0195136047.pdf

704 COMMUNICATION SYSTEMS

10 μs

53.5 μs

15.4 ms

1.27 ms

(a)

(b)

t

t

Figure 15.2.24Voltage waveforms.(a)Applied to horizontal deflection plate.

(b)Applied to vertical deflection plate.

First field of frame

Second field of frame

Vertical retrace time

(1.27 ms)

Vertical retrace time

(1.27 ms)

242.5 lines

20 lines

525 Lines

per frame

242.5 lines

20 lines

Figure 15.2.25Raster scanning in

an NTSC television system.

Now that the fundamentals needed in color television have been explained, it remains to be

seen how the signals are processed by the transmitter and the receiver.

Acolor television transmitterin a transmitting station is shown in Figure 15.2.28 in a block

diagram indicating the most important functions. A mixture of three primary-color signals (having

the visual signal bandwidth of about 4.2 MHz) are transmitted in the standard color television

system in terms of the following three linearly independent combinations generated by the matrix

circuit:

mY(t)= 0. 30 mR(t)+ 0. 59 mG(t)+ 0. 11 mB(t) (15.2.14)

mI(t)= 0. 60 mR(t)− 0. 28 mG(t)− 0. 32 mB(t) (15.2.15)

mQ(t)= 0. 21 mR(t)− 0. 52 mG(t)+ 0. 31 mB(t) (15.2.16)

The following notation is being used:

• mY(t): Luminance signal, to which monochrome receivers respond, and which defines the
  brightness (white or gray level) of the image.


• mI(t),mQ(t): Chrominance signals, which relate only to the color content of the image and
  have bandwidths of about 1.6 and 0.6 MHz, respectively.