MPEG-2 Video Coding - Digital Video and Audio Broadcasting Technology - page 113

each case associated with only one C B value and one C R value each. This
type of irrelevance reduction results in another saving of exactly 25 % data
rate.

Column m Column m + 1 Column m + 2

Y Y Y Line n

Cb

Cr

Y Y Y Line n + 1

Fig. 7.4. 4:2:0 resolution

Vertical blanking

Visible, active picture
720x576 pixel Y
360x576 (288@4:2:0)
pixel Cb, Cr
25 frames/s

625
lines

576
visible lines

Active line

Fig. 7.5. Physical parameters of a SDTV signal

7.1.4 Further Data Reduction Steps

The data reduction carried out up to now has produced the following re-
sult: Beginning with an original data rate of 270 Mbit/s, this ITU BT.R601
signal has now been compressed to 124.5 Mbit/s, i.e. to less than half its
original rate, by applying the following steps:

• ITU BT.R601 = 270 Mbit/s

• 8 bits instead of 10 (-20%) = 216 Mbit/s

• Hor. and vert. blanking (appr. -25%) = 166 Mbit/s

• 4:2:0 (-25%) = 124.5 Mbit/s