QTR-Quadtone RIP

Vincent,
   I'm glad to hear that the curves were useful to you.  To try to answer your questions:

1. The ink limits can be set individually, or by using a default limit.  For each ink, the limit will be set to the lower of the default or the individual limit.

To determine the values for the ink limits, the first step is to print the ink separation file, following the instructions in the various tutorials available here or at the official QTR site.  Then, look at the darkest ink you will use for the curve (probably black for matte papers or C or M for glossy papers).  By eye or using a densitometer or scanner, you want to identify the point where the density stops increasing.  That becomes the ink limit for the darkest inks.  With the UT-14 inks, it's usually 30-35%.  This is probably the most important parameter, as the others tend to be corrected for in the linearization step.

The ink limit for the darkest ink can also be used for the default ink limit, which is what I did for the curves I posted.  I didn't specify lower limits for any of the other inks.

The other parameter that has to be set for each ink is the relative gray value, which represents the density of the ink relative to the darkest ink.  I did this following the method in the tutorial.

2. The CURVE_K parameter, along with equivalent CURVE parameters for the other inks are another way of specifying the initial curves.  These allow you to specify the actual ink levels at specific gray values. This isn't necessary if the ink limits and relative gray values are set.

Whatever means you use to define the curves, the key final step is the linearization, which adjust the final gray values to match an "ideal" curve.  This step corrects for a lot of the variation that might arise from how the initial parameters were set.

I have recently been doing a lot of experimenting with curves, and I hope to post a new set UT-14 curves soon, along with some instructions for the method I have worked out using a scanner as a densitometer.  

I hope this helps.  There are several tutorials available, but the process is rather confusing!

David



--- In QuadtoneRIP@yahoogroups.com, "boulet_v" <boulet_v@...> wrote:
>
> Hi,
> 
> Thanks a lot for your curves. They really help me understand QTR uses with my UT14 kit on my Epson printer.
> Now I want to create some other curves for different papers but how did you determine the DEFAULT_INK_LIMIT ? Apparently it depends of the paper.
> Another question : on curves made by PaulRoark, there is a CURVE_K parameter, what does it mean ?
> Any help will be appreciated.
> 
> Vincent.
> 
>