QTR-Quadtone RIP

Hi Franco,

As you've found experimentation is usually necessary -- it's unpredictable when
you get high ink amounts.

But I'd like to clarify the black boost parameter.  It's basically an
alternate ink limit
i.e. its the same units.  So it really only makes sense to have a
BOOST_K  >=  LIMIT_K  and I usually don't do much more than about 15%
higher than LIMIT_K.

Roy


On 10/22/07, Franco Laeri <franco.laeri@...> wrote:
> 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@...
>
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