QTR-Quadtone RIP

Dear Duane,

thank you for passing your advice that I appreciate very much!
Well, the taper from L* 17.6 to 5.5 refers to black levels between 45% 
and 75 %... Let me contemplate the dilemma from an other perspective:

When printing an image I am primarely interested to obtain a print that 
corresponds to the monitor image as close as possible. As the nature of 
the monitor image (self-luminous) is different from the paper print 
(reflecting ambient light) and the response of the human visual system 
is different for various light levels, one has to carefully consider the 
conditions under which the comparison should be performed. Condition 1: 
Matching the color temperature; condition 2: Matching the light levels - 
I try to match the light levels that pure white produces on the retina. 
Given similar color temperatures - they can be approximately evaluated 
with a spectrophotometer -  usual values for a monitor are around 120 
cd/m^2. That is not particularly bright as anyone who has tried to work 
with the laptop in the garden experienced... So, for a meaningful 
comparison the print should be inspected at a correspondigly low light 
level. The problem then is that at this light level the range of black 
levels that the human eye is able to discern is limited. Depending of 
the level of eye-internal scattering (-> age of the person) depper 
blacks than d'log around 2 are hardly resolved. As a consequence I tend 
to regard a grey level distribution in the print as ideal that matches 
the one I observe at the monitor. I obtained this with Curve Creator 
settings <ink level> 45% and <Black Boost> zero and corresponding 
linearization: QuadTone RIP does a perfect job! However, when such 
prints are inspected at higher light levels - in an extreme case in 
bright sunlight - one recognizes the lack of depth in the deep blacks. 
Although the middle gray distribution is still acceptable, I then would 
like to see deeper blacks. It is for this case that I hoped that setting 
<Black Boost> would help.
However, initiating the linearization with <Blach Boost> at 75% shifts 
the middle grays to dark values. Values that might be acceptable under 
bright light illumination, but when inspected at 120 cd/m^2 do not 
correspond to the gray level distribution shown by the monitor. So my 
question is, did you or somebody found a way out of this dilemma.

Many thanks for comments; regards
Franco


dlruckus schrieb:
> --- In QuadtoneRIP@yahoogroups.com, Franco Laeri <franco.laeri@...> wrote:
>> 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.
>>  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. 
> 
> If your 17.6 L* to "5.5" L* level is correct, it doesn't seem a very
> gradual taper. It represents going from an approximate density of
> d'log 1.62 to one of d'log 2.22. That's considerable.
> 
>> 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.
> 
> That's my understanding also.
> 
>> 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'm no expert Franco but it seems to me that you would want to use or
> not use the black boost from the very beginning step in curve
> building. Once you have your maximum useable d'max as set by limit
> plus any boost you might choose, linearizing should space out the
> steps appropriately. I don't know if the black boost function was
> intended as a means of increasing ink lay down at the dense end for
> inks and papers requiring extra large amounts of black or if it is
> only really intended as a control for slight variation to gain best
> d'max after determining the coarse limit setting or perhaps some other
> purpose entirely. Roy might have some input on that.
> 
> In my case,I prefer to begin with 100% limit and zero boost and only
> use the boost if it can contribute something to the d'max after I have
> coarse set the limit and before linearizing. That may be all wrong
> from other's perspective but it's what I currently do. I'd be
> interested in other's thoughts as well.
> 
> Regards
> Duane
>  
>  
>> I am most grateful to learn from you!
>>
>>
>> Franco Laeri
>>
>> franco.laeri@...
>>
> 
> 
> 
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