Image Processing Reference
pull the film down through the gate. This movement has to be very precise. The film must
be moved by exactly one frame distance. The sprockets must be aligned perfectly each
time or the film will be torn by the claw mechanism.
The shutter allows the light through in order to expose the film in the camera or project it
onto a screen when viewing. The shutter is mounted on a spindle and rotates once per
frame. The projector contrives to flash the image on the screen twice. This effectively pres-
ents the image at 48 fps (frames per second), although the film is only moving at 24 fps
through the gate. Figure 4-2 shows shutter designs for a camera and projector.
Some projectors allow the shutter timing synchronization to be adjusted so as to
open or close the aperture with respect to the gate movement. Even more sophisticated
projectors allow adjustments to how much time the aperture stays open.
Picture Formats and Sizes
Probably the most important parameters that you have to know are the physical charac-
teristics of your source material.
These include the following:
Width in pixels
Height in pixels
Frames per second
Scanning method (interlaced or progressive)
Figure 4-2 Camera and projector shutter designs.