JVET-N0415 CE5: Coding tree block based adaptive loop filter (CE5-4) [N. Hu, V. Seregin, H. E. Egilmez, M. Karczewicz (Qualcomm)]
CE5-4.1
In VTM4, adaptive parameter set (APS) was adopted, each APS contains one set of ALF filters (up to 25 filters for luma and 1 filter for chroma components), up to 32 APSs are supported.
In CE5-4.1 test, an APS containing filters from the previous pictures can be selected in the tile group header. The APSs are updated as a first-in-first-out (FIFO) manner.
CE5-4.2
For luma component, when ALF is applied to a luma CTB, the choice among 16 fixed, 5 previous filter (APSs) or 1 signalled filter sets is indicated. Only the filter set index is signalled.
For a tile group, only one new set of 25 filters can be signalled. If a new set is signalled for a tile group, all the luma CTBs in the same tile group share that filter set. Fixed filter sets can be used to predict the new tile group level filter set and can be used as candidate filter sets for a luma CTB as well.
The fixed filters consist of total 64 7x7 filters (each filter contains 13 coefficients) which are only used for luma component. For each class, a mapping is applied to define which 16 fixed filters from the 64 filters can be used for that class. The choice index (0-15) of each class is signalled as fixed filter index. The total memory needed to store fixed filters is 1132 bytes, consisting of 64 filters x 13 coefficients/filter x 8 bits/coefficient and 16 choices/class x 25 classes x 6 bits/index for mapping table.
For chroma component, when ALF is applied to a chroma CTB, if a new filter is signalled for a tile group, the CTB uses the new filter; otherwise, the most recent previous picture chroma filter satisfying the temporal scalability constraint is applied.
For CE5-4.3ff, see table below.
Test | Description | Tester | Cross-checker |
CE5-4.1 | VTM with temporal filters mimicking APS | Nan Hu (Qualcomm) | Patrice Onno (Canon) |
CE5-4.2 | Luma CTBs with ALF on can switch among 1 tile group level signalled filter set, 16 fixed filter sets and at most 5 available sets in APS. All chroma CTBs with ALF on in a picture can only use the tile group level signalled filter or one temporal filter | Nan Hu (Qualcomm) | Patrice Onno (Canon) |
CE5-4.3 | Test CE5-4.2 with QP = 12, 17, 22 and 27 | Nan Hu (Qualcomm) | Patrice Onno (Canon) |
CE5-4.4 | Test CE5-4.2 without fixed filters | Nan Hu (Qualcomm) | Patrice Onno (Canon) |
CE5-4.5 | Test CE5-4.2 without temporal filters | Nan Hu (Qualcomm) | Patrice Onno (Canon) |
CE5-4.6 | Test CE5-4.5 with QP = 12, 17, 22 and 27 | Nan Hu (Qualcomm) | Patrice Onno (Canon) |
CE6: Transforms and transform signalling (5)
Contributions in this category were discussed Wednesday 20 March 1500–1650 (Track A chaired by JRO).