Page 39 - Video Coding for Mobile Communications Efficiency, Complexity, and Resilience

16 Chapter 2. Video Coding: Fundamentals

video with one luma (Y ) and two chroma (C and C ) components calculated

R
B
as follows:

Y = 219(+0:299R +0:587G +0:114B )+16;

C = 224(−0:169R − 0:331G +0:500B ) + 128; (2.2)

B

C = 224(+0:500R − 0:419G − 0:081B ) + 128;

R

where Y has 220 levels in the range [16; 235]; with black at 16 and white at

235, and C and C have 225levels in the range [16; 240]; with zero di6erence
B
R
at 128. Note that other levels within the 8-bit range [0; 255] are reserved for
synchronization and signal processing head- and foot-rooms.
2.4.4.2 SIF and QSIF
CCIR-601 was de ned mainly for broadcast-quality applications. For storage
applications, a lower-resolution format called the Source Input Format (SIF)
was de ned. This is a progressive 4:2:0 mid-sited format with a luma com-
ponent that is half the CCIR-601 active luma component in both dimensions.
The CCIR-601 format has 720 luminance pels=line, which means that an SIF
format must have 720=2 = 360 luma pels=line. Since 360 is not divisible by 16
(which is the main coding unit within standard video codecs), 8 pels (4 from
each side) are usually discarded to reduce the number of luma pels per line
to 352. Since there are two CCIR-601 systems, there are two SIF formats: the
rst has a luma component of 352 × 240, chroma components of 176 × 120;
and a frame rate of 30 frames=s, whereas the second format has a luma of
352 × 288, chromas of 176 × 144; and a frame rate of 25frames=s.
A lower-resolution version of SIF is the quarter-SIF (QSIF) format. It has
half the dimensions of SIF in both directions. This means it has quarter the
number of samples, hence the name. Again, two versions are available: the rst
has a luma of 176 × 120, chromas of 88 × 60; and a frame rate of 30 frames=s,
whereas the second has a luma of 176 × 144, chromas of 88 × 72; and a frame
rate of 25frames=s. For methods of converting between CCIR-601, SIF and
QSIF, refer to Ref. 15.
2.4.4.3 CIF and Its Family
In order for video codecs to cope with both 525=60 and 625=50 formats,
a common format was de ned. In this format, the luma component has a
horizontal resolution that is half that of both CCIR-601 systems, a vertical
resolution that is half that of the 625=50 system, and a temporal resolution
that is half that of the 525=60 system. This intermediate choice of vertical
resolution from one system and temporal resolution from the other leads to
the name Common Intermediate Format (CIF). The CIF is progressive, with