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Subject: Re: Still images
From: BlueChip (cs_bluechip_at_webtribe.net)
Date: 2004-01-19


That makes sense, thanks ...and no, I had missed the grayscale demo
<cliking now>

> > I chatted briefly with Dogger on irc last night about the display of still
> > images ...how many grey scales do we achieve?
>
>As I wrote before, this is no firm number. It's a smooth transition of what
>you perceive as grayscale to flicker.
>Did you view grayscale.rvf ? from:
>http://joerg.hohensohn.bei.t-online.de/archos/doom/small.zip
>Move your viewing angle up and down, the transition also moves.
>
>If we loop a still file, the max. amount of grayscales is # of frames + 1,
>so for these looping 34 frames you can't have more than 35 shades. For a
>continuous movie, there is no crisp limit to tell.
>
> > If we run at 72fps, and given that the human eye wil perceive animation at
> > 24fps, we have the option of pixel on for 0, 1, 2 or 3 periods, giving
> > four grey-scale values.
>
>No, first your eye is rather slower (that's why they play movies at 24fps,
>to be above), and second I'm also exploiting that the LCD is (a lot more)
>slow.
>
>When I change a bit from 0 to 1 or vice-versa, the LCD doesn't follow that.
>Instead, it does something like an exponential decay. I'm pulsing the pixels
>in a way that 1) would hold them at the desired level, if they'd be _very_
>slow, and 2) switch them as often as possible to avoid flicker.
>
>Fabian does it different, he uses 6 fixed pulse rates to get 6 grayscales. I
>prefer my way...
>
> > If, however, the >4 grey-scales are an optical illusion and my math is
> > correct, a still frame viewer should be able to generate the pixel values
> > real time and therefore remove the prerequirement for transcoding to film
> > before display?
>
>No way, the poor box is just barely fast enough to pump the pre-rendered
>bytes to the display, already coded in optimized assembler. Even for that
>I fall
>a bit short, the display scan is slightly faster. No time left for anything
>like per-pixel math.
>
>Jörg
>
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