Generation
The number of times an electronic signal is copied.
First generation refers to the original material,
usually in its unedited form. The edited videotape
made from this material is considered to be second
generation. All subsequent copies or duplicates
are one generation removed from the material from
which they were copied. Care must be taken to ensure
that distortion and other defects do not degrade
the video and audio quality.
With analog duplication techniques,
distortion and other noticeable problems occur
after only a few generations, typically 7 or 8.
In the digital domain, a minimum of 20 generations
may be made before any defects are noticeable.
Hard
Copy
Also called a printout. A paper printout of computer
data. In editing, a printout of an EDL. topˆ
HDTV
A television system that offers more than twice
the picture resolution of a conventional television.
The SMPTE 240-M system contains 1125 horizontal
scan lines per frame while conventional television
has 525 lines. The screen aspect ratio is typically
16:9 (1.78:1) as opposed to 4:3 (1.33:1) for standard
television images.
HDTV videotape, when converted
to film, compares favorably with the quality of
direct optical photography using motion picture
film cameras. topˆ
Helical
Scan (also known as slant track)
VTR or VCR recording format that wraps the tape
around the video scanner in a helix pattern. There
are essentially two helical scan formats, the
alpha wrap and the omega wrap. The alpha wrap
was the first format to be used in early helical
scan VTRs. The disadvantage of this format is
that it requires the videotape to be wrapped 360
degrees around the scanner. This is cumbersome
especially if the tape must be loaded or unloaded
from the VTR in the middle of the reel.
Current helical scan VTRs and
VCRs use an omega wrap. This configuration wraps
the tape around the drum in a horseshoe or U pattern,
allowing easy threading or removal of the tape.
topˆ
Heterodyne
Color Recording (color under)
A method of recording that translates the encoded
chroma signal to a lower video frequency so that
color recording may be effected in a limited bandwidth.
It also electronically compensates for the timing
jitter inherent in helical scat recorders. Used
in consumer and industrial VCRs. topˆ
Hue
A specific color wavelength in the visible light
spectrum, an attribute of color perception. Flesh
tones, for example, may be changed by adjusting
the hue control (sometimes marked color phase)
on a television receiver or monitor. topˆ
Interlace
The combining of two sequential television field
that make up a complete frame in the NTSC system.
Field 1 contains the odd numbered scan lines,
field 2 the even numbered line. When combined
by interlacing, line 2 falls between 1 and 3,
line 4 falls between 3 and 5, and so on. Interlaced
scanning solves the problem of flicker at reasonable
frame rates. An image repetition rate of less
than 48 per second appears to flicker under typical
viewing conditions. Interlacing provides a field
repetition rate of 60 per second, well above the
flicker threshold. The PAL system, having a field
rate of 50 per second, often exhibits flicker
to those not accustomed to it. Motion picture
projection gets around the problem by using a
2-blade shutter assisted by viewing in a relatively
dark room. Interlace bring with it motion artifacts
that are noticeable at times.
While exhibiting superior motion
rendition compared to 24 frame may show a double
image particularly noticeable in sporting events
or other fast action because of the 1/60th of
a second offset between fields. The equalizing
and vertical serrated pulses in the sync signal
are essential to achieve perfect interlace. topˆ
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