1.5 | HDR and color management

HDR

Introduction

High-dynamic-range video (HDR video) describes video having a dynamic range greater than that of standard-dynamic-range video (SDR video). HDR video involves capture, production, content/encoding and display. HDR capture and displays are capable of brighter whites and deeper blacks. To accommodate this, HDR encoding standards allow for a higher maximum luminance and use at least a 10-bit dynamic range (compared to 8-bit for non-professional and 10-bit for professional SDR video) in order to maintain precision across this extended range.

While technically "HDR" refers strictly to the ratio between the maximum and minimum luminance, the term "HDR video" is commonly understood to imply wide color gamut (WCG) as well.

The goal

The goal of HDR (high-dynamic-range) and WCG (wide color gamut) is to:

• increase image quality
• achieve more naturalistic images

Additionally, it allows for:

• linear compositing, which greatly enhances realism when combining graphics and video

HDR workflow

HDR requires:

• an HDR camera
  • to capture many more f-stops in a single exposure than a traditional video camera
• an HDR-ready transportation medium
  • to ensure optimal bandwidth and compatibility without losing extra information captured by HDR cameras
• an HDR-ready color management system
  • to ensure that the captured light information is interpreted, processed and encoded in a predictable and correct way
• an HDR display (optional)
  • to show brighter highlights without compromising shadows and details

HDR-ready color management

To ensure that HDR video is interpreted, processed and encoded in a predictable and correct way, the HDR-ready color management system needs to deliver:

• control of color gamut encoding
• control of quantization/bit depth
• control of gamma and dynamic range encoding

For each step in the HDR workflow, there are many flavors of encoding, for cameras, media and displays, that the color management system brings together.

Color management in Pixotope

Pixotope provides an HDR-ready color management system to allow for a complete HDR workflow.

Our color management system is based on two open-source color management initiatives:

• Academy Color Encoding System (ACES)
• OpenColorIO (OCIO)

ACES

ACES, or the Academy Color Encoding System, is an open color management and interchange system developed by the Academy of Motion Picture Arts and Sciences (AMPAS) and industry partners. It:

• standardizes the color science used in projects of all types
• gives the industry a standardized color management system that encompasses:
  • production
  • post-production
  • presentation
  • archiving

In an industry with dozens of different camera systems, multiple encoding options, different display devices, etc., the Academy saw a need for a system like ACES to manage color in a precise yet straightforward way, no matter the camera or display being used.

Many software developers have tackled color management in their own applications, but none of those solutions are industry-wide and open. ACES is an industry-standard color management solution that anyone can use to manage the color pipeline of any project.

OCIO

OpenColorIO (OCIO) is a complete color management solution geared towards television and motion picture production with an emphasis on visual effects and computer graphics. OCIO provides a straightforward and consistent user experience across all supporting applications while allowing for sophisticated back-end configuration options suitable for high-end production usage. OCIO is compatible with the Academy Color Encoding Specification (ACES) and is LUT-format agnostic, supporting many popular formats.

OCIO is fully user-configurable, and all color management knowledge resides in the color transforms and human-readable configuration files.

How to create custom color transforms and profiles