QTR-Quadtone RIP

--- In QuadtoneRIP@yahoogroups.com, Kemal Delic <kemdel2000@...> wrote:
>
> 
> 
> Hello list,
> 
> I would like to learn how to make QTR curves. I made
> two tests with 100% and 85% ink limit. Now I want to
> do the ink density calibration. Here is the
> explanation in the QuadTone RIP User Guide:
> 
> *****************************************************
> With a densitometer: 
> 
> 1. measure the 100% Light Black patch: Density 1.29
>  
> 2. measure the 40% Black patch: Density 1.22. I
> selected 40% by eye, but you can use the densitometer
> to find the darkest patch with density less than the
> density of 100% Light Black 
> 
> 3. Measure the density of the next darker patch – 45%
> Black: Density 1.33. Then it's bit of simple math to
> calculate the percentage of black needed to produce
> the same density as 100% Light Black. In this case we
> get a value of 43.2% Black is equivalent to 100% Light
> Black. 
> ******************************************************
> 
> Could somebody, please, explain to me the "simple
> math". I am using UT1 inks and Epson R220 printer.
> 
> Thanks in advance.
> Kemal
>

We're looking for where 1.29 would fall given that 40=>1.22 and 45=>1.33

So  (1.29 - 1.22) / (1.33 - 1.22)  gives  0.64    or 64% of the way from 40 to 45.
The formula = (X - low) / (high - low)

Now the interval 40 => 45 is (45-40) = 5.   So 0.64 x 5 = 3.2 
add that to 40 and we have 43.2

This is probably more accurate than you have to worry about.  Guestimating that
1.29 is in the middle but closer to 1.33 you could get away with just saying 43.

Roy