QTR-Quadtone RIP

--- In QuadtoneRIP@yahoogroups.com, Ernst Dinkla <E.Dinkla@c...> wrote:
> Roy Harrington wrote:
> 
> > Speed of algorithms is very important. The shear amount of data that has
> > to get processed is quite astounding:  consider an R800 printing an 8x10
> > at 2880x1440 dpi.    That's 8x10 x 2880x1440 locations on the page.
> > That's 330 million locations, x 8 inks, 16bit = 2byte internals.
> > Total of 5 gigabytes processed for an 8x10!
> > What about the guy doing a banner on his 9600 -- 40 in x 25 feet?
> 
> According to Robert Krawitz the next version of Gimp-print aka 
> Gutenberg can handle 32 channels with 16 bit input. So it 
> isn't getting less complex. Will there be anyting gained for 
> B&W printing if you ever base QTR on the newer versions of 
> Gimp-print ?

The issue is getting the 16 bits through all the upper levels. I've been using a 16 bit
interface with gimp-print code all along. 

> 
> On EvenTone and Ordered dithering there was something written 
> that's interesting, EvenTone usually unloads the droplets 
> often in one pass even when more passes are used:

Sounds very strange to do it in one pass.  One pass of a head puts down drops in
a very regular pattern -- a 2200 puts down an exact 360x180 set of drops in a pass.

Roy

> 
> Quote:
> 
>   Robert L Krawitz wrote:
> 
>     >Graeme Gill wrote:
>     >   Good point. So to use this type of screening in the 
> real world, it
>     >   would be desirable to have the different color planes 
> screens
>     >   de-correlated once the dot density grow high enough, 
> thereby
>     >   getting the benefits in the highlights where it 
> counts, without
>     >   triggering banding and pattern issues.
>     >
>     >Why would this *trigger* banding issues?  At worst it 
> wouldn't help
>     >solve them, but I don't see how it would actually trigger any
>     >problems.
> 
>     Because if you have two screens that are correlated, they 
> need to
>     be printed in exact alignment (to sub pixel precision) to 
> avoid
>     moiri type effects between them (assuming the pixel 
> density isn't
>     sparse). Banding effectively displaces pixels (generally 
> sub pixel
>     sized displacements) in a pseudo random "banding" fashion, 
> so moiri
>     effects amplify the banding displacements. If the screens are
>     completely uncorrellated, then banding displacements will 
> have much
>     less visible effect.
> 
> Good point.
> 
> One other thing that I've had good experiences with (mostly for a
> different reason) is to use a very good screen (Raph Levien's 
> EvenTone
> Screening) with some perturbation.  In this case, the purpose 
> of the
> perturbation is to break up screening artifacts that create
> patterning, but this slight decorrelation may also favorably 
> affect
> banding.  The EvenTone Screen algorithm suffers from banding 
> more than
> the Ordered (farthest neighbor matrix) dither algorithm that's our
> mainstay, and watching the printer actually print suggests 
> that this
> would be the case.  It's very common for something printed with
> EvenTone to print the vast majority of its drops in one pass, 
> even if
> 4 or 8 passes are being used.  Ordered dithering doesn't 
> suffer from
> this, and is faster.  The problem with ordered dithering, of 
> course,
> is the noise that's visible in the midtones.
> 
> Using the dither matrix to perturb EvenTone screening 
> partially breaks
> this up and reduces the banding a bit.
> 
> -- Robert Krawitz
> 
> End of Quote
> 
>                     --
>            Ernst Dinkla
> 
> 
> www.pigment-print.com
> (         unvollendet         )