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From: jmd@ee.umr.edu (Jim Dumser)
Newsgroups: comp.lang.postscript
Subject: Re: setscreen pixels
Message-ID: <2364@umriscc.isc.umr.edu>
Date: 9 Mar 91 16:00:04 GMT
References: <1454@vidiot.UUCP> <2349@umriscc.isc.umr.edu> <1474@vidiot.UUCP>
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In article <1474@vidiot.UUCP> brown@vidiot.UUCP (Vidiot) writes:
|In article <2349@umriscc.isc.umr.edu> jmd@ee.umr.edu (Jim Dumser) writes:
|<
|<[ Quote from the red (& white) book ]
|
|Ya, I read that, but it doesn't answer the question asked next.  It doesn't
|say how the the number of pixels in the cell is computed, which is what I
|was asking for.
|
|<> [ Vidiot's question about fractions (ie. sqrt(40) = 7.5) ]
|<
|<[p314]:
|<  "the *sethalftone* or *setscreen* operator may make slight
|<  adjustments to the requested frequency and angle to ensure that the
|<  patterns of enclosed pixels remain constant as the screen cells are
|<  replicated over the entire page."
|
|Ya, I read that too.  Still doesn't answer the question.
|
|<>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?
|<
|<In Level 2, halftone dictionaries have an optional entry,
|<AccurateScreens, that cause "extremely precise, but computationally
|<expensive" algorithms to be used.  Also, they can have entries that get
|<set with the actual frequency and angle used.
|
|So, what are the internal formulas??????

Ok, here's your answer:
	They are unspecified.

In otherwords, they are implementation dependent.  Probably a Lintotronic
printer will not use the same algorithm as a LaserWriter.  If you are
writing for Level 2, you can iterate until you get the ActualFrequency
and ActualAngle you want.

Jim