Entropy Coding of Transform Coefficients With Last-Nonzero Flag
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Solution Overview
Problem
Current entropy coding methods, such as CABAC, are inefficient for larger block sizes in video coding due to the need for two scanning passes and are not systematically implemented, leading to reduced compression efficiency.
Innovation Solution
A systematic entropy coding method that uses a flag to indicate the last non-zero coefficient in a block, allowing for encoding and decoding in a single pass, reducing binary bins and improving compression efficiency by coding coefficient values in a given scanning order.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CABAC coding is used for quantized transform coefficients, then coding efficiency is improved, but two scanning passes are required which increases device complexity and processing time
Solution Approach 1:
The patent combines the significance map coding and non-zero value coding into a single unified scanning pass. Instead of performing separate forward zigzag scan for significance map and inverse zigzag scan for non-zero values, the method integrates both operations into one systematic scanning process that processes coefficients in a single pass, thereby reducing device complexity while maintaining coding efficiency.
Solution Approach 2:
The patent segments the coding process by introducing a flag mechanism that identifies the last non-zero coefficient position. This segmentation allows the encoder to systematically process coefficients in one pass by using the flag to terminate processing early when all remaining coefficients are zero, eliminating the need for a second scanning pass and reducing overall processing complexity.
2Productivity
If CABAC coding is used for smaller block sizes, then high coding efficiency is achieved, but performance degrades for larger block sizes
Solution Approach 1:
The patent introduces dynamic adaptation by using a flag to signal the last non-zero coefficient position. This dynamic mechanism allows the coding process to adapt to different block sizes and coefficient distributions automatically. For larger blocks with sparse non-zero coefficients, the flag enables early termination of scanning, improving efficiency. For smaller blocks or dense coefficient patterns, the systematic single-pass approach maintains robust performance, thus providing versatility across different block sizes.
3Loss of information
If two scanning passes are performed for CABAC coding, then significance map and non-zero values are coded separately, but this increases loss of time and reduces productivity
Solution Approach 1:
The patent performs preliminary organization of coefficient information by systematically processing coefficients in a defined scanning order within a single pass. The flag mechanism is set in advance to mark the last non-zero coefficient position, allowing the encoder to organize significance information and value information concurrently in one pass rather than requiring separate passes, thereby reducing processing time while maintaining proper information organization.
Data Source
AI summary
Methods and apparatus are provided for improved entropy encoding and decoding. An apparatus includes a video encoder (200) for encoding at least a block in a picture by transforming a residue of the block to obtain transform coefficients, quantizing the transform coefficients to obtain quantized transform coefficients, and entropy coding the quantized transform coefficients. The quantized transform coefficients are encoded using a flag to indicate that a current one of the quantized transform coefficients being processed is a last non-zero coefficient for the block having a value greater than or equal to a specified value.