[Openicc] Drop size calibration

[Gerhard Fuernkranz]

Robert Krawitz wrote:
> I need to find some time to investigate Raph Levien's EvenBetter Screening. I'm not certain, but this may be multi-level as well as well as handling multiple inks.

Oh, and I was always believing that Gutenprint's "Even Tone" screening
is already yet another implementation of Raph Levien's algorithm.
Obviously I was wrong...
 
> The code's a bit convoluted because it's vector-optimized (and because it's Ghostscript-based -- I always find Ghostscript code harder to figure out).
>   

Raph Levien's original code seems to be pretty easy to use
(independently of GS). Create the EvenBetter object with
even_better_new(), then call even_better_line() for each scan line,
feeding the continuous color data of the scan line into the engine and
getting the dithered pattern out. But there are a couple of parameters
too, which can be / need to be tuned.

Regards,
Gerhard