G

Gain

A term used for amplification of an electronic signal. Also stands for amplitude or volume. In projection systems, the ability of a screen to amplify incident light. In cameras, the ability to amplify the input signal to obtain pictures in low-light conditions.

Gamma

Sometimes called "Gamma Correction" Refers to the accuracy of the light intensity transfer through a video system (monitor). Predistortion of the video components (R, G, and B) are required in order to compensate for the nonlinear response of a monitor (the relationship between the input voltage and the corresponding brightness level is not linear relationship in picture tubes). The gamma factor (typically 2.2 for NTSC) is used in computing the predistortion.

Gamut

The range of voltage permitted for a video signal or video signal component. Voltage levels outside the gamut result in distortions such as cross talk and clipping.

Gate

The aperture assembly at which the film is exposed in a camera, telecine, printer or projector.

Gateway

A computer system for exchanging information across incompatible networks that use different protocols. For example, many commercial services have e-mail gateways for sending messages to Internet addresses.

General Purpose Interface (GPI)

A pulse or contact (switch) closure signal sent from an editor to trigger audio tape recorders, digital video effects devices, and graphics generators to activate for an edit or effect. Some external devices do not have the ability to be directly controlled by the editor. In this case GPI signal is used as a means of telling these devices when to execute a command. The choice of command itself, however, must be set up on the external device and cannot be controlled by the editor.

A TTL level signal used to trigger an event. Graphical User Interface Usually a connection on equipment where a contact closure is used to activate a device or piece of equipment. An audio tone can be used to activate a contact closure to “roll” events. A trigger event!. Software process providing operator access to the overall software application.

Generation

This refers to the number of times the original master videotape is copied. For example, the videotape used by the VTR during the actual shooting is a first generation tape. The edited master made from those original tapes would be second generation.

Generational Loss

The decreasing signal-to-noise ratio resulting when one analog recording is copied to another.

Genlock

A device or a function of a device to lock both the sync and color burst of one signal to the sync and burst of another signal. Synchronization of signals is required for mixing, keying, and switching downstream. A system whereby the internal sync generator in a device, such as a camera, locks on to and synchronizes itself with an incoming signal.

Geometry

The positional and aspect accuracy of a (video) picture element.

Geosynchronous

A term used to describe the orbit of satellites which rotate around the earth in a 24-hour period at an altitude of 22,300 miles; sometimes called Geo-stationary.

Ghost

A secondary image visibly offset from the original video image caused by transmission reflections. Ghosting or lag has been almost entirely eliminated by CCD imagers.

Ghosting

Transparent duplicate image resulting from signal reflections

GIF

Graphics Interchange Format. A graphics format developed by CompuServe using compression technology from Unisys. GIFs are common on Web pages due to their small size.

Gigabyte

A billion bytes. A thousand megabytes.

Gong Bars

Gong bars are 'Rank bars' from a Cintel telecine (from the digiscan), which feature the Rank Organization 'Gong Man' symbol. Depending on your telecine it was either 75% or 100% bars, or both. The pattern also sometimes featured the name/logo of the company that owned the telecine. Some clients wanted the Gong bars on a tape as a way to 'prove' that the transfer was a 4:2:2 digital transfer.

GOP (Group of Pictures)

In an MPEG signal the GOP is a group of frames between successive I frames, the others being P and/or B frames. In the widest used application, television transmission, the GOP is typically 12 frames but this can vary-a new sequence starting with an I frame may be generated if there is a big change at the input, such as a cut. If desired, SMPTE timecode data can be added to this layer for the first picture in a GOP.

Gopher

An Internet server document browsing and searching system that lets you search and retrieve texts on the Internet. Gopher has since been surpassed by the World Wide Web

GPI

1. General Purpose Interface. A simple control interface that sends or receives triggers from/to external equipment. 2. General Purpose Input. A port that receives simple electronic triggers to cause a timed response within the host. 3.General Purpose Interface. A digital signal used for devices not controlled by RS-232 or RS-422 protocols. GPI provides a two-state signal (on, off).

GPO

General Purpose Output. A simple control interface that triggers external equipment.

GPRC

(General Purpose Record Channel) A playlist for recording content controlled or tape-delayed turnaround material (satellite feeds).

Grand Alliance:

The United States grouping, formed in May 1993, to produce "the best of the best" initially proposed HDTV systems. The participants are: AT&T, General Instrument Corporation, Massachusetts Institute of Technology, Philips Consumer Electronics, David Sarnoff Research Center, Thomson Consumer Electronics and Zenith Electronics Corporation.
The format proposed is known as the ATSC format.
See also: ATSC.

Graphics (Computer term)

Text or pictorial artwork created on the computer with software and stored on a hard disk for use in computer-based presentations, desktop publishing, or video applications.

Graphics (Video term)

Text and Graphics created primarily by specialized electronic character generators and graphics systems and used in videotape applications. Personal computers equipped with special video output cards are capable of producing graphics for video production.

Graphics Capability

Some codecs offer a graphics transmission capability that permits the transmission of still-frame images at higher resolution than the motion channel. This feature is used in conjunction with a graphics camera and stand, scanner, or Mavica®.

Graticule

A plastic overlay or electronically generated grid and scale on the waveform and vectorscope displays used in measuring waveform characteristics.

Gray Scale

An even range of gray tones between black and white.

Ground

A point of zero electrical potential (e.g. a metal chassis, the earth, or a ground plane). The metal chassis of most video equipment is "grounded". Equipment is often grounded for safety factors to prevent accidental electrocution.

GSN

Gigabyte System Network is the highest bandwidth and lowest latency interconnect standard, providing full duplex 6400 Megabits per second (800 Megabytes per second) of flow-controlled data transmission. The proposed ANSI standard provides for interoperability with Ethernet, Fibre Channel, ATM, HIPPI-800, and other standards.

Guard Interval

Additional safety margin between two transmitting symbols in the COFDM standard. The guard interval ensures that reflections occurring in the single-frequency network are eliminated until the received symbol is processed.

GUI (Graphical User Interface)

A computer operating system that relies on menus, icons, and a pointing device (mouse) for user interaction. The foundation for the Macintosh™ personal computer and IBM PCs operating with Microsoft Windows™ 3.0.