Sony FS5 Gets HDR via BT.2100 / BT.2020 Firmware Update & What is Hybrid Log Gamma (HLG)? FAQ
The Sony FS5 and PXW-Z150 will receive a firmware upgrade this summer adding HDR support to the cameras. Following BT.2020 & BT.2100 specifications, it adds support for Hybrid Log Gamma (HLG) and Rec. 2020 color space. Let’s delve into what that means.
Rec. 2020 can display colors not shown in the old and dated Rec.709. In comparison to coverage of CIE 1931, DCI-P3 covers 53.6%, and Rec. 2020 75.8%. See the difference in coverage:
As far as HDR standards defined in BT.2100, they include Perceptual Quantization (PQ) and Hybrid Log Gamma (HLG).
PQ was developed by Dolby for it’s own Dolby Vision standard of mastering and delivery. It is a new way of working with video signals because it is an absolute display-referred signal. This makes PQ and HLG different at the core. The problem concerning Perceptual Quantization and broadcast television is that it is not backwards compatible with older SDR standards which is where HLG comes into the picture.
HLG is a delivery format developed by BBC and NHK. The development was important for broadcast because the delivery requires that new TVs with HDR can benefit from the tech, but also that older TV’s would not be affected adversely and still display an accurate SDR image. The lower part of the curve is a traditional gamma curve and the upper part of the curve is based on a logarithmic curve.
HLG is scene referred with the signal representing relative light levels from the scene. Since it is scene referred, metadata is not required and is compatible with existing SDR infrastructure. It combines two different gamma curves to create a third.
The new Sony firmware is currently scheduled to drop in July 2017. For a FAQ on HLG, see this document via the BBC.