[Idea] SDR -> HDR "upconversion"

[CSchmidlapp]

Found this interesting article - hope will be useful: http://www.lightillusion.com/uhdtv.html

Great stuff, this is exactly what I was looking for
So what do you think?

[spoRv]

I think I'll be forced to buy soon an HDR UHD display...

[deleted user]

From the article: 

Meta-data is really needed only for one reason - when HDR was introduced there were no TVs that could match the peak luma and gamut coverage of the mastering/grading displays - specifically peak luma. With the 'absolute' nature of PQ based HDR, not having the same peak luma as the mastering display is something of an issue, as the image will clip. To attempt to overcome this, meta-data was introduced to allow the HDR TV to re-map the image content to attempt to overcome its lesser capabilities - apply a Tone Map roll-off to the EOTF/gamma curve.

How this Dynamic meta-data is generated also helps define the way it works for playback, assisting with understanding of the overall approach.

But, the reality is that the use of meta-data simply distorts the viewed image from the director's & colourist's intent, potentially losing the intended emotional response generated by the colour grade.

The basic approach to the generation of meta-data during grading/mastering is to first grade the HDR content on a professional HDR display, without any form of roll-off/tone mapping, using the highest brightness and colour gamut available (nominally P3 gamut, and between 1000 and 4000 nits). The HDR graded footage is then passed through an analysing system that will re-map the HDR images to SDR, attempting to maintain the original HDR intent, adding Dynamic Meta-data to define the changes between the HDR original and the SDR version. Often, the grading colourist will assist with a 'trim' pass grade to help in maintaining the original artistic intent.

In this way the Meta-data describes the 'grading' changes from the HDR master to the SDR version.

With this meta-data available, when the HDR footage is played back on an HDR display with a lesser peak brightness and/or colour gamut than the original mastering display the dynamic meta-data is used by the display to re-map the footage to a point between the SDR grade and the full HDR grade, based on the capabilities of the playback TV.

However, many home TVs are now getting close to matching the grading display's peak luma and gamut capabilities, especially as most HDR masters are graded on displays with between 1000 and 2000 nits, making the requirement for meta-data an interesting question going forward. If the viewing TV can match the grading display why is there a need for meta-data? The answer is, there isn't...

Very interesting.

So this basically means that the metadata is irrelevant for any true HDR displaying and potentially irrelevant for any HDR->SDR conversion, unless you want it to look the way that semi-automatic analysis system came up with it.

It also means that most displays that don't reach the peak luminance of the mastering display, instead of clipping, will do a form of roll-off/tone mapping in the highlights to fit the whole range of the source image into the available output range. One could argue it would be smarter to simply clip those highlights, or at least make the approach optional.

But this information also makes me wonder whether this metadata might actually be used for recreating the actual "official" SD master of UHDs, like for example the Dark Knight.

Also something that surprised me a little:

The black level of any display has nothing to do with SDR vs. HDR - black is always just the blackest black the display can attain.

Thanks for the link, spoRv!

[CSchmidlapp]

I think I'll be forced to buy soon an HDR UHD display...

Really

I think I'm going to wait

[spoRv]

Another two, brief, articles about HDR and Dolby Vision:

http://www.expertreviews.co.uk/tvs-enter...d-you-care
http://www.expertreviews.co.uk/tvs-enter...difference

[spoRv]

Another HDR paper:

http://people.irisa.fr/Remi.Cozot/pdfs/spie_2016.pdf