Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!uwvax!astroatc!vidiot!brown
From: brown@vidiot.UUCP (Vidiot)
Newsgroups: comp.lang.postscript
Subject: setscreen pixels
Message-ID: <1454@vidiot.UUCP>
Date: 7 Mar 91 07:46:04 GMT
Reply-To: brown@vidiot.UUCP (Vidiot)
Organization: Vidiot's Hangout
Lines: 29


I need something explained that isn't explained in the new "red book", that
I have never seen explained anywhere, at least not in how it works internally.

One of the givens is that the spot function will provide a dot for a pixel.

As I understand it, the screen frequency applied will be the number of pixels
cells per inch, that will make up a 100% black spot.

As an example, if the frequency is 60, and a 300 dpi printer is used, that
leaves 5 pixels to define a shade of gray.  Square that value to get a spot
that is 5x5, or 25 shades.  Since you could have all white, add one to that,
yielding a total number of shades to 26.  The formula that I have seen is:

		       2
	(dpi/frequency) +1

But, nothing has ever said what to do about fractions.  If the frequency is
40, that gives 7.5 to be squared.  You can't have 7.5 dots to a side.  Does
the printer use floor or round to get the number of pixels in the cell?
What affect does the angle have in all of this (see a previous posting)?

In other words, what is the internal working formula for determining what
the printer will use for the number of pixels in the cell?  Are the formulas
different for the Apple LaserWriter IINT and the Lintotronic 1270 dpi?
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