Persistence of Vision is a theory that lies at the core of animation. It is a phenomenon that occurs within the human eye, in which an image remains for approximately 1/25th of a second in the retina. The concept was first written about by the physician Peter Roget in his 1824 paper 'The Persistence Of Vision With Regard To Moving Objects'. In his work, he attempts to describe the effect, and suggests that the eye works in such a way that when it perceives two or more images rapidly replacing one another, it is seen as a continuous flow of motion.
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| Thaumatrope Example |
Roget’s
writings on the subject influenced the development of several
experimental animation devices in the Victorian era. Two such
machines were, the Zoetrope (invented by William Horner) and the
Thaumatrope (invented by Sir John Herschel). These rudimentary
mechanisms helped demonstrate the theory, by demonstrating the above
theory, and they soon became amusing parlour tricks that entertained
many. Many now recognise these devices as the ancestor to the modern
film and animation industry.
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Who's Knocking At The Door, Zoetrope, 1870's |
It was
discovered quite early on, that if a sequence were to be played at
less than 16 frames per second, noticeable flickering would occur in
the movement. Once the frame rate rises past what is known as the
'flicker rate', the sequence will appear fluid, as the blank spaces
between frames are filled in by the residual image in the eye.
Without the ability to perceive the images as an unbroken sequence of
motion, we would be aware of the 'black' gaps between each frame. If
you would like to mimic this experience, try blinking your eyes and
slowly waving a finger in front of your face. Blinking fast, you will
perceive a small break in your vision, but when you blink slowly you
will begin to notice an obvious break in your vision. This is a very
crude example, however, it should serve well enough to demonstrate
the effect.
These
discoveries and the many experiments that were carried out around the
time, influenced the modern frame rate of the motion picture, which
was standardised at 24 frames per second. This was found to be the
best speed to achieve a smooth motion, whilst remaining manageable
with regards to quantities of film used, etc. Animation also stays
close to this, with a standard rate of 25 frames per second. However,
sequences of animation are commonly shot 'On Two's', which means that
every drawing will hold for two frames of film, which basically cuts
the workload in half. Therefore every second of film requires only 12
drawings as opposed to 24. This is a way of saving time, and reducing
the costs involved with producing such features. Fortunately, we are
still able to perceive motion at 12fps, however, it it is noticeably
not as smooth as an animation produced at a higher frame rate. Of
course, if the constraints of budget were not an issue, the
possibilities and creative output would become more flexible and
interesting
It is
safe to say that The Persistence of Vision is a theory that has
helped define an art form. It lies at the heart of the magic that
allows moving media to exist and be enjoyed by millions around the
world. It's discovery led to a massive leap forward in the
development of film and animation, the techniques used and improved
upon, and helped the art forms become what they are today.
Here are some cool links to look into:
(All
pictures used are the copyright of the relevant owners. No copyright
infringement intended.)
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