HDR Signal Reshaping for Backward-Compatible Color Decoding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing video delivery systems struggle with backward compatibility when handling high-dynamic range (HDR) images, as legacy decoders are often unable to properly decode and convert color spaces optimized for HDR, leading to suboptimal picture quality.
Innovation Solution
The implementation of a color-rotation and scaling matrix, combined with tone-mapping, to reshape HDR images from a preferred color space like IPT-PQ to a legacy color space like YCbCr, ensuring that even legacy decoders can produce reasonable picture quality by applying metadata-driven reshaping techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If HDR images are encoded in preferred color spaces (e.g., IPT-PQ) with high dynamic range, then picture quality and color accuracy are improved, but backward compatibility with legacy devices is worsened
Solution Approach 1:
The patent introduces a color-rotation-and-scaling matrix as an intermediary transformation tool. This matrix acts as a mediator between the preferred color space (IPT-PQ) and legacy color spaces (YCbCr, RGB), enabling HDR content to be decoded by legacy devices while maintaining acceptable picture quality. The matrix rotates and scales chroma components to align with legacy device expectations
Solution Approach 2:
The patent applies parameter changes by adjusting color space parameters through the color-rotation-and-scaling matrix. Specifically, it transforms chroma component parameters (Cb, Cr) by rotating them by a calculated angle and scaling them by a factor, thereby adapting the HDR signal to match legacy device color space characteristics while preserving HDR content integrity
2Adaptability or versatility
If color-rotation and scaling matrices are applied to align hue values, then compatibility with legacy color spaces is improved, but computational complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating the optimal rotation angle and scaling factor for the color-rotation-and-scaling matrix during encoding. These parameters are determined in advance based on the relationship between preferred and legacy color spaces, so that during decoding only simple matrix multiplication is required, significantly reducing real-time computational complexity
Solution Approach 2:
The patent uses a simplified copying approach by representing the complex color space transformation as a fixed matrix structure with pre-determined parameters. Instead of performing complex real-time color space conversion, the system copies the pre-computed matrix parameters and applies them directly, reducing computational burden while maintaining color space alignment accuracy
Data Source
AI summary
In a method to improve backwards compatibility when decoding high-dynamic range images coded in a wide color gamut (WCG) space which may not be compatible with legacy color spaces, hue and/or saturation values of images in an image database are computed for both a legacy color space (say, YCbCr-gamma) and a preferred WCG color space (say, IPT-PQ). Based on a cost function, a reshaped color space is computed so that the distance between the hue values in the legacy color space and rotated hue values in the preferred color space is minimized. HDR images are coded in the reshaped color space. Legacy devices can still decode standard dynamic range images assuming they are coded in the legacy color space, while updated devices can use color reshaping information to decode HDR images in the preferred color space at full dynamic range.