BC7 Texture Block Compression via Variable Precision RDO
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Solution Overview
Problem
Existing texture compression techniques, such as BC7 mode 6, often require high precision for interpolation indices and endpoint colors, which is not necessary for all blocks, leading to inefficient use of bandwidth and storage.
Innovation Solution
The proposed solution involves compressing BC7 mode 6 texture blocks using less than 4-bits of precision for interpolation indices and potentially reducing endpoint color precision, while still maintaining low error compression. This is achieved through the use of rate-distortion optimization (RDO) to select the optimal precision levels for storage, and transcoding these blocks back to native BC7 format for presentation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high precision (4-bit) interpolation indices are used in BC7 mode 6 compression, then manufacturing precision of texture data is improved, but quantity of substance (data size) increases
Solution Approach 1:
The patent changes the precision parameter of interpolation indices from the standard 4-bit to variable precision (1-3 bits) based on block characteristics. This parameter change reduces the data size per block while maintaining acceptable visual quality, directly resolving the contradiction between precision and data quantity.
Solution Approach 2:
The patent applies different precision levels to different texture blocks based on their specific characteristics and error metrics. Blocks with low compression error use fewer bits, while blocks requiring higher fidelity use more bits. This local differentiation optimizes the overall balance between precision and data size.
2Manufacturing precision
If high precision endpoint colors are used in BC7 mode 6 compression, then manufacturing precision of texture data is improved, but quantity of substance (data size) increases
Solution Approach 1:
The patent reduces endpoint color precision from the standard 8-bit to 5-bit representation in the compressed format. This parameter change decreases the data size contribution from endpoint colors while the overall visual quality is maintained through the compression and transcoding process.
3Productivity
If BC7 mode 6 compression is used for all texture blocks, then productivity of compression process is improved, but manufacturing precision of rendered texture deteriorates
Solution Approach 1:
The patent introduces rate-distortion optimization (RDO) that evaluates multiple precision configurations (different bit depths for interpolation indices and endpoint colors) and selects the optimal set for each block. This optimization process balances compression efficiency with rendered texture quality, preventing quality deterioration while maintaining high productivity.
Solution Approach 2:
The patent implements a feedback mechanism where compression error metrics are calculated and used to adjust the precision parameters. Blocks with low error allow for lower precision (higher productivity), while blocks with higher error trigger increased precision (better quality), creating a self-regulating system that maintains quality while maximizing productivity.
Data Source
AI summary
Techniques are described for storing BC7 texture blocks on-disk with lower precision index data and transcoding back to the GPU-native BC7 format when the data is loaded. The transcode back to standard BC7 is lossless.