My theory is that the brain automatically 're-frames' the image when you move your eyes. Here's a point - the eyes never move smoothly unless tracking a moving object to keep it stationary within the field of vision. They always dart about. Cinema would not work if our eyes were digital, since the frame rate of our eyes would go out of sync with the pictures. Persistence of vision is why cinema works. Projectors (35mm) show each frame three times, so that there is no flicker to the image, so if there is a 'sampling rate' of the eye then it is certainly higher than the 72 flickers-per-second. Flourescent gas discharge lamps flicker, albeit at a very high speed, so this explains the aliasing effect. This is a great way of explaining aliasing (like cartwheels in a 'Western' movie) because the light is 'sampling' the bicycle wheel. My bicycle wheels are so buckled that this becomes very confusing to look at ;-)
Going back to the spectrum graphing amplitude problem - there should be a way to use peakit~ and build a graphical data structure-based array around its findings. I think data structures are the way forward for this sort of thing since they represent information in an abstract graphical way. examples/ekext/peakit-listmoses.pd (but there's no graphical array yet) Chun did a cool thing - it would be interesting to know how the video was made. Look up 'chun lee glass cloud' on youtube. Gem?
Best, Ed
On 10/22/07, Roman Haefeli reduzierer@yahoo.de wrote:
On Mon, 2007-10-22 at 17:33 -0500, Charles Henry wrote:
On 10/22/07, Martin Peach martin.peach@sympatico.ca wrote:
Mathieu Bouchard wrote:
A very simple way to explain aliased frequencies would be: spin
a bicycle
wheel. When you accelerate it beyond a certain point, it will
begin to look
like it's going backwards instead. This is because the wheel
speed,
together with the repetitiveness of the wheel's appearance, have
crossed
the Nyquist frequency of your eye.
That won't work in sunlight for example.
Haven't you ever seen it? (in sunlight that is)
As implied, I'm 99% positive I've seen it before. You might still be able to convince me that I haven't ;)
i think, that is the point that martin is trying to make.
i am not an expert either, but when i encountered this effect
(watching
the frontwheel, while cycling at night, for instance), there was
always
artificial light involved. to be more precise, there was always kind
of
a fluorescence or any other kind of 'gas discharge lamp' (is that the correct expression?) involved. it doesn't seem to work with common
light
bulbs, since their 'afterglow time' is too long.
for me, it seems, that it is rather related to the light source and
its
frequency and not to a property of the eye.
hey, what do you know, there's even a wiki page on it: http://en.wikipedia.org/wiki/Wagon-wheel_effect
Vision is in fact not purely analog. Although I don't necessarily think the "discrete frame" theory mentioned in the page is true, there is a counterexample. When your eyes make a saccade (fast movement), there is no blurring. There is an inhibition of the movement in between the two visual scenes. There is also nystagmus. Even when images appear perfectly clear, the eye moves in random oscillations. When researchers (I forget the citation/can't find it) used an eye camera to track random oscillations and corrected for the movement (creating a static retinotopic image), the perceived image disappears. There may be something involved in correcting for nystagmus that renders an image in a series of apparently still frames. I don't know for sure.
Chuck
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