Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcdc!hpfclm!hpfcdj!myers
From: myers@hpfcdj.HP.COM (Bob Myers)
Newsgroups: comp.graphics
Subject: Re: Re: ShowScan quality image bit rate
Message-ID: <17670008@hpfcdj.HP.COM>
Date: 7 Feb 89 19:51:16 GMT
References: <18071@glacier.STANFORD.EDU>
Organization: Hewlett Packard -- Fort Collins, CO
Lines: 30

/ hpfcdj:comp.graphics / mcdonald@uxe.cso.uiuc.edu / 11:43 am  Feb  5, 1989 /


>The question of the number of independent frames per second is tougher,
>but let's say 15 per second minimum - that gives 9 gigabits per second.
>Make it ten gigabits for a round number. If done right that wouldn't
>flicker but motion would appear jerky at that rate, unless "smearing" were

If it's a CRT display we're talking about - and some form of CRT seems the
only viable option for high-resolution color in the near future - then the
"frames per second" number becomes much more important.  60 Hz would be the
*minimum* acceptable refresh rate, and for a screen of the proposed size, at
any reasonable brightness, the refresh should be even higher - say, 72 Hz.

But let's stick with 60 Hz, and assume a 300 dpi resolution with an image
1 meter on a side.  This results in approximately a 11000 x 11000 raster;
assuming typical horizontal and vertical blanking numbers (20% and 5% of
the total H and V times, respectively), we get a dot clock of over 9.5 GHz,
and a horizontal sweep rate of 694.7 kHz!!!  (Cold-cathode CRTs offer some
hope of doing away with the sweep, but you'll still need to read the video
out DAMN quickly!)  Note that this says nothing about how fast the digital
store (frame buffer) needs to be updated; it says simply that, assuming
conventional display technology, the video bandwidth is likely a limiting
factor before such high resolutions are reached.



Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
{the known universe}!hplabs!hpfcla!myers |  sentient life-form on this planet.