QTR-Quadtone RIP

Tom Moore wrote:
> 
> Howard
> 
> That's an interesting idea. If it's correct, it seems to me that one would
> only have to make a warm curve (say) and then one could create a cool curve
> by swapping (M and LM for C and LC) inks - for UT7 anyway.
> 
> However, looking at the qidf files for various UT7/paper combinations, the
> warm and cool curves have quite different values for the Toner Curve and
> Linearization settings. That makes me think your idea wouldn't work, but I'm
> not sure why.
> 
If the inks have similar densities across the range at the calibration 
stage then they should be interchangeable without affecting the 
luminance scale. UT7-C & M & UT7-LC & LM were designed with this in 
mind. In reality the two cool inks are slightly darker than the carbon 
ones but the effect is barely noticeable and if it was bothersome 
nothing that a re-linearisation wouldn't sort out. I'm not sure what you 
mean about Toner Curves as none of the standard warm & cool UT7 curves 
use a toner curve.

There are many ways to do split toning in qtr - without even touching 
the toner curves the 'Load curves' and 'Copy curve from' facilites 
provide great flexibility. For example take the current standard Photo 
Rag Warm curve:

K, Gray Ink, Density 100, Limit 70
C, Gray Ink, Density 47, Limit 70
LC, Gray Ink, Density 15, Limit 70

You could change this to:
K, Gray Ink, Density 100, Limit 70
C, Gray Ink, Density 47, Limit 70
LC, Gray Ink, Density 15, Limit 35
LM, Copy Curve from LC, Density 15, Limit 35

The new curve would give warm carbon shadows & midtones moving towards 
more neutral highlights as the LM kicks in. I have halved the limits on 
the LC & LM so they both add up back to 70 as in the original curves LC 
alone. As we are replacing like for like no re-linearisation should be 
necessary.

Howard