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Generation
(loss): The signal degradation caused by successive
recordings. Freshly recorded material is first generation, one
re-recording, or copy, makes the second, etc. This is of major concern
in analog linear editing but much less so using a digital suite.
Non-compressed component DVTRs should provide at least twenty
generations before any artifacts become noticeable, but the very best
multi-generation results are possible with disk-based systems.
Generations are effectively limitless. 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
cycle of NTSC and PAL is well known for its limitations but equal
caution is needed for digital video compression systems, especially
those using MPEG, and the color space conversions that typically occur
between computers handling RGB and video equipment using Y, Cr, Cb. See
also: Color space, concatenation, error concealment, error correction,
error detection.
GIF
(pronounced
jif): Graphics interchange format. A computer graphics file format
developed by CompuServe for use in compressing graphic images, now
commonly used on the Internet. GIF compression is lossless, supports transparency, but allows a
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maximum
of only 256 colors. Images that will gain the most from GIF compression
are those which have large areas (especially horizontal area) with no
changes in color.
GoP:
See: Group of pictures.
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.
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 time code data can be added to this layer for the first
picture in a GoP.
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