HDR Production - Tone Mapping Techniques and Roundtrip Conversion Performance for Mastering With SDR and HDR Sources

The limited contrast and colors in standard dynamic range (SDR) have historically compelled content producers to make hard choices, whereas high dynamic range (HDR) offers them the possibility to show more - meaning telling stories with greater freedom and flexibility. Even so, HDR content presents a challenge of its own. The wide variation in capabilities among HDR displays conflicts with the desire to have any HDR or SDR production play optimally on any display, regardless of whether it is HDR or SDR. Tone mapping is the generic term for the operation that addresses this issue, whether tone compression, which maps from HDR to a lower-luminance HDR or SDR, or tone expansion, which maps from SDR or HDR to a higher-luminance HDR. Though the trend is to produce the highest quality content in HDR, legacy content is ever present, and lots of new content is still produced in SDR. Mixing feeds in production requires tone expansion for SDR content to match the HDR. Distribution paths can then require tone compression back to SDR without degradation. In this context, a perfect SDR-HDR-SDR roundtrip conversion is required to preserve artistic intent for all content. Furthermore, in a live context, such tools need to be automatic and low latency. This article discusses various tone-mapping techniques, including static solutions such as lookup tables (LUTs) and dynamic solutions based on metadata. The relative advantages are considered, and the performance of each is analyzed. Particular attention is paid to the roundtrip performance, which is important to content producers mastering both SDR and HDR sources, yet wanting to exploit the full range of storytelling capabilities an HDR stream can offer. Test results using a proposed solution that has been introduced in practice, 'Advanced HDR by Technicolor,' are described. © 2002 Society of Motion Picture and Television Engineers, Inc.