Batting Practice for the AV Professional
and primer for the novice
4 Page 2
Analog NTSC Color Television
This page outlines the expired technology, analog NTSC color
TV, that laid the framework for digital broadcast television.
A NTSC color TV camera outputs five voltages: red, green, blue,
horizontal sync, vertical sync. But broadcast bandwidth
could not handle all five voltages as is.
NTSC color TV was also required to
maintain backward compatibility with legacy black and white
televisions. NTSC engineers ingenious solution reduced and
combined the five video voltages with a bit of algebraic magic,
a dash of modulating gymnastics, and a clever manipulation of
the human eye.
The Eye & TV Math
The NTSC solution began by combining an understanding of our
sensitivity to light with a black and white luminance
signal. Our sensitivity to light is not equal across the
entire bandwidth of color. We are most sensitive to green
light, less to red light, and least to blue. From the
engineer's point of view, the green was most significant, red
much less, blue least. Then, white light via a prism
produces a rainbow of color, and the reverse recombines the
rainbow as the original white light. Somewhat the same,
NTSC engineers used this illuminating approach to create a black
and white luminance signal. They produced a luminance
signal with a mixture of reduced green voltage, less red, and
even less blue.
The following algebraic expression was their first step in a
recipe toward a workable broadcast signal.
The NTSC engineers had reduced the red, green, blue voltages and
computed the black and white TV luminance voltage. But
this first step was not enough to fit the video within broadcast
Squeezing RGB into A&C
The NTSC engineers next step squeezed the three abbreviated
color voltages into only two color difference signals.
They converted 0.3R
0.59G 0.11B into:
To this point, NTSC engineers had produced a black and white
luminance voltage 'Y
' and reduced RGB
color to A
. The result of Y
, & C
was defined as component video.
The NTSC engineers still had a bandwidth issue.
bandwidth was still too large for
The next step reduced A
= 87.7% of A
The NTSC engineers finally had a bandwidth solution via three
manageable voltages: I
, & Y
They defined I
, & Y
Ready, Set, Broadcast
The next NTSC step converted the three composite video voltages
to radio-frequency (RF)
and encrypted the horizontal and vertical synchronizing signals.
The engineers assigned Y
, & Q
two radio frequencies. Y
was assigned an amplitude
modulated frequency. I
90% out of phase, were assigned a phase modulated frequency.
(similar to FM)
They hid the horizontal and vertical sync signals via a
mathematical manipulation of the I
I will not include the calculation here. You can thank me
later. A separate FM radio frequency carried the audio.
The NTSC signal was ready for broadcast.
A television station broadcast antenna initiated cycles of
electromagnetic waves (continuous controlled sparks) that
generated electromagnetic current in receiving TV
antennas. The receiving television decoded the modulating
RF signal as follows:
- Separate Y
- Calculate the H
orizontal & V
- Recover A
= 87.7% of A
Q = 49.3% of C
A = (I ÷ 87.7) x
C = (Q ÷ 49.3) x (100)
- Recover RGB from A&C
If A = (0.3R - Y) and C
= (0.3R - Y)
0.11B = (0.11B-Y) + (Y)
= (Y) - (0.3R +
(0.3 Red ÷
0.3) x (100)
= (0.59 Green
÷ 0.59) x (100)
Blue = (.011 Blue
÷ 0.11) x (100)
The five video voltages, RGBHV,
were revived. The engineers could now recreate the
frames of lines and illuminated colored pixels captured by the
Ed's AV Handbook
Copyright 2007 Txu1-598-288 Revised 2021
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