Andrew B. Watson
& A. J. Ahumada Jr.
(1983)
NASA Technical Memorandum 84352.
Also published in J. K. Tsotsos (Ed.),
Motion: Perception and representation (pp. 1-10).
New York: Association for Computing Machinery.
Acrobat Version
Abstract
A moving image can be specified by a contrast distribution,
s(x,y,t) over the dimensions of space x,y, and time t.
Alternatively, it can be specified by the distribution
C(u,v,w) over spatial frequency u,v, and temporal frequency w.
The frequency representation of a moving image is shown to have
a characteristic form.
This permits two useful observations.
The first is that the apparent smoothness of time-sampled moving
images (apparent motion) can be explained by the filtering action
of the human visual system.
This leads to the following formula for the required update rate
for time-sampled displays.
wc = wl + r ul ,
where wc is the required update rate in Hz, wl is the limit of human
temporal resolution in Hz, r is the velocity of the moving image in
degrees/sec, and ul is the limit of human spatial resolution in
cycles/deg.
The second observation is that it is possible to construct a linear
sensor that responds to images moving in a particular direction.
The sensor is derived and its properties are discussed.