Downsampling Filter Group Delay for 4:2:2 to 4:2:0 Video Conversion
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Solution Overview
Problem
Existing video signal processing technologies face challenges in converting between 4:2:2 and 4:2:0 formats, particularly in broadcast equipment, leading to blurring and chroma component positional displacements during repeated encoding and decoding processes, especially in interlaced scanning.
Innovation Solution
A signal processing apparatus and method that utilize specific downsampling and upsampling filters with tailored group delay characteristics to convert between 4:2:2 and 4:2:0 formats, ensuring perfect reconstruction filter bank conditions and minimizing pixel displacement, by employing filters with coefficients designed to satisfy specific conditions such as modulo-1 remainder group delays and coefficient sum requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional downsampling and upsampling filters are used for format conversion between 4:2:2 and 4:2:0, then the conversion process is simple and fast, but chroma pixel positional displacements and blurring occur during repeated encoding and decoding
Solution Approach 1:
The patent changes the group delay parameter of the downsampling filter to satisfy specific conditions (modulo-1 remainder equals 0.25, and sum with upsampling filter group delay equals integer). These parameter modifications ensure perfect reconstruction and prevent chroma pixel displacement while maintaining filterbank conditions.
Solution Approach 2:
The patent designs the downsampling and upsampling filters in advance to satisfy perfect reconstruction filterbank conditions and specific group delay requirements. This preliminary design ensures that repeated encoding and decoding operations maintain video quality without chroma degradation.
2Manufacturing precision
If perfect reconstruction filter bank conditions are satisfied with specific group delay characteristics, then chroma pixel positional displacements are prevented, but the filter design and implementation become more complex
Solution Approach 1:
The patent specifies precise group delay parameters for the downsampling filter (modulo-1 remainder of 0.25 at frequency ω=0) and establishes the relationship between downsampling and upsampling filter group delays (sum equals integer). These parameter specifications ensure accurate chroma pixel positioning while providing clear design guidelines.
Solution Approach 2:
The patent establishes feedback conditions where the upsampling filter is designed to complement the downsampling filter, ensuring that their combined group delay satisfies the integer condition. This feedback mechanism guarantees perfect reconstruction and prevents chroma pixel displacement.
3Productivity
If conventional filters are used in cascade connections for repeated encoding and decoding, then processing efficiency is maintained, but chroma degradation accumulates over multiple operations
Solution Approach 1:
The patent designs the filterbank system in advance to satisfy perfect reconstruction conditions, ensuring that each encoding/decoding cycle maintains chroma quality. This preliminary design prevents chroma degradation from accumulating during cascade connections and repeated operations.
Solution Approach 2:
The patent ensures continuous maintenance of perfect reconstruction filterbank conditions and group delay relationships throughout cascade connections. This continuity guarantees that chroma quality is preserved across multiple encoding and decoding operations without degradation.
Data Source
AI summary
A signal processing apparatus converts interlaced 4:2:2-format video signals including a luminance component and two chroma components into interlaced 4:2:0 format video signals. A downsampling low-pass filter has such a group delay that a modulo-1 remainder of the group delay at frequency ω=0 is substantially equal to 0.25. The downsampling low-pass filter is designed together with an associated upsampling low-pass filter such that the first downsampling low-pass filter and the upsampling low-pass filter substantially satisfy perfect reconstruction filter bank condition, and such that a sum of the group delay of the first downsampling low-pass filter and a group delay of a normalized filter obtained by making the sum of all the coefficients of the upsampling low-pass filter equal to 1 is substantially equal to an integer number at frequency ω=0.