In-Loop Filters in HEVC - High Efficiency Video Coding (HEVC) - page 189

luma SAO type (EO, BO, not applied)

EO

BO Not applied

unsigned luma offsets signed luma offsets

luma EO class luma band position

Not applied

EO

chroma SAO type (EO, BO, not applied)

BO

unsigned Cb offsets signed Cb offsets

chroma EO class signed Cr offsets Cb band position

unsigned Cr offsets Cr band position

exit

Fig. 7.19 Illustration of CTU-level SAO information coding when the current CTU is not merged
with the CTU on the left or above. Reproduced with permission from [ 13 ], © 2012 IEEE

to 1), reusing SAO parameters of the above CTU (by setting a syntax element
sao_merge_up_flag to 1), or by transmitting new SAO parameters. The SAO
merging information is shared by all three color components. When SAO merge-
left or SAO merge-up mode is indicated, all SAO parameters from the left or above
CTU are copied and no more information is signaled for the current CTU. This
CTU-based SAO information merging effectively reduces the SAO information that
needs to be signaled [ 31 ].

7.3.4.2 SAO Type and Offsets Signaling

If merging of SAO information is not used, the information for the current CTU
is signaled as shown in Fig. 7.19 . Syntax elements for the luma component are
first sent, followed by the Cb syntax elements and then the Cr syntax elements.
For each color component, the SAO type is transmitted ( sao_type_idx_luma
or sao_type_idx_chroma ), which indicates EO, BO, or not applied (SAO
turned off). If BO or EO is selected, four offsets are transmitted. If BO
is selected, the starting band position ( sao_band_position ) is signaled.
Otherwise, if EO is selected, the EO class ( sao_eo_class_luma or
sao_eo_class_chroma ) is signaled. The Cb and Cr components share the SAO
type ( sao_type_idx_chroma ) and EO class ( sao_eo_class_chroma )