I tried al kind of settings but the picture in pdf always is a combination
of the four proces colours (and not only black and magenta).
Is the combination you see in the PDF looking like the right colour
still? If it's starting with only black and magenta, it probably
shouldn't be GCR or UCR that's affecting it. I wonder if it's an ink
setup thing (if that exists in OPW)? I seem to recall a similar thing
happening years back with a JPEG image inside an artworks file - the
artworks file would appear to tint, but the JPEG part wouldn't.
Something like that anyway.
As an aside, the thing I asked about years back was true duotones. As I
recall at the time, OP had a hybrid of monotones and duotones.
In a normal monotone, you throw away the colour info of the image and
use only the luminosity - effectively treat the image as a greyscale -
but then re-colour it, with the level of new tint depending on the level
of grey. Often, you add a curve to the relationship so that the tint is
not linear with luminosity, eg it could be stronger at the darker end.
Sepia print is an example of real-world monotone. A true duotone (or
tritone) lets you add other colours in, each with their own curve
relating their tint to luminosity. Using it, you can end up with quite
subtle colouring.
As I recall in OP, you have two different colours as endpoints, and
create a single curve between them. It's not as subtle an effect, and
not as flexible as a duotone, but it shouldn't introduce any other
colours either...
