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From: orthlieb@adobe.COM (Carl Orthlieb)
Newsgroups: comp.lang.postscript
Subject: Re: Thin line woes
Message-ID: <5657@adobe.UUCP>
Date: 16 Aug 90 18:59:11 GMT
References: <10244@pt.cs.cmu.edu> <15253@imagen.UUCP>
Reply-To: orthlieb@adobe.UUCP (Carl Orthlieb)
Organization: Adobe Systems Incorporated, Mountain View
Lines: 31

In article <15253@imagen.UUCP> isaak@imagen.UUCP (Mark Isaak) writes:
>The simplest solution otherwise is to specify "0 setlinewidth", which
>will give a nice-looking one-pixel-wide line at all angles.  For slightly
>wider diagonals, some combination of endpoint rounding and/or width
>correction may be desirable.
>
>in article <10244@pt.cs.cmu.edu>, tgl@zog.cs.cmu.edu (Tom Lane) says:
>>   2. In the book "Real World PostScript" (Roth, ed.), Michael Fryd
>> recommends rounding endpoint coordinates to nearest-integer-plus-0.25
>> in device space, whereas the green book just shows rounding to nearest
>> integer.  Which of these is better, and why?
>
>For horizontal and vertical lines, it shouldn't matter in theory, although
>adding +0.25 might avoid some obscure round-off errors in practice  (That
>last part is just a guess).  I'm not sure how the difference would affect
>diagonal lines.

The "Real World PostScript" book is correct. If straight rounding is
performed, lines will be biased to be an even number of pixels wide. If
rounding + 0.5 is performed, lines will be biased towards an odd number of
pixels. Rounding + 0.25 ensures an even (no pun intended) distribution of
even and odd pixel line weights.

0 setlinewidth is discouraged because it is device dependent, lines will
be different point sizes on printers with different resolutions.

To obtain a one-pixel wide line on a 300 dpi device, use the round + 0.25
method and specify 0.12 setlinewidth. This will give you wider diagonals and
maintain a 1 pixel width on horizontal and vertical lines.

Carl 8-)