Opened 11 years ago

Closed 9 years ago

#13 closed defect (fixed)

Current state for inter-layer reference picture

Reported by: Vadim Owned by: jlchen
Priority: minor Milestone: Draft 5
Component: SHVC text and test model Version: Draft 4 version 3
Keywords: Cc: jlchen, yanye, jillboyce, jct-vc@…

Description

Problem:
In HEVC specification, picture type such as short term or long term is involved in the motion vector scaling. In HEVC, picture type of the reference pictures is defined at the time when the picture was current, particularly

The function LongTermRefPic( aPic, aPb, refIdx, LX ), with X being 0 or 1, is defined as follows:
– If the picture with index refIdx from reference picture list LX of the slice containing prediction block aPb in the picture aPic was marked as "used for long term reference" at the time when aPic was the current picture, LongTermRefPic( aPic, aPb, refIdx, LX ) is equal to 1.
– Otherwise, LongTermRefPic( aPic, aPb, refIdx, LX ) is equal to 0.

In SHVC, derived inter-layer reference picture can be used as a collocated picture and the picture type of its reference pictures can be involved in the motion vector scaling. However, since derived inter-layer reference picture is not a coded picture, it was not a current picture when LongTermRefPic is defined. So, the status of the derived inter-layer reference picture being current has to be defined for the marking purpose of its reference pictures to be complaint with the HEVC motion vector scaling process and “HLS” only concept.

Possible solution:
The solution can be the following, by setting the resampled picture to be current during the motion field resampling (marked with bold):
...
– When VpsInterLayerMotionPredictionEnabled[ LayerIdxInVps[ currLayerId ] ][ LayerIdxInVps[ rLId ] ] is equal to 1, the following steps apply:
– The resampled picture rsPic is set to be the current picture at the time when the reference layer picture rlPic is the current picture
– A single slice rsSlice of the resampled picture rsPic is generated as follows:
...

Change history (3)

comment:1 Changed 11 years ago by DefaultCC Plugin

  • Cc jlchen yanye jillboyce jct-vc@… added

comment:2 Changed 11 years ago by yanye

The editors discussed this ticket extensively. The consensus was that the suggested fix, copied below, could not be directly accepted as is.

– The resampled picture rsPic is set to be the current picture at the time when the reference layer picture rlPic is the current picture

The editors then had extensive discussion about how to provide a better fix. Various suggestions were provided. Some required relatively significant changes to the base spec (TMVP derivation process), others were deemed vague and/or editorially insufficient. In summary, all possible fixes discussed were not satisfactory.

During the discussion, the editors came to realize that there is one significant difference between an inter layer reference picture and a temporal reference picture when they are used as the collocated picture in TMVP. Namely, an inter layer reference picture rsPic is always at the same time instance as the EL picture that will use it as collocated picture. In other words, the DPB status (i.e., whether the reference pictures are long term or short term) has not changed. For TMVP derivation, the version 1 base spec says the following:

– If the picture with index refIdx from reference picture list LX of the slice containing prediction block aPb in the picture aPic was marked as "used for long term reference" at the time when aPic was the current picture, LongTermRefPic( aPic, aPb, refIdx, LX ) is equal to 1.

Given this unique characteristic of the inter layer reference (in comparison with temporal reference) as the TMVP collocated picture, the editors formed the opinion that defining the “at the time when X was the current picture” was not essential when X is the inter layer reference picture rsPic.

Hence the suggestion was to not take action on this ticket.

comment:3 Changed 9 years ago by yanye

  • Resolution set to fixed
  • Status changed from new to closed

There was no follow-up discussion on this ticket. Given editors concluded a while ago that no action was needed, the ticket is closed.

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  • Gerhard Tech(Always)
  • jct-vc@…(Subscriber)
  • Jianle Chen(Owner, Subscriber)
  • Jill Boyce(Subscriber)
  • Karsten Suehring(Always)
  • Vadim Seregin(Reporter)
  • yanye(Subscriber, Participant)