Video Compression - Signal Processing Systems - page 49

of bit-rate saving under the same visual quality, respectively [ 11 ] . The advantage
makes H.264/AVC potential for wide range of applications. In recent years, new
profiles were developed to target at the emergent applications like HDTV, streaming,
surveillance, and multiview videos. The above applications and the corresponding
video coding systems are introduced in Sect. 3 .

2 Basic Components of Video Coding Systems

In this section, we introduce the basic components of a video coding system as
shown in Fig. 2 . In the evolution of various video coding standards, every new
standard tries to improve its coding efficiency by further exploring all kinds of
redundancy. In general, the redundancy in a video sequence can be categorized into
perceptual, temporal, spatial, and statistical redundancy. Perceptual redundancy is
the detailed information that human cannot perceive well. Removal of perceptually
redundant information will not lead to severe perceptual quality degradation.
Temporal and spatial redundancy comes from the pixels that are similar to the
neighboring pixels temporally or spatially. We can predict the current pixel with
the neighboring pixels and encode the different value between them. The different
value is close to zero with high probability and good to be encoded with less bits by
entropy coding. Statistical redundancy comes from the information occurred with
high probability if we encode all information with the same number of bits. Short
codewords (with fewer bits) for frequently occurred symbols and long codewords
for infrequently occurred ones can reduce the total data size of the bitstream.

2.1 Color Processing

The first functional block is color processing. Color processing includes color
transform and chroma (chrominance) subsampling [ 12 ] . Image data from sensors
are usually in RGB (Red, Green, and Blue) color format. Each pixel in an image
with the RGB format is first transformed to another color space with one luma
(luminance) component and 2 chroma components. The most frequently used color
space is YCbCr and defined as

Y = 0 . 299 R + 0 . 587 G + 0 . 114 B

Cb = − 0 . 169 R − 0 . 331 G + 0 . 500 B (1)

Cr = 0 . 500 R − 0 . 419 G − 0 . 081 B

Fig. 2 Basic components of
a video coding system