressed in densities but if it works for the tables of 
> a linearised tone range I do not see that it is worse for 
> what shall we call it .......?
> It may be more useful for some to have also tables that show 
> the output after all steps as in many cases there's a black 
> box in between, not in QTR of course.

Sorry, I should have added more details. Right now I try to
profile the B&W mode of the Z3100 driver when used with
Qimage. There are some odd things happening in that process.
HP recommends to use the B&W mode without the application's
CM (Qimage's CM in this case) but to use the HP Z3100 driver
CM instead while it expects greyscale files as well in that
process. Two choices of space in that CM: AdobeRGB and sRGB,
both 2.2 G. The printer's internal calibration per paper
also serves as the fundament for the B&W mode too. Sounds as
a consistent method and it probably is in a way with Photoshop.

There are two choices in Qimage to let the files
through without its CM interfering: CM off or Use Printer
CM. In the last case the embedded profiles go through too
and influence the outcome of the driver's CM. Probably
because Qimage can't pass greyscale but makes RGB files of
them without substituting a Gamma 2.2 with an AdobeRGB
embedded profile and the driver probably considers it as
without profile. With a 21 step monochrome RGB file R=G=B
assigned AdobeRGB it will do it different. At one time I get
near linearised output according to the density numbers
(compared to the "Ideal" density tables) at another time I
guess close to perceptual numbers for an AdobeRGB assigned
21 step wedge. This is the kind of black box I refer to
above. I should have added from what spaces/gammas I start
from but they all are Gamma 2.2 related or the Gray Lab one
that isn't far from it. So there has to be more information
added if tables like that are given which I should have
mentioned. The rendering with an without BPC etc too. The
example I give here is a horror case but there will less
severe cases where some reference to what the numbers should
look like in the end are welcome.


-- 
Met vriendelijke groeten, Ernst


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