Digital BW, The Print

Piotr, Your english is just fine. 

> I have noticed that sometimes after applying the curve (mostly NC) the print looks strange in some parts of midtone and shadow areas after coming out of the printer, visible for example shadow area of the face(under the chin) this was not visible when the image was greayscale and later converted to rgb. 

What do you mean "When the image was grayscale and later converted to rgb."

That is the way to do it. You have a black and white image. Then convert
it to RGB, then load Paul's curve, and print using the color inks. You
do NOT apply the curve to a color image. It should start out as
grayscale, THEN convert to RGB.

Jerry