QTR-Quadtone RIP

Dave

The CurveEval Excel spreadsheet is in the files section now. Note that you
may have to enable macros, depending on your security level setting in
Excel. No macros enabled - no work.

See response below regarding your other question.

Tom

> -----Original Message-----
> From: QuadtoneRIP@yahoogroups.com [mailto:QuadtoneRIP@yahoogroups.com] On
> Behalf Of David Meddings
> Sent: Tuesday, August 30, 2005 4:16 AM
> To: QuadtoneRIP@yahoogroups.com
> Subject: [QuadtoneRIP] Re: Curve building?/Spreadsheet
> 
> Tom,
> 
> I wonder if you might consider uploading that Excel file to the Files
> section here instead?
> 
> I do not have a densitometer so I have to use my Epson 3200 scanner
> for my first attempts at curve creation I now have underway with the
> UT7 inkset. Being able to convert luminosities to densities would be
> very handy and although I could just use the formula from John's post
> I would bet I am not the only one in the 'no densitometer' boat.
> 
> Also Tom, while I have you on line so to speak :~) I wonder if you
> can clarify something from your user guide. In the Ink Density
> Calibration section on page 15 you say:
> 
> "For Ultrachrome inks, the measurements above are all that is
> required. For QuadTone inks, this process is repeated for each
> lighter ink, comparing it to the next darker ink, calculating its
> density relative to that ink and then converting it to a density
> relative to black."
> 
> I believe that what you mean to say is simply that the process is
> repeated for each lighter ink, calculating its density relative to
> black. Is that not correct? All that one needs later in the curve
> generation is the percentage of the black ink stepwedge that
> corresponds (in density terms) to 100% of the other gray inks,
> correct? If so, it seems to me you do not need to in any way compare
> the other grays with each other, but only with the black stepwedge
> densities directly. Thanks to confirm if I've understood things
> correctly here.
> 

What I stated, I think is correct. You could do what you're suggesting
(simply estimating each lighter inks density as a percentage of black) but
doing it in two stages I think is more accurate and not any more work.

Basically:
You compare LK with K. Suppose it's 40% of K.
Next you compare LLK with LK. Suppose its density is 40% of LK. Then its
density is 16% (40% of 40%) of K. The 16% is what you use in QTR. What I was
describing in my document was how you determine the number.

Doing the comparison with K could be done and probably wouldn't make too
much difference in the example I gave. When there are lots of gray inks
(e.g. the K7), the numbers would get pretty small and inaccuracies would
creep in. 


... snip...


Tom