Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!caen!hellgate.utah.edu!uplherc!wicat!meph!gsarff
From: gsarff@meph.UUCP (Gary Sarff)
Newsgroups: comp.lang.postscript
Subject: Re: setscreen pixels
Message-ID: <00088@meph.UUCP>
Date: 15 Mar 91 04:01:30 GMT
References: <1454@vidiot.UUCP> <2349@umriscc.isc.umr.edu> <1474@vidiot.UUCP> <2364@umriscc.isc.umr.edu>
Reply-To: gsarff@meph.UUCP
Organization: WICAT Systems Inc., Orem Utah
Lines: 48

In article <2364@umriscc.isc.umr.edu>, jmd@ee.umr.edu (Jim Dumser) writes:
>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 ]
>|
>|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.
>

Might this then be the answer to a question I have had for some months now?
The question is why does the same postcript code produce different quality of
image on different postscript printers that use the same or similar printing
engines.  I specifically have some digitized images (from an amiga actually)
and have used a conversion program to take IFF graphics file and make a
postcript file (bitmap printing), and printed it on many (more than
are listed here), different printers with mixed results.  The best was a TI
OmniLaser, the output looked almost like a photograph at arms length
distance.  

Printed on a HP LJII with postcript emulation, the graphic (a person's face)
looked pretty awful, large areas of same gray level shading that just were
not evident on the TI printout.  On a HP DeskJet 500 and using a software
postscript interpreter (pixelscript) on the amiga, the quality approached
that of the TI, except that the paper was warped because of the large amounts
of wet ink delivered to it.

On an Apple Laserwriter IINTX, the quality still did not impress me as much
as the TI's.  Since the image was at computer resolution (say 640x400) when
turned into postcript, it was obviously scaled by a large amount, and then
rotated 90 degrees also, to make a landscape printout.  So, is it that the
algorithms differ that causes this difference in image quality?  How can a
potential buyer know, except by having a sample image and printing it on all
the printers in reach?  I have showed this stack of about 15 printouts of the
same image and virtually everyone at work would pick the TI as best quality.
I guess that means I should be quiet and buy one? 8-)

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