Xref: utzoo comp.lang.postscript:1435 comp.text.desktop:657
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From: rcd@ico.ISC.COM (Dick Dunn)
Newsgroups: comp.lang.postscript,comp.text.desktop
Subject: Re: Publishing laserset material (and printer "resolution")
Summary: 300 dpi is 300 dpi, but...
Message-ID: <13747@ico.ISC.COM>
Date: 19 Jan 89 01:21:21 GMT
References: <10322@gryphon.COM> <88@sopwith.UUCP> <10844@gryphon.COM>
Distribution: na
Organization: Interactive Systems Corp, Boulder, CO
Lines: 29

In article <10844@gryphon.COM>, richard@gryphon.COM (Richard Sexton)
replied to a comment about using the printer's full resolution:

> Huh ?  300 dpi is 300 dpi.

However, there are programs that generate output for lower-resolution
printers, then just scale the bits for a laser printer--the result, of
course, is that you get the quality of a dot-matrix printer for the price
of a laser printer.

But more than that, the "300 dpi" business is very deceptive.  All that 300
dpi means is that the spacing between the "dots" the printer can put on the
paper is 1/300".  It doesn't say anything about the size or shape of the
dots, nor about how small a dot will actually show up reliably.  There's
stuff like the quality of the paper surface, the texture of the toner, and
all the nasty things that get out of focus, get dirty or scratched, wear,
etc...all affecting the quality.

The dots don't come out square--that is, you don't just divide the page up
into a grid of squares 1/300" on a side and color in the squares you want.
The dots are much closer to being round (which is probably actually good,
since it reduces the jaggie effect).  Then, consider that the dots have to
be larger than 1/300" diameter, or they wouldn't join over a large area to
make uniform black--there would be holes in the region inside each 4-dot
square.  If the dots were perfectly round, they'd need to be sqrt(2)
larger than the "resolution" to join completely.
-- 
Dick Dunn      UUCP: {ncar,nbires}!ico!rcd           (303)449-2870
   ...A friend of the devil is a friend of mine.