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Merge Mode for Template-based Intra Mode Derivation (TIMD) in ECM

Mohsen Abdoli, Ramin G. Youvalari, Frank Plowman, Alexandre Tissier

TL;DR

The paper addresses the limitation of template-based IPM derivation in TIMD when the immediate template is unreliable. It introduces TIMD-Merge, which builds a merge list from both adjacent and non-adjacent TIMD-coded blocks, reorders candidates using template costs, and inherits the best candidate's IPMs and transform information, with dedicated signaling to the decoder. ECM-14.0/15.0 experiments show a modest luma BD-rate gain around -0.08% in All-Intra, at the cost of a substantial but acceptable runtime increase, and ablation studies confirm the contributions of non-adjacent neighbors and transform inheritance. The work enhances intra coding efficiency in ECM and supports ongoing exploration of post-VVC standards within the JVET framework.

Abstract

This paper presents an intra coding tool, named Merge mode for Template-based Intra Mode Derivation (TIMD). TIMD-Merge has been adopted in the 15\textsuperscript{th} version of the Enhanced Compression Model (ECM) software that explores video coding technologies beyond Versatile Video Coding (VVC) standard. This proposed tool operates on top of the regular TIMD mode that applies a template-based search on a causal adjacent template at top and at left of the current block, in order to find the best Intra Prediction Modes (IPMs) that matches the template. The proposed TIMD-Merge in this paper addresses a shortcoming in the regular TIMD method where due to texture discrepancy, the adjacent template information around the block is not reliable. To do so, the proposed TIMD-Merge constructs a list of all TIMD-coded blocks in relatively larger template area than the template of the regular TIMD, which also includes non-adjacent neighboring blocks. This list, called the merge list, is then sorted on the template to give one best set of TIMD modes. The use of TIMD-Merge mode is signalled at the block level and the implementation in the ECM-14.0 demonstrates -0.08\% performance improvement in terms of luma BDR gain, with negligible encoding and decoding runtime increase of 100.6% and 100.2%, respectively.

Merge Mode for Template-based Intra Mode Derivation (TIMD) in ECM

TL;DR

The paper addresses the limitation of template-based IPM derivation in TIMD when the immediate template is unreliable. It introduces TIMD-Merge, which builds a merge list from both adjacent and non-adjacent TIMD-coded blocks, reorders candidates using template costs, and inherits the best candidate's IPMs and transform information, with dedicated signaling to the decoder. ECM-14.0/15.0 experiments show a modest luma BD-rate gain around -0.08% in All-Intra, at the cost of a substantial but acceptable runtime increase, and ablation studies confirm the contributions of non-adjacent neighbors and transform inheritance. The work enhances intra coding efficiency in ECM and supports ongoing exploration of post-VVC standards within the JVET framework.

Abstract

This paper presents an intra coding tool, named Merge mode for Template-based Intra Mode Derivation (TIMD). TIMD-Merge has been adopted in the 15\textsuperscript{th} version of the Enhanced Compression Model (ECM) software that explores video coding technologies beyond Versatile Video Coding (VVC) standard. This proposed tool operates on top of the regular TIMD mode that applies a template-based search on a causal adjacent template at top and at left of the current block, in order to find the best Intra Prediction Modes (IPMs) that matches the template. The proposed TIMD-Merge in this paper addresses a shortcoming in the regular TIMD method where due to texture discrepancy, the adjacent template information around the block is not reliable. To do so, the proposed TIMD-Merge constructs a list of all TIMD-coded blocks in relatively larger template area than the template of the regular TIMD, which also includes non-adjacent neighboring blocks. This list, called the merge list, is then sorted on the template to give one best set of TIMD modes. The use of TIMD-Merge mode is signalled at the block level and the implementation in the ECM-14.0 demonstrates -0.08\% performance improvement in terms of luma BDR gain, with negligible encoding and decoding runtime increase of 100.6% and 100.2%, respectively.

Paper Structure

This paper contains 5 sections, 5 equations, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Template-based Intra Mode Derivation (TIMD)
  3. Merge mode for TIMD
  4. Experiment result
  5. Conclusion

Figures (5)

  • Figure 1: (a) TIMD template with width of $M$ at left and above of the current block of size $W\times H$, (b) Applying template prediction according to the angular IPM 34 and using the template's reference line (white pixels).
  • Figure 2: (a) Map of the 41 candidate non-adjacent neighbor positions. (b) Proportion of TIMD-merge-coded CUs which use prediction information from a CU covering the position at the relevant normalized offset, when using the non-adjacent neighbor map.
  • Figure 3: Diagram of the ECM decoder with proposed modification of TIMD. Green: Aspects specific to regular TIMD. Blue: Aspects specific to TIMD-Merge. Orange: Shared aspects.
  • Figure 4: Visual demonstration of blocks selected by the regular TIMD (cyan), the proposed TIMD-Merge (yellow) and other intra tools (purple).
  • Figure 5: Example of a TIMD-Merge block (yellow) with uncorrelated template (white), inheriting prediction information from its correlated non-adjacent neighbor (cyan) that is coded with the regular TIMD.