Page 35 - Video Coding for Mobile Communications Efficiency, Complexity, and Resilience

12 Chapter 2. Video Coding: Fundamentals

calculate the luminance=chrominance components from the RGB components.
For example, the PAL system calculates the luminance=chrominance compo-
nents as follows:

Y =+0:299R +0:587G +0:114B ;

U = −0:147R − 0:289G +0:436B =0:493(B − Y ); (2.1)

V =+0:615R − 0:515G − 0:100B =0:877(R − Y );

where R G B are gamma-corrected components in the range [0; 1]. Note that

8

Y is closely related to gamma-corrected luminance and is usually referred to
as luma. The chrominance is calculated as two color-di)erence components

U and V . Again, since they are gamma-corrected, they are referred to as
chroma components. The NTSC and SECAM systems calculate luma in the
same way but use di6erent coeGcients for obtaining the chroma components

(I and Q in NTSC, and D and D in SECAM).
R
B
2.3.3 Analog Video Systems
There are three main analog video systems. In most of Western Europe, a
625=50 PAL system is used. In Russia, France, the Middle East, and Eastern
Europe, a 625=50 SECAM system is used. In North America and Japan, a
525=60 NTSC system is used. All three systems are interlaced with a 4:3
aspect ratio.
The three systems are composite. This means that the chroma components
are rst bandlimited and then combined (for example, by frequency inter-
leaving) with the luma component. The resulting composite video signal has
the same bandwidth as the original luma signal. For example, in the 625=50
PAL system, the luma signal has a bandwidth of 5:5MHz. The chroma sig-
nals are bandlimited to about 1:5MHz and then QAM (quadrature amplitude
modulation) modulated with a color subcarrier at 4:43 MHz above the picture
carrier. For a more detailed discussion of these systems the reader is referred
to Ref. 13. There are also other analog video systems that use separate com-
ponents (component video) or a separate luma component and a composite
chroma component (S-video) [10].
8 In a video system, it is important to convey luminance in such a way that noise and quantiza-
tion have a perceptually similar e6ect across the entire scale from black to white. This is achieved
by applying a nonlinear function to each of the linear RGB components. This process is known
as gamma-correction [12].