HLG Normalized

What is Hybrid Log Gamma?

Hybrid Log Gamma (HLG) is a standard jointly introduced by the BBC and NHK for recording and displaying High Dynamic Range (HDR) content using the Hybrid Log Gamma curve. There are two key references for Hybrid Log Gamma – the HLG BT.2100 standard and the HLG BT.2408 recommendation. HLG is often used in a Scene referred context when a camera records and encodes content to HLG and is used in a Display referred context when media is rendered and displayed for viewing purposes. In a Display referred scenario, it’s main point of difference from the other main HDR format, Perceptual Quantization (PQ), is that HLG brightness levels are always relative as opposed to absolute. In a scene referred context, HLG is often the least understood, yet the most versatile of any Log encoding format out there – better even than the native Log formats offered by many camera manufacturers. HLG BT.2100 has an 18% Middle Gray at 21 IRE whilst the BT.2408 recommendation suggests exposing HLG to the right at 38% IRE. The diagram below is a characteristic curve that plots the HLG BT.2100 and the BT.2408 curves against 10-bit encoded values.

What is HLG Normalized?

The HLG Normalized Plugin, Transform and LUT Pack contain mathematically accurate transforms that allow scene referred Hybrid Log Gamma content – that is content recorded from a camera – to be correctly imported and normalized in Video Editing and Visual Effects applications. The HLG Normalized Transform was initially developed due to a lack of accurate Input Transforms available for recorded HLG media – particularly for ACES workflows inside DaVinci Resolve. The development of the HLG Normalized Transform was subsequently expanded to include normalization of further HLG implementations, including Sony HLG1, HLG2 and HLG3 profiles on top of HLG BT.2100 and HLG BT.2408. The HLG Normalized Plugin was subsequently developed to support normalization of HLG recorded media across additional Video Editing and Visual Effects applications, including Assimilate Scratch, Blackmagic Fusion, Nuke and Natron. The LUT Pack was developed to support additional applications such as Adobe Premiere, Final Cut Pro as well as usage across external monitors and recorders.

What’s the difference between the Plugin and Transform?

The Transform was first developed to be used as an Input Device Transform (IDT) for an ACES workflow inside DaVinci Resolve. The feature-set was then enhanced to include Exposure Correction capabilities and multiple Color and Gamma functions outside of ACES.

The fundamental operation of the Transform and Plugin are the same, though the Transform only works with DaVinci Resolve and has been developed particularly for use as an IDT inside ACES workflows.

The Plugin offers a more streamlined user experience and has more internal smarts. It can be used across multiple non-color managed and color-managed workflows, including ACES and is supported across multiple Video Editing & VFX applications such as DaVinci Resolve Free & Studio, Blackmagic Fusion, Assimilate Scratch, Nuke, Mistika Boutique and Natron amongst others.

If working primarily with ACES Input Transforms in Resolve, the HLG Normalized transform is the preferred option. If additional parameters manipulations are required or if using other editing and VFX applications and multiple color management workflows, the HLG Normalized OFX Plugin is the better choice.

What about the LUT Pack?

A Look-up Table (LUT) offers limited accuracy and is generally a destructive transform. Once a LUT is applied on media, the highlights and shadows are often clipped and cannot be recovered. A LUT needs to perform interpolation between the defined points, which ultimately means a loss of accuracy. The transform and plugin on the other hand are mathematically accurate, with significantly higher precision and can be manipulated in many different ways, including full recoverability of all aspects such as highlights and shadows.

However, there may be instances where a LUT needs to be used, such as with an external Monitor & Recorder (Think Atomos or SmallHD) or in applications that require lower levels of precision such as Adobe Premiere and Final Cut Pro. The HLG Normalized LUT Pack is also available for these purposes. The LUTs have been developed programmatically, meaning the highest level of accuracy possible for a 33 point cube LUT. What’s more, the LUTs are offered in both Data Levels and Video Levels to cover multiple use-case scenarios across video editing applications and monitoring platforms.

Is this Snake Oil like many LUTs on YouTube?

I’m an Engineer, not a social “influencer” or YouTube “celebrity”. I don’t do snake oil. I created the HLG Normalized tools due to the lack of accurate solutions, firstly for use in my own projects and then later released them for others to benefit from my work.

Why don’t you offer it for free?

I have a number of other projects available for free on GitHub. The cost of the HLG Normalized Plugin, Transform and LUT Pack simply go towards covering off the significant amount of time and effort I have invested in developing the respective solutions.

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