Graphics Reference
In-Depth Information
MB 1
MB 2
first
second
third
fourth
H.264/AVC
HEVC
Fig. 7.4
Order of boundaries processing in HEVC and H.264/AVC deblocking. In each group
(first to fourth), boundaries are processed from left to right and from top to bottom. In HEVC all
vertical (horizontal) boundaries can be processed in parallel
brought by HEVC deblocking filtering. The deblocking filter complexity and
parallelization aspects are addressed in Sect.
7.4.1
.
7.2.2
HEVC Deblocking Filter Description
7.2.2.1
Decisions to Filter a Block Boundary
As a compromise between the subjective quality and computational complexity,
the HEVC deblocking filter in case of 4:2:0 chroma subsampling is only applied
to the block boundaries that lie at the luma and chroma sample positions that are
multiples of eight (in H.264/AVC the deblocking is applied on the 4
4 luma and
chroma sample grid). Since the deblocking filtering is only applied to the boundaries
between the coding units (CU), prediction units (PU), or transform units (TU) and
not to the inside areas, the average complexity of the HEVC deblocking is further
decreased compared to the H.264/AVC since HEVC can use larger block sizes.
In HEVC deblocking, the vertical boundaries in a picture are filtered first,
followed by the horizontal boundaries. In a coding unit, the vertical boundaries
between the coding blocks are processed starting from the left-most boundary
towards the right-hand side. The horizontal boundaries are processed starting from
the top-most boundary towards the bottom. In contrast to that, the H.264/AVC
deblocking filter operates on a macroblock (MB) basis, where the four vertical
boundaries in an MB are processed sequentially starting from the left-most MB
boundary, and then the four horizontal MB boundaries are processed starting from
the top-most MB boundary. The order of processing of the block boundaries in
HEVC and H.264/AVC is compared in Fig.
7.4
. One can see that the filtering
order in HEVC deblocking is more regular than that in H.264/AVC. Moreover,
since the deblocking of one vertical (horizontal) boundary in HEVC does not affect
deblocking of other vertical (horizontal) boundaries because of only filtering the
boundaries on the 8
8 sample grid, all the vertical (horizontal) boundaries can be
