Bidirectional Intra Prediction Signaling Overhead Reduction
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Solution Overview
Problem
The introduction of bidirectional intra prediction modes in video coding leads to a high bitrate due to signaling overhead, which existing technologies have not adequately addressed.
Innovation Solution
A method for video coding that includes generating a bitstream for reconstructing a picture by determining whether a bidirectional intra prediction (BIP) flag is to be signaled based on prediction-related information, such as reference sample availability and mode indices, and using context-adaptive binary arithmetic coding (CABAC) contexts to reduce signaling when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bidirectional intra prediction modes are introduced to improve prediction accuracy, then prediction quality is improved, but bitrate increases due to signaling overhead
Solution Approach 1:
The patent applies local quality by making the BIP flag signaling conditional rather than uniform across all blocks. The decision to signal the BIP flag is made locally for each current block based on specific prediction-related information such as the availability of reference samples, the intra prediction mode index, and the block size. This allows BIP mode to be used where beneficial while avoiding signaling overhead where it is not needed, thus improving prediction accuracy locally without uniformly increasing bitrate across the entire picture.
Solution Approach 2:
The patent changes the parameter of BIP flag signaling from a fixed state (always signaled) to a variable state (conditionally signaled). By introducing conditions based on prediction-related information (reference sample availability, mode index ranges, block size thresholds), the signaling behavior dynamically adapts to local picture characteristics. This parameter change allows the system to maintain high prediction accuracy where BIP is beneficial while reducing bitrate by omitting flags where BIP is not applicable or redundant.
2Reliability
If BIP flag is always signaled in bitstream to ensure decoder correctness, then decoding reliability is improved, but signaling overhead increases
Solution Approach 1:
The patent applies preliminary action by determining in advance whether the BIP flag should be signaled based on prediction-related information available during encoding. The encoder evaluates conditions such as reference sample availability, intra prediction mode index, and block size before signaling decisions are made. This preliminary determination ensures that both encoder and decoder have the same understanding of whether BIP mode is active, maintaining decoding reliability without requiring the BIP flag to be universally signaled.
Solution Approach 2:
The patent implements self-service by enabling the decoder to autonomously determine whether BIP mode is active for a current block by evaluating the same prediction-related information conditions that the encoder used. Instead of always receiving an explicit BIP flag, the decoder can infer the BIP mode status from the availability of reference samples, the intra prediction mode index value, and block size, matching the encoder's decision. This self-determination mechanism maintains reliability while reducing signaling overhead.
Data Source
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AI summary
Devices and methods for video coding are described. One method comprises receiving a bitstream, wherein the bitstream comprises prediction related information, and wherein the prediction related information includes at least one of: numbers and positions of available primary reference samples, an intra prediction mode index, or a size of the current coding block; determining whether a bidirectional intra prediction (BIP) flag is signaled in the bitstream based on the prediction related information; and reconstructing the picture. The proposed techniques save overhead or have a better efficiency in entropy encoding or decoding.