Re: [Algorithms] FPS Questions

[<Chr...@Pl...>]

I was going to keep out of this as I don't have time to do it fully
justice, but I feel I have to comment because a lot of incorrect
stuff is being passed around in this thread.

There are two concepts here that people keep getting mixed up:

1) Apparent motion
2) Flicker fusion

Apparent motion is the term used to describe the visual phenomenon where
the display of different distinct static images is perceived as continuous
motion. This phenomenon known as the 'phi phenomenon', first happens at
rather low frame rates, which is why movies are 24 fps and cartoons are
typically half of that.

Flicker fusion, however, happens at the frequency known as the critical
flicker fusion frequency (CFF) and this is where flicker disappears.
The CFF is much higher, around 60Hz, but varies from person to person,
and increases with brightness, viewing angle (the eye being more sensitive
to flicker in the peripheral), etc.

This is why movies stills are shuttered *twice* to get an effective frame
rate of 48 images per second, which works fine for a dark cinema. (If movie
images were displayed at 24 images per second, things would flicker
horribly.)

For a bright living room, around 60 Hz is more appropriate, and for a large
computer screen you want a much higher refresh rate because the viewing
angle is larger (not to mention the fact that a computer screen has a
faster decaying phosphor than a TV screen).


The link someone posted earlier is to a horribly incorrect page and should
be ignored. Instead, here are some links to a few good pages:

http://www.futuretech.vuurwerk.nl/fps.html
http://www.xabcs.demon.co.uk/ergonite/flicfaq.htm
http://www.microsoft.com/hwdev/TVBROADCAST/TempRate.htm
http://www.search.eb.com/bol/topic?eu=119396&sctn=4#s_top
http://www.search.eb.com/bol/topic?eu=55424&sctn=1#160276
http://www.britannica.com/bcom/eb/article/6/0,5716,119396+3,00.html
http://www.britannica.com/bcom/eb/article/5/0,5716,117505+13,00.html

There's also this nice illustration of the phi phenomenon on this page:

http://www.eecs.tufts.edu/~kreisman/phi/index.html


Christer Ericson
SCEA, Santa Monica