Projector Luminance

Hey guys, I am looking into calibrating projectors, ive calibrated my home projector against Rec709 standart so gamma 2.4 and 100NIT (it only does like 85… , its not the best)

Just thinking if you are in a facility with high end projectors , as DCI-P3 specifies just 48 NIT, how do you handle regular Rec709 viewing in a screening room? Do you have 2 seperate profiles one for DCI and one for Rec709? I couldnt find anything in the ACES docs about a Rec709 projector viewing environment.

We have a nice cinema/screening room and I want to write down some recommendations regarding setup.

You will not find any ODT in ACES specifications because DCI-P3 meant to be used with projector in dark room, and rec709 with monitors in dim or bright rooms.

Basically to achieve what you want there is two ways.
First (wrong) is to calibrate your projector to rec709 with gamma 2.6 and D65 or D60 white point and switch modes for appropriate material.
Second (correct one) is to calibrate your projector and room to DCI spec, and convert everything to DCI for viewing.

Yea so I can review my SDR lets say tv-episodical 709 stuff at 48NIT gamma 2.6? If I have a reference oled in the same dark room wouldnt I also have to use gamma 2.6 on that and also 48NIT?

at home I feel like the 100nit (or close to it) on my projector is closer than when I do gamma 2.6/48NIT and use the correct ODT each time , well ok given the monitors are in the same room it might just be the wrong way of comparing…

Or my environment for my oled is too dark , how do tou even measure it to be 5NITs? thats like having 5 candles on your desk or somerhing right, thats about what I get from the spill if my bias light… hmm

So difference from 5 to 0 nits surround warrants a change from 2.4 to 2.6 and a reduction in peak lumianance of about 1/2 … I dont know doesnt seem like that is adding up but I might be missing something .

Gamma is what compensates adaptiveness of human vision. In pure dark with one big source of light (screen) to see perfectly linear gradient from black to white your projector needs to be calibrated to something like gamma 2.6 (NITs is another thing, I write about them latter in this post). To see the same perfectly linear gradient in a dim environment you need to calibrate your (not so big at this time) screen to something like 2.4. And in bright environment it should be something like 2.2. All this numbers is not something set in stone and still subject to research (yep, even in 2021).
Also it depends on what level of black your displaying device can achieve, bt1886 is a gamma that should take this into account (slightly different results depending on black level of your device). Once again - it subject for research, I personally like when home TVs calibrated to bt1886, but hate to grade on a control monitor calibrated to it, and have one college that prefer to grade on bt1886.
What I want to say is you never match projector to a monitor in a same room. And you not need to. What you need is to get the same perception (or filling, or whatever it called) from same material watched on your projector in projecting room and from monitor that sitting in room next to it.

And now about NITs - first DCI compliant projectors just hit 50 nits when displaying white color (or near it). Technology back in the days was not capable of doing more. Also there should be some headroom to correct white point as needed. And this is a main reason to have 48 nits as a standard.

Makes sense?

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Yea thx that actually makes a lot of sense I didnt think about that the size makes a differece but yes it probably does. its just really hard to graps those effects that you cant measure at least for me.

I use Bt.1886 but only because i have a OLED and there it makes no difference to 2.4 hehe.
On my projector I use the full adaption for Bt.1886 which goves me the shadow detail I want back ao I guess I am on the “i like it” side .

The thing that trips me up the most is the relationship between nits and gamma to how it works visually for my psycho visual system. I need to do some more testing here to see stuff matches visually in that context.
I know my brain is a bit skewed from looking at 300NIT SDR for forever… (yea i was one of those crank brighntess to 100 cause it looks better … people") I am since converted and promise i will not do that again, slowley adapting to it and it does help with eye sore…

Really makes me question why macOS colorsync is then trying to be absolute luminance preserving, if you throw in a gamma 2.4 quicktime it will do a gamma adjust to 2.2 or whatever your display is. Thus canceling out all of those desired system-gamma shifts that are supposed to account for differences in surround luminance.

I thought that the aces transforms are doing something similar, and thus only really work when you hold up 2 screens to each other as again luminances will be the same if the only difference is monitor gamma, the DCI projector lut however is set to 48NIT so ill see how that changes the image , I havent done much testing of the viewers outside of 709 srgb and 2021HDR to be honest. really wondering how it adjusts the gamma and luminance shift, as if we want that compensation to happen we basically have to stay with a gamma 2.4 encoded image and only change the primaries to fit into P3 and the whitepoint to go to D60 .

Its really confusing , to me staying absolute luminance preserving just kinda makes sense, maybe just because I cant really see the difference in different surrounds if I walk into a bright room and look at a 2.2 gamma monitor the image still looks lifted va the gamma 2.4 monitor in a dark room, I dont know why, maybe just because the monitors have gotten so large

Apple ColorSync was written long-long time ago, and didn’t`t change much since that days.

yea but aces also does this and also flame(when you set your graghics display to something different than your broadcast screen it will adapt to it"colorimetric" or so its called. so I am not so sure honestly I cant see anyhting positive in watching a 2.4 encode on a 2.2 screen Always feels closer doing the gamma adjust. :thinking: