Digital BW, The Print

Tyler, you wrote:

> Ernst, this is all old Dan Culbertson stuff. You can create
profiles
> for quad inks. You can edit curves into those or any other
printer
> profile with Doctor Pro, other software as well I'm sure.
> However, sep curves created to work on files in a working space
(as
> most used here are) will not work. The idea is to be able to
convert to
> the profile for printing, converting to a quad (or any other)
printer
> profile will significantly alter the RGB values in the file,
therefore
> those curves will not result in the desired final RGB values
for
> printing as they did when applied to the working space they
were
> created in. They were created to work on AdobeRGB (or
whatever).
> So you'd want to edit those curves into a profile that does not
> originally alter the RGB values, like a working space. Doctor
Pro will
> not edit working spaces. Alternatively, you can create a null
printer
> profile, and edit your curves into it. Unfortunately since it
was not
> created from the inkset/paper, it will not have the advantage
of
> preview. It's only usefulness will be to print through, no more
> advantage than running a curve anyway. A null printer profile
is not
> that easy to come by either.
> Another option is to start from scratch. Create the profile
from the
> inkset, attempt to create sep curves that print well on a file
already
> converted to that profile, then edit those in. Unfortunately
the new
> RGB content after conversion is not very useful for creating
optimal
> quad sep curves.
> However, you can do all this on CMYK profiles using old
Culbertson
> tricks.
> Creating really good RGB quad printer profiles, that also
preview well,
> will be much more complex than it may first appear, and editing
in sep
> curves made by trial and error does not take good advantage of
all the
> data provided by the initial profile anyway.

Yesterday I experienced some of the obstacles you describe here.
I still think there are possibilities to overcome them. I am not
after a good screen representation but a good quad printing
profile to be used in other (driver) applications than Photoshop.

In the past I have asked how a null printer profile is created
but never got an answer. The way I think it is possible to create
a good hexatone profile is for example by using Doctor Pro to
convert initial separation curves into a profile based on a null
profile. Use that as the printer profile to print a grey
stepwedge and measuring that wedge to create a general curve
again that will be implanted in the first profile with Doctor Pro
again. That could take care of the RGB shift you describe but
with the advantage that this second step can also be used to
compensate any printer quality drift in time as well. Like
linearisation but in this case at the end of the process.

So the two questions are: how do you create a null printer
profile and is it possible to write a tool that translates
spectrometer or densitometer greyscale data into a PS curve ? If
it doesn't already exists.

Any flaws in this concept ?

I have checked some IP profiles and more than in any other
profiles I came across curves in the profiles that are used to
correct the output. That's an RGB driver as well so it must be
possible to use the curves in the profiles for this purpose.

Related to this:
There's profile creation software that can change a normal colour
profile into a so called "Rich Grey". It is used to get more
neutral prints from colour printers by taking out the colour data
of the colour profile (if I did understand it correctly). I got
some samples of profiles and menu screenpics probably from
Richard Millott on the Colorsync list. www.ICCtools.com is the
company, the software is ICCtoolbox pro. The profiles have an
extension pf but they are cmyk printer profiles, I can't place
them however. Anyone familiar with that application and the
profiles ?

Ernst