Apple Final Cut Pro 5 - Manual (Page 1704)

Appendix A Video Formats 353
V
There are an increasing number of HD tape formats available. Most HD formats only
support a subset of the options shown in the table above, and most camcorders and
video decks do not support every combination.
Type of Video Signal
Video signals are separated into several channels for recording and transmission. There
are different methods of color channel separation, depending on the video format and
historical origins. For example, broadcast video devices were originally designed for
black-and-white video, and color was added later. This is still evident in today’s video
formats that break image information into separate black-and-white and color
information. On the other hand, video and image processing on computers is more
flexible and developed later, so a three-color RGB model was adopted instead of a
luma-chroma model.
The luma (black-and-white channel) and chroma (color channels) information can be
recorded and transmitted several different ways in a video signal.
 RGB (Red, Green, Blue): This is the native format for most computer graphics and
video files. This signal is also used inside traditional color CRTs and flat-panel displays.
Red, green, and blue signals can be combined to make any color, as well as grayscale
images from black (no signal on any channel) to white (full signal on every channel).
RGB signals do not have a separate luma channel, because black-and-white signals
can be represented by equal amounts of R, G, and B signals.
 Component YUV or Y´C
B
C
R
: This three-channel signal has a luma (Y’) signal and two
color difference channels (C
B
and C
R
) 1 . Component video was invented in the 1950s as
a way of making color television signals compatible with existing black-and-white
televisions. Black-and-white televisions could use the luma signal while color
televisions could convert Y’, C
B
, and C
R
back to RGB for display.
The luma signal is derived by combining R, G, and B signals in similar proportions to
the way human vision is sensitive to those three colors. Therefore, the luma signal
approximates the same detail we see for various colors in the spectrum, which
happens to be most sensitive to detail in the green channel. The color difference
channels are so named because they are derived from RGB by subtracting signals
from the luma channel for each of the color channels (for example, R-Y or B-Y).
 S-Video (Y/C): An S-Video signal is also considered a component video signal
because the luma and chroma signals are separate. However, the C signal is derived
by combining the C
B
and C
R
component signals together, which reduces the quality
of the color channel compared to Y´C
B
C
R
.
1. The pair of color difference channels have different names depending on the particular format, but they all serve a
similar function. Some common names for color difference channels include: C
B
, C
R
; R-Y, B-Y; or U,V.