QTR-Quadtone RIP

I have question concerning the QTR grey profile relative table.

I have created a QTR profile for Museo silver rag on the P800, using the Epson driver. DMax is roughly L*2. Converting from a 2.2 workspace using perceptual rendering creates a perfectly linear toe from L*2 all the way to L*30. However manually targeting the black point to L*2 and converting to the QTR profile using relative rendering produces a strange lagging, source values from L*0 to L*4 are all mapped to L*2 and the visible threshold (L*3) is bumped to source value L*5. Reading the patches confirms the D Max actually produced is L*2 so I am reluctant to target a higher black value to push the source values L*1-4 out of maximum black. I am surprised that relative rendering seems to be allowing the CMM to modify ingamut colours by reducing L*3 & 4 to L*2.

Obviously I should be using Perceptual rendering, I‘m just curious to understand this behavior, usually manual black point targeting compresses the luminance scale uniformly, and relative translates the exact values.

Thank you

Eugene

Don’t use the Relative table. These are perceptual profiles only (in my experience) . . .

Walker

> On Jun 30, 2016, at 12:10 PM, info@moisdelaphoto.ca [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:
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> I have question concerning the QTR grey profile relative table.
> 
> 
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> I have created a QTR profile for Museo silver rag on the P800, using the Epson driver. DMax is roughly L*2. Converting from a 2.2 workspace using perceptual rendering creates a perfectly linear toe from L*2 all the way to L*30. However manually targeting the black point to L*2 and converting to the QTR profile using relative rendering produces a strange lagging, source values from L*0 to L*4 are all mapped to L*2 and the visible threshold (L*3) is bumped to source value L*5.  Reading the patches confirms the D Max actually produced is L*2 so I am reluctant to target a higher black value to push the source values L*1-4 out of maximum black.  I am surprised that relative rendering seems to be allowing the CMM to modify ingamut colours by reducing L*3 & 4 to L*2. 
> 
> Obviously I should be using Perceptual rendering, I‘m just curious to understand this behavior, usually manual black point targeting compresses the luminance scale uniformly, and relative translates the exact values.
> 
> 
> 
> Thank you
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> 
> Eugene 
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> 
>

Thanks for the advice. I find the perceptual table works fine for glossy papers, it becomes more of a problem when the Dmax rises to L*18 or higher. Obviously the reproduction curve has to be compressed by 20%, I ‘m just used to targeting the threshold myself so that I can push the compression higher up the curve than most perceptual tables (including QTR).

Would I be able to achieve this if I were to make my own ink level curves and bypass the Epson driver? And would this replace the ICC profile? I’m asking this because, using the PC version I don’t see how I can configure the ICC profile in the QTR gui

Thanks