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. It is used in a Scene referred context when a camera records content using HLG and is used in a Display referred context when media is encoded 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 it’s 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. For a Scene referred context, shown below is a characteristic curve that plots the HLG BT.2100 (Camera Native) and the BT.2408 curves against 10-bit encoded values.

What is HLG Normalized?

The HLG Normalized Plugin and Transform contain mathematically accurate transforms that allow scene referred 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 – especially within an ACES workflow inside DaVinci Resolve. The development of the HLG Normalized Transform was subsequently expanded to include support for the various HLG implementations – HLG BT.2100, HLG BT.2408, Sony HLG1, Sony HLG2 and Sony HLG3. The HLG Normalized Plugin was then developed to support normalization of HLG recorded media across other Video Editing and Visual Effects applications such as Assimilate Scratch, Blackmagic Fusion and Natron.

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 Plugin has more smarts and can be used across multiple Video Editing & VFX applications. The Transform on the other hand has been developed specifically for DaVinci Resolve Studio and has the unique advantage of being available as an IDT inside ACES workflows without requiring use within the Node structure.

Why not use a LUT?

A Look-up Table (LUT) offers limited accuracy and is a completely destructive transform. Once a LUT is applied on media, the highlights and shadows are often clipped and cannot be recovered. A technical transform on the other hand is mathematically accurate and can be manipulated in many different ways with full recoverability of all aspects, including highlights and shadows – that is what’s offered by the HLG Normalized solutions.

Is this Snake Oil like many LUTs on YouTube?

I’m an Engineer, not a wannabe “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 my own personal use and then months later opened up 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 Transform and HLG Normalized Plugin simply go towards covering off the significant time and efforts I have put in developing the solutions.