Lossless Video Coding via CTU-Level Flag Control
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Solution Overview
Problem
Current video coding standards, such as VVC/H.266, face challenges in efficiently managing mixed coding scenarios where both lossless and lossy coding are applied within the same image, leading to compromised coding efficiency due to the current design limitations.
Innovation Solution
The implementation of flags at various levels, such as CTU, slice, picture, and sequence levels, to signal whether lossless coding is applied, allowing for the disabling of specific coding tools like deblocking filters, SAO, ALF, and LMCS, and the selection of residual coding methods, enabling flexible and efficient coding strategies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lossless coding is applied to all CTUs, then quality is improved, but compression efficiency deteriorates
Solution Approach 1:
The patent applies different coding modes (lossless or lossy) to different CTUs within the same picture based on local content characteristics. The ctu_lossless_flag enables selective application of lossless coding only to specific CTUs that require high quality, while other CTUs use more efficient lossy coding, thus achieving local optimization of both quality and compression efficiency.
2Manufacturing precision
If multiple coding tools are enabled for lossless coding, then quality is improved, but device complexity increases
Solution Approach 1:
The patent sets default values for various coding tool flags (deblocking filter, SAO, ALF, LMCS) based on the ctu_lossless_flag value before actual coding processing. When lossless coding is selected, these tools are automatically enabled with appropriate default settings, eliminating the need for separate complex control logic and reducing device complexity while maintaining quality.
3Manufacturing precision
If lossless coding is applied to entire picture, then quality is improved, but bitstream size increases
Solution Approach 1:
The patent divides the picture into multiple CTUs and applies lossless coding selectively to individual CTUs or regions based on content requirements. The ctu_lossless_flag at CTU level enables fine-grained segmentation, allowing lossless coding to be applied only where necessary, thus maintaining quality in critical areas while reducing overall bitstream size compared to applying lossless coding to the entire picture.
Data Source
AI summary
The present disclosure provides apparatuses and methods for performing lossless coding of a code tree unit (CTU). According to certain disclosed embodiments, the methods include: receiving a bitstream comprising a plurality of coding tree unit (CTUs) in a picture, and determining whether lossless coding is applied to the plurality of CTUs, based on a plurality of flags, respectively. The plurality of flags comprise a first flag associated with a first CTU. The method further includes: in response to a determination that lossless coding is applied to the first CTU, performing lossless coding to the first CTU.