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From: rberlin%birdlandEng@SUN.COM (Rich Berlin)
Newsgroups: comp.laser-printers
Subject: Re: Hairlines
Message-ID: <9104171649.AA25773@crayola.cs.UMD.EDU>
Date: 16 Apr 91 22:57:42 GMT
References: <9104151944.AA15613@crayola.cs.UMD.EDU>
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In article <9104151944.AA15613@crayola.cs.UMD.EDU>, ejbehr@RS6000.CMP.ILSTU.EDU (Eric Behr) writes:
|> Here is something that has bothered me for a long time. When I print some
|> PostScript code containing very thin lines (e.g. 0.001 setlinewidth), some
|> of them seem to be thicker than others. To see that it's best to print a
|> rather fine grid - e.g. every 1/8 inch or so. This shows up on two Apple
|> printers I've used - an old II NT and my Personal NT. Since engines are
|> different in the two, I have no clue as to what may be causing that.
|> Did other people notice that? If so, what's the reason?        Eric
|> -- 
|> Eric Behr, Illinois State University, Mathematics Department
|> Internet: ejbehr@rs6000.cmp.ilstu.edu    Bitnet: ebehr@ilstu

The thickness of the line is varying based on where your lines land in
device space.  This is documented behavior in the redbook.  In
PostScript Level 2 there's a feature that you can turn on to fix the
problem; in the meantime you're stuck having to adjust the line width
yourself.  The method is documented, but the basic idea is that for
every coordinate pair you push on the stack, you adjust the
coordinates to land on a pixel boundary.

%!
% Adjust a coordinate pair to land on pixel boundaries
/adj {  % x y => x' y'
    transform
    round exch round exch
    itransform
} bind def

% Then try this test:

.001 setlinewidth
% Regular grid
0 72 8 div 72 {
   /n exch def
   0 n moveto 72 n lineto stroke
   n 0 moveto n 72 lineto stroke
} for

% Adjusted grid
100 0 adj translate
0 72 8 div 72 {
    /n exch def
    0 n adj moveto 72 n adj lineto stroke
    n 0 adj moveto n 72 adj lineto stroke
} for