Re: Dithering (off-topic)

[Siep Kroonenberg <siepo@cybercomm.nl>]

On Fri, Oct 31, 2003 at 12:21:48PM +0100, Michal Kvasnicka wrote:
> Good evening.
> 
> I apologize to ask a little off-topic question, but I don't know where 
> to ask (and it is closely related to TeX and PDF).
> 
> I typeset a church bulleting. It is printed on a laserjet printer (600 
> dpi), and then copied on a copy machine. As for letters, all is right. 
> But figures (photos) are this way spoiled. I guess it would help either 
> to force PDF to print the figures in some very low resolution (150 dpi), 
> or (probably better) to dither the figures and include them in PNG 
> (instead of ordinary JPEG). Can some of you tell me how to do it? I 
> tried ImageMagick's convert to dither the photos, but outcomes were 
> really poor. Is there some good free software for this (in the best case 
> in Linux)? Or can I do it some way in PDF?
> 
> Many thanks for any hint.
> Michal Kvasnicka

A PostScript solution: create a dvips header file for course
rasterization:

%!
/bop-hook {53 45{dup mul exch dup mul
  add 1. exch sub}setscreen} def

These numbers (raster frequency and angle) are probably ok for
600dpi; otherwise, experiment a bit.

Call it coarse.pro and give dvips a parameter -h coarse.pro

-- 
Siep Kroonenberg
siepo@cybercomm.nl