Most of tests here add an additional 6-param affine model. 6-param affine model requires coding 3 CPMVs, compared with coding 2CPMVs for 4-param affine model in BMS affine. Adaptive selection at CU level or slice level are proposed.
Test 4.1.8 propose two types of 3-param model models, scaling model and rotation model. The 3-param model is represented by 1.5 motion vector, top-left motion vector and x or y component of the top-right motion vector.
Switchable 4/6 parameter model provides approx. 0.5-0.6% gain. The switchable 3/3/4 approach does not provide comparable gain (up to 0.2%).
Proponents are requested to provide an analysis about the number of operations, memory usage, etc. for the list construction and the inheritance, also in comparison with BMS affine.
Analysis was shown Sat. 14th 9-10.
The solution of 4.1.3c has least complexity (still significantly less complex than the current BMS with 4 parameters, no scal. No mul. No div.). 4.1.4 is based on it with more candidates, by factor 1.4 more complex. 4.1.5 is still less complex than BMS, but higher complex than 4.1.3/4.1.4. Though it has less shift and additions, it requires scaling/mul/div.
After all, 4.1.3. is asserted to be the simplest solution. For 6 parameters it is 1.5x complex as for the case of 4 parameters, and still significantly less than current BMS with 4 parameters
The signalling and coding mechanisms of 4.1.7c should also further be studied in combination with the new BMS.
The possibility of further switching between 3/3/4/6 models (as from the results of 3.18c might give additional gain) should also further be studied. However, such a modification should only be made when it is not penalized by increased encoder run time, and the methods of MV prediction and merge should be harmonized.