Gamma Gamma has several meanings. In the video world a CRT television monitor's brightness is not linearly proportional to its driving voltage. In fact the light output increases rapidly with drive. The factor, gamma, of the CRT, is generally calculated to be 2.6. This is compensated for in TV cameras by a gamma of 0.45 giving an overall gamma of 0.45 x 2.6 = 1.17 - adding overall contrast to help compensate for domestic viewing conditions. In film, gamma describes the average slope of the D/Log E curve over its most linear region. For negative stocks this is approximately 0.6, for intermediate stocks this is 1.0 and for print stocks 3.0. This gives a system gamma of 0.6 x 1 x 3 = 1.8. This overall boost in contrast is much reduced due to flare and auditorium lighting conditions. With video now available on many varying types of devices there may be a need to re-visit the gamma settings. This can be done by applying suitable LUTs for each version. See also: Internegative, Interpositive
Gamut In image media this usually refers to the available range of colors - as in Color Gamut. This varies according to the color space used; YCrCb, RGB, X'Y'Z' and CMYK all have different color gamuts. See also: Illegal colors
Gateway A device connecting two computer networks. For example, a gateway can connect a local area network (LAN) to a SAN. This way a PC connected on an Ethernet LAN may have access to files stored on the SAN even though the PC is not SAN aware.
Generation loss The signal degradation caused by successive recordings. Freshly recorded material is first generation; one re-recording, or copy, makes the second generation, etc. This was of major concern in analog linear editing.
GPI General Purpose Interface. This is a simple form of control interface typically used for cueing equipment - usually by a contact closure. It is simple, can be frame accurate and therefore can easily be applied over a wide range of equipment.
GPU Graphics processing unit. A chip or digital circuit designed specifically for processing graphics and generally providing the main processing power of a computer graphics card. Having much more graphics power and speed than central processor unit (CPU) chips, GPUs can take over many of complex 2D and 3D processing tasks from the CPU. However GPUs are not as versatile as CPUs and some graphics tasks may still need to go through CPUs or other specific processors. GPUs are now found in a wide
Non-compressed component DVTRs should provide at least twenty tape generations before any artifacts become noticeable but the very best multi-generation results are possible with disk-based systems. These can re- record millions of times without causing dropouts or errors. Generations are effectively limitless... very useful if building multi-layer video effects. Besides the limitations of recording, the action of processors such as decoders and coders will make a significant contribution to generation loss. The decode/ recode cycles of NTSC and PAL are well known for their limitations but caution is needed for digital video compression (coding) systems, including MPEG and DV, as well as the color space conversions that typically occur between computers handling RGB and video equipment using Y,Cr,Cb. See also: Concatenation, Error detection concealment and correction
Ghosting (Stereoscopic) Artifacts typically caused by signal leakage (crosstalk) between the two 'eyes'. A secondary 'ghost' image can be seen. There are several possible causes that can introduce the problem during acquisition, post production and display. One reason can be high contrast levels between an object and its background.
Gigantism (Stereoscopic) Confusing visual cues in a stereoscopic scene that can make an object appear to be the 'wrong' size, i.e. the impression of strangely enlarged size of objects. This is due to the choice of interocular distance relative to the focal length of the camera lenses, e.g. shooting with an interocular distance much less than that of adult human eyes can make a figure appear to be a giant. See also: Miniaturization, Interocular
Gigabit Ethernet See Ethernet
Global (control) The top level of control in a multi-channel DVE system. A number of objects (channels) can be controlled at one time, for example to alter their opacity or to move them all together relative to a global axis - one which may be quite separate from the objects themselves. This way the viewing point of all the assembled objects can be changed. For example, a cube assembled from six channels could be moved in 3D space as a single action from a global control. See also: Axis
GOP (Group Of Pictures) See MPEG-2
Full HD Full HD is a term describing video at 1920 x 1080 resolution. Generally this appears as a logo on flat panel TV sets that have screens able to display all the pixels of the 1920 x 1080 images supplied from HD sources such as broadcast transmissions and HD DVD and Blu-ray Discs. The panels only use progressive scans so they are showing 50P and 59.94P frame rates. The logo will multiply and migrate to spread into consumer areas and appear on the latest consumer camcorders using the 1920 x 1080 image size.
Full motion video A general term for moving images displayed from a desktop platform. Its quality varies and is undefined.
Gamma Gamma has several meanings. In the video world a CRT television monitor's brightness is not linearly proportional to its driving voltage. In fact the light output increases rapidly with drive. The factor, gamma, of the CRT, is generally calculated to be 2.6. This is compensated for in TV cameras by a gamma of 0.45 giving an overall gamma of 0.45 x 2.6 = 1.17 - adding overall contrast to help compensate for domestic viewing conditions. In film, gamma describes the average slope of the D/Log E curve over its most linear region. For negative stocks this is approximately 0.6, for intermediate stocks this is 1.0 and for print stocks 3.0. This gives a system gamma of 0.6 x 1 x 3 = 1.8. This overall boost in contrast is much reduced due to flare and auditorium lighting conditions. With video now available on many varying types of devices there may be a need to re-visit the gamma settings. This can be done by applying suitable LUTs for each version. See also: Internegative, Interpositive
Gamut In image media this usually refers to the available range of colors - as in Color Gamut. This varies according to the color space used; YCrCb, RGB, X'Y'Z' and CMYK all have different color gamuts. See also: Illegal colors
Gateway A device connecting two computer networks. For example, a gateway can connect a local area network (LAN) to a SAN. This way a PC connected on an Ethernet LAN may have access to files stored on the SAN even though the PC is not SAN aware.
Generation loss The signal degradation caused by successive recordings. Freshly recorded material is first generation; one re-recording, or copy, makes the second generation, etc. This was of major concern in analog linear editing.
GPI General Purpose Interface. This is a simple form of control interface typically used for cueing equipment - usually by a contact closure. It is simple, can be frame accurate and therefore can easily be applied over a wide range of equipment.
GPU Graphics processing unit. A chip or digital circuit designed specifically for processing graphics and generally providing the main processing power of a computer graphics card. Having much more graphics power and speed than central processor unit (CPU) chips, GPUs can take over many of complex 2D and 3D processing tasks from the CPU. However GPUs are not as versatile as CPUs and some graphics tasks may still need to go through CPUs or other specific processors. GPUs are now found in a wide Non-compressed component DVTRs should provide at least twenty tape generations before any artifacts become noticeable but the very best multi-generation results are possible with disk-based systems. These can re- record millions of times without causing dropouts or errors. Generations are effectively limitless... very useful if building multi-layer video effects. Besides the limitations of recording, the action of processors such as decoders and coders will make a significant contribution to generation loss. The decode/ recode cycles of NTSC and PAL are well known for their limitations but caution is needed for digital video compression (coding) systems, including MPEG and DV, as well as the color space conversions that typically occur between computers handling RGB and video equipment using Y,Cr,Cb. See also: Concatenation, Error detection concealment and correction
Ghosting (Stereoscopic) Artifacts typically caused by signal leakage (crosstalk) between the two 'eyes'. A secondary 'ghost' image can be seen. There are several possible causes that can introduce the problem during acquisition, post production and display. One reason can be high contrast levels between an object and its background.
Gigantism (Stereoscopic) Confusing visual cues in a stereoscopic scene that can make an object appear to be the 'wrong' size, i.e. the impression of strangely enlarged size of objects. This is due to the choice of interocular distance relative to the focal length of the camera lenses, e.g. shooting with an interocular distance much less than that of adult human eyes can make a figure appear to be a giant. See also: Miniaturization, Interocular
Gigabit Ethernet See Ethernet
Global (control) The top level of control in a multi-channel DVE system. A number of objects (channels) can be controlled at one time, for example to alter their opacity or to move them all together relative to a global axis - one which may be quite separate from the objects themselves. This way the viewing point of all the assembled objects can be changed. For example, a cube assembled from six channels could be moved in 3D space as a single action from a global control. See also: Axis
GOP (Group Of Pictures) See MPEG-2
range of image processing equipment - such as picture color correctors and graders as well as the high-end television graphics equipment including that for live '3D' graphics and virtual sets.
Grading (a.k.a. color timing) Grading is the process of adjusting the color of a clip to get the best out of the material or to match shots perhaps taken at different times or in different lighting conditions. In film, grading was traditionally done when going from internegative to print film by controlling the exposure of the film. In television it was traditionally done off the telecine for commercials or tape-to-tape for long form programs. Both processes were by their nature linear. The advent of non-linear grading systems has changed the rules for color correction. While there is still a requirement for an initial technical scan for film-originated material, from this point on, grading can happen at multiple stages in the post production process. It is to color correct individual layers within composites (which may be shot under different lighting conditions) to ensure that the result is harmonious within itself, and non-linear working means that scene-to-scene comparisons and corrections can be made as the edit unfolds. This eases the final grading process when the finished work is reviewed interactively with the director/ client. Secondary color correction is aimed at controlling a particular color or a narrow range of colors - such as those on a car or product. Here typically the hue, gain and saturation can be changed. See also: Film scanner, Grading, Telecine
Grain management Controlling the amount of 'film' grain visible on a film or digital movie. Its appearance is considered by some to add a certain look to the production. Modern DI equipment can include grain management that can increase or decrease its visibility on film or digitally originated material. Aside from aesthetics, grain affects compression systems as they see it as extra movement and so can waste bandwidth by coding it - adding another reason for controlling the amount of grain according to the different coding requirements for, say, digital cinema and mobile reception.
Granularity Term describing limits of accuracy or resolution. For example, in editing the granularity of uncompressed component video (601 or 709) is one frame; i.e. it can be cut on any frame. The granularity of long GOP MPEG-2 is about half a second - about 12 or 15 frames. In a digital imaging system the granularity of brightness is the minimum change per sample - corresponding to the effect of an LSB change.
GSN Gigabyte System Network. Developed by SGI and others for the efficient movement of large quantities of data, it allows realtime transfers of larger-than-HD images on a network. GSN allows transfer speeds up to 800MB/s, has low latency, and is an ANSI standard compatible with HIPPI, Ethernet, and other standard networks, providing full-duplex data transmission over up to 200m. Website: www.hnf.org
GUI Graphical User Interface. A means of controlling or operating a system through the use of interactive graphics displayed on a screen. Examples in the computer world are the Apple Macintosh and Microsoft Windows, both designed for general-purpose use and usually operated with a mouse as the pointing device. H H.264 See: MPEG-4