B Frame Motion Vector Validation in Fixed Reference Frame Coding
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Solution Overview
Problem
In video coding systems using a fixed reference frame number, B frames often fail to obtain actual reference blocks due to mismatched motion vectors, leading to encoding deviations and image distortion, especially when the forward reference frame exceeds the maximum forward reference frame that B frames can point to.
Innovation Solution
The method involves performing motion estimation for each block of the current B frame, checking if the motion vector exceeds the maximum forward reference frame, and if so, using a modified calculation to ensure the forward and backward motion vectors fall within the valid range, thereby obtaining valid image reference blocks by substituting the nearest forward reference frame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple forward reference frames are used for P frame and B frame, then coding efficiency is improved, but space and time complexity greatly increase
Solution Approach 1:
The patent applies parameter changes by limiting the number of forward reference frames that B frames can access. Specifically, it restricts B frames to access at most 2 forward reference frames (the immediately preceding P frame and I frame), while P frames can access more reference frames. This parameter limitation reduces the search space and computational complexity while maintaining acceptable coding efficiency.
2Measurement precision
If motion vector is used to connect current macro block with reference block beyond maximum forward reference frame, then prediction accuracy is improved, but reference block cannot be obtained due to fixed reference frame number
Solution Approach 1:
The patent applies preliminary anti-action by pre-establishing rules to prevent motion vectors from pointing to invalid reference frames. The method checks whether the reference frame indicated by the motion vector is within the valid range (maximum forward reference frame number), and if not, it adjusts the motion vector to point to the nearest valid reference frame. This prevents the problem of unavailable reference blocks before encoding occurs.
Solution Approach 2:
The patent uses an intermediary mechanism (motion vector validation and adjustment module) that mediates between the motion estimation result and the reference frame selection. When a motion vector points beyond the maximum forward reference frame, this intermediary adjusts it to point to a valid reference frame, ensuring both prediction accuracy and reference block availability.
3Device complexity
If fixed reference frame number is adopted, then space and time complexity are reduced, but B frame cannot obtain actual reference blocks when motion vector exceeds limit
Solution Approach 1:
The patent applies dynamics by making the reference frame selection adaptive rather than completely fixed. While the maximum number of forward reference frames is fixed to control complexity, the actual selection is dynamic based on motion vector validation. The system dynamically adjusts which reference frame is used by checking and modifying motion vectors to ensure they point to valid frames, thus maintaining encoding accuracy within the fixed complexity constraints.
Data Source
AI summary
A method for obtaining an image reference block in a code mode of fixed reference frame number includes the steps of: performing motion estimation for each block of a current B frame and obtaining a motion vector MV of a corresponding block of a backward reference frame; discriminating whether the motion vector is beyond a maximum forward reference frame which is possibly pointed by the B frame, if not, then calculating the forward and backward motion vectors in a normal way; if yes, then using the motion vector of the forward reference frame that the B frame can obtain in the same direction to replace the motion vector of the corresponding block in the backward reference, and calculating the forward and the backward motion vectors of the B frame; finally, two image blocks pointed by the final obtained forward and backward motion vectors as the image reference blocks corresponding to the macro block. The present invention solves the possibly appeared problem of un-matching motion vectors, and can guarantee the coding efficiency to the largest extent.