Color Video Signals

• Luminance–The luminance signal contains all

information required to construct a black and white picture from the signal.

In-phase/Quadrature ChrominanceIn-phase/Quadrature Chrominance

• Chrominance is a combination of both Hue and Saturation

Y = 0.3R + 0.59G + 0.11B

I = 0.6R - 0.28G - 0.32BQ = 0.21R - 0.52G + 0.31B

Primary Color Signals:

R = 0.62Q + 0.95I + YG = -0.64Q - 0.28I + YB = 1.73Q - 1.11I + Y

I = 0.6R - 0.28G - 0.32B

Note:The components (negative) of -0.28G and -0.32B total -0.60, which equals the positive value of 0.60R.These values are chosen to make the amplitude of the I-video signal become zero (0) for white.

Q = 0.21R - 0.52G + 0.31B

Note:The components (positive) of 0.21R and 0.31B total 0.52, which equals the negative component of -0.52G.These values are chosen to make the Q-video signal become zero (0) for white.

• Both the I and Q signals are zero for white, since there is no chrominance information in white.

Y, I, Q Matrix Weightings

Red

Green

Blue

wh yel cy G mg R B blk

R

G

B

Y I Q

0.30

0.59

0.11

0.60

-0.28

-0.32

-0.52

0.21

0.31

Example:An RGB video signal has normalized value of R = 0.2, G = 0.4, B = 0.8. Find the value of Y, I and Q.

Luminance Level to IRE Unit Conversion

IRE = 7.5 + l x (lmax – lmin)

where: l – luminance of a video signal lmax = 100 lmin = 7.5

Example:Find the equivalent IRE units of a video signal which has 80% of the maximum luminance level.

Example:Calculate the luminance signal and the IRE equivalent unit for saturated green and yellow.

Summary of Different IRE UnitsColor Luminance IRE Equiv. UnitWhite 100% 100Yellow 89% 89.825Cyan 70% 72.25Green 59% 62.075Magenta 41% 45.425Red 30% 35.25Blue 11% 17.675Black 0% 7.5

Desaturated Color with White

• The addition of white to desaturate a color increases the luminance value and decreases the chrominance value, compared with 100 percent saturation.

Example:Saturated Magenta(R+B):

Y = 0.41 I = 0.28Q = 0.52

80% (saturation) Magenta: Y = I = Q =