HLG Normalized transform released

[Updated] The HLG Normalized transform has been released for DaVinci Resolve Studio 16 and above and can be purchased from the store. It can be used directly in ACES as an Input Transform (IDT) or used in conjunction with the DCTL OpenFX plugin with additional parameters. I have personally been using this for several months in my works recorded using Hybrid Log Gamma.

[Updated for v2.0] In its base form, the transform is normalized to 38% IRE as per the current ITU-R BT.2408 recommendations. Without normalization, the transform follows the BT.2100 specification for Middle Gray at 21% IRE. As of version 2.0, the transform now supports multiple Hybrid Log Gamma implementations, including:

  • HLG BT.2408 (Mid-Gray at 38% IRE)
  • HLG BT.2100 (Mid-Gray at 21% IRE)
  • Sony HLG1 (Mid-Gray at 19% IRE)
  • Sony HLG2 (Mid-Gray at 20% IRE)
  • Sony HLG3 (Mid-Gray at 21% IRE)

The transform also clamps all negative values, as some cameras such as the Panasonic Lumix series seem to encode values below zero. The default output is to ACES AP0 Color Space (including a chromatic adaptation) with a Linear gamma. This allows the transform to be used directly within an ACES workflow inside DaVinci Resolve, whether using ACES 1.0.x/1.1 or in Resolve Color Managed mode. The transform can also be used within Resolve’s Node structure to expose more options. When opened through the DCTL OpenFX plugin, the transform allows for additional parameter manipulations, such as:

  • Exposure Adjustment in exposure values from -8 to +8 stops
  • Color Space Transform to: ACES AP0/AP1, Rec.709, Rec.2020 or DaVinci Wide Gamut (default ACES AP0)
  • Gamma Transform to: Linear, Scene, ACEScc, ACEScct, Gamma 2.2, Gamma 2.4 and DaVinci Intermediate (default Linear)
  • Clamping values outside 0 – 1 range: None, Negatives, All (default Negatives)
Screenshot of HLG Normalized Transform v2.0 in Resolve

The HLG Normalized output is shown in the sample image below. On the left is a standard Rec.709 interpretation of the image when imported in a standard timeline. On the right is the Resolve HLG ACES 1000 NIT implementation, which is actually an Output Transform (ODT) and is considerably over exposed. In the center is the HLG Normalized Input Transform (IDT), which is at the correct exposure levels.

Left: Rec.709 Interpretation; Center: HLG Normalized Transform; Right: Resolve ACES HLG 1000nit IDT

The HLG curve characteristics are shown in the graph below and provide just under 4.5 stops of latitude above Middle Gray for BT.2408, assuming 18% middle-gray reflectance at 38% IRE. The HLG BT.2100 specification, as native to the camera is also shown for reference.

HLG Normalized characteristic curves

The following table provides additional reference points when over/under exposing using Hybrid Log Gamma with reference to Middle Gray at 38% IRE:

+3 .082.2%

Purchase now from the store: