[Desktop_printing] Smooth dithering

Michael Sweet mike at easysw.com
Fri Feb 17 00:16:56 PST 2006

Kai-Uwe Behrmann wrote:
> Hi,
> preparing a comparision between a standard prepress RIP and an open source 
> PDF workflow for a Linux fair in Germany I have some trouble. Shurely the 
> partipicants of this list have enough inside to cope with the issues.
> The PDF side seems ok with Ghostscript/CUPS for rendering and CinePaint 
> and lcms for displaying. The test runs with the Altona Testsuite, a 
> PDF/X-3 collection from ECI/UGRA/FOGRA.
> The dithering of the propriarity driver is much smoother than 
> Gutenprint's. The inkjet used is a Epson 3000. The device does 720 
> dpi at a fixed drop size.
> Now comparing the propriarity driver output with Gutenprint's rendering 
> shows much more noice peaks in the Gutenprint dithering. It seems that
> Gutenprint puts drops not so very well wighted. This is the case for b/w 
> and for colour printing. The dithering is clearly a minus in the side by 
> side comparision.
> One problem seems to be in not taking the other colour planes into 
> account. So for instance a black drop is too often placed next to a cyan 
> one. Instead, as seen in the propriarity dithering, yellow can be placed 
> near to black and cyan. Black and cyan should have the most distances 
> followed by magenta and yellow. There is no such hierarchy obvious in 
> Gutenprint's dithering results.
> How does other open source drivers perform regarding smooth dithering?

To my knowledge, Gutenprint's dithering is the most advanced WRT
open source inkjet printing.

The CUPS DDK employs a simple stochastic dither (modified Floyd-
Steinberg) with RGB-to-CMYK and CMYK-to-device lookup tables; in
theory, it can produce better output than Gutenprint, however in
practice we haven't spent the time to create the large 3D LUTs that
would be required...

FWIW, similar results can already be achieved with both Gutenprint
and DDK drivers by using ICC profiles to generate CMYK data, however
that is non-optimal for today's N-color photo printers.

Michael Sweet, Easy Software Products           mike at easysw dot com
Internet Printing and Publishing Software        http://www.easysw.com

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