Game Development Reference
In-Depth Information
Fig. 7.8
Band offset signaling in AVS-2
for each band, they are not necessary to transmit to decoder. Only four band offsets
are transmitted to a decoder, together with 2 start band positions. As illustrated in
Fig.
7.8
, first two offset values are used for two consecutive bands from the 1st start
band position and the remaining two offset values are used for two consecutive bands
from the 2nd start band position. For example, suppose that 32 band offset values to
be determined at the decoder are BO[0], BO[1],
, BO[31], two start band positions
are p[0] and p[1], four offset values signaled to the decoder are o[0], o[1], o[2], and
o[3]. Then, the band offset values are determined as follows:
...
...
1. All the band offset values are initialized to 0 as BO[0], BO[1],
, BO[31];
2. Four offset values are copied to the signaled band positions as follows,
BO[p[0]]
=
o[0];
BO[p[0]+1]
=
o[1];
BO[p[1]]
=
o[2];
BO[p[1]+1]
=
o[3].
This band offset signaled method is effective because sample range in an LCU is
quite limited, and most of the samples lie in a few bands.
7.3.2.1 SAO Adaptivity
In order to improve the compression efficiency, SAO designs some syntax elements
used to indicate whether it is disabled in different levels and adopt merge mode to
reduce the bits used in transmitting SAO parameters.
In the sequence parameter set (SPS), one syntax element, SAO_disable_flag, is
used to indicate whether SAO is disabled in the current video sequence. In the
slice header, three syntax elements (SAO_slice_on_Y, SAO_slice_on_Cb,
SAO_slice_on_Cr) indicate whether SAO is enabled for Y, Cb, and Cr in the current
slice. If SAO is enabled in the current slice, SAO parameters of LCUs are interleaved
into the slice data, and the SAO data of one LCU is placed at the beginning of LCU
