Video Encoder Transform Basis Selection for Processing Load
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Solution Overview
Problem
Current video coding standards, such as H.265/HEVC, face challenges in efficiently encoding and decoding video blocks due to limitations in transform basis selection, particularly when block sizes exceed a certain threshold, leading to increased processing load and potential inefficiencies in transform operations.
Innovation Solution
The proposed solution involves an encoder and decoder that selectively choose transform bases among DCT-II, DCT-IV, and DST-IV for encoding and inverse transforming video blocks, excluding DCT-IV and DST-IV when block sizes exceed a threshold, thereby reducing processing load and optimizing transform operations by relying primarily on DCT-II for larger blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If DCT-IV or DST-IV transform bases are selected for encoding, then transform flexibility and potential compression efficiency are improved, but processing load and computational complexity increase
Solution Approach 1:
The patent applies parameter changes by dynamically selecting transform bases (DCT-II, DCT-IV, or DST-IV) based on block size parameters. For blocks exceeding a threshold size, the system restricts selection to DCT-II only, while smaller blocks can utilize DCT-IV or DST-IV. This parameter-based selection strategy optimizes the balance between compression efficiency and processing complexity.
Solution Approach 2:
The patent segments the transform basis selection process into two distinct categories: large blocks (above threshold) that use only DCT-II, and small blocks (at or below threshold) that can use DCT-II, DCT-IV, or DST-IV. This segmentation allows the system to apply different transform strategies to different block sizes, reducing overall processing load while maintaining compression efficiency where beneficial.
2Adaptability or versatility
If multiple transform basis candidates (DCT-II, DCT-IV, DST-IV) are available for selection, then adaptability to different block characteristics is improved, but device complexity and memory requirements increase
Solution Approach 1:
The patent uses block size as a controlling parameter to dynamically change the set of available transform bases. When block size exceeds the threshold, the system changes the parameter state to allow only DCT-II. When block size is at or below the threshold, the system expands the parameter options to include DCT-II, DCT-IV, and DST-IV. This parameter-driven approach provides adaptability without requiring all transform bases to be simultaneously available.
Solution Approach 2:
The patent implements a dynamic transform basis selection mechanism where the available transform options change based on real-time block size conditions. The system dynamically adjusts the candidate transform basis set rather than maintaining a fixed configuration, allowing adaptability to different block characteristics while managing device complexity through conditional availability.
3Loss of time
If DCT-IV and DST-IV are excluded for blocks larger than threshold size, then processing time and computational load are reduced, but transform optimization opportunities for large blocks are limited
Solution Approach 1:
The patent applies a threshold-based parameter change strategy where the maximum block size for DCT-II is set to at most half the maximum size to which DCT-II is applicable in standard HEVC. This parameter adjustment creates a clear division: large blocks use the computationally efficient DCT-II with guaranteed processing time benefits, while smaller blocks can exploit DCT-IV or DST-IV for potential compression gains.
Data Source
AI summary
An encoder that encodes a current block in a picture includes circuitry and a memory coupled to the circuitry. The circuitry, in operation: selects at least one transform basis from among candidates for a transform basis which include a basis of a type-II discrete cosine transform (DCT-II) and at least one of a basis of a type-IV discrete cosine transform (DCT-IV) or a basis of a type-IV discrete sine transform (DST-IV); and transforms prediction error values of the current block, using the at least one transform basis selected. When the size of the current block is greater than a threshold size, the circuitry selects at least one transform basis after excluding at least one of the basis of the DCT-IV or the basis of the DST-IV from the candidates. The threshold size is at most half a maximum size to which the DCT-II is applicable.