Originally Posted by The Luggage
A very basic question (sorry if it is a dumb one) about the SDR2020 mode of Panasonic and the Iris setting of a JVC projector (RS400).
I have a small screen, short throw distance and relatively new lamp, so quite bit of light output (for a projector).
I use low lamp mode all the time.
For SDR content, I close the iris as much as possible (-15 I think).
For HDR content and with the Panasonic in HDR mode (optimizer on, custom curve in my JVC), I open the iris as much as possible.
But I’m wondering what should be done with the iris when the Panasonic is in SDR-2020 mode. Still open because the basic content is still HDR? Or more closed because of the conversion?
And does using the Auto/Digital iris (auto 2) change anything?
I’ll try and find a setting that I like, but I just wanted to know what the general practice is when using SDR 2020. I have only a very limited technical understanding of what exactly happens during this conversion.
(Apologies if this question was answered already, then I missed it).
I think the main concept to keep in mind is that this type of 'SDR' isn't the same as the regular SDR you would have with a conventional Blu-ray. The SDR part of SDR-2020 sent by the UB-820 can be referred to as 'HDR-Lite' to help make this distinction.
Full and accurate HDR display would require a Projector capable of showing anywhere between 1,000 and 10,000 nits, depending on how rigorous you want to be in terms of the definitions. Since none of them come even close, the full HDR range has to be compressed into a narrower range that the Projector can handle. That process is called "Tone-mapping." It can take place in the Player, external Video device (Radiance Pro, MadVR, the upcoming Envy, etc.), the Projector, etc. The idea is that it maximizes the use of the available dynamic range of a given projector and set-up, to provide the least amount of compromise in displaying HDR content.
So given all that, it would be expected that you would use different settings on your Projector to take full advantage of what it can do, for 'SDR-lite' than you would for conventional SDR. This would often include opening up the Iris, and/or switching to High Lamp. How much, and which options, to use, will depend on the specifics of one's set-up (screen size and gain, throw distance, etc.).
Using the Dynamic Iris (Auto 2 is usually spoken of as the preferred choice, as it is less 'aggressive') is a separate consideration. The goal here is to again maximize the available dynamic range of the Projector, so on at least a theoretical basis, its use would be encouraged. The downside is that its use can be associated with various artifacts (Iris 'pumping', Gamma 'blooming', etc.). How much of an issue these are will vary from system to system, and sensitivity to these will vary from person to person, so some use it, some don't.
For me, the benefits outweigh the negatives, so I leave it engaged.
ETA: Dominic posted as I was composing my reply, and his comments are always on-point!