The Joint Collaborative Team on Video Coding (jct-vc) of itu-t wp3/16 and iso/iec jtc 1/ sc 29/ wg 11 held its tenth meeting during 11-20 July 2012 at the City Conference Centre (ccc), a k. a

JCTVC-J0065 AhG5/AhG6: On SAO type index coding [Y. H. Tan, C. Yeo (I2R)]

This contribution proposes two modifications to the coding of SAO type index. In the first modification, the SAO type index is coded with a truncated unary code instead of a unary code. In the second modification, only first 2 bins (signaling SAO on/off and band/edge offset) of the syntax element are coded with contexts while the edge offset type is coded with a fixed length code in bypass mode. Both modifications reportedly reduce the maximum number of context coded bins for each syntax element coded while improving chroma coding performance by ~0.3%.

2^nd version uses context coding for type and for one more bin for EO/BO, fixed length code for type.

Several experts raise the opinion that it might be better to use context coding only for on/off, and use bypass coding for type

Related contributions: J0178, 0104, 0148, 0268

None of the five contributions (except 148) modifies on/off coding

Except for J0065, the four methods are different in binarization of type:

• 
  J0104 : trunc. unary, 4 bins max.
  
• 
  J0148 : same as 104
  
• 
  J0178 : fixed length 3 bins
  
• 
  J0268 : one flag EO/BO, fixed length 2 bins in case of EO (max total 3 bins)
  

J0065 has two versions, one is identical to 104, the other is similar to J0268 but using context coding for EO/BO.

One argument is brought that a scheme which give same chances at least to the four edge directions appears to have an additional benefit

Candidate for adoption: J0268: Version with one context-coded bin on/off, remaining bins bypass: One flag EO/BO, fixed length 2 bins for edge orientation in case of EO

J0207 is using the same binarization as J0104, but applies context coding to the type part as well. This is undesirable.