Picture-Header Flag for Lower-Cost Bi-Directional Decoding
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Solution Overview
Problem
The existing solutions in VVC incur unnecessary bit costs due to signaling slice types and bi-directional prediction tools when they are not needed, and it is not straightforward to determine if a coded picture is bi-directional inter coded.
Innovation Solution
Decoding a codeword from the bitstream to indicate the presence of bi-directional inter coded slices, allowing derivation of parameter values to decode segments without explicit signaling of slice types and conditionally enabling bi-prediction tools based on this codeword.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If slice types and bi-directional prediction tools are explicitly signaled in the bitstream, then the decoder can accurately determine picture coding modes, but unnecessary bit costs are incurred when these tools are not needed
Solution Approach 1:
The patent introduces a preliminary flag in the picture header structure that indicates in advance whether bi-directional prediction tools are enabled for the entire picture. This preliminary information allows the decoder to avoid decoding slice type information for all slices, thereby reducing bit cost while maintaining accurate determination of picture coding modes. The flag is set before slice-level decoding occurs, enabling early decision-making about tool usage.
Solution Approach 2:
The patent extracts the bi-directional prediction tool enablement information from the slice-level signaling and places it at the picture header level. This separation allows the slice type signaling to be omitted or simplified when the picture-level flag indicates uniform tool usage across all slices, thereby eliminating redundant information transmission while preserving the ability to accurately determine coding modes.
2Measurement precision
If slice types are signaled for every slice, then the decoding accuracy is improved, but the bitstream complexity and processing overhead increase
Solution Approach 1:
The picture header structure includes a preliminary flag that indicates whether bi-directional prediction tools are enabled for the entire picture. This preliminary information allows the decoder to skip slice type signaling and processing when the coding mode is uniform across all slices, thereby reducing decoding complexity while maintaining accurate determination of slice types through the picture-level indication.
3Adaptability or versatility
If bi-directional prediction tools are enabled for all slices, then decoding flexibility is improved, but bit cost increases due to unnecessary signaling
Solution Approach 1:
A flag in the picture header structure is introduced to preliminarily indicate whether bi-directional prediction tools are enabled for the entire picture. When this flag indicates that the tools are enabled, the decoder can proceed with bi-directional decoding for all slices without requiring individual slice type signaling, thereby maintaining decoding flexibility while avoiding unnecessary bit cost. When the flag indicates tools are disabled, the decoder can skip related processing entirely.
Data Source
AI summary
A methods and apparatuses for encoding or decoding a segment in a coded picture. The decoding may include obtaining from a bitstream a value of a first codeword that indicates whether the coded picture may contain bi-directional inter coded segments or not. The decoding may include, based on the value of the first codeword, deriving one or more parameter values by either (a) decoding one or more parameters from the bitstream to obtain the one or more parameter values or (b) inferring the one or more parameter values. The decoding may include decoding the segment in the coded picture based on the one or more parameter values. The encoding may include encoding the first codeword to the bitstream and determining whether to encode one or more parameter values in the bitstream based on a determination of whether the coded picture will contain bi-directional inter coded segments or not.