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
On Fri, 31 Oct 2003 12:21:48 +0100
Michal Kvasnicka
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?
I suspect you need to halftone the photos before including them. All the gray pixels must be converted into a pattern of black and white equivalents. On Linux you have the netpbm package which has everything you need. The specific utility is pgmtopbm with various switches. There are other utilities for converting to and from the netpbm file formats. Here is an example of a pipeline I use to do several manipulations at once: pnmscale -width=1950 pleiades.pnm | pnmsmooth -size 5 5 | pgmtopbm -fs -value 0.5 | pnmtopng > pleiades.png pnmscale: expand to a known size pnmsmooth: try to obscure the halftone of the original photo pgmtopbm: apply new halftone, -fs = "floyd-steinberg" halftoning pnmtopng: convert to png for inclusion into pdf The trouble with halftone images is that they are not resolution-independent. You may have to adjust the image size and parameters depending on your printer. Also, halftoned images do not display well in some graphics programs, although acroread does a pretty good job when they are included in pdf files. -Bill -- Sattre Press The King in Yellow http://sattre-press.com/ by Robert W. Chambers info@sattre-press.com http://kiy.sattre-press.com/
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.
On Tue, 04 Nov 2003 14:34:54 +0100
Michal Kvasnicka
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 info@sattre-press.com http://pp.sattre-press.com/
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
participants (3)
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Bill McClain -
Michal Kvasnicka -
Siep Kroonenberg