International organisation for standardisation organisation internationale de normalisation

CE5: Depth intra modes (40)

(Chaired by A. Vetro)

1. Summary (1)

14.1.1.1.1.1.1.1.49JCT3V-G0025 CE5 Summary Report: Depth Intra Modes [H. Liu]

Coding Efficiency

JCT3V-G0101: Segment-wise depth inter mode coding, proposes three aspects to improve the inter SDC.

1. 
   Simplification of the inter SDC:
   
   1. 
      Only apply inter SDC to CUs that are coded with 2Nx2N partition mode.
      
   2. 
      Allow DC residual in inter SDC mode to be zero.
      
2. 
   Improvement of the DC residual: search the best DC residual from {deltaDC – 1, deltaDC, deltaDC + 1} through view synthesis optimization process at encoder, where deltaDC refers to the DC residual generated in inter SDC mode in 3D-HTM 9.0r1.
   
3. 
   Improvement of the DC residual: search the best DC residual from {deltaDC – 2, deltaDC – 1, deltaDC, deltaDC + 1, deltaDC + 2} through view synthesis optimization process at encoder, where deltaDC refers to the DC residual generated in inter SDC mode in 3D-HTM 9.0r1.
   

Item #2 and item #3 are non-normative methods. Among these two options, it seems preferred to get the maximum gain with a larger search.

For #1b, the normative change is start the residual coding from 0 rather than 1 for inter SDC. There is minor coding loss and benefit is not clear.

Support was expressed to adopt the simplification in #1a and the non-normative increase in search space in #3.

Decision: Adopt (#1a + #3)

JCT3V-G0058: This contribution is based on JCT3V-G0101, which allows the DC residual to be equal to zero in the inter SDC mode. The main difference is that it proposes to keep the non-zero constraint of the DC residual magnitude in 3D-HEVC to remove the overlap between the skip mode and the inter SDC mode. This gives an additional 0.07% gain, which is rather small.

WD text was reviewed. An additional branch is added based on merge mode. Although the concept is simple, the syntax change is more than expected.

No action.
JCT3V-G0122: Generic SDC for all Intra modes in 3D-HEVC, this contribution proposes two aspects to improve the intra SDC coding. One item is in the scope of the CE.

1. 
   Generalization of the intra SDC: generalize intra SDC to all depth intra prediction modes.
   

One item of this proposal is considered as outside of the CE scope.

2. 
   Simplification of the depth mode parameter syntax table: enable DMM4 for 4x4 blocks to further simplify the depth mode parameter syntax table.
   

As noted in the table below, #1 gives 0.3% coding gain and there is negligible loss from the proposed simplification.

WD text was reviewed, and there was support to adopt the syntax.

It was remarked that the all-intra complexity is relatively high: 20% increase without the encoder optimization, and 47% with the encoder optimization.

Decision: Adopt (with optimization in CTC)

G0102: related to G0122, and proposes to only apply intra SDC to modes that are included in MPM list or DMM modes in order to reduce the encoder complexity. It was remarked that G0122 may be simplified using non-normative techniques and signalling proposed in the G0122 design. It was believed that this provides more flexibility and the benefits of constraining the design are unclear.

Further study of design could be considered, clarifying the benefits of a constrained design.