QTR-Quadtone RIP

Hi Walther,

I am not an expert with the QTR program but I can give you a quick  
explanation of what I think is happening. The underlying function for QTR  
is that of the .quad file. It divides the black levels printed onto the  
paper into 256 levels corresponding to an 8 bit integer. Each possible ink  
output is divided into 65536 levels corresponding to a 16 bit integer. At  
any given 8 bit input level, QTR references the .quad file to determine  
which inks and how much of each ink to dispense. There may be multiple  
inks being used because of the overlap in the transitions between inks and  
possible use of color inks to set the tone. How many inks there are is  
determined by the printer and ink set you are using. It is also further  
complicated by the fact that there are multiple ink dots printed for each  
actual image pixel and there is also dithering used to determine the how  
the dots get printed.

The .quad file is generated by the curve creation part of QTR. It uses  
some algorithm, which I don't have any information about, to derive the  
individual ink values for each 8 bit level from the information in the  
.qidf file.  This information is set during the calibration process by  
selecting the type of printer, the ink set being used, and then printing  
the ink pattern page, setting the ink limits and ink density values, and  
then printing the 21step file to determine the linearization levels. You  
can read the black levels from the test prints with a special instrument  
or with a scanner and photo editing program. If you are using a color ink  
set, you have to determine how much of the color inks you have to add to  
the basic black ink(s) to set the desired output tone, cool, neutral,  
warm, etc. All of this has to be done for each paper, printer, and ink set  
combination that you use since all these factors affect the finished print.

Jon Cone supplies his own .quad files for some paper/printer combinations  
for his K7 and other related ink sets. Some people also use the ICC curve  
generation capabilities in QTR, but I have not so I can't tell you much  
about them.

QTR is a great program at a great price and everything works pretty well  
and you have quite a bit of flexibility and control using it. It does not  
go so far as having sliders for each ink for you to play with and as I  
found, the built-in algorithms don't seem to work with some papers. Maybe  
there is something else that I am missing but that is my understanding at  
the moment. Hope this helps you get a better feel for what is going on.
Steve



On Mon, 21 Apr 2008 12:34:12 -0700, W.L. Walraven  
<walraveninnovation@...> wrote:

> Dear  Steve,
>
> I just ran into QTR;- I have a 4800 pro epson printer branched on a mac  
> pro
> intel computer. So far I was not able to print nice BW prints on  
> Hahnemule
> rag brite papers. They look gray or are to dark. Detail is missing. On
> glossy paper everything i fine in the black prints.
>
> This weekend I started to use QTR. BW prints look a lot better though in  
> the
> deep shadow parts the blacks are far to saturated and look ugly  
> greenisch.
>
> I do not understand the system of calibrating. I am a gratuated enigeneer
> and used to math. But the way things are explained is not lolgical for  
> me.
>
> I am curius wat steps you take to calibrate. Why are there no sliders to
> ajust all the ink separately.
>
> After calibration mesurement how can I tell the printer what to do.
>
> Greetings Walther Walraven
>
>
>

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