56 2. FIVE STORIES TO A MODEL OF VIDEO STRUCTURE
We need a little more though. e illusion of motion is normally
brought about by the slight changes in data from frame to frame when
played back at the intended or nominal speed of the medium. A viewer
of a collection of random photographs could arrange a set of prints
or digital les and allot a set time period for viewing each image and
set an order in which they would be viewed, but this would not nec-
essarily present any perception of motion, nor would it necessarily be
considered a representation of motion. It would be, essentially, a slide
show; it might have thematic coherence, yet would not be a moving
image document.
For another case to consider, we turn to a recent development
in video to nd a transitional case—the Ken Burns eect. Documen-
tarian Ken Burns developed a technique by which “Action is given
to still photographs by slowly zooming in on subjects of interest and
panning from one subject to another.” e illusion of motion is gener-
ated by moving the camera (or software version of a camera) over the
image, thus producing a set of frames that have the sort of dierence
between any two consecutive frames we discussed above. e image
on the screen, the stimulus set to the eyes of a viewer, is changing at
a standard rate; the illusion of motion though is motion of the still
photograph rather than of the objects in front of the original camera.
Here a sample of frames from two seconds of panning to the left across
an image of a city street.
is is not necessarily a cheat in terms of message making or
story telling and the eect does depend on the same persistence of vi-
sion that seems to account for what would normally be called a movie,
yet there is no illusion of motion in the ordinary sense of some objects
moving against a static backdrop and with regard to one another. We
are speaking here of message making, of a lmmaker coding a mes-
sage; as Blair [Hayes too sort of ] suggests, the lmmaker dances with
the viewer, making assumptions about the viewer’s decoding abilities.
Persistence of vision sets limits on coding practices; it frames the rate of change in the visual data
stream at playback. Too little change from frame to frame and the viewer perceives no motion; too
much change from frame to frame and the ability to merge the data is lost.
Any single pixel address within a frame is comprised of four values: red, green, blue, and
opacity—RGBA or RGBα. For any pair of frames two additional values are added to the pixel