Graphics Reference
In-Depth Information
Chapter 8
Entropy Coding in HEVC
Vivienne Sze and Detlev Marpe
Abstract
Context-Based Adaptive Binary Arithmetic Coding (CABAC) is a
method of entropy coding first introduced in H.264/AVC and now used in the latest
High Efficiency Video Coding (HEVC) standard. While it provides high coding
efficiency, the data dependencies in H.264/AVC CABAC make it challenging to
parallelize and thus limit its throughput. Accordingly, during the standardization
of entropy coding for HEVC, both aspects of coding efficiency and throughput
were considered. This chapter describes the functionality and design methodology
behind CABAC entropy coding in HEVC.
8.1
Introduction
Context-Based Adaptive Binary Arithmetic Coding (CABAC) [
46
] is a form of
entropy coding used in H.264/AVC [
63
] and also in HEVC [
64
]. Entropy coding is
a lossless compression scheme that uses the statistical properties to compress data
such that the number of bits used to represent the data is logarithmically proportional
to the probability of the data. For instance, when compressing a string of characters,
frequently used characters are each represented by a few bits, while infrequently
used characters are each represented by many bits. From Shannon's information
theory [
72
], when the compressed data is represented in bits {0,1}, the optimal
average code length for a character with probability p is
log
2
p.
V. S z e (
)
Massachusetts Institute of Technology (MIT), Cambridge, MA, USA
e-mail:
sze@mit.edu
D. Marpe
Fraunhofer Institute for Telecommunications Heinrich Hertz Institute (HHI), Berlin, Germany
e-mail:
Detlev.Marpe@hhi.fraunhofer.de
