Re: [NTG-context] Dithering (off-topic)

2003-11-04 Thread Michal Kvasnicka
Dear Sir,

many thanks for your kind help. This is precisely what I was searching for.

Bill McClain wrote:

  pnmscale -width=1950 pleiades.pnm | pnmsmooth -size 5 5 | pgmtopbm
-fs -value 0.5 | pnmtopng  pleiades.png
BTW, is there some easy way to set the size of the dithering points (eg. 
2x2 pixels, 3x3 pixels), or should I do it ex post in some image editor 
(Gimp, imagemagick)?

Many thanks once more.
M.K.


___
ntg-context mailing list
[EMAIL PROTECTED]
http://www.ntg.nl/mailman/listinfo/ntg-context


Re: [NTG-context] Dithering (off-topic)

2003-11-04 Thread Bill McClain
On Tue, 04 Nov 2003 14:34:54 +0100
Michal Kvasnicka [EMAIL PROTECTED] wrote:

 BTW, is there some easy way to set the size of the dithering points
 (eg. 2x2 pixels, 3x3 pixels), or should I do it ex post in some image
 editor (Gimp, imagemagick)?

I haven't studied the Floyd-Steinberg algorithm, but it seems to be an
error-difusion technique that handles that automatically. The
resulting pixel dimensions of the image are the same as the
original. There are other halftoning methods you can experiment with in
pgmtopbm.

Although I did some experimentation, I am by no means an expert at this.
My method is simply to expand the orginal image to so that a pixel in
the image will be a dot on the output. Using the example I posted
before, the image was 3.5 inches wide, the printer was 600 dots per
inch, so I sized the graphic to 3.5 x 600 = 1950 pixels before
halftoning. I've dealt with only one printer so far, but the results
have been good.

Depending on the original grayscale image, it may need to be normed
(pgmnorm) or smoothed (pgmsmooth) before halftoning.

-Bill
-- 
Sattre Press  Pagan Papers
http://sattre-press.com/by Kenneth Grahame
[EMAIL PROTECTED]  http://pp.sattre-press.com/ 
___
ntg-context mailing list
[EMAIL PROTECTED]
http://www.ntg.nl/mailman/listinfo/ntg-context


Re: [NTG-context] Dithering (off-topic)

2003-10-31 Thread Siep Kroonenberg
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
[EMAIL PROTECTED]
___
ntg-context mailing list
[EMAIL PROTECTED]
http://www.ntg.nl/mailman/listinfo/ntg-context