Organisation internationale de normalisation

Test C.3 – Copy-from-previous-row mode

Proponent: Qualcomm, JCTVC-R0202, JCTVC-S0174

Crosschecker: MediaTek, JCTVC-S0203

In this test, a mode of “copy from previous rows” for the palette coding was tested. This method enables copying pixels from previously coded rows beyond the row above in the current CU. This is defined as an additional palette mode besides the existing “copy from left”, “copy above” and “escape” modes. The reference row index is coded in the bitstream to indicate which row is copied from. Restrictions on the number of rows available for ‘copy from previous rows” will be tested.

Note: An encoder-only RDO algorithm change is applied to estimate the run bits more precisely.

Gain is 0.0 to 1.4%, depending on the category of test material.

The gain of C.2 and C.3 are reported to be approximately additive (not cross-checked).

(Further discussion chaired by GJS on Monday 10-20 p.m.)

S0178 was a related contribution that was suggested by the BoG to be reviewed in this further discussion.

It was remarked that the gain would be larger if IBC was tested with a more constrained search region, which is somewhat anticipated.

Results of the combination of C.2 and C.3 were reported in the late contribution S0188 and were since cross-checked (S0288 (NCTU) and S0295 (Nokia)).

Further discussion was chaired by GJS on Thursday 10-23 a.m.

It was commented that we should not complicate and destabilize the design for gains this small. This also applies to our CEs – we should not be studying things that appear to have only a very minor potential for improvement (at least if they are complicating the design).

It was asked how important it is to consider gains that only apply in the lossless case, and commented that lossless coding is not higher priority than the lossy case.

These principles were agreed (CE plans suggested earlier in the meeting should take this into account).

A BoG (Robert Cohen & Yu-Wen Huang) considered CE6-related non-CE contribs.