Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!execu!sequoia!cb
From: cb@sequoia.UUCP (Christopher D. Brown)
Newsgroups: comp.graphics
Subject: Re: Need Half-Toning Algorithm suited for HP-Laserjet
Message-ID: <578@sequoia.UUCP>
Date: 29 Jun 89 13:25:45 GMT
References: <8022@ppgbms.UUCP> <11390020@hpldola.HP.COM>
Reply-To: cb@sequoia.UUCP ()
Organization: Execucom Systems Corp., Austin, Texas
Lines: 27

In article <11390020@hpldola.HP.COM> paul@hpldola.HP.COM (Paul Bame) writes:
>I've played with HP laserjet dithering before (logical, since I work for HP)
>and have been very pleased with the standard dithers usually used on screens
>most of the time.  The time when I was displeased was trying to have the
>images look right at 300 dpi.  A test image, white on the left and changing
>continuously to black on the right "appeared" wrong even though I counted
>some pixels and they were correct (dithered with FS dithering).  I suspect
>either or a combination of:
>
>	1) Some phychovisual quirk which is really bad at 300dpi but not so
   ...
>	2) All laserjets are not equal.  There are adjustments which vary
   ...

I'd like to add that, in a similar situation, I convinced myself of
the following:

        3) Laser printing uses a charge to attract toner.  When a
           pattern like "X X X X " (i.e. 50% grey) is printed at
           sufficiently high resolution, the area between the pixels
           behaves as though it is charged.  If the pattern "XX    XX"
           draws 4 units of toner, than the pattern "X X X X " draws
           5 or 6 units of toner.  I produced nearly linear results
           using dither patterns which avoid alternating pixels.  E.G.
           6 by 6 spiral.

Nice story ... Chris Brown