Redistributing the Precision and Content in 3D-LUT-based Inverse Tone-mapping for HDR/WCG Display

TL;DR

This paper introduces a novel 3D-LUT-based inverse tone-mapping method for HDR/WCG displays that uses multiple smaller LUTs with a contribution map to improve efficiency and accuracy in converting SDR footage to HDR/WCG.

Contribution

It proposes a multi-LUT approach with non-uniform packing and a contribution map to enhance inverse tone-mapping efficiency and precision, integrating AI for content redistribution.

Findings

The method reduces error in HDR/WCG conversion compared to traditional fixed LUTs.

Subjective and objective tests confirm improved visual quality and efficiency.

Ablation studies validate the effectiveness of the multi-LUT and contribution map design.

Abstract

ITM(inverse tone-mapping) converts SDR (standard dynamic range) footage to HDR/WCG (high dynamic range /wide color gamut) for media production. It happens not only when remastering legacy SDR footage in front-end content provider, but also adapting on-theair SDR service on user-end HDR display. The latter requires more efficiency, thus the pre-calculated LUT (look-up table) has become a popular solution. Yet, conventional fixed LUT lacks adaptability, so we learn from research community and combine it with AI. Meanwhile, higher-bit-depth HDR/WCG requires larger LUT than SDR, so we consult traditional ITM for an efficiency-performance trade-off: We use 3 smaller LUTs, each has a non-uniform packing (precision) respectively denser in dark, middle and bright luma range. In this case, their results will have less error only in their own range, so we use a contribution map to combine their best parts to final result. With the guidance of this map, the elements (content) of 3 LUTs will also be redistributed during training. We conduct ablation studies to verify method's effectiveness, and subjective and objective experiments to show its practicability. Code is available at: https://github.com/AndreGuo/ITMLUT.