cplai@daisy.UUCP (Chung-Pang Lai) (07/11/89)
I have written a PS program to experiment with the halftoning parameters.
The program can be used as a framework for anyone who is interested to see
various halftoning effects.
Note: According to the red book, the screen setting is fine tuned for
the printer by the manufacturor. Hence, setting your own screen may not
get better results.
Please read the comments to find out where you can change the screen parameter.
==== grays.ps =====
%!PS
% This program illustrates the effects of the halftoning parameters
% Change the frequency, grid angle and spot function if you like to
% experiment with them
10 dict begin % set up local dictionary
% define variables to draw the stripes
/str 20 string def % tmp string holder
/box { % - => - draw a 1x1" box of current gray
72 0 rlineto
0 72 rlineto
-72 0 rlineto
closepath
fill
} bind def
/strip { % step => - overlap step # of box to form a strip
/step exch def
0 setgray
0 -12 moveto
step str cvs show
( steps) show
0 1 step {
step div
newpath
dup 720 mul 0 moveto
setgray
box
} for
} bind def
/page { % fctr => - draw a page with 5 strips, fctr = change factor of frequency
/fctr exch def
gsave
currentscreen % get default setting
% stack : freq angle spot-func
% skip the next section to leave default spot function intact
pop % remove spot function
% replacement spot function, uncomments only one of the following
% { pop pop 1} % random
{ exch pop abs 1 exch sub } % lines
% { dup mul exch dup mul mul 1 exch sub } % crosses
% { abs exch abs add 2 div } % diamonds
% { mul } % Bowties
% { dup dup mul mul exch dup dup mul mul add abs 1 exch sub } % lines & dots
% { dup mul exch dup mul add 1 exch sub } % dots
3 1 roll % stack : spot-func freq angle
% skip the next section to leave grid angle intact
2 mul
3 1 roll % stack : angle spot-func freq
fctr div % divide it with change fctr
dup /freq exch def % save a copy for display
3 1 roll % stack : freq angle spot-func
setscreen
36 0 translate
0 50 moveto
(frequency: ) show
freq str cvs show
0 100 translate
10 strip % draw a strip with 10 overlapping boxes
0 100 translate
50 strip % draw a strip with 10 overlapping boxes
0 100 translate
100 strip
0 100 translate
200 strip
0 100 translate
300 strip
showpage
grestore
} bind def
% end of prolog
/Times-Roman findfont 12 scalefont setfont
0 792 translate
-90 rotate
1 1 6 { page } for % print page with change factor to frequency ranged from 1 to 6.
end
--
.signature under construction ...
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