Intra Block Copy Reference Constraints for Split Memory Access
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In hardware implementations of intra block copy prediction for video codecs like H.265 and AV1, memory access operations for reference blocks are inefficient due to the need to switch between on-chip and off-chip memory, which affects bit rate and quality.
Innovation Solution
Constrain the location of reference blocks for intra BC prediction to be entirely within an inner or outer search area of the current picture, avoiding overlap between the two areas, with on-chip memory storing the inner search area and off-chip memory storing the outer search area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the reference block is allowed to be anywhere in previously reconstructed content including right next to the current block, then prediction effectiveness is improved, but memory access operations become slow and inefficient due to split access between on-chip and off-chip memory
Solution Approach 1:
The search area is divided into two segments: an inner search area and an outer search area. The inner search area is further divided into a first inner search area and a second inner search area. This segmentation allows the system to distinguish between regions that can be accessed efficiently and those that require slower memory access, enabling optimized reference block selection.
Solution Approach 2:
Different parts of the search area are assigned different access characteristics. The first inner search area is configured for fast on-chip memory access, while the second inner search area and outer search area use slower off-chip memory access. This local differentiation of access quality allows the system to optimize for both speed and prediction effectiveness.
2Speed
If stricter constraints on reference block locations are applied (as in AV1 format), then memory access efficiency is improved, but prediction effectiveness decreases
Solution Approach 1:
The system dynamically adapts the reference block search constraints based on the specific requirements of each picture or coding unit. Rather than applying fixed strict constraints, the system flexibly configures the inner and outer search areas to balance memory access efficiency with prediction effectiveness for different content types.
Solution Approach 2:
The system changes the search area configuration parameters adaptively. By adjusting the size and location of the inner and outer search areas, the system can optimize the balance between memory access efficiency and prediction effectiveness for different video content characteristics.
3Loss of energy
If the reference block is constrained to be entirely within inner or outer search area but not overlapping both, then split memory access is avoided, but the flexibility in reference block selection is reduced
Solution Approach 1:
The search area is segmented into non-overlapping inner and outer regions, which prevents split memory access patterns. This segmentation maintains memory access efficiency while providing sufficient flexibility through the adaptive configuration of the segmented regions.
Solution Approach 2:
The system applies partial constraints by allowing reference blocks in both inner and outer search areas, but with the restriction that a single reference block cannot span both regions. This partial constraint approach maintains enough flexibility for effective prediction while eliminating the harmful split memory access pattern.
Data Source
AI summary
When encoding/decoding a current block of a current picture using intra block copy (“BC”) prediction, the location of a reference block is constrained so that it can be entirely within an inner search area of the current picture or entirely within an outer search area of the current picture, but cannot overlap both the inner search area and the outer search area. In some hardware-based implementations, on-chip memory buffers sample values of the inner search area, and off-chip memory buffers sample values of the outer search area. By enforcing this constraint on the location of the reference block, an encoder/decoder can avoid memory access operations that are split between on-chip memory and off-chip memory when retrieving the sample values of the reference block. At the same time, a reference block close to the current block may be used for intra BC prediction, helping compression efficiency.