Xref: utzoo comp.graphics:12380 alt.graphics.pixutils:152
Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uwm.edu!cs.utexas.edu!samsung!zaphod.mps.ohio-state.edu!ncar!boulder!uswat!mcain
From: mcain@uswat.uswest.com (Michael Cain)
Newsgroups: comp.graphics,alt.graphics.pixutils
Subject: Re: Summary and possible solution: pixel aspect ratio in GIF images
Message-ID: <9475@uswat.UUCP>
Date: 13 Jul 90 20:11:44 GMT
References: <9866@pt.cs.cmu.edu> <9894@pt.cs.cmu.edu>
Sender: news@uswat.UUCP
Organization: US WEST Advanced Technologies, CO, USA
Lines: 33

In article <9894@pt.cs.cmu.edu> tgl@zog.cs.cmu.edu (Tom Lane) writes:
>
>Erik Talvola (talvola@janus.Berkeley.EDU) points out that a GIF picture
>of size 320x200 pixels is almost surely intended for an IBM CGA display,
>one of 640x350 pixels for an IBM EGA display.  In either case, the
>standard physical screen aspect ratio is 4:3, so a CGA pixel has aspect
>ratio 1.2, an EGA pixel about 1.37.  VGA displays fill the same physical
>screen with 640x480 pixels, so their pixels are square.  Images of other
>dimensions might have come from anywhere.
>

I have been converting a number of GIF images of late for display
on a Hercules display adaptor using the PBMPLUS package.  Images
that are 320x200, 640x350 or 640x480 are almost always (certainly
more than 95% of the time) intended for display on a monitor with
4:3 aspect ratio.  I just resize them for the Hercules 720x348 and
they look fine.  My own experience has been that GIFs of other sizes
are mostly (say more than 80% of the time) intended for displays
with 1:1 aspect ratios.

Most of the 320x200 pixel images I've seen were actually intended
for brain-damaged VGA displays that only supported 256 colors in
that resolution.

For those with access to a UNIX platform to do the conversion, the
PBMPLUS tools are very nice.  The images produced by converting
a 256-color GIF to monochrome bitmap using the PBMPLUS tools  are
enormously better than the images obtained with CSHOW 8.10 (the
only GIF viewer I've found that supports monochrome Hercules displays).

Michael Cain
U S WEST Advanced Technologies
mcain@uswat.uswest.com