Graphics Reference
In-Depth Information
Tabl e 8. 5
Differences between prediction unit coding in HEVC and H.264/AVC
HEVC
H.264/AVC
Properties
Intra Mode
AMVP
Merge
Intra Mode
MVP
Max number of
candidates in list
3
2
5
1
1
Spatial neighbor
used
used
used
used
used
Temporal co-located
neighbor
not used
used
used
not used
not used
Number of contexts
2
10
2
6
20
Max regular coded bins
per PU
2
16
2
7
98
The number of regular coded bins was reduced for intra mode coding in HEVC
relative to the corresponding part in H.264/AVC, where both the flag and the 3 fixed-
length bins of the remainder mode are regular coded using two separate context
models. In HEVC, the flag is regular coded as well, but the remainder mode is
a fixed-length 5-bin value that is entirely bypass coded. The most probable mode
index (
mpm_idx
) is also entirely bypass coded. The number of contexts used to
code
intra_chroma_pred_mode
is reduced from 4 to 1 for HEVC relative
to H.264/AVC. To maximize the impact of fast bypass coding, the bypass coded
bins for luma intra prediction mode coding within a CU are grouped together in
HEVC [
19
]. This is beneficial when the partition mode is PART_NxN, and there are
four sets of prediction modes.
8.5.3
Comparison of HEVC and H.264/AVC
The differences between H.264/AVC and HEVC in signaling of syntax elements
at the PU layer are summarized in Table
8.5
. HEVC uses both spatial and temporal
neighbors as predictors, while H.264/AVC only uses spatial neighbors (unless direct
mode is enabled). In terms of the impact of the throughput improvement techniques,
HEVC has around 6
fewer maximum regular coded bins per inter-predicted PU
than H.264/AVC. HEVC also requires around 2
fewer contexts for PU syntax
elements than H.264/AVC.
8.6
Transform Unit Syntax Elements
In video coding, both intra and inter prediction are used to reduce the amount of data
that needs to be transmitted. In addition, rather than sending the original samples of
the prediction signal, an appropriately quantized approximation of the prediction
error is transmitted. To this end, the prediction error is blockwise transformed
