RE: [Algorithms] FPS Questions

[Pallister, K. <kim...@in...>]

I too, can boldly propegate the never ending thread!

Tom's point is correct, but not as simple as that. The eye doesn't just have
a 'response time' (time from when light hits the retina until the rods &
cones on the retina do their thing and call up the brain to say they've seen
something).

The eye actually has a response curve, and it changes for different
wavelengths (color) of light and amplitude.

After a similarly never-ending thread on this subject (eye response, maximum
frame rates, etc) about a year ago I went out and looked for research on it.
Turns out there has been quite a bit, most by NASA, the airforce, and
various optical/vision societies. A couple I did find were:

Window of Visibility: a psychophysical theory of fidelity in time sampled
visual motion displays (Watson et al, 85]
The Optimal Motion Simulus (Watson et al, 94)

Anyhow, if I remember correctly, what it comes down to is that the frame
rate at which people can no longer perceive discrete frames is somewhere
between 40 and 90 frames per second (yeah, I know some of you disagree and
will say it's higher), and this depends on:

- speed of objects moving
- size of objects on screen
- color of objects, background, contrast between
- lighting
- etc
- etc

and oh yeah, everyone's response curves are different.

Which leads me to a question: do you folks think that the eyes & brain can
be trained to better perceive such errors? The movies never used to bother
me until I became a graphics programmer. Now it bugs me. Also, PAL didn't
used to bother me, but now I find the lower frame rate intolerable, which is
why I make a point of not watching TV when I am in the UK, but spend the
time in pubs instead!

Kim Pallister

We will find a way or we will make one.
                     - Hannibal


> -----Original Message-----
> From: Tom Forsyth [mailto:to...@mu...]
> Sent: Tuesday, August 01, 2000 8:38 AM
> To: gda...@li...
> Subject: RE: [Algorithms] FPS Questions
> 
> 
> ...except that eye's don't have a "shutter" or a "framerate" 
> - they have a
> response time, but it's continuous, not discrete like a movie 
> camera. So you
> can't say that the eyes are "out of sync" - they don't _have_ a sync.
> 
> As for finding the optimum details settings to get "n"Hz on a 
> machine, with
> continuous LoD methods, you can get quite close (+/- 5Hz is 
> not too hard to
> achieve 95% of the time). You have some sensible defaults for 
> rendering
> quality (i.e. how many passes), according to card type, allow 
> the user to
> override them if they feel like it, and then CLOD up or down 
> to get the
> right frame rate (within sane limits).
> 
> Tom Forsyth - Muckyfoot bloke.
> Whizzing and pasting and pooting through the day.
> 
> > -----Original Message-----
> > From: Jim Offerman [mailto:j.o...@in...]
> > Sent: 01 August 2000 15:58
> > To: Algorithms List
> > Subject: Re: [Algorithms] FPS Questions
> > 
> > 
> > I gave my original query some more thought, and I think I 
> have found a
> > plausible explanation as to why 60 fps might be perceived as 
> > being smoother
> > than 30 fps.
> > 
> > The human eye in many ways works like a camera (note: 
> > actually, it is the
> > other way around): the retina is exposed to light for a small 
> > period of time
> > and then the accumulated light signal is transmitted to the 
> > brain before the
> > retina is exposed again.
> > 
> > Let's assume for a while that the eyes record at a steady 30 
> > fps. If our
> > game also runs at 30 fps, the eye sees one frame at the time. 
> > However, if
> > the game runs at 60 fps, the eye sees two frames at the time, 
> > which are
> > blurred together, resulting in a form of motion blur.
> > 
> > Another important aspect is that your eyes will _never_ be in 
> > sync with the
> > frame rate of your game, so it is possible that there exists 
> > a moment where
> > your eye records a frame, but there is nothing to record 
> > (since the monitor
> > is doing a vblank). This will certainly be perceived as a 
> > discontinuity of
> > the ongoing motion on the screen. The higher the framerate, 
> > the less likely
> > that such situations occur.
> > 
> > Finally, I must agree with the lower latency factor, since 
> > while our eyes
> > may be relatively slow, our responses (generally) are _really_ fast.
> > Specially, if someone is trained in some response, then it becomes a
> > reflex... An experienced FPS player might be using his brain 
> > as little as
> > 25% of the time, the rest of the time, his actions are merely 
> > reflexes.
> > Hence the phrase 'mindless killer' ;-).
> > 
> > > Why not just ask the player what they want and then scale 
> > the engine to
> > that
> > > speed.  If they want 'liquidity' at high frame rates then 
> > scale back and
> > use
> > > lower level of detail models.  If they can't tell the 
> > difference then
> > > they'll pull the frame rate down to 30fps and get better 
> > looking visuals.
> > 
> > We usually achieve this by offering the player some controls 
> > over detail.
> > Though it might be nice if your engine includes a little util 
> > which finds
> > the optimum detail settings to get n fps on a given 
> > machine... but I can
> > tell you that _won't_ be very easy, so better put that on the 
> > 'things to do
> > when I have time left' list ;-).
> > 
> > Jim Offerman
> > 
> > Innovade
> > - designing the designer
> 
> 
> 
> 
> 
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