The AMIRA supports workflows for live multi-camera productions in HDR according to BT.2100.
One HDR option – recommended by the BBC for live productions – is to use the Hybrid Log Gamma (HLG) signal. This cost-efficient solution allows a multicast HDR and SDR distribution, includes SDR and HDR feeds and outputs, and can be used with HD and UHD formats. It can also be used with various framerates.
HLG is defined as backward compatible to SDR. The SDI monitors need to support Rec. 2020 primary colors. This backward compatibility is achieved by the HLG characteristic curve being similar to an SDR signal from a camera with maximal knee settings. HDR monitors then rectify the highlight compression of the knee function. On SDR (supporting Rec. 2020 primary colors), the signals are shown with compressed highlights.
For the described workflow, we recommend that matching or painting should be done with a converted SDR Rec. 709 signal on an SDR reference monitor. This makes the HDR output show more dark and bright details with typical images, while the most relevant image parts are in the mid tones.
The system is made up of AMIRA (or ALEXA Mini) cameras, with look “ARRI 2100 HLG 1K 200” selected. The Output Color Space for SDI is “Rec. 2020 HLG”. Sony Remote Control Panel RCP 1500 (or compatible) can be used for camera matching and paintings (see the AMIRA Multicam White Paper for more details)
External Sources include: a character generator for captions and graphics and video feeds. Please note that SDR content needs to be converted from SDR to HLG, using a converter like the AJA FS-HDR.
There are no specific requirements for the switcher in this workflow, and no specific settings are needed on the switcher compared to SDR Rec. 709. The switcher PGM output is an HDR HLG signal, and for a SDR Rec. 709 signal the output needs to be converted to SDR by a converter like the AJA FS-HDR. The Multiviewer signal is provided in HLG.
The setup requires professional HDR Studio monitors, for example Sony X 300, Eizo CG 3145, TV Logic LUM-310R or comparable models; an SDR Studio monitor supporting Rec. 2020 (HLG SDR signal requires a Rec. 2020 capable monitor); and a lower cost HDR (or SDR) monitor for Multi-viewer monitoring.
The HDR workflow is very similar to established SDR workflows for live productions, and, as stated above, it is recommended by the BBC (see Report ITU-R BT.2408-0, Operational practices in HDR television production, ITU Geneva, 10/2017).
The same video signal is used for production and distribution, and the HDR HLG signal is backward compatible to SDR Rec. 2020 for live images. The HLG signal can be monitored as in preview quality also with a Rec. 709 SDR monitor (like a camera monitor), just by de-saturating the monitor colors.
HLG is supported by the vast majority of HDR tools and devices in the broadcast industry. The camera outputs and potentially recorded files in the camera, include the identical HLG look. The HLG signal is provided at the camera SDI outputs with the looks included in camera. Despite this, Parallel Log C recording on card is still possible.
In summary, this workflow is proposing a smooth step into the world of HDR, without scarifying SDR and without big changes in established workflows.
If you require further information, or have any comments or questions, please contact the ARRI sales team.