note: I posted this on dpreview as well, but its sorta technical so I thought I might get additional responses here...
This weekend I was working on generating new quadtonerip profiles for my epson 7800. My methodology is to avoid linearization if at all possible and I was pleased to find that the 7800 was quite linear already and after some careful work I was able to make the output quite linear using only the highlight/dark/ink limit/gamma adjustments. So then I set about comparing the quadtone rip setup with the epson driver used in various ways. (ABW and color mode printing of b&w)
I use an i1 isis and sometimes a colormunki for all my color measurements. My test involved printing a 256 gray target in 5 different ways and measuring it with the isis. I was surprised to find that I was entirely unable to get the epson driver + PS to do what I understand that black point compensation is SUPPOSED to do to begin with (namely map the darkest black of the output device profile to the darkest black L=0 and then provide clean gradation from there to the white point). This puzzles me very much. Here are some charts of what happened with the 256 gray chart.
the blue lines are all the L values. You can see that the darkest black for all the techniques is at about the same place (~ L=12.5) but that all the epson driver prints had the same oddity that they clearly did NOT cleanly shade from the darkest black it ended up blocked up from RGB 0-14 instead. Anyone know why? Black point compensation was on in photoshop for all of these, and all color management for the epson driver was done by ACE inside PS.
Man, I do love how clean and smooth the quadtone rip tonal gradation is... This is my 'untoned non-neutralized' qtr profile btw so its a pleasant slightly golden color.