Originally Posted by Manni01
No, that's exactly what I'm trying to do with my curves
I only use my last effective control point (80% or around 1200nits) to adjust the roll-off from 70% (around 800nits), but others could also use the 70% or even the 60% control point (240nits) if they wanted to start rolling off earlier. I wouldn't suggest rolling off before 50% (100nits).
This is why I don't like the idea of the ST2390 curve, it starts rolling off way too early to my taste.
OK, now I just blazed through the last few pages, so forgive me if I missed something, but I've been thinking about this....
First, we know that SDR is mastered for 100 nits peak white, and in general we calibrate our projectors for about 50 nits peak white. Now SDR uses a relative curve, so everything scales well.
Now, for HDR, we have ST.2084 which is an absolute curve. We know that HDR is intended to be roughly the same (brightness wise) as SDR, up to 100 nits, with the range above that being for highlights.
So the question is, why do we not want to use a 2x multiplier in Calman for calibrating HDR? That would make content 100 nits equal to 50 nits on screen, which would seem to be exactly what we're looking for . Then for a custom curve, wouldn't you calibrate it "linear" all the way up to the 100 nit point, and then apply the roll off between 100 nits (is that ~50%?) and 4000 nits or so?
It seems to me that 4, 5, 6x multipliers are far too large, for example if I tell Calman to apply a 5x multiplier, and then calibrate everything "perfectly", content that's supposed to be 100 nits (per the PQ curve) will only be 20 nits, which is less than half as bright as we want (50 nits). This is actually what I found myself when I was playing around with the multiplier in Calman, I attempted to calibrate with a very high multiplier (like 10x) because I had calibrated to a peak white of under 100 nits (iris was somewhat closed), the result was everything was way too dark, much darker than if I had my Pansonic do DRC and output SDR.
I do intend to try and make my own custom PQ/Gamma curve when I get some time to play with it. I really want to try a 2x multiplier. If I understand how that works in Calman, that should be the HDR equivalent of how we calibrate SDR.
Of course the trick is, that curve will be unique to each particular setup (screen size, aperture, lamp, throw, etc).
I'm not criticizing at all, bravo for all the great work and information you've provided. Just trying to understand and hopefully help get to the bottom of this.
Thanks to the great info here and with Calman, it's invaluable.