Intra Prediction Mode Control for Flat-Region Image Encoding
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Solution Overview
Problem
Conventional encoding methods, such as H.265, cause image quality deterioration in flat regions due to the propagation of encoding errors in intra predictive encoding, particularly in boundary blocks between complex and flat regions.
Innovation Solution
An encoding apparatus and method that determines the flatness of pixel values in blocks and controls the selection of intra prediction modes to increase the likelihood that they differ from reference blocks, thereby reducing error propagation in flat regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If DC prediction is used for flat blocks to simplify encoding, then encoding complexity is reduced, but encoding error propagates continuously in the rightward direction causing image quality deterioration
Solution Approach 1:
The patent applies periodic action by alternately selecting different intra prediction modes (DC prediction and horizontal/vertical prediction) for adjacent flat blocks based on their position. Specifically, when a flat block is detected, the patent determines its horizontal position and selects DC prediction for even-positioned blocks and horizontal/vertical prediction for odd-positioned blocks, creating a periodic pattern that prevents continuous error propagation while maintaining encoding efficiency
Solution Approach 2:
The patent changes the prediction mode parameter dynamically based on block position. By modifying which prediction mode is applied to each block (DC vs. horizontal/vertical) according to the block's horizontal coordinate, the system optimizes the balance between encoding complexity and image quality without requiring complex per-block analysis
2Ease of operation
If the same intra prediction mode is applied to all flat blocks, then encoding process is simplified, but encoding error propagates continuously causing visible deterioration
Solution Approach 1:
The patent implements periodic action by establishing a regular alternation pattern between different prediction modes for adjacent flat blocks. The selection depends on the horizontal position of each block, creating a simple periodic sequence that is easy to implement while effectively breaking continuous error propagation paths
Solution Approach 2:
The patent applies local quality by selecting different prediction modes for different local positions within the image. Instead of using a uniform prediction mode across all flat blocks, the system adapts the prediction mode based on the specific horizontal position of each block, optimizing image quality locally while maintaining overall process simplicity
Data Source
AI summary
There is provided an encoding apparatus. A determination unit determines whether a degree of flatness of pixel values in a first block among a plurality of blocks that compose an image exceeds a predetermined criterion. A selection unit executes processing for selection of an intra prediction mode for the first block. In a case where it has been determined that the degree of flatness in the first block exceeds the predetermined criterion, a control unit controls the processing for selection so as to increase a possibility that the intra prediction mode for the first block is different from each of one or more intra prediction modes for respective one or more reference blocks. An encoding unit applies intra predictive encoding to the first block in accordance with the intra prediction mode selected through the processing for selection.