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 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 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 then developed to support normalization of HLG recorded media across additional Video Editing and Visual Effects applications, including Assimilate Scratch, Blackmagic Fusion, Nuke 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 such as DaVinci Resolve Free & Studio, Blackmagic Fusion, Assimilate Scratch and Natron amongst others. The Transform on the other hand only works with DaVinci Resolve Studio and has been developed specifically for Resolve with the unique advantage of being available as an IDT inside ACES workflows. Whilst the transform can also be used in other color management workflows, the Plugin offers a more streamlined user experience, especially where an ACES IDT is not desired. In summary, if working primarily with ACES in Resolve Studio, the HLG Normalized transform is the preferred option. If working in Resolve Color Managed and non-Color Managed workflows, or if using the Free edition of DaVinci Resolve other editing and VFX applications, the HLG Normalized OFX Plugin is the natural 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 technical transform on the other hand is mathematically accurate, with significantly higher precision and can be manipulated in many different ways with full recoverability of all aspects, including highlights and shadows – that precision and accuracy are offered by the HLG Normalized Plugin and HLG Normalized Transform.
With all that said, there may be instances where a LUT needs to be used, such as on an external Monitor/Recorder or in Applications with lower levels of precision such as Adobe Premiere. The HLG Normalized LUT Pack is available for these specific purposes.
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 my own personal use and then months 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 solutions.
I jumped at this tool and was really pleased to see it “just works.” The tool is straight forward, the documentation is solid and I am getting good, consistent results. It is exactly what I needed to go out and shoot footage with confidence that I can bring it in and integrate it into my composites in Fusion and my overall ACES pipeline with confidence!Michael Knobelsdorf – Lead CG Artist