Well, hello again It looks like this thread is becoming my favorite one… As requested, I share my naive question about midgray here, hoping that you may find it relevant. As explained before, I am here to make sure team CG is heard…
Main question is about midgray. Currently 0.18 scene-referred pegs at 0.10 in display linear light, because of theaters, right ? Do we want to stick to that ? I guess it brings another question : should movie theaters be the main target of the Output Transforms ? With Netflix and 5G being here ?
There have been already some proper answers about this topic. Here are a few :
This seems like a resonable point to debate. It’s not just because it’s a theatre, but because that’s where SDR content in a theatre is usually placed. In an HDR world it might make sense to move it up … frankly, we can move it per output though so it’s not a super important decision.
and currently the Dolby 108-nit OT places gray at 7.2 nits, while 1000+nit OTs place it at 15 nits. at one point the dolby one was tested at 10 nits, which made it hold to the 10% of peak white that we have in SDR (48:4.8). however, at a certain point that 10% ratio breaks down - you don’t want it at 100 nits for 1000 nit display! additionally, i had to point out that the dolby 108 nit odt only really added a stop of headroom, and by moving gray up a whole stop, you were not really gaining anything in the highlights - hence the 7.2, which allowed for a little more oomph by default but still left a little more headroom for highlights
certainly the BBC team have talked about HLG diffuse white being typically a stop higher than SDR
BBC recommend 203nit diffuse white, partly I think so HDR doesn’t look darker than SDR which you switch a consumer TV. ITU-R BT.2408 formalises that.
Kind of have same remark as to whether we still want to have sdr theater as the golden target other OT should match. I think this was discussed when we talked about preserving intent vs. using the medium to it’s full extent. I guess with more technically derived OT this kind of questions are less relevant.
I am just curious because ACES is now a standard in the CG industry and not only in the movie industry. What about folks watching a TV/Youtube/Vimeo show on their mobile, tablets or screens at home ? Is there such a thing a completely dark theater (most of them in Paris have ambient lighting coming from the floor/stairs and emergency exits for security reasons…) ?
I have more questions than answers for sure… I guess OT are tricky because they are not only mathematical but also perceptual. More questions will come about :
- Surround : a pure power function pushes midgray, right ? Is this questionable for imagery ?
- Refactor existing VS indepedent new beginning ? I am curious to see if there is agreement on this one. What should we do about per channel lookup and the infamous sweeteners of the RRT (glow module, red modifier and global desaturation) ?
- max(RGB). I have often been told that it should not be used as a tone-mapper but more of a 2 stage solution, which would include gamut mapping… We are looking at a norm that literally delivers the chromaticity directly at the same energy level, right ?
Thanks for your help and insight !