Below is a copy of some posts I copied so I could remember from months back. Hope it is useful
From Kris Deering "Alright, here is the deal. I think a lot of people on these boards aren't 100% in their understanding of HDR and how it pertains to projectors. Therefore, the following comments APPLY TO PROJECTOR IMPLEMENTATION ONLY!!!
First, THERE IS NO SUCH THING AS SDR vs HDR. The reason you see this moniker is to make it easier to understand the base calibration that should be performed. There is no such thing as taking HDR and making it SDR. There is only tone mapping. Because the projector can only reach a low nit level you have three options: the projector tone maps (HDR GAMMA MODE), a custom tone map (ARVE) or the player tone maps (SDR2020). ALL of these solutions are trying to accomplish the same thing, taking a HDR signal and making it work with a low light display.
Projector tone maps are all based on best guess/research by the company. There is no standard. Arve tool is similar, though I believe he may be taking into account the suggestions made for tone mapping in BT2390. But it is still doing the same thing, it just allows the end user to tailor the curve more to their MEASURED display max and allows choices for aggressiveness. But the Arve curve does some things wrong with color support/desaturation, which you can read up on in the MadVR thread. The SDR2020 is just another tone map that is generated by the player to a specified brightness level (set by the slider). You calibrate the projector to a known state (gamma 2.4) so that Panasonic (or whoever is doing it, Oppo did something similar) knows what the underlying gamma their tone map is being applied to. The UB820 changes the tone map dynamically based on the metadata read from the disc. The Arve curves are setup for specific circumstances (1000 nits, 1200 nits, 4000 nits) and the hope is these will be good enough for most images you watch (and they look quite good all things considered). The Panasonic actually changes its tone map on a title by title basis, so long as the title has different values to change to (MaxCLL levels that vary). This maximizes your light usage on a title by title basis, so long as the information on the disc is right. It also applies the proper color handling, unlike the Arve curves.
The only other option is what you mentioned above, using an Arve curve INSTEAD of the projector HDR mode and then sending a tone mapped HDR signal (HDR Optimizer ON and HDR). This would be applying the Optimizer on top of your Arve curve. The Optimizer would be working with the assumption of a 500 nit display base, but that is also changed with the slider.
I can't think of any reason to do that final option unless you had a projector that would not accept 2020 color unless it was actually seeing an HDR signal (I know this doesn't apply to either the Sony models I've tested or the JVCs). I would recommend using the SDR2020 mode in ALL usage cases that I'm aware of. This would (IMHO) give you the best tone mapping which would be adaptive to the content, have proper color handling, and can be adjusted "to taste" on the fly for content that may need additional tweaking.
Panasonic isn't telling me everything they do, that would be giving out their R&D work for others to use. But for SDR2020 I imagine they are applying desaturation based on a 1000 nit tone map (Optimizer OFF) and where the slider is for display max. With Optimizer ON, they would apply based on the tone map (which is based on either the MaxCLL or MaxDML) and where the slider is for your display.
It is important that you zero out all the settings on your projector beforehand to allow the tone mapping to go to work. In my case, I set up a Custom setting for SDR2020 with my JVC rs620 set to BT.2020, Custom 1 (D6500, and 2.4 gamma. Everything telse o 0.
Then, I upped the dynamic range slider to +6 to give the image some brightness, then I played with the black and white tone controls. They look good at 0, but I went ahead and set the white tone to +1 and the black tone to -1.
Kris about Optomizer
With output set to SDR - If you have HDR optimizer OFF, the player does a generic tone map with all content tone mapped at 1000 nits (because most content falls around 1000 nits max) and it assumes your display is around 350 nits (based on not changing the slider). This will actually work well with the majority of content because again, the majority of content is 1000 nits and the majority of SDR type displays work well with 350 nits. If you turn the optimizer ON, the only difference now is the player intelligently tone maps based on the discs metadata, so no more just always tone mapping to 1000 nits. This will optimize on a per disc basis for titles that have information different than just 1000 nits (think Sony, Warner, Lionsgate). Now the tone map will be based on the specific title to the peak value you set for your display. So if you have a title that is 1000 nits (Fox and Disney), it will look exactly the same as Optimizer off, but if you have titles with MaxCLL that is a lot higher or lower, it will optimize the tone map for those titles. Obviously the farther away from 1000 nits, the more optimization occurs. So YMMV on a title by title basis. "
JVC RS600, 110"d StudioTek 130, Panny 820 4k Player, Denon AVR-X6500H, 5.2.4 DIY Sound Group speakers, Crown XLS 2502 Sub amp,