Luma Mapping With Chroma Scaling in Low-Delay GDR Decoding

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Solution Overview

Problem

Intra coded pictures in video coding standards like AVC, HEVC, and VVC lead to increased encoder to decoder delay, which is undesirable for low delay applications, and techniques like Gradual Decoding Refresh (GDR) face compatibility issues with luma mapping with chroma scaling (LMCS) during decoding.

Innovation Solution

Prevent luma mapping with chroma scaling decoding processes for GDR pictures by applying specific conditions, such as checking for virtual boundaries and dirty areas, to ensure accurate decoding without using LMCS processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If GDR is applied to reduce encoder to decoder delay, then delay is reduced, but compatibility with LMCS is lost

Engineering Contradiction:

Improveencoder to decoder delayVSAvoidcompatibility with LMCS

Core Design Contradiction:

Loss of timeVSAdaptability or versatility

Solution Approach 1:

The patent applies different decoding strategies to different regions of the picture based on the GDR type. For GDR type 1 pictures, LMCS is completely disabled. For GDR type 2 pictures, LMCS is applied only to non-refresh blocks while refresh blocks use alternative decoding. This local differentiation resolves the contradiction by preserving LMCS compatibility in regions where it can coexist with GDR while disabling it only where necessary.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent segments the picture into refresh blocks and non-refresh blocks, and further segments the GDR approach into two types. This segmentation allows selective application of LMCS to specific regions, enabling the system to achieve low delay through GDR while maintaining LMCS compatibility in appropriate areas, thus resolving the binary contradiction.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If intra coded pictures are used at random access point, then random access is enabled, but encoder to decoder delay increases

Engineering Contradiction:

Improverandom access capabilityVSAvoidencoder to decoder delay

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The patent implements periodic intra-refreshing through GDR, where refresh blocks are systematically introduced at regular intervals rather than requiring a complete intra picture. This periodic refresh approach enables random access capability while distributing the bit cost over multiple pictures, thereby reducing the delay compared to using full intra coded pictures at random access points.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS12413755B2Luma mapping with chroma scaling for gradual decoding refresh

Publication Date: 2025.09.09 NOKIA TECHNOLOGIES OY

AI summary

A method, apparatus, and computer program product provide for management of luma mapping with chroma scaling (LMCS) processes for Gradual Decoding Refresh (GDR) pictures. In the context of a method, the method accesses a picture to be decoded and determines whether the picture is a GDR picture. The method can also prevent a LMCS decoding process from being applied to the GDR picture. Another method can determine whether a virtual boundary is within a current coding tree unit of the gradual decoding refresh picture and if so, prevent a chroma residual scaling decoding process associated with LMCS from being applied to one or more coding units within a clean area. Another method can pad a neighboring pixel area from one or more reconstructed pixels in a clean area for a chroma residual scaling decoding process associated with LMCS.