有兩種濾波，一個deblock filter用來減弱因為transform和預測邊界的不聯系性；另外一個是SAO，通過減弱振鈴效應和改變像素的強度來提升畫質。https://blog.csdn.net/u014470361/article/details/94641124解釋什么是塊效應和振鈴效應。

• ?Deblocking Filter

塊效應的產生：

1.

2.

since the deblocking of one vertical (horizontal) boundary in HEVC does not affect
deblocking of other vertical (horizontal) boundaries because of only fltering the
boundaries on the 88 sample grid, all the vertical (horizontal) boundaries can be
?processed in parallel。

? 去效應濾波，對于亮度，BS必須大于0；對于色度，BS必須大于1.

HEVC有2個filter mode，normal ，strong；

Strong filter mode滿足的條件是：

?

normal filter mode：

?

?

?

?

• strong filter Mode?

?用在平坦的區域，這個塊效應會更加明顯。

• Chrome Deblocking?

. Chroma
deblocking only modifes one sample from each side of the block boundary.

?Adaption：sending parameterstc_offset_div2and beta_offset_div2in the
slice header or picture parameter set (PPS) [46]. These parameters specify offsets
(divided by two) that are added to a QP value before determining “and tC from the
look-up tables. This gives an encoder a possibility to adapt the deblocking strength

• Sample Adaptive Offset (SAO)

在一定的范圍內，通過選擇的分類器把像素分為不同的類別，然后加上一定的offeset來減少像素的損失。有兩種類型的SAO type，一種edge offset，另外一種是band offset。

In Edge， a sample is based on its neighborhood, i.e. on the comparison between the current
sample and its neighboring samples. In BO, the classifcation is based on the sample
value。

• ?edge Offset

?

?

?

• ? Band Offset

?The sample values range is divided into 32 equal bands. For 8-bit samples
in the range from 0 to 255, the width of a band is 8. Thus, sample values from 8k to
8k C7 belong to band k, where k ranges from 0 to 31. The difference between the
original samples and reconstructed samples in a band (i.e. the offset of a band) can
be signaled to the decoder.

• SAO Parameter Signaling?

?sample_adaptive_offset_enabled_flag：SAO enble or not

slice_sao_luma_flag and slice_sao_chroma_flag, indicate if SAO
is enabled for luma and chroma, respectively, in the current slice

• ?SAO Parameters Merging

?1.reusing SAO param
eters of the left CTU (by setting a syntax element sao_merge_left_flag

2.

to 1), reusing SAO parameters of the above CTU (by setting a syntax element
sao_merge_up_flag to 1)

?

總結

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