Graphics Reference
In-Depth Information
6.6
Coding Performance
The different transform sizes used in a coding block in HEVC are signaled in a
quadtree structure [
29
]. The maximum transform size to use in a coding block
is signaled in the sequence parameter set. Table
6.6
compares the coding perfor-
mance of HEVC when all transform sizes (up to 32
32) are used to the coding
performance when only 4
4and8
8 transforms are used as in H.264/AVC.
The standard Bjøntegaard Delta-Rate (BD-Rate) metric [
2
] is used for comparison.
Tab le
6.6
shows that there is a bit rate savings in the range of 5.6-6.8 % on average
because of the introduction of larger transform sizes (16
16 and 32
32) in HEVC.
The bit rate savings are higher at larger resolution video such as 4K (2560
1600)
and 1080p (1920
1080). The HEVC Test Model, HM-9.0.1 [
13
] was used for the
simulations and the video sequences and coding conditions used were as described
in [
4
].
Tab le
6.7
compares the coding performance of the HEVC 4
4and8
8
transforms to that of the corresponding H.264/AVC transforms. The H.264/AVC
4
4and8
8 transforms were converted to 8-bit precision and implemented in the
HM-9.0.1 Test Model. Only the 4
4and8
8 transform sizes were enabled in the
simulations. It can be seen from Table
6.7
that the HEVC 4
4and8
8 transforms
perform better than the corresponding H.264/AVC transforms in terms of coding
performance.
Tabl e 6. 6
BD-rate savings of using larger transform sizes (16 16 and 32 32) on
top of the smaller transform sizes (4 4and8 8)
All Intra (%)
Random access (%)
Low delay B (%)
4K
9.1
10.1
n/a
1080p
6.7
8.0
9.1
WVGA
2.5
4.3
6.0
WQVA
2.2
2.8
3.7
720p
7.7
n/a
8.4
Overall
5.6
6.4
6.8
Tabl e 6. 7
BD-Rate savings of the HEVC 4 4and8 8 transforms versus the
H.264/AVC 4
4and8
8 transforms
All Intra (%)
Random access (%)
Low delay B (%)
4K
1.2
0.7
n/a
1080p
0.6
0.4
0.3
WVGA
0.2
0.2
0.1
WQVA
0.1
0.0
0.1
720p
0.5
n/a
0.2
Overall
0.5
0.3
0.2
