Greg's Sandbox
Production Video Techniques for Film Production
VIDEO STANDARDS
Component and Composite
COMPONENT. The component system comes in several different
varieties. The one most often used at Video Image is Red, Green, Blue,
and Sync (RGBS). The red, green, and blue signals determine the brightness
of their respective colors, and the sync signal determines where
on the screen the colors exist. This is the system used in the SGIs and
the Macs. Component is very high quality, but is very awkward to deal with
outside the computer.
COMPOSITE. By heavily processing the RGBS signals
in a color encoder, one single, complex video signal may be produced with
most of the information in the original RGBS picture. This composite signal,
even though quite a bit lower in quality than the original RGBS, has certain
attractions. It travels down a single wire, it can be recorded on a video
tape machine, and it can be broadcast. This is the system used in the BetaCam
edit room and much of Video Village.
The Display Device
The most common display medium for video is the CATHODE
RAY TUBE, or CRT. (see diagram below) An electron beam is directed
across the face of the tube, scanning from left to right, top to bottom,
much like one reads a book. The beam strikes phosphors which are on the
face of the CRT, causing them to glow. The beam varies in intensity in
direct relation to the voltage of the video signal. Once the beam reaches
the bottom right corner of the tube, it is turned off, and RETRACES
back to the top left corner of the CRT.
NTSC and INTERLACED VIDEO
INTERLACED SCAN - Each video FRAME consists
of two video FIELDS (see diagram below). The first field is a display
of all the odd scan lines, after which a retrace occurs, and then the second
field is scanned, which displays all the even scan lines. In NTSC video
this process is repeated approximately thirty times each second. The interlaced
scan method was adopted to reduce flicker of the video display.
COMPOSITE COLOR VIDEO
COMPOSITE VIDEO SIGNAL - NTSC was originally adopted
to maintain compatibility of the color television signal with the original
black and white signal. The color information is carried on a second waveform,
or subcarrier, which is "pasted" atop the main video waveform, which carries
the luminance information (see diagram below). Black and white television
displays the luminance signal only, color television displays both the
luminance and the color signals.
VARIOUS VIDEO FORMATS USED IN FILM
We use several video formats in production video. With the
exception of 525-30, all of these formats are custom and cannot be found
at conventional video or production facilities. They are here to enlighten
the would be and professional video technician.
Click Here for Details on 525-30
Click Here for Details on 525-24
Click Here for Details on 655-24
Click Here for Details on 625-24
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