Wide-Angle Intra Prediction for High-Aspect-Ratio Image Blocks
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Solution Overview
Problem
Existing image and video coding technologies face inefficiencies in directional intra prediction, particularly for non-square blocks, as the limited range of prediction directions (between -45 to +45 degrees) does not optimally utilize reference samples, leading to suboptimal coding efficiency for blocks with high aspect ratios.
Innovation Solution
Introduce wide-angle prediction directions forming obtuse angles with the top-left direction, allowing for the use of reference samples beyond the traditional 45-degree range, and encode these directions directly in the bitstream, with the choice of primary and wide-angle modes determined by the block shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional directional intra prediction with limited angle range (-45 to +45 degrees) is used, then the coding process is simple, but the prediction accuracy is insufficient for non-square blocks
Solution Approach 1:
The patent dynamically adjusts the prediction direction range based on block shape characteristics. For non-square blocks, wide-angle prediction modes (obtuse angles) are introduced and selected when beneficial, while traditional narrow-angle modes remain available for other cases. This dynamic adaptation resolves the contradiction by making the system flexible rather than fixed.
Solution Approach 2:
The patent changes the angular parameter of prediction directions from the traditional -45 to +45 degree range to include wide-angle modes with obtuse angles relative to the top-left direction. This parameter expansion allows better utilization of reference samples for non-square blocks, improving prediction accuracy without permanently increasing system complexity.
2Productivity
If wide-angle prediction directions are introduced to improve prediction accuracy, then the coding efficiency improves, but the bit rate increases due to additional mode encoding
Solution Approach 1:
The patent applies wide-angle prediction modes selectively rather than universally. By introducing wide-angle directions only when they provide benefit for specific block shapes (particularly non-square blocks), the system achieves improved coding efficiency without requiring full encoding overhead for all blocks, thus balancing bit rate increase against efficiency gain.
Solution Approach 2:
The patent applies different prediction direction strategies to different blocks based on their local characteristics (shape, aspect ratio). Wide-angle modes are applied locally to non-square blocks where they provide benefit, while traditional modes are used for other blocks, optimizing the trade-off between coding efficiency and bit rate on a block-by-block basis.
3Measurement precision
If reference samples beyond traditional 45-degree range are utilized, then the prediction quality improves for non-square blocks, but the complexity of reference sample selection increases
Solution Approach 1:
The patent dynamically determines which reference samples to use based on the selected prediction mode and block shape. When wide-angle modes are selected for non-square blocks, the reference sample selection process adapts to include samples from the extended angular range. This dynamic approach resolves the contradiction by making reference sample selection flexible rather than uniformly complex for all blocks.
Data Source
Figure 1a~1b
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Figure 2b
AI summary
The invention relates to a method for decoding, comprising receiving a bitstream comprising encoded image data, forming from the bitstream in a computer memory a set of reference pixels having reference pixel values for intra-picture directional prediction, predicting a pixel value in a predicted image block by intra-picture directional prediction by using values of one or more selected reference pixels in forming a predicted a pixel value, wherein the selected reference pixels are selected from a prediction direction with respect to the predicted pixel, and the prediction direction being a wide-angle prediction direction that forms an obtuse angle with top-left direction of the predicted pixel, repeating the pixel prediction for a number of pixels to form a predicted image block, and using the predicted image block in decoding an image block from the bitstream to obtain a decoded image block. A corresponding method for decoding as well as a decoder, an encoder, computer program products for the same purpose, and a signal are provided.