Palette Mode Bit Depth Signaling for Lower Video Bitstream Overhead
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Solution Overview
Problem
The AV1 codec's palette mode intra prediction for high bit depth encoding results in inefficient coding performance due to bitstream overhead, as palette colors are written without entropy coding, leading to increased bit consumption for 10-bit and 12-bit signals compared to 8-bit signals, despite improved accuracy.
Innovation Solution
Introduce syntax elements palette_bit_depth and palette_bit_offset in the bitstream to indicate the bit depth precision for palette mode coding, allowing for 8-bit representation of palette colors when necessary, thereby reducing unnecessary overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If palette mode intra prediction is used for high bit depth encoding (10-bit and 12-bit signals), then prediction accuracy is improved, but bitstream overhead increases due to writing palette colors without entropy coding
Solution Approach 1:
The patent introduces two syntax elements (palette_bit_depth and palette_bit_offset) that allow dynamic adjustment of the bit depth parameter for palette color representation. By changing the parameter from fixed high bit depth to variable bit depth (8, 10, or 12 bits), the patent reduces bitstream overhead when 8-bit precision is sufficient while maintaining high bit depth accuracy when needed, thus resolving the contradiction between prediction accuracy and bit consumption
Solution Approach 2:
The patent makes the palette color bit depth dynamic rather than static. The decoder adapts the bit depth based on the palette_bit_depth and palette_bit_offset syntax elements, allowing the system to switch between 8-bit, 10-bit, and 12-bit representations as needed. This dynamic approach enables efficient bitstream encoding by using lower bit depth when appropriate while preserving the capability for high bit depth when required for accurate prediction
Data Source
AI summary
Syntax elements are written to a bitstream to designate bit depth precision for palette mode coding of video blocks. During encoding, a bit depth to use for palette mode coding a current block may be based on an input video signal including the current block or based on some change in bit depth precision. A prediction residual for the current block is encoded to a bitstream along with syntax elements indicative of the bit depth used for the palette mode coding of the current block. In particular, the syntax elements include a first element indicating the palette mode coding bit depth used and a second element indicating whether to apply a bit offset to the palette mode coding bit depth. During decoding, values of the syntax elements are read from the bitstream and used to determine a bit depth for palette mode coding the encoded block.