Block Vector Clipping for Screen Content Coding
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Solution Overview
Problem
In video coding using the Intra-block copy (IntraBC) mode, issues arise when block vectors point to unavailable or invalid reference blocks, leading to inefficiencies in prediction and encoding due to unreconstructed areas within the current picture.
Innovation Solution
A method involving block vector clipping is introduced, where the original block vector is adjusted to ensure it points to a valid reference block within the current coding unit, and if reference pixels are unavailable, replacement pixel data is used to form a valid reference block for IntraBC compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If block vector prediction is used for IntraBC mode, then coding efficiency is improved, but invalid or unavailable reference blocks are pointed to, causing prediction errors
Solution Approach 1:
The patent applies preliminary action by checking the validity of reference blocks before using them for prediction. The system determines whether a reference block is valid based on whether it is located in a previously reconstructed area, and only uses valid reference blocks for IntraBC prediction, preventing prediction errors from invalid references
Solution Approach 2:
The patent introduces an intermediary mechanism through the use of a flag signal and validity checking process. This intermediary layer between block vector prediction and actual prediction operations ensures that only valid reference blocks are used, mediating the potential conflict between coding efficiency and prediction accuracy
2Reliability
If block vector is clipped to point to valid reference block, then prediction accuracy is improved, but encoding complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the block vector parameters (horizontal and vertical components) based on the position of the current block within the CTU. The clipping operation adjusts the vector components to point to valid reference blocks, changing the parameters dynamically based on spatial location to maintain prediction accuracy
Solution Approach 2:
The patent implements local quality by applying different block vector clipping rules based on the local position of the current block within the CTU. Different regions of the CTU have different validity constraints for reference blocks, so the clipping operation is customized for each local area to ensure reference blocks are both valid and appropriately positioned
3Productivity
If reference block is relocated to available area, then IntraBC compensation is enabled, but block vector distortion occurs
Solution Approach 1:
The patent applies partial action by selectively clipping only the necessary components of the block vector to achieve valid reference block positioning. Rather than completely redesigning the prediction process, the system applies minimal necessary clipping to the block vector components to enable IntraBC compensation while maintaining as much original vector precision as possible
Data Source
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AI summary
A method of video coding using coding modes including IntraBC mode (Intra-block copy mode) for a picture is disclosed. The system determines whether the current reference block is located above a current coding unit (CU) containing the current prediction unit (PU) in a vertical direction and whether the current reference block is located on a left side of the current CU in a horizontal direction based on the original block vector (BV). If both results are not true, the original BV is clipped to a clipped BV so that a relocated reference block corresponding to the clipped BV is above the current CU in the vertical direction or to the left side of the current CU in the horizontal direction. The clipped BV is used as a predictor for encoding or decoding of a current BV or used for IntraBC encoding or decoding of the current PU.