International organisation for standardisation

5.8.4Subtest 2: Adaptive loop filter with fixed set of filters

5.8.4.1.1.1.1.1.1JCTVC-F285 CE8 Subtest 2: Parametric Adaptive Loop Filter [E. Maani, W. Liu (Sony)]

Parametric ALF is composed of a set of fixed filters which are classified based on their direction and strength for a CU. The number of filter sets in the implementation is 32 for luma and chroma, respectively. The number can be reduced to 12 or 24 depending on filter shape. Test 1 and 2 use 9x7 tap for luma and 5x5 tap for chroma, and ALF in HM3.0 and PALF may be switched CU by CU. Test 3 uses 9x5 tap for luma and 5x3 tap for chroma.

There were three sub-subtests in subtest 2.

Toshiba studied the source code for one of the three sub-subtests.

The ability to switch on a CU basis may be helpful in reducing encoder complexity.

Fixed filter tap values were partially (but not entirely) trained on the test set.

Decoder storage, about 400 * 10 bits each.

Initially, it was planned to have the filter values to be sent at the SPS level as well as at the PPS level and slice level (a hierarchy of overrides). This plan was then replaced by a later decision for an adaptation parameter set (discussed elsewhere in this report).

There is an analogy to default quant matrix values.

There are some symmetries in the current filter structure. These symmetries are not kept in the proposal, which could increase decoder complexity. This is undesirable.

It was planned that (eventually) we should have default values (TBD), but these should have the same shape/symmetry properties as currently exists for coded coefficients – unless justified by sufficient evidence. Further study on this topic was encouraged.

5.8.4.1.1.1.1.1.2JCTVC-F163 CE8.2: Verification results of Sony Proposal JCTVC-F285 [T. Yamakage, T. Watanabe (Toshiba)] [late upload 07-06]

5.8.4.1.1.1.1.1.3JCTVC-F170 CE8 Subtest2: Cross-verification on Sony Parametric Adaptive Loop Filter (JCTVC-F285) [A. Minezawa, K. Sugimoto, S. Sekiguchi (Mitsubishi)] [late upload 07-11]
5.8.4.1.1.1.1.1.4JCTVC-F312 CE8 Subset 2: Cross-Verification of Sony adaptive loop filter (JCTVC-F285) by Qualcomm [I. S. Chong, M. Karczewicz (Qualcomm)]