[Bibio]

hhhmm. i thought this thread was to switch HDR on. i got a bit board half way though so please accept my apology if you have figured out a way to send the metadata to a tv/monitor to enable HDR.

HDR is a metadata to tell your tv/monitor to auto switch to a different 'picture profile' which is HDR. once the metadata has ended your tv/monitor switches back to the 'standard' picture profile, so as HD/SD content looks correct.

people with a true capable HDR tv/monitor know this as a logo usually appearers 'on screen' to tell the user that HDR has been engaged and playing HDR content at which point the tv/monitor switches the picture profile to HDR.

my understanding of the subject was to make it so the film producers could set different colour profiles for each 4k title so when the metadata was passed on your tv/monitor it set the correct 'hdr picture profile' but in reality its not and its just another settings profile that the user can choose to alter if they wish.

dolby came up with a way to set metadata per frame and at the moment its another 'format war' which i believe HDR will win as its open source.

from what i can see all your doing is just setting different 'colour' profiles which you should be able to do on your tv/monitor anyway.

  
Sort of - but not quite.

Most HDR content currently being played is Rec 2020 (which means a different colour gamut with different RGB colour primaries and a different RGB->YCbCr mathematical conversion matrix to Rec 709) AND PQ (ST.2084) EOTF aka HDR10.

PQ is a very proscriptive standard and specifically maps video levels to specific absolute light levels on a pixel-by-pixel basis. The accompanying metadata is to help displays correctly decide how to cope with levels in the video they can't display or how to best handle the video they can. HDR10 is on a show-by-show or movie-by-movie basis, HDR10+ and Dolby Vision handle this kind of metadata scene-by-scene, shot-by-shot or frame-by-frame potentially I believe. The metadata is about assisting the display to best display a PQ source.

So we have to flag both Rec 2020 and a PQ EOTF (i.e. HDR) is being used.

HDR10 displayed in an SDR display without conversion is not at all nice. 

You can display HDR10 content with static 'fake' metadata (which is what happens when you manually force your TV into HDR10 mode) but this won't allow the display to benefit from the average and max light level metadata that is flagged within the HDR10 metadata.

HLG is not based on a PQ EOTF - though usually uses Rec 2020 colour gamut (though there are Rec 709 implementations of HLG) - and HLG is SDR backwards compatible, with no need of specific metadata. It also looks pretty good on SDR display without conversion. (That's a major USP for it)  

you have said it better than me but thats what i was getting at :-)

forcing a 'colour profile' is not HDR. i suppose that the workaround is a hack to get round being able to watch HDR 'washed out' content on a non HDR 4k display which is all fine and well.