Adaptive Quantization Level Clipping for HEVC Overflow Control
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Solution Overview
Problem
High-Efficiency Video Coding (HEVC) faces overflow issues during the de-quantization process due to the dynamic range of reconstructed transform coefficients exceeding the 32-bit data representation, leading to potential system failures when a quantization matrix is introduced.
Innovation Solution
The method involves adaptive clipping of the quantization level after quantization, determining clipping conditions based on the quantization matrix, quantization parameter, video source bit-depth, and transform size to restrict the dynamic range and prevent overflow, using pseudo codes to illustrate the clipping process, which can be implemented in both encoder and decoder sides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If quantization level clipping is not performed, then the dynamic range of transform coefficients can be preserved, but overflow occurs during de-quantization causing system failures
Solution Approach 1:
The patent applies preliminary action by performing quantization level clipping before the de-quantization process. The clipping operation constrains quantization levels to safe ranges based on transform unit size and bit-depth parameters, preventing overflow conditions from occurring during subsequent de-quantization operations. This proactive constraint ensures system reliability while maintaining acceptable reconstruction quality.
2Ease of manufacture
If a fixed clipping range is used for all transform units, then implementation is simplified, but adaptability to different transform sizes and bit-depths is reduced
Solution Approach 1:
The patent implements dynamic clipping ranges that adapt to different transform unit sizes (4x4, 8x8, 16x16, 32x32) and bit-depth configurations. The clipping thresholds are calculated based on the specific transform parameters, allowing the system to optimize for each case rather than using a fixed conservative range. This dynamic approach maintains adaptability while providing clear calculation rules for implementation.
3Reliability
If quantization levels are heavily clipped to prevent overflow, then system reliability is improved, but reconstruction accuracy deteriorates
Solution Approach 1:
The patent carefully adjusts clipping parameters based on transform unit size and bit-depth to find the optimal balance between overflow prevention and reconstruction accuracy. Larger transform units have different clipping thresholds than smaller ones, and the clipping ranges are tuned to preserve as much dynamic range as possible while still preventing 32-bit overflow during de-quantization. This parameter optimization minimizes quality loss.
Data Source
AI summary
A method and apparatus for clipping a transform coefficient are disclosed. Embodiments according to the present invention avoid overflow of the quantized transform coefficient by clipping the quantization level adaptively after quantization. In one embodiment, the method comprises generating the quantization level for the transform coefficient of a transform unit by quantizing the transform coefficient according to a quantization matrix and quantization parameter. The clipping condition is determined and the quantization level is clipped according to the clipping condition to generate a clipping-processed quantization level. The clipping condition includes a null clipping condition. The quantization level is clipped to fixed- range represented in n bits for the null clipping condition, where n correspond to 8, 16, or 32. The quantization level may also be clipped within a range from -m to m-1 for the null clipping condition, where m may correspond to 128, 32768, or 2147483648.