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-J0193 AHG5: Crosscheck of bypass coding for SAO syntax elements in JCTVC-J0043 [C.-M. Fu, Y.-W. Huang (MediaTek)]

Comment: by-pass should be used for SAO magnitude coding.

JCTVC-J0106 AHG6/AHG5: SAO offset coding [I. S. Chong, J. Sole, M. Karczewicz (Qualcomm)]

Additionally to JCTVC-J0043 modifies SAO magnitude binarization. Before TU was used for SAO magnitudes coding. Combination of TU and fixed length code is proposed in this contribution. As results 94% of ctx coded SAO bins reduction in the worst case (the same with J0043) and 62% reduction for total amount of SAO bins in the worst case.

Specification change is additional 11 lines paragraph describing TU and fixed length binarization for SAO magnitude.

No need to combine truncated unary and fixed length. Several experts confirm that in bypass mode, unary code with maximum length 31 bins can also be done in one cycle (but requires more buffer potentially).

It is not obvious that J0106 would give an advantage – more evidence and study needed. Count of maximum number of coded bins does not give the whole figure, as fixed length bins, context-coded bins and unary bins cannot be weighted equally.

In software the plain unary code would be less complex.

Combination of fixed + unary is already used in last position coding (but there it is context coded bins). Remaining level coding is similar (combination of exp Golomb and Rice-Golomb with transition parameter)

Would be desirable to define minimum number of binarization schemes (from the perspective of the spec). Not define a specific binarization scheme just for SAO offset. It is reported that EG0 was tried, but a loss of 0.15% was observed.

What is the current maximum length of unary code in bypass mode for any syntax element? 23. With the solution of J0043 this would be extended to 31 (in HE10 settings), for main profile, the maximum length of unary code for SAO offset would be 7 anyway. No need to define a specific binarization scheme in main profile.

In principle, the standard text does not limit the maximum number of bins in unary code, but the limitation is implicit by the maximum length allowed by any syntax element.

Further study is suggested, particularly w.r.t. extension of SAO to higher bit depth and the related binarization of the syntax elements.

(Note: J0178 suggests something similar for type coding).