Video Compression

VideoNerd

This section is a resume of a public discussion with Luc Trudeu in LinkedIn.

In AV1 as well as in HEVC/H.265 chroma partition mimics luma one as long as the block sizes are permitted. For example, in case of 4:2:0, the 16×4 luma partition can’t produce a 8×2 in chroma (because the partition 8×2 is invalid). In that case, a single 8×4 chroma is produced from two 16×4 luma partitions. In my opinion, there is one problem which encoder designers miss. Let’s consider the situation when two 16×4 luma blocks have different MVs and references.  In such case a discontinuity in chroma prediction block might be present (because the chroma block is actually composed from different references). However, Motion Estimation is commonly executed on luma samples (at least for 4:2:0 case), therefore discontinuities in chroma prediction blocks are merely skipped from consideration. So, i recommend either include chromas in motion estimation or exclude 16×4 partitions if luma MVs significantly differ.

11 Responses

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