QTR-Quadtone RIP

Dear List,

as a newcomer to QuadToneRIP I am trying to create profiles for my 
printer-paper combination (Epson R2400-Hahnemuhle FineArt Pearl 285 
g/m^2), and I am afraid not to understand some basic concepts, like the 
<Black Boost> setting in the Curve Creator.

Preface.
As probably all of you experts I found out that for having the Curve 
Creator producing a valid linearization, the <Default Ink Limit> should 
be set at some 5% below the limit at which the grey steps become visibly 
undistinct. The linearization procedure usually involves the inversion 
of the grey level transfer matrix. Obviously the inversion is performed 
on the basis of the "literal" densitometer values without taking care 
for a possible non-regularity of the matrix. As soon as the ink steps 
become undistinct the matrix becomes irregular. Truncation on values 
below this point corresponds to a mathematical brute force 
regularization. The program code so given, this is the only possibility 
at the moment. In my printer-paper case I choose to truncate at a K-ink 
level of 45% leading to a luminosity L* of 17.6. L* then slowly taperes 
off to reach the lowest level of 5.5 at the 75% K-ink level. One might 
discuss shifting the <Default Ink Limit>, but that might be paid by an 
excessivly uncertain linearization. Thus, being forced to put the black 
end of the gray scale below "real" black, the <Black Boost> option is 
most valuable - but...

Problem.
Linearization with above parameter set leads to an acceptably smooth 
InkLevel-L*-function. When I set <Black Boost> to zero then a 
5%-increase in the InkLevel translates to a consistent L*-difference of 
around 4.1. However, if I go through the linearization with <Black 
Boost> set at 75% the L*-difference between 5% patches increases to 4.5, 
with the last step from 95% to 100% up at 6.5. Thus <Black Boost> steeps 
up the whole curve, so shifting the middle gray tones to darker values - 
not exactly what I intended. It seems to me, that in this way the <Black 
Boost>=75%-curve practically corresponds to a curve obtained with a 
<Default Ink Limit> of 75% and <Black Boost> of zero. Up to now it was 
my understanding that boosing the blacks is intended to increase dMax 
and should limit is action to the dark black image tones, but leaving 
the middle grays unaffected.

Is my understanding wrong? Is somebody suggesting the alternative 
approach of linearizing with <Black Boost> set to zero and only after 
linearizing setting the <Black Boost>-level to a higher value, for 
example 75% ? What do the long time experts think?

I am most grateful to learn from you!


Franco Laeri

franco.laeri@...