Adaptive Loop Filter Pixel Padding at Slice Boundaries
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Solution Overview
Problem
In video encoding and decoding processes, adaptive loop filter (ALF) filtering at slice boundaries faces challenges when adjacent pixels are outside the slice boundary, as pixel padding is not performed consistently, leading to inefficiencies in encoding and filtering effects.
Innovation Solution
A method and apparatus determine whether a slice including an adjacent pixel is different from the current pixel, and if so, determine the adjacent pixel's value as a closest pixel in the horizontal direction, calculate an adaptive loop filter with filter coefficients based on pixel values, and apply the filter to correct the current pixel's value, ensuring proper padding and filtering even when pixels are outside the slice boundary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If adaptive loop filter is applied at slice boundary without consistent pixel padding, then encoding speed is maintained, but filtering quality deteriorates due to incorrect pixel values
Solution Approach 1:
The patent applies different handling methods for different regions: pixels inside slice boundaries use normal filtering, while pixels outside boundaries (upper-left and lower-right) use padding with replicate or zero values. This local differentiation ensures filtering quality at boundaries without compromising overall encoding efficiency.
Solution Approach 2:
The patent performs preliminary determination of slice boundary locations and identifies which adjacent pixels fall outside boundaries before applying the adaptive loop filter. This advance preparation ensures that padding is applied correctly during filtering, improving quality without adding significant encoding overhead.
2Stability of the object's composition
If pixel padding is applied to all adjacent pixels including those inside slice boundary, then filtering consistency is improved, but encoding complexity increases
Solution Approach 1:
The patent applies padding selectively only to adjacent pixels located outside slice boundaries (upper-left and lower-right pixels when current pixel is at boundary), while leaving pixels inside boundaries unchanged. This localized approach maintains filtering consistency where needed without unnecessarily increasing encoding complexity.
Solution Approach 2:
The patent applies padding as a partial action - only to the extent necessary (boundary pixels only) rather than to all pixels. This avoids excessive processing while still achieving the goal of consistent filtering at critical boundary locations.
3Ease of manufacture
If adjacent pixels outside slice boundary are used without padding, then encoding simplicity is maintained, but filtering accuracy deteriorates
Solution Approach 1:
The patent converts the potentially harmful effect of missing boundary pixels into a benefit by using padding to provide reasonable placeholder values (replicate or zero) for pixels outside slice boundaries. This allows the simple adaptive loop filter structure to work accurately even at boundaries where pixels would otherwise be unavailable.
Data Source
AI summary
In a video encoding and decoding process, provided are a method and apparatus for determining whether a slice including an adjacent pixel located at the upper-left or lower-right side of a current pixel from among adjacent pixels used for an adaptive loop filter of the current pixel is different from a slice including the current pixel, when the slice including the adjacent pixel at the upper-left or lower-right location is different from the slice including the current pixel, determining a value of the adjacent pixel located at the upper-left or lower-right side as a value of a closest pixel in a horizontal direction of the adjacent pixel located at the upper-left or lower-right side from among pixels included in the slice including the current pixel, determining an adaptive loop filter including a filter coefficient for the current pixel and the adjacent pixels based on values of the current pixel and the adjacent pixels, correcting the value of the current pixel by using the values of the adjacent pixels, by applying the adaptive loop filter to the current pixel, and encoding/decoding a current block including the current pixel.