Video Basics
WHITE
YELLOW
CYAN
MAGENTA
GREEN
RED
BLUE
BLACK
WHITE LEVEL
100 IRE
3. 58 MHZ
COLOR BURST
( 9 ± 1 CYCLES)
20 IRE
7. 5 IRE
BLACK LEVEL
BLANK LEVEL
20 IRE
40 IRE
SYNC LEVEL
BLANK LEVEL
LUMINANCE LEVEL
COLOR
SATURATION
PHASE = HUE
that led to using Y, U, and V data
to represent color information. A
technique was then developed to
transmit this Y, U, and V information
using one signal — instead of three
separate ones — in the same bandwidth as the original grayscale video
signal. The general relationship
between YUV and gamma-corrected
RGB (R´G´B´) is:
Y = 0.299R´ + 0.587G´ + 0.114B´
U = – 0.147R´ – 0.289G´ + 0.436B´
= 0.492 (B´ – Y)
V = 0.615R´ – 0.515G´ – 0.100B´
= 0.877(R´ – Y)
R´ = Y + 1.140V
G´ = Y – 0.395U – 0.581V
B´ = Y + 2.032U
In order to transmit the color
information so that black-and-white
televisions would still display the
grayscale image, the color information (U and V) is modulated onto a
3. 58 MHz (NTSC) or 4. 43 MHz
(PAL) subcarrier and added to the
grayscale video signal.
FIGURE 1. NTSC composite video signal for 75% color bars.
composite color video = Y + U sin wt
+ V cos wt + timing
technique occupied 3x more bandwidth than the current
grayscale solution, so alternate methods were developed
w = 2pFsc
Fsc = ~ 3. 58 MHz for NTSC; ~ 4. 44 MHz for PAL
FIGURE 2. NTSC luminance (Y) video signal for 75% color bars.
Indicated luminance levels are 10-bit values.
E
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c
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r
o
n
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c
s
NUTS & VOLTS
F
o
r
E
v
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y
t
h
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n
g
YELLOW
WHITE
GREEN
MAGENTA
RED
CYAN
1.020 V
BLACK
BLUE
WHITE LEVEL (800)
671
626
100 IRE
554
510
442
398
326
0.357 V
0.306 V
7. 5 IRE
BLACK LEVEL (282)
BLANK LEVEL (240)
40 IRE
0.020 V
SYNC LEVEL ( 16)
60
The resulting NTSC composite video signal (Figure 1)
is what the NTSC, PAL, and
SECAM video standards are
still based on today.
S-video was later developed
for connecting consumer
equipment together (it is
not used for broadcast
purposes). It is a set of two
analog signals — the grayscale
(Y) signal (shown in Figure 2)
and the chroma (C) signal
that carries the U and V color
information in a specific
format (shown in Figure 3).
Note that if Y and C are added
together, the result is a
composite video signal. Once
available only for S-VHS,
S-video is now supported
JANUARY 2005
