CCTV Glossary
Cascadia Video Products LLC
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Plumbicon. - Thermionic vacuum tube developed by Philips, using a lead oxide photoconductive
layer. It represented the ultimate imaging device until the introduction of CCD chips.
Polarizing filter. An optical filter that transmits light in only one direction (perpendicular to the light
path), out of 360° possible. The effect is such that it can eliminate some unwanted bright areas or
reflections, such as when looking through a glass window. In photography, polarizing filters are
used very often to darken a blue sky.
POTS. - Plain old telephone service. The telephone service in common use throughout the world
today. Also known as PSTN.
P-picture. - Prediction-coded picture. An MPEG term to describe a picture that is coded using
motion-compensated prediction from the past reference picture.
Preset positioning. - A function of a pan and tilt unit, including the zoom lens, where a number of
certain viewing positions can be stored in the system’s memory (usually this is in the PTZ site
driver) and recalled when required, either upon an alarm trigger, programmed or manual recall.
Primary colors. - A small group of colors that, when combined, can produce a broad spectrum of
other colors. In television, red, green and blue are the primary colors from which all other colors in
the picture are derived.
Principal point. - One of the two points that each lens has along the optical axis. The principal
point closer to the imaging device (CCD chip in our case) is used as a reference point when
measuring the focal length of a lens.
PROM. - Programmable read only memory. A ROM that can be programmed by the equipment
manufacturer (rather than the PROM manufacturer).
Protocol. - A specific set of rules, procedures or conventions relating to format and timing of data
transmission between two devices. A standard procedure that two data devices must accept and
use to be able to understand each other. The protocols for data communications cover such things
as framing, error handling, transparency and line control.
PSTN. - Public switched telephone network. Usually refers to the plain old telephone service, also
known as POTS.
PTZ camera. - Pan, tilt and zoom camera.
PTZ site driver (or receiver or decoder). - An electronic device, usually a part of a video matrix
switcher, which receives digital, encoded control signals in order to operate pan, tilt, zoom and
focus functions.
Pulse. - A current or voltage that changes abruptly from one value to another and back to the
original value in a finite length of time. Used to describe one particular variation in a series of wave
motions.
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