Variable Length Coding With One-Way Probability Table Switching
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Solution Overview
Problem
Existing variable length coding methods for picture data, such as H.263, face inefficiencies due to the inability to adaptively switch probability tables effectively when coefficient values decrease after initially increasing, leading to reduced coding efficiency.
Innovation Solution
A method that scans coefficient values from higher-frequency to lower-frequency components and switches probability tables in one direction when an absolute value exceeds a threshold, maintaining the same table for subsequent values even if they decrease, allowing for more adaptive updates and biased probability distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If probability tables are switched based on the absolute value of the previous coefficient value in both directions, then the coding method can adapt to varying coefficient magnitudes, but the probability tables cannot maintain high bias when coefficients decrease after increasing, leading to reduced coding efficiency
Solution Approach 1:
Instead of switching probability tables bidirectionally based on coefficient magnitude changes, the invention inverts the approach by allowing switching only in one direction (when coefficient magnitude increases). This prevents the probability tables from losing their bias when coefficients decrease, thereby maintaining coding efficiency while still providing adaptability when needed.
Solution Approach 2:
The probability table switching mechanism is made dynamic and asymmetric: tables are switched when coefficient magnitudes increase to adapt to changing conditions, but once switched, the system maintains the new table even if coefficients decrease. This dynamic behavior optimizes the balance between adaptability and maintaining coding efficiency.
2Adaptability or versatility
If probability tables are updated to reflect the frequency of input binary data, then the tables adapt to the data distribution, but the tables cannot maintain high bias when coefficient values fluctuate, reducing compression performance
Solution Approach 1:
The invention inverts the conventional bidirectional switching logic by implementing unidirectional switching based on coefficient magnitude thresholds. This ensures that probability tables maintain their bias characteristics and do not lose compression performance, while still adapting to data distribution changes when coefficient magnitudes increase.
Solution Approach 2:
The invention changes the parameter controlling probability table selection from bidirectional coefficient magnitude comparison to unidirectional threshold-based switching. This parameter change ensures that tables maintain high bias for better compression while still adapting to data distribution when coefficients exceed the threshold.
Data Source
AI summary
A variable length coding method is comprised of: a coefficient value scanning step in which an RL sequence generation unit 203, a reordering unit 202, and a binarization unit 203 scan coefficient values within a block in a predetermined scanning order starting at a higher-frequency component toward a lower-frequency component; and an arithmetic coding step in which an arithmetic coding unit 205 and a table storage unit 204 perform arithmetic coding on the absolute values of the coefficient values according to the scanning order used in the coefficient value scanning step, by switching between probability tables 1˜4 for use, wherein, in the arithmetic coding step, a probability table to be used is switched to another probability table in one direction, when the arithmetic-coded absolute values of the coefficient values include an absolute value exceeding a predetermined threshold value.