Signal Processing - September 2016 - 165

YUV

Frame
Buffers

Transform

Quantization

Coefficients

Entropy
Coding

Bitstream

Inverse
Quantization
Inverse
Transform

Intra
Prediction
Motion
Compensation

Motion
Estimation

Forward
Frame Buffer

Backward
Frame Buffer

Motion Vectors

DC-Blocking

Mode
Decision

Other Parameters

Figure 1. A block diagram of an IVC encoder.

are derived with motion estimation.
The main coding tools of the IVC are
described in the following paragraphs.

Intraprediction
Spatial domain intraprediction is used in
intramacroblock coding. The decoded
boundary samples of adjacent blocks
are used as reference data for the spatial
prediction. For the luma component in
a macroblock, it can be coded by either
one 16 # 16 macroblock partition or
four 8 # 8 macroblock partitions. Each
8 # 8 macroblock partition can be further coded with four 4 # 4 macroblock
partitions. The four prediction modes
(i.e., Intra_Vertical, Intra_Horizontal,
Intra_DC, Intra_Down_left, and Intra_
Down_right) shown in Figure 2 can be
used for a 16 # 16 macroblock partition,
an 8 # 8 macroblock partition or a
4 # 4 macroblock partition. For the
chroma components in a macroblock,
they are only coded by an 8 # 8 macroblock partition, and four prediction
modes (i.e., Intra_Chroma_DC, Intra_
Chroma_Horizontal, Intra_Chroma_
Vertical, and Intra_Chroma_Plane) can
be used for each 8 # 8 macroblock partition. The intraprediction mode for each
macroblock partition is directly coded
into the bitstream without prediction

from the intraprediction modes of
neighboring macroblock partitions.

Interprediction
An intermacroblock can be coded by
one 16 # 16 macroblock partition, two
16 # 8 macroblock partitions, two 8 #
16 macroblock partitions, or four 8 #
8 macroblock partitions. Five interprediction modes (i.e., skip, forward prediction, backward prediction, multiple
hypothesis, and symmetrical prediction)
are defined for intermacroblock partitions. For each intermacroblock partition, one to four modes are available to
be selected depending on the current
picture coding type and partition size,
as shown in Table 1.
1) Skip: Skip mode is one of the prediction modes that skips the encoding of all syntax elements except its
mode-type information. If skip
mode is selected for the current
macroblock, both the motion vector
difference and prediction residuals
are forced to zeros.
2) Forward prediction: Forward prediction mode uses only one block in
one of its forward reference pictures
to predict the current macroblock
partition. The motion vector difference and the prediction residuals of
IEEE Signal Processing Magazine

September 2016

1
2 : DC

Figure 2. The intraprediction modes for the
luma component.

the current macroblock partition are
transmitted in the bitstream.
3) Backward prediction: Backward
prediction mode uses only one block
in its backward reference picture to
predict the current macroblock partition. The motion vector difference
and the interprediction residuals of
the current macroblock partition are
transmitted in the bitstream.
4) Multiple hypothesis: In this mode,
as shown in Figure 3, the interpredictor of the macroblock partition
(c) is derived by averaging two forward predictors (H1 and H2) [10].
The motion vector (MV1) of the first
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Table of Contents for the Digital Edition of Signal Processing - September 2016