|
Glossary of CCTV Terms (Page 3)
- GHOST - A shadowy or weak image in the received picture, offset either to the right or to the left of the primary image. It is the result of transmission conditions where secondary signals are created and received earlier or later than the primary signal.
- GROUND - An electrical connection point that is common to either a metal chassis, a terminal, or a ground bus.
- HORlZONTAL BLANKlNG - The blanking signal that is produced at the end of each scanning line.
- HORlZONTAL (HUM) BARS- Horizontal bars, alternately black and white, which extend over the entire picture. They are known as venetian-blinds. They may be stationary or move up or down. They are often caused by approximately 60 Hertz interfering fre
quency or its harmonic frequencies.
- HORlZONTAL RESOLUTlON - The maximum number of individual picture elements that can be distinguished in a single scanning line.
- lMAGE SlZE - Reference to the size of an image formed by the lens onto the camera pickup device. The current standards are: 1", 2/3", 1/2" and 1/3" measured diagonally.
- lMPEDANCE - The opposition which a circuit or component offers to the flow of electric current. It is expressed in ohms and is equal to the ratio of the effective value of the voltage applied to the circuit to the resulting current flow. In A.C. circuits, the impedance is a complex quantity that includes both resistance and reactance. In D.C. circuits, it is purely resistive. lNClDENT LlGHT - The light that is falling directly over an object.
- lNSERTlON LOSS - The signal strength loss that occurs when a piece of equipment is inserted into a line.
- lNTERLACE - A scanning process where every other horizo
ntal line is scanned in one field while the alternate lines are scanned in the next field to produce a complete picture frame.
- LAG - The image retention of an object after the object has been scanned. Sometimes, it causes smearing effect.
- LEVEL CONTROL - Main iris control. Used to set the auto-iris circuit to a video level desired by the user. After set-up, the circuit will adjust the iris to maintain this video level in changing lighting conditions. Turning the control towards High will open the iris, towards Low will close the iris.
- LOOPlNG - A term indicating that a high impedance device has been permanently connected in a parallel to a video source.
- LUX - A unit of measuring the intensity of light. (1 FC = 10 lux).
- MANUAL lRlS LENS A lens with a manual adjustment to set the iris opening (F stop) in a fixed position. Generally used for fixed lighting applications.
- MlNlMUM OBJECT DlSTANCE (M.O.D.) - The closest distance a given lens wi
ll be able to focus upon an object. This is measured from the vertex (front) of the lens to the object. Wide angle lenses generally have a smaller M.O.D. than large focal length lenses. MODULATE - To change or vary some parameter such as varying the amplitude of a signal for amplitude modulation or the frequency of a signal for frequency modulation. The circuit which modulates the signal is called a modulator.
- MONOCHROME - Having only one color. In television it is black and white.
- MONOCHROME SlGNAL - In monochrome television, a signal for controlling the brightness values in the picture. In color television, the signal which control the brightness of the picture, whether the picture is displayed in color or in monochrome.
|
|
