Re: Principles of HDR in chrome

Hi all,

I'm afraid that the document has a number of inaccuracies in its description of the Hybrid Log-Gamma (HLG) and Perceptual Quantizer (PQ) standards and the intended methods of use.  Further, it misrepresents the British Broadcasting Corporation's view.

HLG displays do not clip the video signal.  HLG displays show the entire video signal and apply a different Opto-optical Transfer Function ("end-to-end system gamma") based on the display's peak brightness and the viewing conditions.

The equations for the system gamma variance are given in ITU-R BT.2100 for a reference viewing environment and in ITU-R BT.2390 for non-reference viewing environments.  These equations are based on subjective measurements undertaken at BBC R&D and the EBU and are shown to allow a good perceptual match between different screens under different viewing environments.  Further information is available in papers presented at IBC 2016 and IEEE ICCE-Berlin 2017.

Best Regards

Simon

--
Simon Thompson MEng CEng MIET
Project R&D Engineer
BBC Research and Development South Laboratory