Graphics Reference
In-Depth Information
Chapter 6
HEVC Transform and Quantization
Madhukar Budagavi, Arild Fuldseth, and Gisle Bjøntegaard
Abstract
This chapter provides an overview of the transform and quantization
design in HEVC. HEVC specifies two-dimensional transforms of various sizes
from 4
4to32
32 that are finite precision approximations to the discrete cosine
transform (DCT). In addition, HEVC also specifies an alternate 4
4integer
transform based on the discrete sine transform (DST) for use with 4
4 luma Intra
prediction residual blocks. During the transform design, special care was taken
to allow implementation friendliness, including limited bit depth, preservation of
symmetry properties, embedded structure and basis vectors having almost equal
norm. The HEVC quantizer design is similar to that of H.264/AVC where a
quantization parameter (QP) in the range of 0-51 (for 8-bit video sequences) is
mapped to a quantizer step size that doubles each time the QP value increases
by 6. A key difference, however, is that the transform basis norm correction factors
incorporated into the descaling matrices of H.264/AVC are no longer needed in
HEVC simplifying the quantizer design. A QP value can be transmitted (in the form
of delta QP) for a quantization group as small as 8
8 samples for rate control
and perceptual quantization purposes. The QP predictor used for calculating the
delta QP uses a combination of left, above and previous QP values. HEVC also
supports frequency-dependent quantization by using quantization matrices for all
transform block sizes. This chapter also provides an overview of the three special
coding modes in HEVC (I_PCM mode, lossless mode, and transform skip mode)
that modify the transform and quantization process by either skipping the transform
or by skipping both transform and quantization.
M. Budagavi (
)
Texas Instruments Inc., Dallas, TX, USA
e-mail:
madhu072@yahoo.com
A. Fuldseth G. Bjøntegaard
Cisco Systems Norway, 1366 Lysaker, Norway
