Quantized PCM Video Coding for Visual Coherence
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Solution Overview
Problem
Current video coding standards, such as HEVC, lack a flexible mechanism to control the maximum amount of data for coding units, leading to potential data overflow and undesirable visual artifacts due to the presence of both lossy and lossless parts in a video frame, especially with larger bit-depths and varying content.
Innovation Solution
The introduction of a quantized Pulse Code Modulation (PCM) mode, where video samples are quantized before PCM coding, allowing for flexible control of output bit-depth and introducing controlled loss to align with lossy compression, thereby reducing visual discrepancies between lossy and lossless areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If quantized PCM mode is introduced with flexible quantization step control, then data overflow is prevented and visual coherence is improved, but device complexity increases due to additional quantization processing
Solution Approach 1:
The patent applies parameter changes by introducing a quantization step parameter that can be flexibly controlled. The quantization step is derived from the quantization parameter (QP) and can be adjusted to achieve desired distortion levels. This parameter change enables consistent distortion across lossy and lossless regions, preventing visual shock while maintaining compression efficiency.
Solution Approach 2:
The patent segments the video coding process into distinct modes: lossy compression mode and lossless PCM mode. By segmenting the coding process and allowing selective application of quantization, the system can prevent data overflow in specific regions while maintaining visual coherence across the entire frame.
2Quantity of substance
If lossless PCM coding is applied to all regions, then data overflow is prevented, but visual artifacts occur due to inconsistency with lossy compressed regions
Solution Approach 1:
The patent applies local quality by allowing different coding modes in different regions of the video frame. Lossless PCM coding can be applied to specific regions where data overflow prevention is critical, while lossy compression is applied to other regions. The quantization step is locally adjusted to ensure consistent distortion levels, preventing visual artifacts at the boundaries between regions.
3Reliability
If quantization step is increased to reduce distortion, then visual coherence improves, but compression efficiency decreases due to higher bit-depth requirements
Solution Approach 1:
The patent uses parameter changes by dynamically adjusting the quantization step based on the quantization parameter (QP). The quantization step is derived from QP and can be modified to achieve desired distortion levels. This allows the system to balance visual coherence with compression efficiency by optimizing the quantization parameter according to the specific coding requirements.
Data Source
AI summary
A quantized PCM mode includes the step of quantizing samples so that distortion is added to coded video. In this way, video blocks coded with quantized PCM appear more uniformly with adjacent video blocks that have been coded with other lossy compression techniques, such as inter-prediction coding or intra-prediction coding. A video encoder may first quantize input video samples with a quantization step prior to PCM coding the quantized samples. This quantization step may be signaled to a decoder in the encoded video bitstream. A video decoder may receive the encoded video bitstream that includes quantized PCM coded video samples. These samples are first decoded using pulse code demodulation and then are inverse quantized with the same quantization step used to encode the video. The video decoder may extract this quantization step from the output bit-depth in the encoded video bitstream.