Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcso!hpfcdj!myers
From: myers@hpfcdj.HP.COM (Bob Myers)
Newsgroups: comp.graphics
Subject: Re: Hexagonal Pixels
Message-ID: <17400010@hpfcdj.HP.COM>
Date: 13 Sep 89 18:13:18 GMT
References: <2477@canisius.UUCP>
Organization: Hewlett Packard -- Fort Collins, CO
Lines: 38

>Just today I was discussing with a professor of mine about the use of
>hexagonal pixels.  Someone that I had talked to at Siggraph this year
>was telling me about how "in France there are monitors which use
>hexagonal pixels", yet my prof still believes that if a hexagonal
>tessalation is used, it is most likely converted into rectangular
>pixels.  Could anyone point me into the right direction on this
>subject?

As far as the *monitor* is concerned, "hexagonal pixel" (or rectangular, for
that matter) is a meaningless phrase.  All the monitor knows is that the
beam(s) in the CRT was turned on for X amount of time, during this particular
scan line.  The rise/fall times of the video amplifier, plus the shape of the
beam itself (ignoring other shape-distoring items like geometry correction
magnets) determines the shape of the spot.  The electron beam itself is most
often viewed as having a Gaussian cross-section; the best you can do, then
as far as actual pixel shape in concerned is a circular spot (which actually
falls off from the center in Gaussian manner along both axes).  In reality,
the limits of rise and fall times tend to distort this slightly, which is why
single-pixel-wide vertical lines tend to be dimmer than single horizontal
lines, unless your display system is smart enough to "stretch" single pixels.

Color CRTs complicate this issue by placing a shadow mask in the path of the
beam; however, the beams themselves are still Gaussian, and there is NEVER
a guarantee that a given pixel in the image lines up precisely with exactly
one red/green/blue phosphor triad, even when you're running at the highest
resolution permitted by the phosphor pitch.  The shape of a single pixel
as displayed on the screen looks more like a circular spot viewed through
a screen door; it is definitely not a nice clean square or rectangle.  There
may, for all I know, be monitors which use a shadow mask with hexagonal holes,
but this will not produce hexagonal pixels - it'll just "screen" them
differently.  Your conceptual model of the image would still be a rectangular
array of dots.  (Unless there's somebody out there designing a REALLY funky
frame buffer! :-))


Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
myers%hpfcla@hplabs.hp.com               |  sentient life-form on this planet.