JVET-O0482 CE8-related: Modulo operations for IBC block vectors [X. Xu, X. Li, S. Liu (Tencent)]

In this contribution, a modulo operation is performed on the decoded IBC block vector, such that after the operation, the reference block indicated by the modified block vector falls into the potentially available reference area (e.g. in current CTU or left CTU), which are the allowed search range for IBC compensation.

It is reported that the proposed modification converts some of the bitstream conformance constraints for IBC into operations in the decoding process. It is asserted to be easier for the encoders to generate compliant bitstreams by using the proposed conversions.

Simulation results reportedly show that no RD performance or runtime impact were observed with the proposed modification.

From the discussion, it is noted that some additional checks are necessary at the picture boundary.

Only the range is tested at the decoder, and then the vector is truncated into the valid range.

Availability constraints would still be necessary in the bitstream, and availability checks at the encoder.

It is pointed out that the modulo value might also be variable depending on position.

It is requested to provide data about the maximum number of operations per 4x4 block.