Graphics Reference
In-Depth Information
Fig. 3.10
Tile-based raster
scan order of CTUs with nine
tiles of different sizes in the
picture. Note that the tile
boundaries are marked with
bold dashed lines
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Tile
Boundary
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Fig. 3.11
Two different ways of fragmenting an exemplary tile partitioning using two tiles into
slices and slice segments.
Left
: One slice including four dependent slice segments.
Right
:Three
slices, each containing one dependent slice segment. Note that the tile boundaries are marked
with
bold dashed lines
, the slice boundaries with
bold solid lines
, and the boundaries between slice
segments with
dotted lines
. The CTUs belonging to the independent slice segments are
blue shaded
same slice. For each slice segment and tile at least one of the following conditions
shall be true in a picture: All CTUs in a slice segment belong to the same tile, or all
CTUs in a tile belong to the same slice segment. Note that as a consequence of these
constraints, a slice or slice segment whose starting point does not coincide with the
starting point of a tile cannot span multiple tiles. An example of this situation is
given in Fig.
3.11
, which shows the same partitioning of a picture into two tiles with
two different ways of fragmentation into slices and slice segments.
Tiles do not require communication between processors for CTU-level entropy
decoding and reconstruction, but communication is needed if in-loop filtering
stages operate in the cross tile-border filtering mode. Although the cross tile-border
filtering mode may be switched off to avoid data exchange between processors, it
can result in visual artifacts at tile boundaries.
Compared to slices, tiles usually provide a better coding efficiency since
reduced spatial distances in tiles lead to a potentially higher exploitation of spatial
correlations between samples within a tile. Furthermore, the use of tiles may
reduce slice header overhead, at least in cases where not exactly one slice per tile
