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wiki: Persistence of Vision.
The phrase covers several phenomena, and the jury is still out as to which is the actual 'cause'. The Phi phenomenon, Beta Movement or the 3 phenomena that are part of the Lilac Chaser, are all part of the PoV.
Frame rates as low as 10 - 12 frames per second can also be interpreted as continuous motion - depending on the time that the frame is held stable in vision and the 'blank' time it is being exchanged for the next frame.
Frames rates lower than 10 - 12 start to be seen as individual images or rather as 'jerkiness'. Frame rates in the 6 - 8 can trigger epilepsy (strobe lights or the sun flashing hrough tres while speeding on a motorway can do the same). Alpha waves are electromagnetic oscillations in the brain of 8 - 12 Hz. (there's a neuronal pacemaker). Beta rhythms in the brain are from 12 - 30 Hz, Gamma waves average about 40 Hz (but range from 25 - 100 Hz. Theta waves are 6 - 10 Hz.
Strangely, the early 20th C audiences for e.g. Charlie Chaplin movies never saw the speeded up motion that is now iconic for 'silent movies'. The lack of standards at the time for filming and projections speeds (until the mid '20s the cameras and projected were hand-cranked), along with the cost of early nitrate film stock, meant that shooting speeds of 12 frames per second were common - and the projectionists would attempt to match these speeds in showing the film. As motors were added, a frame rate of 16 fps became standard.
By the time the 'silent movies' were revisited, the technology for presenting the movies at their original frame rates were no longer generally available. Thus they were run at faster frame rates of fixed speed projectors.
You can't be me, I'm taken
It is hard to know what is myth, but it is said that films moved up from that 16-18 frames per second average to 24 frames in order to get smooth sound! not for the purpose of some science of sight (as we are generally taught.)
There is a group (mentioned in the next document) named the EDCF (European Digital Cinema Forum, part of whose work has been to keep the Hollywood powers-that-be aware that there are different needs outside the US. A most obvious example is that much of the music recorded around the world is recorded at 25 frames per second, not 30 (or variations of 25 and 30 to get away from phase beating from the electricity pulse, like 19.96....) These recordings have to be changed in some way by US post houses, such that the original pitch is changed or edited in some fashion.
The sub-group that pushed this was headed by Kommer Kleijn, who successfully got attention and results on an international level for this aspect, as well as lower and high speed alternative display frame rates. Here is a presentation that he gave a couple years ago: Flexibility in Frame Rates. (He mentions IMAGO in the first slide, which is the European Association of Cinematographers.)
As part of this work on behalf of archivists the world over, he worked with the chief engineer at the French and American server company Doremi, Francois HELT. They gave a demonstration 18 months ago that showed what could be done with projectors and old material. They came across the idea that 24*3, which is a natural frame rate in the digital projector, could be utilized to show 18*4. We all sat entranced while they played +100 year old, converted-to-digital films, via a digital projector. We saw some of the first camera tricks for movies from before and shortly after 1900.
I can't say enough nice things about the EDCF, who will gladly allow membership rights to interested parties for a relatively low fee.
Never underestimate their intelligence, always underestimate their knowledge.
Frank Delaney ~ Ireland
I'll have to read up on EDCF, thanks ;-)
You can't be me, I'm taken
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